[DNFSB
LETTERHEAD]
The Honorable Jessie Hill Roberson
Assistant Secretary for Environmental
Management
Dear Ms. Roberson:
The staff of the Defense Nuclear Facilities
Safety Board (Board) recently reviewed the Transuranic (TRU) Waste Retrieval
Project at the Hanford Site. This effort
includes the retrieval of more than 38,000 containers of TRU waste from the
The Board notes its continued concern with
the 12 drums that contain significant quantities of plutonium-238. The Board identified the need for a
disposition path for these drums in a letter dated
Therefore, pursuant to 42 U.S.C. § 2286b(d), the Board requests that the
Department of Energy provide a written response within 90 days of receipt of
this letter that describes specific actions planned to:
(1)
Safely
retrieve and handle these 12 drums;
(2)
Verify the
integrity of the drums soon after retrieval and take corrective actions if needed;
(3)
Establish a
safe storage condition for these drums pending final disposition; and
(4)
Appropriately
repackage and disposition the drums.
These actions could also be applicable to other
unique drums encountered during the TRU retrieval operation.
Sincerely,
John T. Conway
Chairman
c: Mr.
Keith A. Klein
Mr. Mark B. Whitaker, Jr.
Enclosure
DEFENSE NUCLEAR FACILITIES SAFETY BOARD
Staff Issue Report
MEMORANDUM
FOR: J. K. Fortenberry, Technical Director
COPIES: Board
Members
FROM: D.
Qgg
SUBJECT: Transuranic
Waste Retrieval,
The staff of the Defense Nuclear Facilities
Safety Board (Board) reviewed the plans of the Department of Energy (DOE) and
its contractor to retrieve buried transuranic (TRU) waste at the Hanford Site. Staff members D. Ogg and D. Winters visited
the Hanford Site during
Background. The
Hanford Solid Waste Operations Complex includes eight burial grounds covering
approximately 1,400 acres, and contains low-level waste, mixed low-level waste,
remote-handled TRU waste, and contact-handled TRU waste. Between 1970 and the late 1980s, DOE placed
TRU waste drums into retrievable storage in five of these eight burial grounds.
From 1998 to 2001, DOE and its
contractor removed more than 1,400 drums of TRU waste (only those drums not
covered with soil) from trenches in some of the burial grounds. However, more than 38,000 drums and boxes of
TRU waste remain covered with soil in retrievable storage.
DOE and its contractor now plan to retrieve
contact-handled TRU waste that is covered with soil. This new project, called the TRU Waste
Retrieval Project, includes the removal of drums and boxes from seven trenches
in two burial grounds (281-W-4B and 28 l-W-4C) that contain about 90 percent by
mass of the remaining TRU waste. Remote-handled TRU may be moved during this
activity but will not be processed until a new remote-handling facility becomes
available.
Plutonium-238
Drums. Trench 1 in burial ground 4C contains 12
unique drums that were retrievably stored in 1977. These 12 drums contain packaged plutonium
oxide with a high plutonium-238 (Pu-238) content. The plutonium loading in these drums ranges
from approximately 200 to 500 grams per drum, about 18 percent being Pu-238.
These drums pose greater hazards than the
typical drum to be handled as part of the TRU retrieval program. The high specific activity of the
alpha-particle-emitting Pu-238 causes the packaged material and drums to be
thermally hot: a thermal analysis
performed prior to placement of the drums in the trench estimated that the
centerline temperatures in the storage containers would reach 682°F. Also, the isotopic composition of the material
would pose an internal radiation exposure hazard considerably in excess of
weapons grade plutonium in the event of an intake.
The control for this hazard relies on the
integrity of the layers of packaging. The plutonium oxide was packaged in a robust
system which includes two sealed aluminum containers inside a metal-gasketed
stainless steel container, all inside a 55-gallon drum. However, the lengthy storage period under
higher than normal heat and radiation fields raises concerns about the
condition of the containers. DOE has
reported experience at the Savannah River Site showing aluminum containers under
similar conditions often spall and lose their integrity. The potential for deterioration of these
packages does not support extended delay in dispositioning this high hazard
material.
The Board raised concerns with these 12
drums in a letter to DOE dated
The contractor currently intends to proceed
with the TRU waste retrieval activities without a firm plan for Pu-238 drums. It appears that the tentative plan is to set the
Pu-238 drums aside after they have been retrieved and to store them above
ground until a disposition path is developed. However, many of the hot cells and shielded
gloveboxes at
The Board’s staff believes it would be
prudent for DOE to carefully plan for the safe retrieval and handling of these
drums in the near future, to verify the integrity of the drums soon after they
are retrieved, to establish a safe storage condition for the drums while
awaiting disposition, and to carefully consider options for the repackaging and
disposition of the drums.
Accident
Analyses. The staff reviewed the Master Documented
Safety Analysis (MDSA) for the Solid Waste Operations Complex, which includes
the Low-Level Burial Grounds. One design
basis accident of particular interest is the single-drum deflagration accident.
Contractor analysts determined that the
unmitigated consequence for a collocated worker in this postulated accident is
a dose of 260 rem (off-site consequences are well below evaluation guidelines).
Since this evaluated dose is considered
significant, the DOE Standard Preparation
Guide for U.S. Department of Energy Nonreactor Nuclear Facility Documented Safety
Analyses, DOE-STD-3009-94, Change Notice 2, suggests that
safety-significant controls be developed and implemented to mitigate the hazard.
Guidance from the DOE-RI, manager to the
contractor on the functional classification of safety controls requires this
level of control.
For this accident, contractor analysts
proposed a safety-significant administrative control for venting waste
containers, a safety-significant Drum Venting System, and several other administrative
control programs.
After the contractor submitted the MDSA to
DOE, DOE issued its Safety Evaluation Report and noted that additional controls
were necessary for the single-drum deflagration accident. DOE added a time limit for staging unvented
containers, as follows:
During TRU
Retrieval operations, un-vented TRU, suspect TRU, and other waste containers
requiring venting SHALL be accumulated in batches. Once more than 50 containers are accumulated
in a batch, a 90-day clock SHALL be initiated. All drums within the batch SHALL be vented in
accordance with TSR-AC 5.6.1 within the 90-day time period. The total number of un-vented containers not
on a 90-day clock SHALL not exceed 50. Backlogged un-vented containers previously
identified in the LLBG [Low Level Burial Grounds] SHALL be vented within 120
days of the drum venting system being declared operational. A QUARTERLY SURVEILLANCE SHALL be performed to
assure containers requiring venting are segregated AND accumulated batches of
50 or more containers are within the 90-day clock.
The contractor then added this requirement
to the Container Management program in the Administrative Control section of
the Technical Safety Requirements (TSRs), and DOE-RL approved the MDSA and TSRs.
The staff did not agree that the control set
for the single-drum deflagration accident was adequate for several reasons:
The staff’s comments were transmitted to
site personnel and discussed during two teleconferences in September. As a result of these discussions, DOE-RI,
decided to make some changes in the controls, including the following:
Unvented drums that may generate oxygen or
that are bulged shall be overpacked and then vented within 5 days.
The Board’s staff views this set of TSRs as
an improvement over the previous set, and believes that the new TSRs provide
some additional conservatism. However,
the staff remains concerned that no limit exists to prevent having as many as
23 drums exposed and unvented for an indefinite period of time. In addition, the details of how the controls
will be procedurally implemented were not available for review. The staff plans additional discussions with
the site to cover these topics.