1. Purpose
This analysis covers a design of the potential repository backfill emplacement system, specifically within the emplacement drifts. Surface operations, backfill preparation, and transport of the backfill from the surface to the emplacement drifts is outside the scope of this analysis. Also, this analysis does not address performance assessment of the backfill material itself; these issues will be addressed in future analyses. The current direction for Approach to Implementing the Site Recommendation Design Baseline (Stroupe 2000, Attachment 1, p. 1) specifies "no emplacement drift backfill;" however, the directive further "protects the option to physically install emplacement drift backfill." This analysis covers that option. In order to meet the objectives and complete the tasks outlined in the Development Plan (CRWMS M&O 2000a), a conceptual layout, including the number of emplacement drifts, was required. The Activity Evaluation (CRWMS M&O 1999a, p. 1) for this work package specifies that the design will be based on the Enhanced Design Alternative (EDA) II concept. The Enhanced Design Alternative II Report (CRWMS M&O 1999b) was used for assumptions concerning the conceptual layout.1.1 Objective
The objectives of this analysis are to support the Repository System Operation revision of Section I of related System Description Documents (SDDs), provide a basis for the SDD 2 (System Description), and support Repository System Operation with writing the SDD Section 2 as appropriate to support the Site Recommendation (SR).1.2 Primary Tasks
The portion of the backfill emplacement system covered in this analysis addresses only the equipment and methodology for the placement of backfill within the emplacement drifts. This is the only portion of the backfill emplacement system which has changed from the Viability Assessment of a Repository at Yucca Mountain (DOE 1998, Vol. 2, Section 5.3), due to the introduction of drip shields over the waste packages, based on the EDA II concept. The introduction of drip shields reduces the area available for backfilling equipment and requires the backfill material to be placed on the drip shields rather than directly on the waste packages. Also considered in this analysis are the handling and physical characteristics of candidate backfill materials being considered for SR by the Subsurface Performance Testing Section. The handling and physical characteristics of the backfill material must be considered in adaptation of the emplacement equipment and methodology proposed, and in determining the configuration of the backfill material, as it would be emplaced within the drifts. The equipment concepts and methodology used in this analysis for the placement of backfill have been adapted from the Backfill Strategy and Preliminary Design Analysis (CRWMS M&O 1997a). The Backfill Strategy and Preliminary Design Analysis (CRWMS M&O 1997a, Section 8.3), completed as an initial study, evaluated differing design concepts for the placement of backfill within the emplacement drifts and concluded that the placement of backfill over waste packages by dump stowing was the most favorable method. This approach has been carried forward in this analysis with the addition of a drip shield over the waste packages and with consideration given to the candidate backfill materials proposed. Design criteria from the Backfill Emplacement System Description Document (CRWMS M&O 2000b) specifically pertaining to the subsurface components of the backfill system and emplacement are addressed. Design constraints established on the basis of the Monitored Geologic Repository Project Description Document (CRWMS M&O 1999c, Section 2.2) were used to establish the physical parameters of the emplacement drifts and components impacting backfill emplacement. Primary tasks of this analysis include:2. Quality Assurance
This activity has been evaluated (CRWMS M&O 1999b) in accordance with QAP-2-0, Conduct of Activities, and has been determined to be quality affecting and subject to the requirements of the Quality Assurance Requirements and Description document (DOE 2000). However, scheduling is exempt from QARD requirements per QAP-2-0. This analysis was prepared in accordance with AP-3.10Q, Analyses and Models, and the approved Development Plan (CRWMS M&O 2000a). The design analysis Classification of the MGR Backfill Emplacement System (CRWMS M&O 1999d, Section 7.), performed in accordance with QAP-2-3, Classification of Permanent Items, has concluded that the backfill emplacement system is Quality Level 2 (QL-2). This classification is made on the basis that failure of the backfill emplacement system could indirectly result in a condition adversely affecting public safety (CRWMS M&O 1999d, Section 6.1).3. Computer Software and Model Usage
No software or models subject to the requirements of the Quality Assurance Requirements and Description (DOE 2000) were used in the preparation of this document. Only a project approved office automation system (word processor) and computer aided drafting and design (CAD, used solely for visual display and graphical representation of concept)—not required to be qualified per AP-SI.1Q, Section 2.1, Software Management—were used. All calculations were performed manually, based on accepted mathematical formulation, without the aid of computer modeling or computer-generated analysis. No qualification of software was required and all software was appropriate for the application.4. Design Input
Unqualified data and input requiring confirmation are identified and are tracked in accordance with AP-3.15Q, Managing Technical Product Inputs. Requests for input, and control, receipt, and transmittal of inputs have been exchanged in accordance with AP-3.14Q, Transmittal of Input.4.1 Data and Parameters
4.1.1 Backfill Material Characteristics
In the evaluation of dry bulk materials conveyance, there are a number of material characteristics and properties which are important. The SME (Society of Mining Engineers) Mineral Processing Handbook, "Dry Bulk Material Transport" (Hays and Van Slyke 1985, Chapter 3), was used to identify material handling characteristics and physical properties that are important in the consideration of backfill transport and emplacement concepts. The Mineral Processing Handbook (Hays and Van Slyke 1985) is one of the few handbooks that provides information and guidance in the area of materials handling characteristics. Its principals are widely accepted and applied throughout the industry. Material characteristics from the handbook identified as important in the consideration of backfill transport and emplacement concepts are:4.1.2 Candidate Backfill Materials and Range of Physical Characteristics
An Input Request (CRWMS M&O 1999e) was sent to the Subsurface Performance Testing Section to establish the backfill materials being considered for the SR and a range of values for the material handling (physical) characteristics (Section 4.1.1). An Input Transmittal (CRWMS M&O 2000c, Item 1), including the Table, "Summary of the Range of Material Physical Characteristics for Backfill Materials Being Considered for SR," (included in this analysis as Table 1) was provided by the Subsurface Performance Testing Section in response to the Input Request. This information has been used in Section 6.2.1 in the discussion of backfill material handling characteristics; in Section 6.3.6 in the discussion of adaptation of proposed backfill emplacement equipment and methodology to candidate backfill materials; and in Section 6.4.1 to establish bounding conditions for the range of backfill configurations, based on maximum and minimum angles of repose. The approximate size and manufacturer’s specifications for the particle size range and distribution of the candidate backfill materials, indicated above in Table 1, are used in Section 6.2.1. This information is used for reference only, and does not require confirmation because these material characteristics are non-impacting to the system proposed nor to the conclusions of the analysis. The qualified data for bulk density and the minimum and maximum angles of repose are discussed in Sections 6.4.5 and 6.4.1.2, respectively, and have been used in Sections I-3, I-4, I-5, I-6, I-9, and I-10 for the calculation of the backfill volumes and tonnages.4.1.3 Drip Shield Design
