CONTENTS
APPENDIX A
IHECSBE BENCHMARKS 63
A.1 HEU-SOL-THERM-025 -- URANIUM NITRATE SOLUTIONS WITH GADOLINIUM 65
A.1.1 Overview of Experiment 65
A.1.2 Description of Experimental Configuration 65
A.2 HEU-SOL-THERM-027 -- URANIUM NITRATE SOLUTION WITH CENTRAL BORON CARBIDE OR CADMIUM ABSORBER ROD 70
A.2.1 Overview of Experiment 70
A.2.2 Description of Experimental Configuration 70
A.3 HEU-SOL-THERM-028 -- URANIUM NITRATE SOLUTIONS WITH CENTRAL BORON CARBIDE ABSORBER ROD 73
A.3.1 Overview of Experiment 73
A.3.2 Description of Experimental Configuration 73
A.4 HEU-SOL-THERM-029 -- URANIUM NITRATE SOLUTION WITH CLUSTER OF SEVEN BORON CARBIDE ABSORBER RODS 77
A.4.1 Overview of Experiment 77
A.4.2 Description of Experimental Configuration 77
A.5 HEU-SOL-THERM-030 -- URANIUM NITRATE SOLUTIONS WITH CLUSTER OF SEVERAL BORON CARBIDE ABSORBER RODS 80
A.5.1 Overview of Experiment 80
A.5.2 Description of Experimental Configuration 81
A.6 HEU-SOL-THERM-031 -- URANIUM NITRATE SOLUTION WITH 18 OR 36 BORON CARBIDE ABSORBER RODS IN 4.0- OR 6.0-CM-PITCH TRIANGULAR LATTICES 84
A.6.1 Overview of Experiment 84
A.6.2 Description of Experimental Configuration 84
A.7 HEU-SOL-THERM-035 -- BORON CARBIDE ABSORBER RODS IN URANIUM (89% 235U) NITRATE SOLUTIONS 89
A.7.1 Overview of Experiment 89
A.7.2 Description of Experimental Configuration 89
A.8 HEU-SOL-THERM-036 -- SQUARE-PITCHED LATTICES OF BORON CARBIDE ABSORBER RODS IN URANIUM NITRATE SOLUTION 93
A.8.1 Overview of Experiment 93
A.8.2 Description of Experimental Configuration 93
A.9 HEU-SOL-THERM-037 -- HEXAGONALLY PITCHED LATTICES OF BORON CARBIDE ABSORBER RODS IN URANIUM NITRATE SOLUTION 96
A.9.1 Overview of Experiment 96
A.9.2 Description of Experimental Configuration 96
A.10 IEU-COMP-THERM-002 -- WATER-MODERATED U(17)O2 ANNULAR FUEL RODS WITHOUT ABSORBER AND WITH GADOLINIUM OR CADMIUM ABSORBERS IN 6.8-CM-PITCH HEXAGONAL LATTICES AT DIFFERENT TEMPERATURES 100
A.10.1 Overview of Experiment 100
A.10.2 Description of Experimental Configuration 100
A.11 IEU-SOL-THERM-001 -- GRAPHITE-REFLECTED URANYL SULPHATE (20.9% 235U) SOLUTIONS 106
A.11.1 Overview of the Experiment 106
A.11.2 Description of the Experiment Configuration 106
A.12 LEU-COMP-THERM-031 -- WATER-MODERATED HEXAGONALLY PITCHED PARTIALLY FLOODED LATTICES OF U(5%)O2 ZIRCONIUM CLAD FUEL RODS 111
A.12.1 Overview of Experiment 111
A.12.2 Description of the Experimental Configuration 111
A.13 LEU-COMP-THERM-032 -- UNIFORM WATER-MODERATED LATTICES OF RODS WITH U(10%)O2 FUEL IN RANGE FROM 20C TO 274C 115
A.13.1 Overview of Experiment 115
A.13.2 Description of Critical Fuel Rod Arrays and Details of Active Cores 115
A.14 LEU-SOL-THERM-005 -- BORON CARBIDE ABSORBER RODS IN URANIUM (5.64% 235U) NITRATE SOLUTION 120
A.14.1 Overview of Experiment 120
A.14.2 Description of Experimental Configuration 120
A.15 LEU-SOL-THERM-006 -- BORON CARBIDE ABSORBER RODS IN URANIUM (10% 235U) NITRATE SOLUTION 122
A.15.1 Overview of Experiment 122
A.15.2 Description of Experimental Configuration 122
LIST OF FIGURES
A.1 Sketch of critical assembly for HEU-SOL-THERM-025
(vertical cut) 66
A.2 Arrangement of critical assembly
in the room for HEU-SOL-THERM-025 67
A.3 Diagram of a cylindrical tank
for HEU-SOL-THERM-025 68
A.4 Critical assembly for HEU-SOL-THERM-027 71
A.5 Arrangement of critical assembly in the room
for HEU-SOL-THERM-027 72
A.6 Critical assembly for HEU-SOL-THERM-028 74
A.7 Arrangement of critical assembly in the room
for HEU-SOL-THERM-028 75
A.8 Core tank of the critical assembly
for HEU-SOL-THERM-029 78
A.9 Arrangement of the critical assembly in the room
for HEU-SOL-THERM-029 79
A.10 Core tank of the critical assembly
for HEU-SOL-THERM-030 82
A.11 Arrangement of the critical assembly in the room
for HEU-SOL-THERM-030 83
A.12 Core tank of the critical assembly
for HEU-SOL-THERM-031 85
A.13 Core tank of the critical assembly for HEU-SOL-THERM-031 86
A.14 Arrangement of the critical assembly in the room
for HEU-SOL-THERM-031 87
A.15 Critical assembly for HEU-SOL-THERM-035 89
A.16 Core tank of the critical assembly for HEU-SOL-THERM-035 91
A.17 Critical assembly for HEU-SOL-THERM-036 94
A.18 Critical assembly for HEU-SOL-THERM-037 96
A.19 Core tank of the critical assembly for HEU-SOL-THERM-037 99
A.20 Fuel rod for IEU-COMP-THERM-002 102
A.21 Absorber element for IEU-COMP-THERM-002 103
A.22 Lattice plate loading chart for assemblies without absorber elements
for IEU-COMP-THERM-002 104
A.23 Longitudinal section of the critical assembly with structural elements of the facility for IEU-SOL-THERM-001 107
A.24 Cross section of the critical assembly with arrangement
of the channels (N=1,,8) and structural elements of the facility
for IEU-SOL-THERM-001 108
A.25 Longitudinal section of the assembly core
for IEU-SOL-THERM-001 109
A.26 Configuration of the critical assembly with water tank
for LEU-COMP-THERM-031 112
A.27 Schematic of the fuel rods placement in the core 113
A.28 Fuel rod for LEU-COMP-THERM-031 114
A.29 The assembly on stocks for LEU-COMP-THERM-032 116
A.30 The placement of fuel rods in the active core for LEU-COMP-THERM-032 117
A.31 Fuel rod for LEU-COMP-THERM-032 117
A.32 Configuration of fuel rod array 1 for LEU-COMP-THERM-032 119
A.33 Critical assembly for LEU-SOL-THERM-005 121
A.34 Critical assembly for LEU-SOL-THERM-006 123
A.35 Core tank of the critical assembly for LEU-SOL-THERM-006 124
LIST OF TABLES
A.1 Dimensions of the cylindrical tanks for HEU-SOL-THERM-025 68
A.2 Critical dimensions for HEU-SOL-THERM-025 69
A.3 Critical dimensions for HEU-SOL-THERM-027
73
A.4 Critical dimensions for HEU-SOL-THERM-028 76
A.5 Critical dimensions for HEU-SOL-THERM-029 80
A.6 Critical dimensions for HEU-SOL-THERM-030 84
A.7 Critical dimensions for HEU-SOL-THERM-031 88
A.8 Critical dimensions for HEU-SOL-THERM-035 92
A.9 Critical dimensions for HEU-SOL-THERM-036 95
A.10 Critical dimensions for HEU-SOL-THERM-037 100
A.11 Critical parameters of assemblies without absorber elements
for IEU-COMP-THERM-002 105
A.12 Critical parameters of assemblies with Gadolinium absorber elements
for IEU-COMP-THERM-002 105
A.13 Critical parameters of assemblies with cadmium absorber elements
for IEU-COMP-THERM-002 105
A.14 Configurations of benchmark experiments for IEU-SOL-THERM-001 111
A.15 Numbers of fuel rods and height of water for critical uniform configurations
for LEU-COMP-THERM-031 115
A.16 Critical fuel rod array descriptions for LEU-COMP-THERM-032 118
A.17 Critical dimensions for LEU-SOL-THERM-005 122
A.18 Critical dimensions for LEU-SOL-THERM-006 124
APPENDIX A
IHECSBE BENCHMARKS
APPENDIX A
IHECSBE BENCHMARKS
The following descriptions of the critical experiments were adapted from the IHECSBE, which is listed as
Reference 1 in the main body of this report. The limited descriptions included here are intended to provided the
reader a general overview of each experiment, and do not provide all information used in creating the
computational models.
