WASHINGTON -- Tanks containing radioactive waste at the U.S. Department of Energy Savannah River Site, a nuclear weapons facility in South Carolina, should not necessarily be sealed as soon as the bulk of the waste has been removed, says a new congressionally mandated report from the National Academies' National Research Council. Postponing closure of tanks with difficult-to-remove residual wastes for five to 10 years would give DOE time to overcome obstacles to using emerging technologies that could remove more of the residual waste and better immobilize what is left in the tanks. This could be done without delaying final closure of the "tank farm," added the committee that wrote the report.
Once the bulk of the radioactive waste is removed from tanks at the Savannah River Site, DOE plans to fill the tanks with grout to close most of them permanently. But given that the small amount of residual waste left in the tanks has a much lower likelihood of causing significant radioactive contamination of the environment, the department need not rush to grout all the tanks -- a step that is practically irreversible. Instead, the committee urged DOE and South Carolina to decouple the schedules for cleaning the tanks and sealing them, timelines that appear to be linked under a Federal Facility Agreement. Doing so will allow DOE to use emerging technologies to enhance tank cleanup, improve how the residual waste is immobilized, and better prevent water from seeping into closed tanks.
On the other hand, tank closure does not have to be delayed if there is very little residual waste or if special circumstances warrant closure, the committee said. It added that revising the closure schedule for tanks with insoluble wastes does not need to affect previously agreed-upon milestones for final closing of the tanks. In fact, if new technologies become available, they may speed up tank cleanup and closure, possibly leaving less waste behind.
The Savannah River Site also faces what DOE calls a crisis in the amount of compliant tank space available to store waste from ongoing operations at the site, including tank cleanup itself. Tanks are considered compliant if they have a secondary containment system, so that they are essentially tanks within tanks; noncompliant tanks have no second wall or only a partial one. A certain amount of compliant space also must be reserved for an emergency, such as a tank leak.
The committee agreed that the lack of compliant space is a major problem, but questioned DOE's plans for freeing up space in existing tanks. DOE plans to use a physical separation process to remove radioactivity from some salt wastes, and then grout and permanently store those wastes in on-site vaults. But the committee noted that while waste from this process represents only 8 percent of the volume of radioactive waste to be generated during salt-waste processing, the waste contains 80 percent to 90 percent of the radioactivity projected to be in the vaults. Chemical processes that can remove more radioactivity from salt wastes are scheduled to begin in 2007 and 2009. Until then, DOE should consider other options for preserving or better utilizing its limited compliant tank space, such as setting aside carefully selected nonleaking, noncompliant tanks for emergency storage, or reducing waste streams to compliant tanks.
In a follow-up report expected early next year, the committee will further evaluate environmental risks at the Savannah River Site and examine DOE's plans for managing radioactive tank wastes at sites in Idaho and Washington state.
The study was sponsored by the U.S. Department of Energy. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science and technology advice under a congressional charter. A committee roster follows.
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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