Section 4.2.3.4 specifies the requirement for a drip shield. An Input Transmittal was supplied by Waste Package Operations for the Drip Shield Design (CRWMS M&O 1999f) to be evaluated and documented for SR. The drip shield design and dimensions used in this analysis are shown in Section 6.1. Following issuance of the above Input Transmittal, the Structural Calculations of the Drip Shield Statically Loaded by the Backfill and Loose Rock Mass (CRWMS M&O 2000d, Attach. II, p. 1) was issued with drip shield dimensions slightly different than those provided by the Input Transmittal (-7 mm in bulkhead width, -2 mm in bulkhead height, and +23 mm to the maximum height). These slight variations in drip shield dimensions, if applied, would result in backfill volume calculations slightly different than those contained in this analysis, which was based on earlier information. However, for the purpose for which this information is intended, these changes are non-impacting to the conclusions of this analysis. Input from the Drip Shield Design (CRWMS M&O 1999f) was used to define the physical parameters for backfill emplacement. Although the drip shield dimensions provided in the Structural Calculations of the Drip Shield Statically Loaded by the Backfill and Loose Rock Mass (CRWMS M&O 2000d, Attach. II, p. 1) are approved and the best available information, the current drip shield design remains conceptual. The drip shield configuration used in this analysis is unqualified (see Section 7.3).4.1.4 Invert/Ballast Structure
Section 4.2.3.5 specifies that a carbon steel frame and granular ballast material is to be used to construct the invert. The steel invert/ballast design used in this analysis is based on the current steel invert design from the Invert Configuration and Drip Shield Interface technical report (CRWMS M&O 2000e, Figure 5). This design and associated dimensions are shown in Section 6.1. Input from the invert/ballast design was used to define the physical parameters for backfill emplacement.4.2 Design Criteria
The design criteria used in this analysis are based on Backfill Emplacement System Description Document (CRWMS M&O 2000b) and the Monitored Geologic Repository Project Description Document (CWRMS M&O 1999c, Section 2.2).4.2.1 System Performance
4.2.1.1 Emplacement Period
The system shall be capable of placing the total repository backfill within a period of 10 years as part of subsurface closure activities (CWRMS M&O 2000b, Section 1.2.1.1). This criterion is addressed in Section 6.4.6.4.2.1.2 Emplacement Drift Length
The system shall install prepared backfill material in emplacement drifts having a maximum length of 700 m (CWRMS M&O 2000b, Section 1.2.1.2). In the context used in the SDD (CWRMS M&O 2000b), "emplacement drift" refers to one-half of the total length of an emplacement drift. However, in the context it is used in this analysis, "emplacement drift" refers to the total length of the drift (refer to Section 5.5). This criterion is addressed in Sections 6.3.3 and 6.4.3.4.2.2 Safety Criteria
4.2.2.1 Remote Operation
The system shall use remotely operated equipment in subsurface emplacement areas that are restricted from human access (i.e., emplacement drifts while waste is emplaced in the repository) (CWRMS M&O 2000b, Section 1.2.2.1.1). This criterion is addressed in Sections 6.3.4.4.2.3 System Interfacing Criteria
4.2.3.1 Clearance Envelope
The system shall operate within a Ground Control System clearance envelope of 300 mm inside the drift diameter, as defined in Figure I-1 in the Backfill Emplacement System Description Document (CWRMS M&O 2000b, Section 1.2.4.3). This criterion is addressed in Sections 6.1 and 6.3.5.4.2.3.2 Emplacement Drift Grade
The system shall be capable of transporting and placing the backfill over a maximum grade of +/- 1.0 percent within the emplacement drifts (CWRMS M&O 2000b, Section 1.2.4.5). This criterion is addressed in Section 6.3.3.4.2.3.3 Emplacement Drift Diameter
The excavated emplacement drift diameter shall be nominally 5.5 meters (CRWMS M&O 1999c, Section 2.2.1.1.3). This criterion is addressed in Sections 6.1 and 6.3.5.4.2.3.4 Drip Shield
A free-standing drip shield shall be installed, at the time of repository closure, between the waste package and the backfill (CRWMS M&O 1999c, Section 2.2.1.1.9). This criterion is addressed in Sections 6.1 and 6.3.4.2.3.5 Invert/Ballast
The invert along the bottom of drifts shall be constructed of a carbon steel frame with granular natural material used as ballast (CRWMS M&O 1999c, Section 2.2.1.1.6). This criterion is addressed in Sections 6.1 and 6.3.4.3 Codes and standards
This section is not applicable to this analysis. No codes or standards are used.5. Assumptions
5.1 Gantry Traversing System
The drive mechanism for the backfill system gantries will be similar to concepts previously designed for other gantries designed to operate within the emplacement drifts utilizing the gantry/third-rail electrification system. Rationale: Detailed drive designs, based on similar operational parameters for gantries with a total load capacity in excess of 150 MT (including waste package), have been developed well beyond the concepts in the Preliminary Waste Package Transport and Emplacement Equipment Design analysis (CRWMS M&O 1997b, Sections 7.4.3.3, 7.4.3.8, and 8.4.3). They also utilize the gantry/third-rail electrification system. Therefore, it is reasonable to assume that similar drive units can be developed for the lighter-weight, reduced-payload, backfill emplacement system gantries proposed in this analysis. Confirmation of this assumption is not critical to the content of this analysis. Information regarding similar gantry drive designs was used for reference only. Alternative modes of propulsion will not affect the backfill emplacement system or methodology proposed. This assumption is applied in Section 6.3.3.5.2 Data Communication System
The communication systems required to transmit and receive data for the monitoring and control functions of the remotely operated backfill emplacement system proposed in this analysis are based on technologies currently available. Rationale: A number of different data communication technologies currently available have been previously examined and evaluated in the Subsurface Waste Package Handling – Remote Control and Data Communications Analysis (CRWMS M&O 1997c, Section 7.4.2 – 7.4.4). That analysis discusses, in detail, several data communication options applied to remotely operated gantries within the emplacement drifts, including complicated monitoring and control of gantries that perform detailed tasks associated with waste package handling and emplacement. Currently available data communication technologies discussed in the analysis for mobile rail equipment include: direct radio, leaky feeder, and slotted microwave guide systems. Therefore, it is reasonable to assume that these same technologies can be applied to transmit and receive data for the lesser-complicated monitoring and control functions of the backfill emplacement system. Confirmation of this assumption is not critical to the content of this analysis. Information regarding currently available data communication technologies was used for reference only. Alternative methods of monitoring and controlling the functions of the remotely operated backfill emplacement system will not affect the backfill emplacement system or methodology proposed. This assumption is applied in Section 6.3.4.6.5.3 Scheduling Parameters for Backfill Emplacement
The actual time of backfill emplacement per day is 7.755 hrs/day based on a 2-shift/day, single operation, allowing for maintenance and waiting time. The personnel work schedule used for scheduling purposes is on the basis of a 250 days/year operation. Rationale: The scheduling of backfilling is based on the Backfill Strategy and Preliminary Design Analysis (CRWMS M&O 1997a, Section 4.3.11 and Attachment I). Work schedule components are described below:| 1) | 52 weeks/year @ 5 days/week = | 260 days/year - 10 days/year (holidays, etc.) 250 days/year available |
| 2) | 8.0 hrs/shift total - 1.5 hrs/shift non-production 6.5 hrs/shift production |
| 3) | 2 shifts/day |
5.4 Diameter of Ventilation Raise
The diameter of the ventilation raise located at the drift center in all of the emplacement drifts is 2.0 m. Rationale: The Enhanced Design Alternative II Report (CRWMS M&O 1999b) does not specify any change in the diameter of the ventilation raise. Therefore, the diameter of the ventilation raise is assumed to remain unchanged from the Viability Assessment design of 2.0 m (DOE 1998, Section 4.2.2.3). This assumption does not require confirmation. This information was used in the calculation of backfill volumes for scheduling purposes, a non-Q item (Section 2). This assumption is referenced in Section 6.3.6, its application is discussed in Section 6.4.4, and is used in Sections I-4 and I-6 for calculating the backfill volumes in the end sections.5.5 Number of Emplacement Drifts