A.1 HEU-SOL-THERM-025 -- URANIUM NITRATE SOLUTIONS WITH
GADOLINIUM
A.1.1 Overview of Experiment
The eighteen measurements included in this evaluation are part of a series of experiments performed in 1987 at
the Solution Physical Facility of the Institute of Physics and Power Engineering (IPPE), Obninsk, Russia with
highly enriched (89.0 wt % 235U) uranium. Critical experiment measurements were made with uranyl nitrate
solutions poisoned with gadolinium nitrate in a cylindrical tank with inner diameter 40 cm inserted in another
cylindrical tank with inner diameter 59.4 cm with uranyl nitrate solutions without gadolinium. Natural
gadolinium was used in the experiments. On the bottom and side, the cores were surrounded by thick water
reflectors. A total of eighteen experimental configurations were documented in this evaluation.
A.1.2 Description of Experimental Configuration
The diagram of the critical assembly is shown in Figure A.1 (vertical cut). The arrangement of the critical
assembly in the room is shown in Figure A.2 (vertical cut).
The critical assembly consisted of three open-topped coaxial cylindrical tanks (labeled 1, 2 and 3 in the figures).
The inner tank (1) was filled with a water solution of uranyl nitrate (UO2(NO3)2) with some excess of nitric acid
(HNO3) and also gadolinium nitrate (Gd(NO3)3) in most cases. The critical height of the solution in the inner
tank is designated as H1. The middle tank (2) was filled with distilled water in the first five experiments and with
water solution of uranyl nitrate with some excess of nitric acid in the other experiments. The height of water or
solution in this tank is designated as H2. The outer tank (3) was empty in experiments 2, 3, 4, and 5, and was
filled with distilled water in the other experiments. The height of water in the outer tank is designated as H3.
Heights H1, H2, and H3 were measured from the inside bottoms of the corresponding tanks. In Figure A.3 a
diagram of a cylindrical tank is shown, and the corresponding dimensions of the tanks used in the experiments
are given in Table A.1.
Table A.1 Dimensions of the cylindrical tanks for HEU-SOL-THERM-025
| Dimension | H, cm | D, cm | R, cm | HB, cm | RF, cm | HF, cm |
| Inner tank | 120.0 | 40.0 | 0.3 | 0.6 | 2.5 | 1.0 |
| Middle tank | 120.0 | 59.4 | 0.5 | 0.8 | 2.5 | 1.0 |
| Outer tank | 120.0 | 80.0 | 0.5 | 0.8 | 2.5 | 1.0 |
The cylindrical tanks were suspended in one another by the tank flanges and angle bars (see Figure A.1). In the
first three experiments, the inner tank was suspended above the bottom of the middle tank by the height
H = 15.1 cm (see Figure A.1); in all other experiments, the inner tank stood on the bottom of the middle tank
(H = 0). The middle tank always stood on the bottom of the outer tank.
All three cylindrical tanks were arranged over two square tanks (4 and 5 in Figure A.2). Tank 5 was always
filled with distilled water. The height of this water was not fixed exactly. It varied from 80 to 110 cm. Tank 4
was empty in the first three experiments with H = 15.1 cm. But Tank 4 was filled with distilled water up to the
bottom of outer Tank 3 in the experiments with H = 0 (when the inner tank rested on the bottom of the middle
tank).
All tanks were made of stainless steel 1X18H10T.
The solution temperature was 20 ± 2C in all experiments.
The dimensions and reactivity excesses are listed in Table A.2.
Table A.2 Critical dimensions for HEU-SOL-THERM-025
| Case number | Solution
height
H1, cm |
Solution
height
H2, cm |
Water
height
H2, cm |
Water
height
H3, cm |
Bottom
water height
H, cm |
Reactivity
excess,
eff |
| 1 | 23.8 | - - | 44.7 | 46.1 | 15.1 | 0.02 |
| 2 | 23.8 | - - | 45 | - - | 15.1 | 0.08 |
| 3 | 42 | - - | 65 | - - | 15.1 | 0.03 |
| 4 | 23.1 | - - | 28.8 | - - | - - | 0.03 |
| 5 | 18.8 | - - | 28.7 | - - | - - | 0.15 |
| 6 | 36.1 | 37.5 | - - | 45 | - - | 0.03 |
| 7 | 31.1 | 38.3 | - - | 45 | - - | 0.11 |
| 8 | 38.3 | 39 | - - | 45 | - - | 0 |
| 9 | 27.3 | 27.9 | - - | 40 | - - | 0.03 |
| 10 | 26.9 | 27.9 | - - | 40 | - - | 0.04 |
| 11 | 32 | 32.7 | - - | 35 | - - | 0.03 |
| 12 | 32.2 | 32.9 | - - | 42 | - - | 0.02 |
| 13 | 40.5 | 41.3 | - - | 47.5 | - - | 0.11 |
| 14 | 35.9 | 36.4 | - - | 40 | - - | 0.1 |
| 15 | 42.2 | 43 | - - | 43 | - - | 0.02 |
| 16 | 30.7 | 31.2 | - - | 50 | - - | 0 |
| 17 | 36.8 | 37.4 | - - | 50 | - - | 0 |
| 18 | 41.2 | 43.8 | - - | 50 | - - | 0 |
A.2 HEU-SOL-THERM-027 -- URANIUM NITRATE SOLUTION WITH
CENTRAL BORON CARBIDE OR CADMIUM ABSORBER ROD
A.2.1 Overview of Experiment
A large number of critical experiments with absorber elements of different types in uranium nitrate solutions of
different enrichments and concentrations were performed in 19611963 at the Solution Physical Facility of the
Institute of Physics and Power Engineering (IPPE), Obninsk, Russia. The nine experiments included in this
evaluation were performed with uranium enriched to 89 wt % 235U. Uranium nitrate solution was pumped into
the core or inner tank, a stainless steel cylindrical tank with inner diameter 40.07 cm. In eight of the nine
experiments, an absorber rod of various diameters with boron or cadmium was inserted in the center of the core
tank. There was no outer reflector in these experiments.
A.2.2 Description of Experimental Configuration
A diagram of the critical assembly is shown in Figure A.4. The experiment was performed in a room with
dimensions 7.5 × 5.5 × 8.8 m. The arrangement of the critical assembly in the room is shown in Figure A.5. The
critical assembly consisted of two open-topped coaxial cylindrical tanks (labeled 1 - inner tank, and 2 - outer tank
in the figures). The inner tank was 40.07 cm inner diameter, 130 cm tall, with wall thickness 0.3 cm, and bottom
thickness 0.6 cm. The outer tank was 198.4 cm inner diameter, 300 cm tall, with wall thickness 0.8 cm, and
bottom thickness 1.0 cm. When mounted, the distance between the bottom (outer surface) of the inner tank and
the bottom of the outer tank (inner surface) was 170 cm.
The inner tank (1) was partially filled with the aqueous solution of uranyl nitrate UO2(NO3)2 with some excess of
nitric acid (HNO3). The outer tank (2) was empty in all cases.
An absorber rod was inserted in the center of the inner tank in Cases 29. This absorber rod was a stainless steel
tube with outer diameter shown in Table A.1, 130 cm long, with wall thickness 0.1 cm, and bottom thickness
0.8 cm. This tube was filled with two types of absorbers. In Cases 25 a powder of boron carbide was used.
In Cases 6 9, a water-filled cadmium tube, with an outer diameter 0.1 cm less than the inner diameter of the
stainless-steel tube and a wall and bottom thickness of 0.05 cm, was used.
The experimental results obtained for the different experimental conditions are presented in Table A.3.
The experiments were performed at room temperature (approximately 20C).
Table A.3 Critical dimensions for HEU-SOL-THERM-027
| Case number | Type of absorber rod | Tube of absorber rod
outer diameter,
cm |
Solution volume,
liters |
| 1 | none | -- | 24.4 ± 0.1 |
| 2 | boron | 5.0 | 28.0 ± 0.2 |
| 3 | boron | 7.4 | 30.6 ± 0.2 |
| 4 | boron | 10.0 | 34.9 ± 0.2 |
| 5 | boron | 12.0 | 40.2 ± 0.2 |
| 6 | cadmium | 5.0 | 26.9 ± 0.2 |
| 7 | cadmium | 7.4 | 30.0 ± 0.2 |
| 8 | cadmium | 10.0 | 35.1 ± 0.2 |
| 9 | cadmium | 12.0 | 41.6 ± 0.2 |
A.3 HEU-SOL-THERM-028 -- URANIUM NITRATE SOLUTIONS WITH
CENTRAL BORON CARBIDE ABSORBER ROD
A.3.1 Overview of Experiment
A large number of critical experiments with absorber elements of different types in uranium nitrate solution of
different enrichments and concentrations were performed in 19611963 at the Solution Physical Facility of the
Institute of Physics and Power Engineering (IPPE), Obninsk, Russia. The eighteen experiments included in this
evaluation were performed with uranium enriched to 89 wt % 235U. Uranium nitrate solution with a uranium
concentration of 76 or 286 g/l was pumped into stainless steel cylindrical tanks of various diameters. In nine of
the eighteen experiments, a boron carbide absorber rod was inserted in the center of the tank. The critical
conditions were determined with and without the absorber rod for each case. There was a thick side and bottom
water reflector in all experiments.
A.3.2 Description of Experimental Configuration
A diagram of the critical assembly is shown in Figure A.6. The experiment was performed in a room with
dimensions 7.5 × 5.5 × 8.8 m. The arrangement of the critical assembly in the room is shown in Figure A.7. The
critical assembly consisted of two open-topped coaxial cylindrical tanks (labeled 1 - core tank, and 2 - reflector
tank in the figures). Six core tanks of different diameters were used in these experiments. All core tanks were
130 cm tall, with wall thickness 0.3 cm, and bottom thickness 0.6 cm. The inner diameters of the tanks are
shown in Table A.1. The reflector tank was 198.4 cm in inner diameter, 300 cm tall, with wall thickness 0.8 cm,
and bottom thickness 1.0 cm. In all experiments the core tank was suspended in the reflector tank with the tank
flanges and angle bars. When mounted, the distance between the bottom (outer surface) of the core tank and the
bottom of the reflector tank (inner surface) was 170 cm. The reflector tank always stood on the floor.
