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NNSA RESPONDS TO DNFSB CONCERNS ABOUT DESIGN OF UPF
In advance of next week’s Defense Nuclear Facilities Safety Board public hearing on the Uranium Processing Facility in Knoxville, the National Nuclear Security Administration has provided a detailed response to safety-related design issues raised earlier by the Board and said it was committed not only to improvements in the design but also to making sure “a robust safety basis review and approval process is in place.” The design concerns range from the ability of UPF’s ancillary facilities to withstand an airplane crash to the possibility of glovebox fires during an earthquake and concerns about toxic releases if there were fires in areas where warhead parts are being staged.
The Nov. 21 report by the NNSA, with a cover letter by Acting Administrator Bruce Held, addressed each of the 13 issues that the Board identified in late August as ongoing safety-related concerns in the design of the multibilliondollar project at the Y-12 National Security Complex. Not all of them had been addressed, at least not fully, but the NNSA provided a path forward for addressing the concerns.
The DNFSB will hold a public hearing Tuesday, Dec. 10 in Knoxville to discuss issues pertaining to the operational safety and emergency response capabilities at Y-12, as well as the safety issues associated with the design of the UPF. Held is scheduled to testify at that hearing, along with other top headquarters, field and contractor officials. DNFSB Chairman Peter Winokur acknowledged in his August letter that the NNSA had made progress in addressing safety issues identified in 2012, and Held said he was encouraged by the efforts to integrate nuclear safety into the design of UPF. “I am confident that the UPF project will continue to improve execution of an effective safety basis program that will ensure safety controls are identified and incorporated into design,” Held wrote to Winokur.
Plane Crash Scenarios Draw Concern
One of the issues drawing the most attention is the ability of the UPF design to withstand a plane crash, especially the planned connector between the main building and the nearby Highly Enriched Uranium Materials Facility, where the nation’s primary stockpile of weapons-grade uranium is stored. Some of the support facilities associated with UPF weren’t designed to deal with the impact of a plane crash, apparently because of the perceived unlikelihood of such an event. According to the latest report from the NNSA, the UPF Main Building and X-Ray Vaults are designed to withstand an airplane crash. At this time, however, the administration connector, the loading dock/truck bay, and the enclosed dock/dock vestibule are not designed to withstand an airplane crash, the report stated.
There also are questions that remain regarding the connector to the highly enriched uranium storage facility. “The structure exceeds the frequency threshold (to require hardening for a plane crash), but the quantities and types of materials present in any given time in the connector are still being determined,” the NNSA’s report to the defense board said. The NNSA said there are multiple design options for the connector, including:
— Designing the entire structure to withstand the airplane crash;
— Designing the walls of the structure to withstand the airplane crash with some administrative controls on material-at-risk in the connector; and
— Establishing specific administrative controls on material-at-risk in the connector.
For those structures that are not to be hardened to withstand a plane crash, there apparently would be administrative limits on how much material could be there at any one time and how long it could stay there. “This is acceptable because these areas do not routinely contain the hazardous materials,” the NNSA report said. A number of planning activities are under way to make sure the ultimate design for the connector and other ancillary structures meets the necessary safety marks, according to the report.
Fire Protection Systems Addressed
Another issue is whether the fire protection systems in design are sufficient to actually prevent toxic materials associated with the canned subassemblies from releasing to the workers and the public. The report indicates that the design of mezzanines inside the UPF may be important to capture the heat early during a fire scenario and activate the fire-suppression system sooner. “A critical path in the schedule is to determine where the mezzanine floors are required so that the building structural analysis may proceed,” the response to the DNFSB stated. That determination is supposed to be made in the first quarter of FY 2014. The concern that a seismic event could cause a fire in gloveboxes—which under normal operating conditions are safeguarded by the inert gas atmosphere that doesn’t allow combustion—seemed to be downplayed by the NNSA response.
The amount of combustibles in a glovebox is limited by the process, the agency said. “The strategy for demonstrating safety is to document that the ignition sources and the types of combustibles inside a glovebox are insufficient to generate enough heat to result in a release of toxicological materials,” the NNSA stated. “Furthermore, the scenario requires simultaneous fires in multiple gloveboxes over the same significant duration in time before co-located and public thresholds are reached.”
The report said fire-protection controls are effective for “all but a seismic event that affects more than one glovebox.” If the subsequent analysis shows that a release is possible, then the amount of toxic material could be controlled through administrative controls if necessary, the response said. Also, the process areas that could be potentially affected by this (presumably talking about the assembly of warhead components and others task associated with Beta-2E) are part of the deferred scope of UPF, the report notes.
—From staff reports