The number of emplacement drifts used in this analysis is 50. Rationale: Table A-4 of the Enhanced Design Alternative II Report (CRWMS M&O 1999b, Section A.4) clearly defines the total number of drifts as 58, with 8 excluded for other uses, totaling 50 remaining drifts with useable emplacement length. In the context in which it is used here, "emplacement drift" refers to the total length of an emplacement drift, including both sides, separated in the middle by the physical stand-off distance for the ventilation raise (see Section 5.6). This assumption does not require confirmation. This information was used in the calculation of backfill volumes for scheduling purposes, a non-Q item (Section 2). This assumption is referenced in Section 4.2.1.2, its application is discussed in Sections 6.4 and 6.4.4, and is used in Section I-9 for calculating the backfill volumes.5.6 Stand-Off Distances
The total stand-off distances, i.e., unusable space, in each emplacement drift is 34 m. Rationale: Stand-off distances are necessary to shield the access drifts and to provide ventilation throughout the backfill emplacement operation. Stand-off distances are areas void of waste packages and, thus, will receive no backfill during closure. Therefore, allowances have been made for these voids in the calculation of backfill volumes. The stand-off distances for EDA II are defined in Table A-6 in the Enhanced Design Alternative II Report (CRWMS M&O 1999b, Section A.6) and remain unchanged in this analysis. A thermal/radiological stand-off distance of 15 m at the ends of the emplacement drifts, and a physical stand-off distance of 4 m, at the drift center, for the central ventilation raise has been used in the calculation of the backfill volumes. This amounts to a total stand-off distance of 34 m per drift. This assumption does not require confirmation. This information was used in the calculation of backfill volumes for scheduling purposes, a non-Q item (Section2). This assumption is referenced in Section 5.5, its application is discussed in Sections 6.4 and 6.4.4, and is used in Sections I-4, I-6, and I-9 for calculating the backfill volumes.6. Design Analysis
6.1 Physical Parameters for Backfill Emplacement
Design parameters established in Sections, 4.1.3, 4.1.4, 4.2.3.1, and 4.2.3.3 define the physical parameters for the placement of backfill within the emplacement drifts. The drift diameter, drip shield and invert conceptual designs, and ground control system clearance envelope respective to these sections define the physical parameters within which backfill is to be emplaced. Figure 1 shows a cross-section of a typical emplacement drift with the current drip shield and invert designs (Sections 4.2.3.4 and 4.2.3.5). The backfill system is designed to utilize the emplacement gantry rail/electrified third-rail system used for waste emplacement (Section 6.3.1).6.2 Candidate Backfill Materials
Four different candidate backfill materials (Section 4.1.2), in three different particle-size classifications (based on Hays and Van Slyke 1985, Table 16, p. 10-33) have been selected and are being evaluated by the Subsurface Performance Testing Section for SR: Overton sand, deriving its name from its origin, Overton, Nevada; "4-10" silica aggregate, deriving its name from the gradation of the product, 4 to 10 mesh; Topopah Tuff, typical of the proposed repository horizon host rock; and Wyoming White Marble, a dolostone (dolomitic limestone). The candidate materials, particle size ranges, and physical properties as tested, are listed in Table 1. This section of the analysis looks at the physical properties of the candidate backfill materials, determined in testing by the Subsurface Performance Testing Section, and weighs them against material handling characteristics and physical properties which are important in the consideration of backfill transport and emplacement concepts (Section 6.3.1) adopted in this analysis.6.2.1 Material Handling Characteristics
Principles for the selection of conveyor or feeder-type equipment depend on the physical and chemical properties (i.e., the materials handling characteristics) of the material to be transported, the manner by which the material is loaded on and discharged from the conveyor or feeder, and the profile over which the material must traverse. In turn, where materials are being adapted to transport and conveyance design concepts, it is equally important to evaluate material handling characteristics for a "fit" to the system. The environment existing in the potential repository, and emplacement of backfill within the emplacement drifts by remote operation, requires specialized equipment and systems. These special circumstances will require an accurate appraisal of all material handling characteristics and physical properties of the backfill candidate materials. When evaluating materials for dry bulk transport, there are a number of material handling characteristics and physical properties which must be considered. Key characteristics to be considered, as determined from input based on Section 4.1.1, in the handling, transport, and emplacement of backfill over the drip shields in the emplacement drifts are:6.3 Backfill emplacement Equipment and Methodology
6.3.1 Introduction
The concepts for the backfill emplacement equipment and methodologies used in this analysis were developed in the Backfill Strategy and Preliminary Design Analysis (CRWMS M&O 1997a, Sections 7.3 through 8.3), which concluded that: "Dumping provides the most favorable method of stowing [backfill] on the basis of assured waste package coverage, variable stowing and material feed rate, operational reliability, and mobility… ." In the context used in this analysis, stowing refers to the physical emplacement of backfill within the emplacement drifts with the addition of drip shields over the waste packages. This design includes backfilling equipment (within the emplacement drifts) consisting of three independent, complementary traveling gantry structures: a stower and two gantry shuttlecars. The concept and equipment is similar to proposed waste package emplacement equipment, which utilizes a gantry structure to straddle the waste packages, and accesses and travels within the emplacement drift on a gantry rail system powered by an electrified third-rail (CRWMS M&O 1997a, Section 7.5 and 7.3.1). The body of the gantry shuttlecars is a commercially available, bottom-mounted, double chain drive (chain-face) flight conveyor commonly used in the mining industry. Each unit has a closed-side, open-ended, elongated body which is inclined upward from the back to front, and is designed to integrate with another shuttlecar or the receiving end of the stower. The framework of the shuttlecar is an elevated gantry structure, which allows each unit to straddle emplaced waste packages and travel to the stower (CRWMS M&O 1997a, Sections 7.3.1 and 7.3.3.1). The concept is that one gantry shuttlecar travels back-and-forth, receiving backfill material at the emplacement drift entrance (transfer dock) and supplying the stowing (emplacement) operation as it progresses through the drift. The other shuttlecar receives the material from the first, and integrates and supplies the stower as it emplaces the backfill. If the travel distance (determined by the emplacement drift length) or the desired stowing rate surpasses the shuttlecar capacity, the size (length and/or width) of the shuttlecar may be increased to carry more material per trip, or additional shuttlecars can be added to supply material in tandem. The stower is a mobile, track-mounted, open steel-framed, self-propelled, gantry structure which consists of a gantry, material delivery unit, power unit, and drive. The stower is not an off-the-shelf item, though the individual components are commonly used in commercial applications (CRWMS M&O 1997a, Section 7.5.1). Backfill material is emplaced as it is fed from the supplying shuttlecar gantry. The material is unloaded from an overhead conveyor either as a batch or in a steady stream. The Backfill Strategy and Preliminary Design Analysis (CRWMS M&O 1997a, Attachment I) completed a detailed outline of the overall backfill operations, based on an average stower discharge rate of 75 m3/hr. This discharge rate is based on the midpoint of the production rate of an 18 inch wide belt conveyor (CRWMS M&O 1997a, Section 7.5.3). It is not the intent of this analysis to readdress, or change, the details of the mechanics of the overall backfill operations nor limit the study to one emplacement (stowing) rate. One of the primary tasks of this analysis is to address a range of emplacement rates, based on conveyor discharge rates applicable to the equipment proposed. The range selected (Section 1.2) encompasses the range used in the prior analysis (CRWMS M&O 1997a, Section 7.5.3) and the capacity to increase the size of the conveyor, if desired, in the final design. The limiting factor from the prior analysis was the time required to haul (supply) the material from the surface to the emplacement drifts and transfer it to the stower (CRWMS M&O 1997a, Section 7.2.3). If higher discharge rates are desirable in the final design, this factor, which is outside the scope of this analysis, must be