The inner tank (1) was partially filled with the aqueous solution of uranyl nitrate UO2(NO3)2 with some excess of
nitric acid (HNO3). The outer tank (2) was filled with distilled water in all cases. The height of the water
reflector measured from the bottom (inner surface) of the core tank was 120 cm.
The absorber rod was inserted in the center of the inner tank in each even numbered case. The absorber rod was
a stainless steel tube with an outer diameter of 5.8 cm, a height of 140 cm, a wall thickness 0.4 cm, and a bottom
thickness 0.8 cm. This tube was filled with a powder of boron carbide.
The experimental results obtained for the different experimental conditions are presented in Table A.4.
All experiments were performed at room temperature (approximately 20C).
Table A.4 Critical dimensions for HEU-SOL-THERM-028
| Case number | Uranium
concentration,
g/l |
Core tank inner
diameter,
cm |
Absorber rod present? | Solution volume,
liters |
| 1 | 76.0 | 28.07 ± 0.14 | no | 16.7 ± 0.1 |
| 2 | yes | 33.3 ± 0.2 | ||
| 3 | 30.06 ± 0.15 | no | 17.3 ± 0.1 | |
| 4 | yes | 26.9 ± 0.2 | ||
| 5 | 31.93 ± 0.18 | no | 17.8 ± 0.1 | |
| 6 | yes | 24.8 ± 0.1 | ||
| 7 | 40.07 ± 0.20 | no | 23.1 ± 0.1 | |
| 8 | yes | 26.5 ± 0.2 | ||
| 9 | 286.0 | 22.04 ± 0.11 | no | 9.9 ± 0.1 |
| 10 | yes | 26.2 ± 0.2 | ||
| 11 | 24.05 ± 0.12 | no | 10.1 ± 0.1 | |
| 12 | yes | 16.4 ± 0.1 | ||
| 13 | 28.07 ± 0.14 | no | 11.2 ± 0.1 | |
| 14 | yes | 14.3 ± 0.1 | ||
| 15 | 31.93 ± 0.18 | no | 13.1 ± 0.1 | |
| 16 | yes | 15.2 ± 0.1 | ||
| 17 | 40.07 ± 0.20 | no | 17.4 ± 0.1 | |
| 18 | yes | 18.9 ± 0.1 |
A.4 HEU-SOL-THERM-029 -- URANIUM NITRATE SOLUTION WITH
CLUSTER OF SEVEN BORON CARBIDE ABSORBER RODS
A.4.1 Overview of Experiment
A large number of critical experiments with absorber elements of different types in uranium nitrate solution of
different enrichments and concentrations were performed in 19611963 at the Solution Physical Facility of the
Institute of Physics and Power Engineering (IPPE), Obninsk, Russia. The purpose of these experiments was to
determine the effects of enrichment, concentration, geometry, neutron reflection, and type, diameter, number,
and arrangement of absorber rods on the critical mass of light-water-moderated homogeneous uranyl nitrate
solutions. The experiments included ones with a central boron carbide or cadmium rod, clusters of boron carbide
rods, and triangular lattices of boron carbide rods in square or cylindrical tanks of different dimensions filled
with solutions of uranyl nitrate.
The seven experiments included in this evaluation were performed with uranium enriched to 89 wt % 235U.
Uranium nitrate solution was pumped into the core or inner tank, a stainless steel cylindrical tank with inner
diameter 40.07 cm. One experiment was performed without absorber rods. In six of the seven experiments, a
cluster of seven boron carbide absorber rods was inserted in the core tank. The cluster was an arrangement of
one central absorber rod and six absorber rods placed around the central one. A different rod pitch was used for
each of the six experiments. There was a thick side and bottom water reflector in each experiment.
A.4.2 Description of Experimental Configuration
A diagram of the core tank of the critical assembly is shown in Figure A.8. The experiment was performed in a
room with dimensions 7.5 × 5.5 × 8.8 m. The arrangement of the critical assembly in the room is shown in
Figure A.9.
The critical assembly consisted of two open-topped coaxial cylindrical tanks (labeled 1 - core tank, and
2 - reflector tank in the figures). The core tank was 40.07 cm in inner diameter, 130 cm tall, with wall thickness
0.3 cm, and bottom thickness 0.6 cm. The reflector tank had 198.4 cm inner diameter, was 300 cm tall, with wall
thickness 0.8 cm, and bottom thickness 1.0 cm. In all experiments the core tank was suspended in the reflector
tank with the tank flanges and angle bars. When mounted, the distance between the bottom (outer surface) of the
core tank and the bottom of the reflector tank (inner surface) was 170 cm. The reflector tank always stood on the
floor.
The core tank was partially filled with the aqueous solution of uranyl nitrate UO2(NO3)2 with some excess of
nitric acid (HNO3). The reflector tank was filled with distilled water in all cases. The height of the water
reflector measured from the bottom (inner surface) of the core tank is shown in Table A.5 for each case. The
experimental results obtained for the different experimental conditions are presented in Table A.5.
The cluster of seven absorber rods was inserted in the center of the core tank in Cases 2 7. The absorber rods
were stainless steel tubes with outer diameter of 5.8 cm, 140 cm long, with wall thickness 0.4 cm, and bottom
thickness 0.8 cm. These tubes were filled with a powder of boron carbide.
The space between the absorber rods was ensured by two stainless steel lattice plates. These plates were 0.5 cm thick. The upper plate was placed at the top of the core tank, as shown in Figure A.8. The diameter of the upper
Table A.5 Critical dimensions for HEU-SOL-THERM-029
| Case number | Cluster present? | Absorber rods
pitch,
cm |
Solution volume,
liters |
Water reflector
height(a),
cm |
| 1 | no | -- | 18.2 ± 0.1 | 14 |
| 2 | yes | 6.0 | 25.4 ± 0.1 | 120 |
| 3 | yes | 7.0 | 27.9 ± 0.2 | 120 |
| 4 | yes | 10.5 | 34.9 ± 0.2 | 120 |
| 5 | yes | 12.3 | 31.5 ± 0.2 | 120 |
| 6 | yes | 14.0 | 26.3 ± 0.1 | 120 |
| 7 | yes | 16.0 | 22.2 ± 0.1 | 120 |
(a) ± 0.2 cm; measured from the bottom (inner surface) of the core tank.
plate was 45 cm. The lower plate was placed inside the core tank at a distance of 40 cm above the inner surface
of the bottom. The diameter of this plate was 39.4 cm. There were seven 5.9-cm-diameter holes for the absorber
rods in these plates. One of these holes was located at the center of the plates and the other six holes were
located at the corners of a right hexagon. The hole pitch for each experiment is shown in Table A.5.
There were no lattice plates in Case 1, the experiment without absorber rods.
The experiments were performed at room temperature (approximately 20C).
A.5 HEU-SOL-THERM-030 -- URANIUM NITRATE SOLUTIONS WITH
CLUSTER OF SEVERAL BORON CARBIDE ABSORBER RODS
A.5.1 Overview of Experiment
A large number of critical experiments with absorber elements of different types in uranium nitrate solution of
different enrichments and concentrations were performed in 19611963 at the Solution Physical Facility of the
Institute of Physics and Power Engineering (IPPE), Obninsk, Russia. The seven experiments included in this
evaluation were performed with uranium enriched to 89 wt % 235U. Uranium nitrate solution with uranium
concentration of 76 or 289 g/l was pumped into the core or inner tank, a stainless steel cylindrical tank with inner
diameter 40.07 cm. Two experiments were performed without absorber rods. In five of the seven experiments, a
cluster of three, four, or six boron carbide absorber rods was inserted in the center of the core tank. There was a
thick side and bottom water reflector in these experiments.
A.5.2 Description of Experimental Configuration
A diagram of the core tank of the critical assembly is shown in Figure A.10. The experiment was performed in a room with dimensions 7.5 × 5.5 × 8.8 m. The arrangement of the critical assembly in the room is shown in
Figure A.11.
The critical assembly consisted of two open-topped coaxial cylindrical tanks (labeled 1 - core tank, and
2 - reflector tank in the figures). The core tank was 40.07 cm in inner diameter, 130 cm tall, with wall thickness
0.3 cm, and bottom thickness 0.6 cm. The reflector tank had 198.4 cm inner diameter, was 300 cm tall, with wall
thickness 0.8 cm, and bottom thickness 1.0 cm. In all experiments the core tank was suspended in the reflector
tank with the tank flanges and angle bars. When mounted, the distance between the bottom (outer surface) of the
core tank and the bottom of the reflector tank (inner surface) was 170 cm. The reflector tank always stood on the
floor.
The core tank was partially filled with the aqueous solution of uranyl nitrate UO2(NO3)2 with some excess of
nitric acid (HNO3). The reflector tank was filled with distilled water in all cases. The height of the water
reflector measured from the bottom (inner surface) of the core tank is shown in Table A.6 for each case. The
experimental results obtained for the different experimental conditions are presented in Table A.6.
