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.
John T. Conway
c: Mr. Keith A. Klein
Mr. Mark B. Whitaker, Jr.
DEFENSE NUCLEAR FACILITIES SAFETY BOARD
Staff Issue Report
MEMORANDUM FOR: J. K. Fortenberry, Technical Director
COPIES: Board Members
FROM: D. Qgg
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
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.