addressed. However, the waiting time for stower production used in Backfill Strategy and Preliminary Design Analysis (CRWMS M&O 1997a, Attachment I, No. 5) is consistent with that assumed in this analysis (Section 5.3). Equipment designs developed in the Backfill Strategy and Preliminary Design Analysis (CRWMS M&O 1997a) remain unchanged, except for modifications to the height of the equipment and elimination of lateral movement of the belt conveyor system. The emplacement gantry has been elevated to the maximum height possible and still operate within the ground control system clearance envelope (Section 4.2.3.1). The purpose is to provide the maximum backfill profile possible while utilizing these equipment concepts. Maximum backfill profiles eliminate the need for the side-to-side discharge of backfill when stowing in order to guarantee drip shield coverage. The height of the sides of the trailing gantry shuttlecar have also been modified to accommodate the reduced clearance between the ground control clearance envelope and the introduction of the drip shield. Backfilling by dumping material over the drip shields in the emplacement drifts is also conceptually and practically the simplest approach. The material is discharged from an overhead conveyor either in a batch or in a steady stream, which cascades down over the drip shield, taking the form of its natural angle of repose. This action creates a conical pile that peaks just below the discharge point. By retreating along the drip shield length at steady discharge and travel rates, a single, uniform conical pile can be extended to form a "windrow" or elongated pile (see Figure 2). Favorable aspects of dump backfilling include relative simplicity in operation and increased surety of [drip shield] coverage (CRWMS M&O 1997a, Section 7.4.1.4). This section of the analysis describes the backfill emplacement system design concept in the following subsections:6.3.2 Backfill Emplacement Equipment
6.3.2.1 Gantry Shuttlecar
The gantry shuttlecar receives backfill material from the material transport system at the emplacement drift transfer docks, which are located at the entrance of each emplacement drift. The gantry shuttlecar (see Figure 3) has a closed-side, open-ended elongated body, flared at the receiving end to integrate with the trailing gantry shuttlecar and is fitted with a chain-face conveyor bottom, which allows the gantry shuttlecar to be self-loading and self-discharging. The gantry shuttlecars are loaded such that the material is centrally located, well removed from the ends, to avoid spillage during transit. Remote control of the feeder/conveyor mechanism allows the operation to be unattended. The gantry shuttlecars traverse through the emplacement drifts by remotely controlled drive mechanisms utilizing the gantry rail system. The gantry shuttlecar integrates with the trailing gantry shuttlecar through the insertion of a narrowed discharge end into the flared receiving end of the trailing gantry shuttlecar, equipped with a motorized gate. When the loaded gantry shuttlecar engages with the trailing gantry shuttlecar, the gantry shuttlecar discharges the load into the trailing gantry shuttlecar, and then returns to the emplacement drift dock for recharging. All operations are remotely controlled and monitored (Section 6.3.4). The preliminary design of the gantry shuttlecar remains basically the same as in previous analysis (CRWMS M&O 1997a, Section 7.3.3.1), with the exception of modification to the gantry height to match the elevation of the trailing shuttlecar and emplacement gantry, to attain maximum backfill emplacement heights (Section 6.3.5).6.3.2.2 Trailing Gantry Shuttlecar
The trailing gantry shuttlecar is basically the same piece of equipment as the gantry shuttlecar. The receiving end of the trailing shuttlecar has been modified to receive material from the self-unloading gantry shuttlecar. In turn, the trailing gantry shuttlecar is self-loading, and receives material synchronous with the discharge rate of the gantry shuttlecar. Loading (recharging) of the gantry trailing shuttlecar occurs only when empty and the emplacement of backfill is halted (compensation for this waiting time has been taken into account in the assumptions of the scheduling parameters for backfill emplacement, Section 5.3, Item C). The gantry shuttlecar is equipped with a motorized gate. Once recharging is completed, the gate closes to retain the material without spillage when the gantry shuttlecar pulls away. This frees the gantry shuttlecar to return to the emplacement drift transfer dock for recharging while backfill emplacement is proceeding. The sides of the trailing gantry shuttlecar are tapered to fit within the ground control system clearance envelope 300 mm inside the drift diameter (Section 4.2.3.1). An allowance of 0.15 m between the top of the drip shield and the bottom of the gantry structure has been retained to assure clearance (see Figure 4). The trailing gantry shuttlecar feeds the material directly onto the conveyor belt of the emplacement gantry through a narrowed discharge hopper. The size of the conveyor belt is undetermined and will depend on the stowing rate, length of emplacement drifts, etc., of the final design. The feed rate will match the emplacement conveyor discharge rate. This provides uniform flow of the material from supply to emplacement. The trailing gantry shuttlecar and emplacement gantry are coupled together by a tow bar and travel in unison at speeds to match the discharge rate with the desired level of backfill (see Figure 5). The gantries traverse through the emplacement drifts by remotely controlled drive mechanisms utilizing the gantry rail system. The monitoring and control of these systems will be done remotely (Section 6.3.4).6.3.2.3 Emplacement Gantry
The emplacement gantry is the key piece of equipment for backfill emplacement. The quality and quantity of the backfill emplacement is controlled by the accuracy of the discharge rate and travel speed of the gantry. The emplacement gantry (see Figure 6) consists of a gantry-mounted belt conveyor. The belt conveyor is fed directly from the discharge end of the trailing gantry shuttlecar transfer hopper. The emplacement gantry transfers backfill material up the belt conveyor and discharges directly on the drift centerline over the drip shields. The discharge rate is closely matched with the feed rate of the trailing gantry shuttlecar (Section 6.3.2.2). The belt conveyor is cantilevered forward to prevent backfill from interfering with the gantry rail structure and wheels as it is emplaced. The backfill will cascade out, due to the natural angle of repose of the material, as it is dumped into the end of the conveyor (see Figure 7). The length of this extension is not set, and would be based on the angle of repose of the backfill material selected. The preliminary design of the emplacement gantry remains basically the same as in the previous analysis (CRWMS M&O 1997a, Section 7.5), with the exception of modifications to the gantry to achieve the maximum emplacement height (Section 6.3.5), elimination of the conveyor support to fit in the physical space between the drip shield and drift clearance envelope (Section 6.1), and the elimination of lateral movement capabilities of the emplacement conveyor (Section 6.3.1). The mechanisms of the emplacement gantry are to be operated remotely (Section 6.3.4).6.3.2.4 Applicability of the Conceptual Equipment
The three independent equipment units comprising the backfill emplacement system are gantry structures, on which commercially available equipment such as a shuttlecar or a belt conveyor are mounted. Gantry structures are safe, fabricated-steel structures utilized in the construction of many types of equipment, from heavy-lifting cranes to bridges. The wheel system, or bogies, supporting and effecting the travel and motion of the gantries are accepted world-wide for all types of track vehicles. The commercially available shuttlecar bodies, described in Section 6.3.1 and adopted to be used on the gantry shuttlecar and trailing gantry shuttlecar, are used world-wide in a number of applications. The operating system, extensively used in the mining industry, is a proven chain-face conveyor. Belt conveyors are also key components of many industries. They are constructed of commercially available components, such as belting and idlers, can be installed at virtually any angle of inclination, and have been used to transport all types of materials from dust to boulders. Therefore, the equipment proposed for the handling, transport, and emplacement of any of the candidate backfill materials is considered to be appropriate, reliable, and will yield the desired performance.6.3.3 Traversing System