The cluster of several absorber rods was inserted in the center of the core tank in Cases 2, 3, 57. There were
three cluster configurations, each with a different number of absorber rods, used in these experiments. The first
configuration was three absorber rods placed uniformly on a circle of diameter of 19.2 cm. The second
configuration was four absorber rods the central one and three rods placed uniformly around the central rod on
the circle of the previously mentioned diameter. The third configuration was six absorber rods placed uniformly
on the circle of the same diameter.
The absorber rods were stainless steel tubes with outer diameter of 5.8 cm, 140 cm long, with wall thickness
0.4 cm, and bottom thickness 0.8 cm. These tubes were filled with a powder of boron carbide.
The experiments were performed at room temperature (approximately 20C).
Table A.6 Critical dimensions for HEU-SOL-THERM-030
| Case number | Uranium
concentration,
g/l |
Number of absorber rods | Solution volume,
liters |
Water reflector
height,(a)
cm |
| 1 | 76 .0 | -- | 23.6 ± 0.1 | 18 |
| 2 | 3 | 32.7 ± 0.2 | 120 | |
| 3 | 4 | 42.0 ± 0.2 | 120 | |
| 4 | 289.0 | -- | 18.1 ± 0.2 | 14 |
| 5 | 3 | 20.7 ± 0.1 | 120 | |
| 6 | 4 | 23.2 ± 0.1 | 120 | |
| 7 | 6 | 29.1 ± 0.2 | 120 |
(a) ± 0.2 cm; measured from the bottom (inner surface) of the core tank.
A.6 HEU-SOL-THERM-031 -- URANIUM NITRATE SOLUTION WITH
18 OR 36 BORON CARBIDE ABSORBER RODS IN 4.0- OR 6.0-CM-PITCH TRIANGULAR LATTICES
A.6.1 Overview of Experiment
A large number of critical experiments with absorber elements of different types in uranium nitrate solution of
different enrichments and concentrations were performed in 19611963 at the Solution Physical Facility of the
Institute of Physics and Power Engineering (IPPE), Obninsk, Russia. The four experiments included in this
evaluation were performed with uranium enriched to 89 wt % 235U. Uranium nitrate solution with uranium
concentration of 289 g/l was pumped into the core or inner tank, a stainless steel cylindrical tank with inner
diameter 40.07 cm. Eighteen or thirty-six boron carbide absorber rods were inserted in the center of the core
tank. The rods were arranged in hexagonal lattices with pitches of 4.0 and 6.0 cm. There was a thick side and
bottom water reflector in these experiments.
A.6.2 Description of Experimental Configuration
A diagram of the core tank of the critical assembly is shown in Figure A.12 and in Figure A.13. The experiment
was performed in a room with dimensions 7.5 × 5.5 × 8.8 m. The arrangement of the critical assembly in the
room is shown in Figure A.14.
The critical assembly consisted of two open-topped coaxial cylindrical tanks (labeled 1 - core tank, and 2 - reflector tank in the figures). The core tank was 40.07 cm in inner diameter, 130 cm tall, with wall thickness 0.3 cm and bottom thickness 0.6 cm. The reflector tank had a 198.4-cm inner diameter, was 300 cm tall, with wall thickness 0.8 cm, and bottom thickness 1.0 cm. In all experiments the core tank was suspended in the reflector tank with the tank flanges and angle bars. When mounted, the distance between the bottom of the core
tank (outer surface) and the bottom of the reflector tank (inner surface) was 170 cm. The reflector tank always
stood on the floor.
The core tank was partially filled with the aqueous solution of uranyl nitrate UO2(NO3)2 with some excess of
nitric acid (HNO3). The reflector tank was filled with distilled water in all cases. The height of the water
reflector measured from the bottom (inner surface) of the core tank was 50 cm. The experimental results
obtained for the different experimental conditions are presented in Table A.7.
Table A.7 Critical dimensions for HEU-SOL-THERM-031
| Case number | Number of absorber rods | Lattice pitch,
cm |
Solution volume,
liters |
| 1 | 18 | 4.0 | 24.9 ± 0.1 |
| 2 | 36 | 43.4 ± 0.2 | |
| 3 | 18 | 6.0 | 26.3 ± 0.1 |
| 4 | 36 | 35.8 ± 0.2 |
Eighteen or thirty-six absorber rods in a hexagonal lattice were inserted in the core tank. There was no central
rod in the lattices. The pitches of the lattices were 4.0 cm or 6.0 cm. In configurations with eighteen absorber
rods all rods were the same type ("thick" rods). In configurations with thirty-six absorber rods twenty-seven rods
were "thick" and nine rods were "thin". The "thin" rods were alternated with "thick" ones in the outer rows of the
rods (see Figure A.13).
The absorber rods of the first type ("thick") were stainless steel tubes with outer diameter of 2.1 cm, 140 cm
long, with wall thickness 0.2 cm, and bottom thickness 0.3 cm, filled with a powder of boron carbide. The outer
diameter of the absorber rod of the second type ("thin") was 1.8 cm and the other characteristics were the same as
for the "thick" rods.
The space between the absorber rods was ensured by two stainless steel lattice plates. These plates were 0.5 cm
thick. The upper plate was placed on top of the core tank, as shown in Figure A.12. The diameter of the upper
plate was 45 cm. The lower plate was placed inside the core tank at a distance of 40 cm above the inner surface
of the bottom. The diameter of this plate was 39.4 cm. There were thirty-seven holes arranged in a hexagon
pattern of 4 holes on a side for the absorber rods in these plates. Twenty-eight holes, including the center hole,
were 2.2 cm in diameter. Nine holes in the outer rows for the "thin" rods were 1.9 cm in diameter. Two sets of
lattice plates provided the hole pitches for these experiments, 4.0 cm and 6.0 cm. Also there were three 4-cm-diameter holes for control rods and two holes for the feed and drain tubes. The positions of these holes are not
known exactly.
The experiments were performed at room temperature (approximately 20C).
A.7 HEU-SOL-THERM-035 -- BORON CARBIDE ABSORBER RODS IN
URANIUM (89% 235U) NITRATE SOLUTIONS
A.7.1 Overview of Experiment
A large number of critical experiments with absorber elements of different types in uranium nitrate solution of
different enrichments and concentrations were performed in 19611963 at the Solution Physical Facility of the
Institute of Physics and Power Engineering (IPPE), Obninsk, Russia. The nine experiments included in this
evaluation were performed with uranium enriched to 89 wt % 235U. Uranium nitrate solution with uranium
concentration of 37.51 g/l, 74.87 g/l, or 152.3 g/l was pumped into the core or inner tank, a stainless steel
cylindrical tank with inner diameter 110 cm. Three experiments were performed without absorber rods. In six
experiments different numbers of boron carbide absorber rods were inserted in the core tank. The absorber rods
were arranged in a hexagonal lattice with different pitches. There was a thick side and bottom water reflector in
these experiments.
A.7.2 Description of Experimental Configuration
A diagram of the critical assembly is shown in Figure A.15. The experiment was performed in the same room as
the other uranium-solution experiments at IPPE. The room had dimensions 7.5 × 5.5 × 8.8 m. The core central
axis was 2 m from the north wall, 5.5 m from the south wall, and 2.75 m from the west and east walls. All the
walls, the ceiling, and the floor were concrete. The thickness of the walls was approximately 100 cm, the
thickness of the ceiling was 75 cm, and the thickness of the floor was 20 cm.
The critical assembly consisted of two open-topped coaxial cylindrical tanks. The core tank was 110.0 cm in
inner diameter, 250.0 cm tall, with wall thickness 0.6 cm and bottom thickness 1.5 cm. The reflector tank had
198.4 cm inner diameter, was 300 cm tall, with wall thickness 0.8 cm and bottom thickness 1.0 cm. The core
tank stood on a pedestal inside the reflector tank. The height of the pedestal was 36.0 cm. No other
characteristics of the pedestal are known. The reflector tank stood on the floor.
The core tank was partially filled with the aqueous solution of uranyl nitrate, UO2(NO3)2, with some excess of
nitric acid (HNO3). The reflector tank was filled with distilled water in all cases. The height of the water
reflector measured from the bottom (inner surface) of the core tank is shown in Table A.8.
Three experiments were performed without absorber rods. One arrangement of the absorber rods for the
different cases is shown in Figure A.16. The experimental results obtained for the different experimental
conditions are presented in Table A.8.
Table A.8 Critical dimensions for HEU-SOL-THERM-035
| Case number | Uranium
concentration,
g/l |
Number of absorber rods | Number of holes in the lattice plates | Solution
volume,
liters |
Water reflector
height,
cm |
| 1 | 37.51 | none | 163 | 184.0 ± 0.3 | 40.0 |
| 2 | 19 | 163 | 215.0 ± 0.4 | 40.0 | |
| 3 | 18 | 163 | 213.0 ± 0.4 | 40.0 | |
| 4 | 19 | 163 | 200.0 ± 0.4 | 40.0 | |
| 5 | 74.87 | none | 163 | 134.0 ± 0.2 | 40.0 |
| 6 | 19 | 85 | 146.0 ± 0.2 | 40.0 | |
| 7 | 152.3 | none | --(a) | 113.0 ± 0.2 | 95.0 |
| 8 | 19 | 85 | 118.0 ± 0.2 | 95.0 | |
| 9 | 61 | 163 | 116.4 ± 0.2 | 95.0 |
(a) No lattice plates.
The absorber rods were stainless steel tubes with outer diameter of 5.5 cm, 255 cm long, with wall thickness
0.5 cm, and bottom thickness 0.7 cm. These tubes were filled with a powder of boron carbide.
The space between the absorber rods was ensured by two stainless steel lattice plates. These plates were 1.7 cm
thick. The upper plate was placed on top of the core tank, as shown in Figure A.15. The diameter of the upper
plate was 115 cm. The lower plate lay on the bottom of the core tank. The diameter of this plate was 109.6 cm.
Two sets of lattice plates were used in these experiments. There were 85 holes 5.55 cm in diameter arranged in a
triangular lattice with pitch 10.6 cm for absorber rods in the first set of plates, as shown, for example, in
Figure A.5. There were 163 holes 5.55 cm in diameter arranged in a triangular lattice with pitch 7.6 cm for
absorber rods in the second set of plates, as shown, for example, in Figure A.16.
There were no lattice plates in Case 7, one of the experiments without absorber rods. There was only the lower
lattice plate and no upper lattice plate in Cases 1 and 5, the other experiments without absorber rods.
The experiments were performed at room temperature (approximately 20C).
A.8 HEU-SOL-THERM-036 -- SQUARE-PITCHED LATTICES OF
BORON CARBIDE ABSORBER RODS IN URANIUM NITRATE
SOLUTION
A.8.1 Overview of Experiment
The four experiments included in this evaluation were performed in 1969--1970 at the Solution Physical Facility
of the Institute of Physics and Power Engineering (IPPE), Obninsk, Russia. The purpose of these experiments
was to determine the effect of boron carbide absorber rods on the critical mass of light-water-moderated
homogeneous uranyl nitrate solution.
The experiments were performed with uranium enriched to 89 wt % 235U. Uranium nitrate solution with uranium
concentration of 92.7 g/l was pumped into a stainless steel square tank with inner dimensions 72.6 × 72.6 cm.
One experiment was performed without absorber rods and three experiments were performed with different
numbers of absorber rods arranged in a square uniform lattice with different pitches, inserted in the tank. There
was no reflector in these experiments.
A.8.2 Description of Experimental Configuration
A diagram of the critical assembly is shown in Figure A.17. The experiment was performed in the same room as
the other uranium-solution experiments at IPPE. The room had dimensions 7.5 × 5.5 × 8.8 m. The core central
axis was 2 m from the north wall, 5.5 m from the south wall, and 2.75 m from the west and east walls. All the
walls, the ceiling, and the floor were concrete. The thickness of the walls was approximately 100 cm, the
thickness of the ceiling was 75 cm, and the thickness of the floor was 20 cm.
The critical assembly was in an open-topped square tank. The tank was 72.6 × 72.6 cm in inner dimensions, 110.0 cm tall, with wall thickness 0.3 cm, and bottom thickness 0.5 cm. To decrease the effect of the room-returned neutrons the tank bottom and sides were covered on the outside by 0.05-cm-thick cadmium sheets. The tank stood on a pedestal in the room.
The tank was partially filled with the aqueous solution of uranyl nitrate UO2(NO3)2 with some excess of nitric
acid (HNO3). The experimental results obtained for the different experimental conditions are presented in
Table A.9.
Table A.9 Critical dimensions for HEU-SOL-THERM-036
| Case number | Number of absorber rods | Pitch of absorber rods, cm | Solution volume,
liters |
| 1 | -- | -- | 83.36 ± 0.2 |
| 2 | 36 | 12.0 | 104.1 ± 0.3 |
| 3 | 64 | 9.0 | 157.1 ± 0.4 |
| 4 | 81 | 8.0 | 327.8 ± 0.7 |
The square lattice of boron carbide absorber rods was inserted in the solution in Cases 2 4. The number of the
absorber rods in the lattice and their pitch are shown in Table A.9.
The absorber rods were stainless steel tubes with outer diameter of 3.4 cm, 130 cm long, with wall thickness
0.15 cm, and bottom thickness 0.5 cm. These tubes were filled with a powder of boron carbide.
The spacing between the absorber rods was ensured by two stainless steel lattice plates. These plates were
0.3 cm thick. The upper plate was placed on top of the core tank, as shown in Figure A.17. In the upper plate
were 36, 64, or 81 holes 3.45 cm in diameter arranged in a square lattice with pitch 12.0, 9.0, or 8.0 cm,
respectively, for the absorber rods. The lower plate lay on the bottom of the tank. In the lower plate were 36, 64,
or 81 holes 0.3 cm in diameter arranged in a square lattice with pitch 12.0, 9.0, or 8.0 cm. The dowels of the
absorber rods were inserted in these holes.
There were no lattice plates in Case 1, the experiment without absorber rods.
Four boron carbide control rods were suspended above the surface of the solution. The control rods were
stainless steel tubes with outer diameter 3 cm and wall and bottom thickness 0.2 cm filled with boron carbide
powder. The distance between the critical solution surface and the bottom of the control rods varied from 10 to
20 cm above the solution.
The experiments were performed at room temperature (approximately 20C).
A.9 HEU-SOL-THERM-037 -- HEXAGONALLY PITCHED LATTICES
OF BORON CARBIDE ABSORBER RODS IN URANIUM NITRATE
SOLUTION
A.9.1 Overview of Experiment
A large number of critical experiments with absorber elements of different types in uranium nitrate solution of
different enrichments and concentrations were performed in 19611963 at the Solution Physical Facility of the
Institute of Physics and Power Engineering (IPPE), Obninsk, Russia. The nine experiments included in this
evaluation were performed with uranium enriched to 89 wt % 235U. Uranium nitrate solution with uranium
concentration of 41.9 g/l, 61.4 g/l, or 83.0 g/l was pumped into the core or inner tank, a stainless steel cylindrical
tank with inner diameter 160 cm. Three experiments were performed without absorber rods. In six experiments
different numbers of boron carbide absorber rods were inserted in the core tank. The absorber rods were
arranged in a hexagonal lattice with pitch 6.0 cm. There was a thin side and bottom water reflector in these
experiments.
A.9.2 Description of Experimental Configuration
A diagram of the critical assembly is shown in Figure A.18. The experiment was performed in the same room as
the other uranium-solution experiments at IPPE. The room had dimensions 7.5 × 5.5 × 8.8 m. The core central
axis was 2 m from the north wall, 5.5 m from the south wall, and 2.75 m from the west and east walls. All the
walls, the ceiling, and the floor were concrete. The thickness of the walls was approximately 100 cm, the
thickness of the ceiling was 75 cm, and the thickness of the floor was 20 cm.
The critical assembly consisted of two open-topped coaxial cylindrical tanks. The core tank was 160.0 cm in
inner diameter, 200.0 cm tall, with wall and bottom thickness 0.65 cm. A stainless steel jacket with outer
diameter 170.6 cm, 155.95 cm tall, with wall, top, and bottom thickness 0.65 cm was welded to the core tank.
The jacket was concentric with the core tank. The distance between the outer wall surface of the core tank and
the inner wall surface of the jacket was 4.0 cm. The distance between the bottom (inner surface) of the core tank
and top (inner surface) of the jacket was 150.0 cm. The distance between the bottom (outer surface) of the core
tank and bottom (inner surface) of the jacket was 4.0 cm. The reflector tank had 198.4 cm inner diameter, was
300 cm tall, with wall thickness 0.8 cm, and bottom thickness 1.0 cm. The core tank was suspended in the
reflector tank with 1.5 cm thick tank flanges. When mounted, the nominal distance between the bottom (outer
surface) of the jacket and the bottom of the reflector tank (inner surface) was 95.85 cm. The reflector tank stood
on the floor.
The core tank was partially filled with the aqueous solution of uranyl nitrate, UO2(NO3)2, with some excess of
nitric acid (HNO3). In all cases the jacket was filled with distilled water up to the top of the jacket. The reflector
tank was empty in all cases.
Three experiments were performed without absorber rods. The arrangement of the absorber rods for the different
cases is shown in Figures A.2 A.4.
The absorber rods were stainless steel tubes with outer diameter of 3.2 cm, 215 cm long, with wall thickness
0.25 cm, and bottom thickness 0.4 cm. These tubes were filled with a powder of boron carbide.
The space between the absorber rods was ensured by two stainless steel lattice plates. These plates were 0.5 cm
thick. The lower plate was fastened inside the core tank at a distance of 15.0 cm above the inner surface of the
bottom. The diameter of this plate was 159.4 cm. The upper plate, with fastened absorber rods, was movable in
vertical direction. In the lower position the upper lattice plate was placed on top of the core tank, as shown in
Figure A.18, and the absorber rods touched the core tank bottom. In the upper position the distance between the
ends of the absorber rods and the core tank bottom was 10.0 cm. The diameter of the upper plate was not known.
There were 451 holes 3.25 cm in diameter arranged in a triangular lattice with pitch 6.0 cm for the absorber rods
in these plates, as shown in Figure A.19.
There were no lattice plates in Cases 1, 3, and 6, the experiments without absorber rods.
For this evaluation only the experiments without absorber rods and with fully inserted absorber rods were
selected. The experimental results obtained for the different experimental conditions are presented in
Table A.10.
Table A.10 Critical dimensions for HEU-SOL-THERM-037
| Case number | Uranium
concentration,
g/l |
Number of absorber rods | Solution volume,
liters |
| 1 | 41.9 | none | 358.0 ± 0.7 |
| 2 | 313 | 544.0 ± 1.0 | |
| 3 | 61.4 | none | 299.0 ± 0.6 |
| 4 | 313 | 388.0 ± 0.7 | |
| 5 | 379 | 478.0 ± 0.9 | |
| 6 | 83.0 | none | 273.0 ± 0.5 |
| 7 | 313 | 320.0 ± 0.6 | |
| 8 | 379 | 381.0 ± 0.7 | |
| 9 | 451 | 575.0 ± 1.1 |
The experiments were performed at room temperature (approximately 20C).