Section 4.2.1.2 specifies the backfill emplacement system shall install prepared backfill material in emplacement drifts having a maximum length of 700 m. Section 4.2.3.2 specifies the system shall be capable of transporting and placing the backfill over a maximum grade of +/- 1.0 percent within the emplacement drifts. Addressing the emplacement drift length, the concept of the system is that the backfilling of each emplacement drift will begin at the center of the drift and progress from the interior (end of the drip shield next to the ventilation raise) to the exterior (end of the drip shield nearest the emplacement dock). Backfill will be emplaced by the emplacement gantry by dumping material over the drip shield, fed by a trailing gantry shuttlecar linked to the emplacement gantry. As backfilling is achieved to the desired height (see Section 6.3.4.1 for monitoring and control), the trailing gantry shuttlecar and emplacement gantry will slowly be driven along the gantry rail system. A shuttlecar will intermittently supply the backfilling operation, driving back and forth from the supply point at the emplacement dock to the point of backfilling progress. It can be seen that, theoretically, this concept is limited not by distance, but by drive potential. The important concept here is how the gantries will be driven and powered to traverse the emplacement drifts. The drive mechanism for the backfill system gantries will be similar to concepts previously designed for other gantries within the emplacement drifts, utilizing the gantry/third-rail electrification system (Section 5.1). The gantries are self-propelled and remotely controlled. Locomotion will be provided by DC variable-speed electric motors powered through direct contact with the gantry/third-rail electrification system (see Section 6.3.4.1 for control). This propulsion system is not bounded by length. The gantry/third-rail system is designed to run the length of each emplacement drift and may be extended to service any desired length. The design for the waste package transporter (CRWMS M&O 1997b, Sections 7.4.3.3 and Attachment V, Section 3.2B) takes into consideration a 150+ MT gantry traversing an incline force equivalent to a +1% grade. It is reasonable to assume that similar drive units can be developed for the lighter-weight backfill system gantries proposed in this analysis. The backfill gantries will be equipped with two independent fail-safe braking systems, a primary and a secondary (emergency braking system), to stabilize and control the gantry movement in the event the final design calls for a negative gradient (see Section 6.3.4.1 for control). In addition to specified performance criteria for length and grade, the backfill emplacement equipment may encounter unpredictable obstacles, e.g., degradation of the invert/ballast may result in unevenness, and minor ground control degradation may result in debris on the track in the form of small rocks. In the event that these situations are significant, special adaptation to the traversing system to compensate for them may be required, e.g., a suspension system to compensate for track unevenness; fitting plows in front of the wheels to push debris from the track, etc. These requirements, and to what degree these situations must be addressed, will have to be evaluated at the time of emplacement.6.3.4 Remote Operation, Monitoring and Control
The backfill emplacement vehicles are the most critical components of the backfill emplacement system. The backfill emplacement gantry and the gantry shuttlecar are designed to operate within the high-temperature, high-radiation environment inside the emplacement drifts, and will, therefore, be controlled exclusively by operators at a remote location (Section 4.2.2.1). During backfilling operations, access by personnel to areas with radiation fields (i.e., the emplacement drifts) will be restricted. Remote controlled operations will be used to limit occupational radiation doses to a level that is as low as reasonable achievable (ALARA). The design of the backfill emplacement control system must impose limitations on system complexity if it is to perform its intended functions in a highly reliable manner. Reliability of the remotely operated monitoring and control system will be further enhanced by incorporating high-quality software and hardware components. These components include dual-redundant programmable control computers, instrumentation, and communications equipment. Design strategies such as employing diverse technologies, physically separating redundant components, and providing backup data communication systems, will be implemented to ensure fault-tolerant operation.6.3.4.1 Locomotion and Braking Controls
6.3.4.2 Conveyor Controls
Each gantry shuttlecar’s chain-face conveyor (Figures 3 and 5) will incorporate an electrical powered drive motor located at one end of the conveyor. The on-board power and control system for this motor will be similar to that for the shuttlecar’s drives discussed in Section 6.3.4.1. The emplacement gantry’s belt conveyor (Figure 6) will incorporate an electrical powered drive motor located at one end of the conveyor. The on-board power and control system for these motors will be similar to that for the gantry’s drives discussed in Section 6.3.4.1.6.3.4.3 Vision System
The vision systems for both the gantry shuttlecars and the emplacement gantry will provide operators at the remote control console with real-time feedback about the operating environment and vehicle performance. Each vehicle’s vision system will consist of several on-board, high-resolution, articulated, closed-circuit television (CCTV) cameras and a series of high-intensity lights.6.3.4.4 Fire Protection System
The gantry shuttlecars and the emplacement gantry will each be equipped with fire protection systems. The fire suppression system will respond automatically should an on-board fire be detected. The fire detection/alarm system will immediately notify the site fire protection system of the location and nature of the fire. The type of fire suppressant has not been specified. However, it is highly unlikely it will be water, for a number of reasons, including the electrified third rail needed to power the system.6.3.4.5 Miscellaneous Instrumentation
The clearance space between the inside surface of the legs of the gantry shuttlecars and the emplacement gantry and the outer surface of the drip shields is expected to be critically narrow. Therefore, a means for detecting any interferences is required, especially an interference that could prevent the vehicles from freely straddling the drip shields, is suggested, depending upon drip shield placement. Interferences of this nature could be detected by proximity sensors strategically placed on-board each vehicle. As discussed in Section 6.3.4.1, the actual height of the backfill material discharged over the waste packages during a backfilling operation must be continuously monitored to ensure a uniform distribution of material. This could be accomplished with solid-level sensing instruments placed at or near the discharge end of the gantry.6.3.4.6 Data Communication System
The gantry shuttlecars and the emplacement gantry will each utilize one of several alternative mobile communication technologies to transmit and receive data for monitoring and control functions. A number of different technologies currently available have been previously examined and evaluated for similar applications (Section 5.2). The data communication technologies being considered for the backfill emplacement system include: direct radio, leaky feeder, and slotted microwave guide systems. Due to the critical need for a reliable data communication system for both the shuttlecars and the gantry, the current design approach will be to implement dual-redundant systems on each vehicle. Additionally, two of the three communication technologies noted previously will be implemented to further ensure reliability. Thus, each vehicle will be capable of interfacing with remote operators over two completely different, separate, and individually dual-redundant communication networks. This application of diverse technologies will reduce the likelihood of common-mode failures because of the type of fault causing the failure of one system will not likely cause the failure of the other system.6.3.5 Adaptation of Backfill Equipment to Physical Parameters for Backfill Emplacement