A.10 IEU-COMP-THERM-002 -- WATER-MODERATED U(17)O2
ANNULAR FUEL RODS WITHOUT ABSORBER AND WITH
GADOLINIUM OR CADMIUM ABSORBERS IN 6.8-CM-PITCH
HEXAGONAL LATTICES AT DIFFERENT TEMPERATURES
A.10.1 Overview of Experiment
Critical approach experiments with stainless steel clad UO2 fuel rods (17 wt % 235U) in a water-filled tank were
performed in 19701973 in the MATR facility at the Institute of Physics and Power Engineering, Obninsk,
Russia. The fuel rods were arranged in hexagonal lattices with a pitch of 6.8 cm. Each lattice comprised one of
three forms of the fuel rod: without absorber element, with gadolinium absorber element, or with cadmium
absorber element in the center of each fuel rod. The lattices were fully reflected on all sides with water. The
critical mass was defined for "cold" (~ 20C) and "hot" (~ 200C) assemblies. The six assemblies were zero-power experiments. Water for the "hot" assemblies was heated by an external electric heater.
A.10.2 Description of Experimental Configuration
The experiments were performed in a stainless steel tank with outer diameter 1.5 m and inside height 2.2 m.
The wall and bottom thicknesses of the tank were each 15 cm. The top of the tank during the room-temperature
experiment was open, but it was closed by a 22-cm-thick stainless steel cover for the high temperature
experiments.
A stainless steel cylindrical annulus with outer diameter of 88.0 cm, wall thickness of 2.0 cm, and height of
125.0 cm was placed inside the tank and enveloped the assemblies.
The tank was placed in the center of a hall with dimensions 6 × 5 × 7 m high. The concrete walls of the hall
were 1.2 m thick. The ceiling of the hall was made from concrete also and had a thickness of about 50 cm. The
concrete floor thickness was approximately 20 cm.
Construction and dimensions of the fuel rod are presented in Figure A.20. The fuel region consisted of two
annular parts. The inner part was two concentric stainless steel tubes of 60.6 cm length with outer diameters of
2.92 and 2.40 cm and wall thickness of 0.03 cm. The annular space between these tubes was filled with uranium
dioxide. The outer part of the fuel region had similar construction, length, and wall thickness but the tubes' outer
diameters were 4.18 and 3.66 cm. The total length of the fuel was 60 cm. The top and bottom of the fuel
annuluses were closed by 0.3-cm-thick annular stainless steel plugs. The length of the inner tube of each fuel
annulus was 64.6 cm, to correctly position the fuel in the rod as shown in Figure A.2. Stainless steel annular
plugs (0.3 cm thick) were welded to the top edge of the inner tube of each fuel annulus. These plugs were
slightly smaller in diameter than the outer tubes to allow water to enter.
A stainless steel spiral of diameter 0.3 cm (solid wire) was welded to the outer surface of the tube of diameter
2.92 cm to maintain the space between the two fuel elements. The pitch of the spiral was 40 cm.
Both fuel rod parts were placed in a stainless steel tube with outer diameter of 4.58 cm and wall thickness
0.03 cm. The length of this tube was 64.9 cm. The tube bottom was closed by a 0.3-cm-thick stainless steel plug
with holes to pass water.
Construction and dimensions of the absorber element are presented in Figure A.21. These elements, which were
inserted in the central tube of the fuel rod, were stainless steel tubes with outer diameter of 1.10 cm and wall
thickness 0.03 cm filled by a mixture of Gd2O3 or CdO with Al2O3. The total length of the mixture was 48 cm.
The positions of the fuel rods were fixed at the bottom by a stainless steel bottom lattice plate that rested atop a
stainless steel support plate. Both plates had a diameter of 82.0 cm. The bottom lattice plate was 2.0 cm thick
and had ninety-one 1.5 cm diameter holes arranged in a hexagonal pattern of 6 holes on a side. The support plate
was 1.5 cm thick and had ninety-one 4.7-cm-diameter holes with centers aligned with the bottom lattice plate's
hole centers.
These plates were supported by a stainless steel cylindrical ring with 81.0 cm outer diameter and 19.0 cm height.
The thickness of this ring was 0.5 cm.
The upper lattice plate was 82.0 cm in diameter, 2.0 cm thick, and had 90 holes with diameter of 4.7 cm and a
central hole with diameter of 5.06 cm for the central channel containing the neutron counter. In addition to these
holes, the upper plate had four 3.2 cm diameter holes containing the stainless steel tubes for the safety/control
rods.
The lattice pitch for all plates was 6.8 cm.
During experiments, the tank was completely filled with distilled water. The thickness of the bottom water
reflector, determined by assembly construction, was about 25 cm (including the support plates). Taking into
account that the critical radius of the core in the present experiments is no more than 35 cm, the minimum
side-reflector thickness was equal to 25 cm (including the steel cylinder). The top water reflector was greater
than 35 cm thick.
Three fuel rod lattices were investigated at both room temperature ("cold" assemblies) and at raised temperatures ("hot" assemblies). Critical conditions were achieved with the same loading at two different temperatures for each of three assemblies. Arrangement of the rods without absorber elements in both cold and hot assemblies is shown in Figure A.22. This same grid plate was used for all configurations.
The pressure of the hot assemblies was 4.0 MPa.
In Table A.11Table A.13 the parameters of the assemblies for the "cold" and "hot" experiments are shown. Stated temperatures are averaged values for all thermocouples.
Table A.11 Critical parameters of assemblies without absorber elements
for IEU-COMP-THERM-002
| Case | Number of
fuel rods |
Temperature,
C |
keff |
| 1 | 34 | 22.7 ± 0.3 | 1.0004 |
| 2 | 34 | 218.4 ± 0.3 | 1.0005 |
Table A.12 Critical parameters of assemblies with Gadolinium absorber elements
for IEU-COMP-THERM-002
| Case | Number of
fuel rods |
Temperature,
C |
keff |
| 3 | 74 | 16.4 ± 0.3 | 1.0007 |
| - | 74 | 18.2 ± 0.3 | 1.0011 |
| - | 74 | 20.3 ± 0.3 | 1.0013 |
| - | 74 | 21.8 ± 0.3 | 1.0014 |
| 4 | 74 | 151.0 ± 0.3 | 1.0004 |
| - | 74 | 184.0 ± 0.3 | 0.9940 |
Table A.13 Critical parameters of assemblies with cadmium absorber elements
for IEU-COMP-THERM-002
| Case | Number of
fuel rods |
Temperature,
C |
keff |
| 5 | 68 | 14.5 ± 0.3 | 1.0002 |
| 6 | 68 | 150.6 ± 0.3 | 1.0000 |
| - | 68 | 165.6 ± 0.3 | 0.9980 |
A.11 IEU-SOL-THERM-001 -- GRAPHITE-REFLECTED URANYL
SULPHATE (20.9% 235U) SOLUTIONS
A.11.1 Overview of the Experiment
The purpose of these experiments, performed at the Russian Research Center "Kurchatov Institute" in
19801981, was to investigate nuclear safety issues for a special-purpose compact reactor with an aqueous
solution of uranyl sulphate (20.9 at. % 235U) and graphite reflector. Four configurations of critical assemblies
with different concentrations of uranium in the solution are involved in this work.
A.11.2 Description of the Experiment Configuration
The experiments were performed on critical assemblies of the facility located in a special room 220 cm long,
210 cm wide, and 375 cm high. The facility is situated in the center of the room, so the distances from the core
axis to the concrete walls are 110 cm lengthwise, and 105 cm crosswise. The lowest point of the hemispherical
bottom of the core vessel is 77.4 cm above the concrete floor of the room. Schematics of the critical assembly
with the main structures of the facility are presented in Figure A.23 and Figure A.24, which also give all the
necessary dimensions of the experimental configuration.
The core vessel is a welded steel cylinder with a hemispherical bottom and a lid, the latter penetrated by
vertically arranged steel pipes which form leak-tight channels (Figure A.25). Core vessels of two wall
thicknesses were used, 0.5 cm and 0.3 cm. A coiled cooling pipe (a water-filled tubular cylindrical spiral) is
placed inside the vessel.
The core vessel is surrounded with a graphite reflector. There is a clearance between the cylindrical part of the
vessel and the graphite reflector over the entire height. An appropriate hemispherical cavity was machined into
the graphite to hold the bottom of the core vessel. There is no clearance between the graphite reflector and the
bottom of the vessel with 0.5-cm wall thickness. There is a small fit-up clearance between the hemispherical
surfaces of the graphite reflector and the bottom of the vessel with wall thickness of 0.3 cm, which rests on the
graphite at the bottom of the hemispherical cavity. The graphite reflector contains five vertical channels and one
horizontal channel machined into the graphite blocks.
In its external shape the graphite reflector with the shield is represented by a rectangular parallelepiped. The side
surface of the graphite reflector is surrounded by a shield of borated polyethylene. On top of the reflector is a
steel plate. The reflector with the shield is placed in a steel tray which is fastened to a support plate, separated
from the floor by a clearance.
An aqueous solution of uranyl sulphate is placed in the steel vessel. The inner diameter of 30.5 mm is the same
for vessels of both wall thicknesses. Three benchmark experiment configurations have vessel wall thicknesses
of 0.5 cm, and one configuration has a vessel wall thickness of 0.3 cm. The vessel is recessed into the graphite
reflector to a depth of 65.6 cm from the reflector top (Figure A.23). The thicker vessel is 71.5 cm high from its
end to the inner surface of the bottom (along the axis), and its cylindrical part is 56.25 cm long (Figure A.25).
The vessel lid is 5.9 cm in thickness.
Inside the vessel there is a coiled cooling pipe in the form of a steel cylindrical spiral containing distilled water as coolant. The average diameter of the coiled pipe spiral is 27.5 ± 0.3 cm, and its pitch is 2.0 ± 0.2 cm (Figure A.25). The coiled pipe is 0.6 cm in inner diameter, and its wall is 0.2 cm in thickness. Coolant is supplied to the lower portion of the coiled pipe, and carried away from its upper portion through supply/return
pipes whose diameter and wall thickness are the same as those of the coiled pipe. Axes of the coolant
supply/return pipes are positioned symmetrically on the 21.8 cm diameter circle, and their arrangement is shown
in Figure A.24 and Figure A.25.
Leak-tight steel channels passing through the plate and the vessel lid are submerged in the fuel solution to the
same depth so that the clearance between the inner surface of the vessel bottom and the lower outer surface of the
central channel is 3.0 ± 0.1 cm. The total length of each channel is 72.4 cm (Figure A.25). An empty
experimental channel is located in the center of the core, and the other two channels, intended for poison rods,
are placed symmetrically on the circle 15 cm in diameter (Figure A.24). The steel channels are 4.8 cm in outer
diameter, and their wall thickness is 0.2 cm.
In its external shape the graphite reflector with the shield is a rectangular parallelepiped of height 110 cm. The
thickness of the shield of borated polyethylene, which surrounds the vertical outer surface of the graphite
reflector, is 5.0 ± 0.5 cm, 4.0 ± 0.5 cm, and 3.0 ± 0.5 cm (Figure A.24). There is no borated polyethylene shield
on the top and bottom surfaces of the graphite reflector. Between the cylindrical part of the core vessel and the
graphite reflector there is a clearance of height 49.85 cm (Figure A.25). The width of the clearance is
2.0 ± 0.1 cm for the 0.5-cm-thick vessel and 2.2 ± 0.1 cm for the 0.3-cm-thick vessel.
The reflector has five vertical channels 11.4 cm in diameter, and one horizontal channel for neutron beam
rejection (Figure A.24). Channel #4 goes through the full height of the reflector, and the other vertical channels
are 75.0 ± 0.5 cm in length (from the reflector top). The horizontal channel of section 14×14 cm is directed
tangentially relative to the core vessel. The channel axis is located at 25.0 ± 0.5 cm from the assembly axis, and
at 53 cm from the lower surface of the reflector (Figure A.23). The reflector channels are air filled, and are not
lined with any material.
The upper steel plate of thickness 5 cm has a rectangular cross section of 178×137 cm. Arrangement of the
openings at the plate section and their diameters are the same as in the graphite reflector. In its center, the plate
has an additional opening 36 cm in diameter. The upper plate is located at 9 cm from the upper surface of the
graphite reflector, and at 2.6 ± 0.2 cm from the vessel lid (Figure A.25). The upper plate is mounted on four
hollow box-shaped posts that are placed at the corners of the plate outside the graphite reflector with the shield,
and rest on the support plate at the bottom. The posts are made of 0.6-cm-thick channels, joined by welding.
The post cross section is 9×10 cm in outer dimensions.
The critical assembly is placed in a steel tray of height 40 ± 1 cm (Figure A.23). The tray has the same thickness
of 0.4 cm at all locations. There is a 0.6-cm clearance between the surface of the borated polyethylene and the
side surface of the tray. The tray is fastened to the steel support plate of thickness 1.2 cm. There is a 9.6-cm
clearance between the tray and the steel support plate. The support plate, in its turn, is located at 21.8 cm from
the floor of the room.
Critical configurations differed in uranium concentration in the aqueous solution of uranyl sulphate, and in
thickness of the core vessel wall. Description of the benchmark experiments is given in Table A.14. The critical
condition was determined through addition of a portion of the uranyl sulphate solution to the assembly core. On
addition of the next portion of the solution, the inverse curve was plotted as a function of volume of the added
solution, from which the size of the subsequent portion was determined. In the vicinity of the critical condition
the solution was added in portions with an error of no greater than 1 cm3. In doing so, positive reactivity was
determined each time through direct measurement of the asymptotical period, as well as with an analog-digital
reactivity meter (Reference 3). The condition was considered critical when the measured positive reactivity did
not exceed 0.001$. Thus, the uncertainty in determining the critical condition in reactivity units is ±0.001$.
Table A.14 gives critical parameters for the solution temperature of 20C.
Table A.14 Configurations of benchmark experiments for IEU-SOL-THERM-001
| Configuration
number |
Uranium
concentration
(gU/liter) |
Vessel thickness,
(cm) |
Critical volume
(liters) |
| 1 | 263.3 ± 0.5 | 0.5 ± 0.01 | 28.50 ± 0.03 |
| 2 | 382.2 ± 0.8 | 0.5 ± 0.01 | 18.40 ± 0.03 |
| 3 | 382.2 ± 0.8 | 0.3 ± 0.01 | 17.60 ± 0.03 |
| 4 | 505.0 ± 1.0 | 0.5 ± 0.01 | 15.55 ± 0.03 |
Critical parameters of the configurations were determined with both control rods withdrawn from the core, the
rod bottoms being at 1013 cm from the upper surface of the critical volume of the core.
A.12 LEU-COMP-THERM-031 -- WATER-MODERATED
HEXAGONALLY PITCHED PARTIALLY FLOODED LATTICES
OF U(5%)O2 ZIRCONIUM CLAD FUEL RODS
A.12.1 Overview of Experiment
A series of critical experiments with water-moderated hexagonally pitched lattices with low enriched
(approximately 5% 235U) cylindrical fuel rods was performed in 1961 in RRC "Kurchatov Institute." These
critical experiments consisted of water-moderated uniform lattices of stainless steel or zirconium clad cylindrical
fuel rods. In the some of these experiments the water moderator was poisoned by boric acid.
This evaluation describes six critical configurations with partially flooded hexagonal lattices of zirconium clad
fuel rods with a pitch value of 8 mm.
A.12.2 Description of the Experimental Configuration
Experiments were performed in a 25-mm-thick, open-top, steel tank as shown in Figure A.26. The inside
diameter of the tank was 1800 mm and its outside height was 2200 mm. The top level of the tank coincided with
the floor of the experimental room. The height of the experimental room was 9 meters. The stainless steel tank
support ring, with an inner diameter of 1300 mm and a thickness of 30 mm, sat upon the floor. Under floor,
which was made of 10-mm-thick steel plates, was a basement. The critical assembly upper support ring lay upon
the tank support ring. All details of the assembly, including bottom support plate and the top and bottom lattice
plates, were fixed to the upper support ring by six 40-mm-diameter stainless steel rods. The distance between
these rods and the core was more than 400 mm. Approximately 300 cm above the core was a frame holding the
servomotors for the control rods.
The bottom caps of the fuel rods rested on the 35-mm-thick steel support plate as shown in Figure A.26 and Figure A.27. Outer diameter of the support plate was 1500 mm.
The pitch of the fuel rods was maintained by two aluminum alloy D1 lattice plates as shown in Figure A.27.
The bottom 5-mm-thick lattice plate was placed at 5 mm above the support plate and the top 10-mm-thick lattice
plate was placed at 600 mm above the bottom lattice plate. Holes for the fuel rods were 6.3 mm in diameter
(0.2 mm larger than the fuel rod diameter).
The top water surface was within the fuel region for six experiments. The bottom water reflector was at least
1100 mm thick. The radial reflector was greater than 500 mm thick. Therefore bottom and side reflectors were
effectively infinite.
The cylindrical fuel rods used in these experiments consisted of a 0.75 ± 0.01 mm thick zirconium alloy 110 clad, into which were placed pellets of uranium dioxide, as shown in Figure A.28. According to measurements of more than 100 rods by the X-ray radiography method, the average fuel height was 596.6 ± 2.4 mm. The pellets fit tightly within the clad so that there was no radial gap between fuel and clad. The fuel rods had top and bottom 20 mm high cylindrical zirconium alloy 110 caps above and under the fuel region. There was an air gap of approximately 3.4 mm between the fuel and the top cap. There was also a radial air gap between the end caps and the rod cladding. Its outer diameter was 4.6 mm.
All six critical configurations of hexagonally pitched fuel rods with pitch value 8.0 mm were assembled "dry"
with nearly circular cross sections. They were flooded by water until criticality was reached. The temperature of
the critical assemblies varied in the range of 18C to 20C.
A set of fuel rods consisted of rods from three lots that had slightly differing enrichments, and the critical number
of fuel rods could possibly depend on their distribution within the core. But is was reported that special
experiments proved that the critical number of fuel rods was not dependent on the distribution of the lots within
the core. In these experiments, the lots of the fuel rods were placed as clusters in the core, while in the other
experiments, including the experiments being documented here, the fuel rods were carefully mixed. There was
no observable difference in experimental results between the two methods of fuel-rod arrangement.
The numbers of fuel rods and critical water heights for the six configurations are summarized in Table A.15.