The backfill emplacement equipment originally designed in a prior analysis (Section 6.3.1) was developed for the emplacement of backfill directly over the waste packages. However, as can be ascertained from the figures and descriptions presented in this analysis, the same, or similar, equipment may be adapted to emplacing backfill over current drip shield designs with little modification. One of the primary tasks of this analysis is to establish a range of maximum backfill profiles, based on the current emplacement methodology. It is the goal of this analysis to maximize backfill emplacement height and coverage (see related discussion in Section 6.4.2.1). Section 6.1 established the physical parameters for backfill emplacement. Considering the backfill equipment, evaluated in the previous section, the maximum backfill emplacement height can be ascertained by projecting the maximum backfill emplacement gantry height within the physical parameters (Figure 1). Figure 8 shows the arrangement of an emplacement gantry elevated to the maximum height interfacing with the ground control clearance envelope at the crown of the drift. This height positions the discharge point of the belt conveyor at approximately 0.5 m below the drift crown. Therefore, a height of approximately 4.2 m from the top of invert can be achieved as the maximum backfill emplacement height possible when utilizing this type of emplacement system, based on these emplacement parameters. The specified clearance envelope for the ground control system (Section 4.2.3.1) has been followed in this analysis. However, the degree of maintenance and possible infringement of this clearance envelope, due to degradation of the ground control system during the period leading up to closure, should be considered in the revision of related system description documents.6.3.6 Adaptation to Candidate Backfill Materials
Section 6.2.1 identified and discussed key candidate backfill material handling characteristics to be considered in design concepts for backfill material conveyance and transport. This section discusses these characteristics as adaptated to the backfill equipment and methodologies proposed. A small bulk-density range (average) for the candidate backfill materials has been established, 1,488 – 1,514 kg/m3, based on limited materials testing (Table 1). The bulk density of a material is generally one of the factors that governs the tonnage rating of conveyors or feeders. In this case, neither of the materials tested are exceptionally heavy (nor are any of the materials not tested expected to be), and would have minimal impact on the emplacement concept. The flowability of a material generally determines the load that can be carried and the ease with which the material will flow through openings or transfer points. Based on the angles of repose, all flowability characteristics for the candidate backfill materials are average to free-flowing. The design concepts for the backfill equipment and methodology do not introduce any challenging or unconventional transfer or conveyance points. However, the evaluation of flowability should not be limited to materials handling. In the dump stowing concept, backfill material is discharged from an overhead conveyor. The backfill cascades down over the drip shield, taking the form of its natural angle of repose. In this context, flowability is also important to backfill flow and emplacement. Maximum lump size is a consideration from an impact standpoint. The backfill emplacement configurations considered in this analysis require that the discharge head be elevated to maximum height (see Figure 8). This will maximize the drop distance and, in turn, the kinetic energy induced on the drip shield during initial coverage. After the initial layer is in place, material falling on itself will minimize this concern. If lumps in the backfill are too large, impact on the drip shield may damage it by indentation or scarring, possibly introducing a point which may challenge the integrity of the drip shield in long-term performance. All of the candidate backfill materials evaluated fall within the very-fine-to-granular size range (Table 1). The limited occurrence of impact time in any one area of the drip shield, and the relatively small maximum lump size (Table 2), is not expected to have any impact in the adaptation of the backfill emplacement system and methodologies proposed. A high content of freely associated, light-weight fines in the backfill medium will result in excessive airborne dust being introduced during emplacement. Although the transfer action of the gantry shuttlecar is slow and controlled, discharge from the emplacement conveyor will project the backfill material into the air, where fines would be scattered and picked up in the ventilation airstream. This could cause excessive amounts of airborne dust. Airborne dust creates concerns from a health and safety standpoint, and hampers remote video and monitoring operations (Section 6.3.4). This, in turn, would ultimately challenge consistent, uniform emplacement. Although no personnel will be present in the emplacement drifts, continuous ventilation will be required to lower the in-drift temperature during backfill emplacement to protect the emplacement and monitoring equipment. Continuous ventilation will also serve as the method to remove and control dust. Any dust created will be picked-up in the airstream, flowing from the perimeter drifts, through the emplacement drifts, down the ventilation raise located in the center of the drift (Section 5.4), and out the exhaust main, where dust collectors or filtering devices will collect the dust. Three of the candidate backfill materials evaluated: Overton sand, fine Topopah Tuff, and the 50-200 mesh Wyoming White Limestone, are projected to have very high dustiness ratings (Table 2). These materials could be expected to introduce high levels of dust during emplacement. Some degree of dust could be expected in the handling of any of the materials proposed, unless screened and washed prior to emplacement. However, with continuous ventilation and the emplacement methods proposed, dust control is expected to be manageable. Candidate backfill materials with higher contents of freely associated, light-weight fines may require additional measures for dust control to be taken into account in the backfill emplacement ventilation and monitoring design. Conveyor and feeder materials transport and handling systems are, in general, widely versatile and adaptable to any of the candidate materials. Bulk density, flowability, and maximum lump size have little to no impact on the system design concepts. The high amount of fines in three of the materials evaluated could introduce high dust levels without additional control measures; however, these measures are expected to be manageable within the design concept.6.4 Backfill Emplacement Parameters, Volumes, and Schedule
Section 6.1 established the physical parameters for backfill emplacement within the emplacement drifts. Section 4.1.2 established the range of material handling characteristics for the candidate backfill materials being considered for SR. Section 6.3.5 established the maximum backfill emplacement height which may be attained, based on the backfill equipment and methodology proposed. Sections 5.5 and 5.6 have established the number of emplacement drifts and stand-off distances in the drifts (unusable emplacement space), respectively. Assumption 5.3 has established scheduling parameters for backfill emplacement. This section of the analysis, in conjunction with Attachment I:6.4.1 Backfill Configuration Parameters
The backfill configuration parameters used in this analysis were determined by the range of angles of repose of the candidate backfill materials (Table 1) and the physical parameters for backfill emplacement. Minimum and maximum angles of repose were used, resulting in two cases (profiles) (see Section 6.4.2). The final selection of a backfill material and, thus, the actual angle of repose, will be determined in subsequent analysis. This range establishes bounding conditions meant for scoping purposes, and preliminary volume and scheduling calculations only, and encompass a range of emplacement configurations for a range of backfill materials.6.4.1.1 Maximum Backfill Depth
The maximum backfill depth that can be emplaced is based on the height limitation of the backfill emplacement gantry within the emplacement drift, established in Section 6.3.5. As shown in Figure 8, the backfill emplacement conveyor can accommodate a discharge height to within 0.5 meters of the tunnel crown.6.4.1.2 Backfill Materials Range of Angle of Repose
The range of angle of repose for the candidate backfill materials has been established in Table 1. This range varies from a minimum angle of 28° for Overton sand, to a maximum of 42° for 50-200 mesh Wyoming White Marble. This range will be used to establish the bounding parameters for the angle of repose of emplaced backfill.6.4.2 Backfill Emplacement Configurations
The bounding parameters outlined in Section 6.4.1 form the basis for the backfill configurations analyzed in this analysis, and are the basis for the backfill volumes and schedules calculated in Attachment I. The backfill emplacement parameters are designated by the following cases, shown in Figure 9:6.4.2.1 Minimum Backfill Configurations