Table A.15 Numbers of fuel rods and height of water for critical uniform configurations
for LEU-COMP-THERM-031
| Case
number |
Critical height
of water, mm(a) |
Critical
number of fuel rods |
Measured sensitivity(b) of
reactivity to water level
/h (10-5/mm) |
| 1 | 337.6± 0.1 | 3717 | 57.0 |
| 2 | 344.9 ± 0.1 | 3710 | 52.8 |
| 3 | 407.0 ± 0.1 | 3011 | 33.0 |
| 4 | 408.9 ± 0.1 | 2903 | 33.6 |
| 5 | 414.3 ± 0.1 | 2877 | 30.0 |
| 6 | 452.3 ± 0.1 | 2649 | 25.0 |
(a) The height was measured from the bottom plane of the fuel region.
(b) Uncertainies of the measurements were approximately 2%.
A.13 LEU-COMP-THERM-032 -- UNIFORM WATER-MODERATED
LATTICES OF RODS WITH U(10%)O2 FUEL IN RANGE FROM
20C TO 274C
A.13.1 Overview of Experiment
This evaluation describes nine critical experiments that were part of a set of 10% enriched uranium fueled lattice
experiments performed in the Russian Research Center "Kruchatov Institute" between 1965 and 1967. This set
of experiments consisted of hexagonal arrays of fuel rods that were fully flooded with water. A critical
configuration was determined for fuel lattice pitches of 0.7, 1.4, and 1.852 cm each evaluated at three different
temperatures ranging from 20C to 274C.
A.13.2 Description of Critical Fuel Rod Arrays and Details of Active Cores
Experiments at room temperature were performed in a 15-mm-thick, open-top, stainless-steel tank. The inside
diameter of the tank was 1590 mm and the inside height was 2550 mm.
Experiments at high temperatures were carried out in a pressure vessel with a pressure 14.7 MPa. The inside diameter of the vessel was 1400 mm, the inside height was approximately 3000 mm and the average wall thickness was approximately 150 mm. The active core was heated by circulating the water moderator through an external electric heater.
The central part of the critical assembly's active core could be moved out (down) or pushed in to compensate for
changes in reactivity and to control criticality. A general view of the assembly is shown in Figure A.29. At
certain temperatures, the mobile section of the fuel was pushed in completely and the active core then became a
uniform lattice of fuel rods.
The goal of these experiments was to determine the temperature at which the fuel rods could be fully inserted to
obtain a critical configuration for each lattice pitch. Three critical uniform lattices were configured for each
lattice pitch at three temperatures of 20C and above.
.
The placement of the fuel rods in the uniform active core is shown in Figure A.30. The pitch in both parts of the core was maintained by three lattice plates. The plates were perforated with holes, which formed the hexagonal 7.0-mm-pitch lattice.
The fuel rods had a circular cross section with the dimensions shown in Figure A.31.
The critical numbers of fuel rods, experiment temperature, and temperature coefficient of reactivity
corresponding to each evaluated configuration are listed in Table A.16. Figure A.32 gives a plan view of a
critical configuration.
Table A.16 Critical fuel rod array descriptions for LEU-COMP-THERM-032
|
Array number |
Pitch, cm |
Temperature, C |
Critical number of fuel rods |
Temperature
coefficient of
reactivity × 104,
(C)-1 |
| 1 | 20 | 2002 | -0.2 | |
| 2 | 0.7 | 166 | 2323 | -3.0 |
| 3 | 263 | 3058 | -5.2 | |
| 4 | 20 | 421 | +0.2 | |
| 5 | 1.4 | 206 | 481 | -3.0 |
| 6 | (0.7 × 2) | 274 | 565 | -5.7 |
| 7 | 20 | 523 | +0.7 | |
| 8 | 1.852 | 193 | 523 | -1.0 |
| 9 | (0.7 × 7) | 263 | 559 | -2.0 |
A.14 LEU-SOL-THERM-005 -- BORON CARBIDE ABSORBER RODS IN
URANIUM (5.64% 235U) NITRATE SOLUTION
A.14.1 Overview of Experiment
A large number of critical experiments with absorber elements of different types in uranium nitrate solution of
different enrichments and concentrations were performed in 19611963 at the Solution Physical Facility of the
Institute of Physics and Power Engineering (IPPE), Obninsk, Russia. The three experiments included in this
evaluation were performed with uranium enriched to 5.64 wt % 235U. Uranium nitrate solution with uranium
concentration of 400.2 g/l was pumped into the core or inner tank, a stainless steel cylindrical tank with inner
diameter 110 cm. One experiment was performed without absorber rods, another one with central rod, and another
one with cluster of seven absorber rods arranged in a hexagonal lattice with pitch of 31.8 cm, inserted in the center
of the core tank. There was a thick side and bottom water reflector in these experiments.
A.14.2 Description of Experimental Configuration
A diagram of the critical assembly is shown Figure A.33. The experiment was performed in a room with dimensions
7.5 × 5.5 × 8.8 m. All the walls, the ceiling, and the floor were concrete. The thickness of the walls was
approximately 100 cm, the thickness of the ceiling was 75 cm, and the thickness of the floor was 20 cm.
The critical assembly consisted of two open-topped coaxial cylindrical tanks. The core tank was 110.0 cm in inner
diameter, 250.0 cm tall, with wall thickness 0.6 cm, and bottom thickness 1.5 cm. The reflector tank had 198.4 cm
inner diameter, was 300 cm tall, with wall thickness 0.8 cm, and bottom thickness 1.0 cm. The core tank stood on
a pedestal inside the reflector tank. The height of the pedestal was 36.0 cm. All other characteristics of the pedestal
are not known. The reflector tank stood on the floor.
The core tank was partially filled with the aqueous solution of uranyl nitrate UO2(NO3)2 with some excess of nitric
acid (HNO3). The reflector tank was filled with distilled water in all cases. The height of the water reflector
measured from the bottom (inner surface) of the core tank was 108.0 cm.
The three experiments performed were: one without absorber rods; another one with central absorber rod; and another
one with seven absorber rods in hexagonal lattice with pitch 31.2 cm.
The absorber rods were stainless steel tubes with outer diameter of 5.5 cm, 255 cm long, with wall thickness 0.5 cm,
and bottom thickness 0.7 cm. These tubes were filled with a powder of boron carbide.
The experimental results obtained for the different experimental conditions are presented in Table A.17.
Table A.17 Critical dimensions for LEU-SOL-THERM-005
| Case number | Number of absorber rods | Solution volume,
liters |
| 1 | -- | 548.0 ± 0.9 |
| 2 | 1 | 606.0 ± 1.0 |
| 3 | 7 | 983.0 ± 1.5 |
The experiments were performed at room temperature (approximately 20C).
A.15 LEU-SOL-THERM-006 -- BORON CARBIDE ABSORBER RODS IN
URANIUM (10% 235U) NITRATE SOLUTION
A.15.1 Overview of Experiment
A large number of critical experiments with absorber elements of different types in uranium nitrate solution of
different enrichments and concentrations were performed in 19611963 at the Solution Physical Facility of the
Institute of Physics and Power Engineering (IPPE), Obninsk, Russia. The five experiments included in this
evaluation were performed with uranium enriched to 10 wt % 235U. Uranium nitrate solution with uranium
concentration of 420.5 g/l was pumped into the core or inner tank, a stainless steel cylindrical tank with inner
diameter 110 cm. One experiment was performed without absorber rods. In each of four experiments a different
number of boron carbide absorber rods was inserted in the core tank. The absorber rods were arranged in a
hexagonal lattice with different pitches. There was a thick side and bottom water reflector in these experiments.
A.15.2 Description of Experimental Configuration
A diagram of the critical assembly is shown in Figure A.34 (vertical cut). The experiment was performed in the
same room as the other uranium-solution experiments at IPPE (see Appendix B of HEU-SOL-THERM-014).
The room had dimensions 7.5 × 5.5 × 8.8 m. The core central axis was 2 m from the north wall, 5.5 m from the
south wall, and 2.75 m from the west and east walls. All the walls, the ceiling, and the floor were concrete. The
thickness of the walls was approximately 100 cm, the thickness of the ceiling was 75 cm, and the thickness of the
floor was 20 cm.
The critical assembly consisted of two open-topped coaxial cylindrical tanks. The core tank was 110.0 cm in
inner diameter, 250.0 cm tall, with wall thickness 0.6 cm, and bottom thickness 1.5 cm. The reflector tank had
198.4 cm inner diameter, was 300 cm tall, with wall thickness 0.8 cm, and bottom thickness 1.0 cm. The core
tank stood on a 36 cm tall pedestal inside the reflector tank.
The core tank was partially filled with the aqueous solution of uranyl nitrate UO2(NO3)2 with some excess of
nitric acid (HNO3). The reflector tank was filled with distilled water in all cases. The height of the water
reflector measured from the bottom (inner surface) of the core tank was 108.0 cm.
One experiment was performed without absorber rods. An arrangement of the absorber rods in the grid plate is
shown in Figure A.35. The experimental results obtained for the different experimental conditions are presented
in Table A.18.
Table A.18 Critical dimensions for LEU-SOL-THERM-006
| Case number | Number of
absorber rods |
Number of holes in the lattice plate | Solution volume,
liters |
| 1 | none | 85 | 210.0 ± 0.3 |
| 2 | 7 | 85 | 231.5 ± 0.4 |
| 3 | 18 | 163 | 251.3 ± 0.4 |
| 4 | 19 | 163 | 255.5 ± 0.4 |
| 5 | 31 | 85 | 306.3 ± 0.5 |
The experiments were performed at room temperature (approximately 20C).