It is speculated that hundreds or even thousands of years into postclosure is when the ground support system will fail and rock blocks will fall from the drift walls. This will be the most critical time for the backfill to protect the drip shield from impending impact. If backfill material is initially emplaced in the configurations depicted in Cases 1 and 2, the minimum backfill cover over the drip shield will be the perpendicular distance between the material slope, as it is emplaced, and the drip shield (shown as backfill thickness in Figure 9). However, the emplaced material may slump, either through settlement, or even level out in the long term, due to seismic activity. One of the primary tasks of this analysis is to analyze the resultant condition of material slump and/or leveling, by calculating the minimum backfill depth remaining over the apex of the drip shield if the emplaced profiles are leveled to a flat profile (Section 1.2) since this would be the most conservative case. If, or when, prescribed minimum backfill depths are developed in future analysis, those requirements may be compared to these resultant long-term depths. The resultant minimum backfill profiles for Cases 1 and 2 have been approximated in Attachment I, Sections I-7 and I-8, respectively, and are designated as the following cases, shown in Figure 9:6.4.3 Maximum Emplacement Drift Length
Section 4.2.1.2 establishes that the system will install prepared backfill material in emplacement drifts having a maximum length of 700 m (one-half of the maximum emplacement drift length). Since this is the criteria set for maximum emplacement drift length, it will be used as the bounding condition for the length of each drift in the calculation of backfill volumes. As clarified in Section 4.2.1.2, the context in which "emplacement drift" is used in the criterion refers to one-half of the total length of an emplacement drift. Therefore, the total emplacement drift length is actually 1,400 m.6.4.4 Backfill Volumes
The calculation of required backfill volumes (as applied to the range of possible backfill profiles) is important in checking system capabilities. The system must be capable of emplacing the required volumes within 10 years as a part of subsurface closure activities (Section 4.2.1.1). One of the primary tasks of this analysis is to complete the preliminary calculations of backfill volumes, based on the range of possible backfill profiles. The calculation of backfill volumes will provide input into the development of preliminary backfill emplacement schedules (Section 6.4.6) as a check against the requirements. The detailed calculation of required backfill volume for the two cases described in Section 6.4.2 can be found in Section I-9. The volume of backfill material required to adequately cover the total number of waste packages (covered by drip shields) is defined as the cross-sectional area of the backfill "as-emplaced" (Sections I-3 and I-5) multiplied by the maximum emplacement drift length (Section 6.4.3) less the stand-off distance (Section 5.6), multiplied by the number of emplacement drifts (Section 5.5), plus the volume of the end sections (Sections I-4 and I-6) multiplied by the number of end sections. Calculation of the cross-sectional area of the backfill, based on the physical emplacement parameters established in Section 6.1, is straight-forward. However, calculation of the end sections is complicated by the complexity of the shape of the sections and the interfacial relationship between the interior end sections and the ventilation raise at the center of the drift. Emplaced waste is positioned within each drift in two sections, with a total physical stand-off of 4 m at the drift center to account for the central ventilation raise (Section 5.6). Based on this physical separation, each emplacement drift will have two sections of emplaced waste, for a total of four ends. The drip shield will have to be emplaced in the same manner to avoid conflict with the ventilation raise, which will be required to supply air throughout the emplacement operations. Two drip shield ends will be located on the perimeter (next to the mains), and two on the interior (next to the ventilation raises). Backfill will be emplaced over one section at a time, starting from the interior end and progressing outward toward the perimeter. As backfill is dumped over each end section, material will naturally cascade out, past the end of the drip shield, into a conical-shaped pile (see Figures I-4 and I-6). The extent of the pile of material past the end of the drip shield will be determined by the height from which the backfill is being dumped and the angle of repose of the material. Emplacement of backfill material to the ends of the drip shield is important to insure coverage to a uniform depth at all points. The total volume of the end sections in each case is based on the volume of the four end sections, two perimeter and two interior, multiplied by the number of drifts. Note, however, that the volumes for the interior end sections are different than those on the perimeter, due to positioning. The interior end sections, separated by only 4.0 m, will actually meet at the center and are subtended by a 2.0 m ventilation raise located at the drift center (Section 5.4). Although it is realized that the emplacement of one interior end will precede the other, these sections have been calculated as two separate sections bisected in the middle. For the purposes of this analysis, the ventilation raises have been extended high enough to accommodate the introduction of backfill, in each case, without interference. However, modification and design of the ventilation duct is outside the scope of this analysis. The calculation of backfill volumes for each case are shown in Section I-9 and the results were used to determine the preliminary scheduling impacts in Section 6.4.6. The results are tabulated in Section 6.5, Table 3.6.4.5 Calculation of Backfill Tonnage
One of the material characteristics requested from the Subsurface Performance Testing Section for the candidate backfill materials was bulk density (Section 4.1.1). Bulk density is discussed in Section 6.2.1, and it was concluded in the discussion of adaptation of the backfill equipment and methodologies proposed (Section 6.3.6) that the bulk densities provided will have little impact on the design concept. However, the calculation of a range of backfill tonnages, based on the bulk densities provided (Table 1), have been included as a part of this analysis to provide an estimate of the tonnage of backfill material that may be required. The calculations of backfill tonnage for each case are shown in Section I-10. The calculation of the backfill tonnage is simply the volume (m3) required in each case, multiplied by the bulk density of the backfill material used The average bulk densities provided are: 1,488 kg/m3 for Overton sand, and 1,514 kg/m3 for 50-200 mesh Wyoming White Marble (Table 1). The results for the backfill tonnage required for each case are tabulated in Section 6.5, Table 3.6.4.6 Backfill Emplacement Schedule
Section 4.2.1.1 specifies the system shall be capable of placing the total repository backfill, within a period of 10 years, as part of subsurface closure activities. The Monitored Geologic Repository Concept of Operations (CRWMS M&O 1999g, Section 3.5.1) establishes the subsurface closure activities as: removing underground equipment, preparing the openings to receive backfill, backfilling the emplacement drifts and openings, and emplacing repository seals. The openings to be backfilled include main drifts, shafts, ramps, boreholes, and emplacement drifts. This would indicate that for all of the subsurface closure operations to be completed within the estimated 10 years, backfilling of the emplacement drifts must take place as quickly and efficiently as possible because backfilling of the emplacement drifts must be completed first in the sequence of closure activities. Backfilling of the emplacement drifts will require access along the entire length of the access mains, and continued ventilation will be required to cool the drifts and ventilate the working areas throughout the emplacement operation. For this reason, it is important in the conceptual design to analyze preliminary scheduling impacts for each case, to assure that backfilling of the emplacement drifts can be completed in time to allow completion of the other closure activities. One of the primary tasks of this analysis is to calculate the preliminary backfill emplacement schedules, based on the backfill volumes required (Section 6.4.4) and stowing rates from 30 m3/hr to 200 m3/hr. The stowing rates are based on a range of conveyor discharge rates applicable to the equipment proposed, and have been specified in the description of the task (Section 1.2) in order to bound the calculation, based on a wide, but reasonable, range. Section 5.3 established the actual time of backfill emplacement per day at 7.755 hrs/day, based on a 2-shift/day operation, allowing for maintenance and gantry waiting time. The personnel work schedule used for scheduling purposes is on the basis of a 250 days/year operation. The calculation of the preliminary backfill emplacement schedules for each case are shown in Section I-11. In each case, the number of emplacement gantries has been increased, if needed, to comfortably address the criteria discussed above. Results have been used to determine preliminary scheduling impacts based on the number of years required to complete backfilling and the number of emplacement gantries required. The results are tabulated in Section 6.5, Table 3. The bases of the calculation of these schedules are:6.4.7 Cross-Sectional Area Occupied By Backfill
During closure, continued ventilation to support personnel and operations will be necessary in areas of work-in-progress. During backfilling of the emplacement drifts, continued ventilation will be necessary to maintain the drift temperature and prevent dust build-up (Section 6.3.6). The area available for air passage through the emplacement drifts during and after backfill emplacement is directly proportional to the amount of space occupied by the backfill material and the void area remaining above the backfill after emplacement. In order to demonstrate how much of the available cross-sectional area of the emplacement drift that could be backfilled employing the methods and materials proposed in this analysis, the percentage of actual area filled, in relation the area available, was calculated. The area available for backfill emplacement, based on the physical parameters of the emplacement drifts (Section 6.1) and the percentage of area that may be occupied by backfill, has been calculated as a part of Sections I-3 and I-5, for both cases. The results are discussed at the end of Section 6.5. This information may also be valuable in ventilation or air flow considerations during postclosure. These relationships will remain basically unchanged as backfill emplacement profiles deteriorate in postclosure due to settlement or leveling, because the cross-sectional areas remain closely the same.6.5 Results, Backfill Emplacement Volumes, and Schedule
The results of the backfill emplacement volumes and schedules, based on the physical emplacement parameters (Section 6.1) and range of angles of repose (Section 6.4.1.2) for the candidate backfill materials, have been summarized in Table 3. The source of all values in Table 3 have been calculated, and are found in Attachment I, "Backfill Configurations and Volume Calculations," following the text. Two bounding cases, bounded by the minimum and maximum angles of repose of the backfill materials have been evaluated. Both cases are based on emplacing the material in the drift to the maximum achievable emplacement height, based on the clearance envelope, the emplacement methodologies proposed, and maximum emplacement drift length, based on system requirements (Section 4.2.1.2). The total backfill volumes vary based on the emplacement characteristics of the materials. The total backfill tonnages vary based on the bulk densities of the materials. The emplacement schedules have been calculated based on a range of emplacement (stowing) rates. The number of emplacement gantries has been increased in each case to meet the required closure period and leave sufficient time for the completion of all other closure operations. These schedules may be accelerated, if necessary, as discussed in Section 6.4.6. For Case 1, a material possessing an angle of repose of 28° would fill 77.9% of the available space, leaving approximately 3.59 m2 of open area remaining above the backfill following emplacement. For Case 2 and a material possessing an angle of repose of 42° , the percentage of available void space filled decreases to 61.2%, and the cross-sectional area remaining above the backfill increases to 6.32 m2. These relationships will remain, basically, unchanged in postclosure, as the cross-sectional areas remain closely the same.7. conclusions and recommendations
7.1 Conclusions
This analysis covers design of the repository backfill emplacement system, specifically within the emplacement drifts. The design is based on an evolving EDA II design concept, specifically pertaining to the introduction of the drip shield over the waste packages. The analysis covers the physical installation of backfill in the emplacement drifts, independent of inclusion as a design component or as an option. The objective of this analysis is to support revision of Section 1 of related SDDs and to provide a basis for Section 2 of the SDDs appropriate to support SR. Input based on design criteria from Section 1 SDDs, physical parameters for backfill emplacement defined by the EDA II concept, and emplacement characteristics of candidate backfill materials being considered for SR were used. A Backfill Strategy and Preliminary Design Analysis (CRWMS M&O 1997a) was previously completed addressing the emplacement of backfill directly over the waste packages. The current analysis evaluates adaptation of this backfill emplacement system to the introduction of drip shields and a range of handling characteristics of the candidate backfill materials. One of the primary tasks of the analysis was to emplace backfill to a maximum height within the drift to compensate for material settlement and leveling that may occur over time. The backfill emplacement system proposed consists of three independent, traveling gantry structures:7.2 Recommendations
This analysis is a preliminary evaluation of a conceptual system for the emplacement of backfill within the emplacement drifts, based on the EDA II design concept. It has met all of the design criteria, presently developed, which are applicable. Note that the conclusions and recommendations in this analysis are considered preliminary. Many of the results and conclusions are based on evolving concepts, and should be checked against, or revised to, current concepts and designs before any information is used or applied.7.3 TBV Impact
This document may be affected by technical product input information that requires confirmation. Any changes to the document that may occur as a result of completing the confirmation activities will be reflected in subsequent revisions. The status of the input information quality may be confirmed by review of the Document Input Reference System database. Data in Section 4.1.3 requires confirmation. Qualification of the drip shield dimensions may affect the backfill volume calculations and the types of equipment, configurations, or arrangements selected for backfill material handling and emplacement. If the drip shield is significantly increased in size, the limits of the equipment not infringing on the clearance envelope may be exceeded and a different system or method of emplacement may be required. If the drip shield is significantly reduced in size, significantly larger volumes of backfill material may be required; however, as discussed in Section 7.1, the backfill emplacement system proposed in this analysis is independent of backfill volume and scheduling requirements, and changes in drip shield dimensions should have no impact on the system or methodology proposed.8. References
8.1 Documents Cited
CRWMS M&O 1997a. Backfill Strategy and Preliminary Design Analysis.8.2 Codes, Standards, Regulations, and Procedures
AP-3.10Q, Rev. 2, ICN 0. Analyses and Models. Washington, D.C.: U.S. Department of Energy, Office of Civilian Radioactive Waste Management. ACC: MOL.20000217.0246. AP-3.14Q, Rev. 0, ICN 0. Transmittal of Input. Washington, D.C.: U.S. Department of Energy, Office of Civilian Radioactive Waste Management. ACC: MOL.19990701.0621. AP-3.15Q, Rev. 1, ICN 1. Managing Technical Product Inputs. Washington, D.C.: U.S. Department of Energy, Office of Civilian Radioactive Waste Management. ACC: MOL.20000218.0069. AP-SI.1Q, Rev. 2, ICN 4. Software Management. Washington, D.C.: U.S. Department of Energy, Office of Civilian Radioactive Waste Management. ACC: MOL.2000223.0508. QAP-2-0, Rev. 5. Conduct of Activities. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19980826.0209. QAP-2-3, Rev. 10. Classification of Permanent Items. Las Vegas, Nevada: CRWMS M&O. ACC: MOL.19990316.0006.8.3 Source data
GS000383351030.001. Particle Size Data for Potential Candidate Backfill Materials (Overton Sand, Sand Ramp Sand, 12-20 Sand, 8-20 Sand, 4-10 Silica, and 4-10 Crushed Tuff) Used in the Engineered Barrier System, 11/11/98 to 07/27/99. Submittal date: 03/23/00. GS000383351030.002. Angle of Repose, Particle Density, and Uncompacted Bulk Density Data for Analyses Performed on Potential Candidate Backfill Materials. Submittal date: 03/24/00.9. Attachments
Attachment 1