WASHINGTON -- Tanks containing radioactive waste at the U.S. Departmentof Energy Savannah River Site, a nuclear weapons facility in SouthCarolina, should not necessarily be sealed as soon as the bulk of thewaste has been removed, says a new congressionally mandated report fromthe National Academies' National Research Council. Postponing closureof tanks with difficult-to-remove residual wastes for five to 10 yearswould give DOE time to overcome obstacles to using emergingtechnologies that could remove more of the residual waste and betterimmobilize what is left in the tanks. This could be done withoutdelaying final closure of the "tank farm," added the committee thatwrote the report.
Once the bulk of the radioactive waste is removed from tanks at theSavannah River Site, DOE plans to fill the tanks with grout to closemost of them permanently. But given that the small amount of residualwaste left in the tanks has a much lower likelihood of causingsignificant radioactive contamination of the environment, thedepartment need not rush to grout all the tanks -- a step that ispractically irreversible. Instead, the committee urged DOE and SouthCarolina to decouple the schedules for cleaning the tanks and sealingthem, timelines that appear to be linked under a Federal FacilityAgreement. Doing so will allow DOE to use emerging technologies toenhance 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 ifthere is very little residual waste or if special circumstances warrantclosure, the committee said. It added that revising the closureschedule for tanks with insoluble wastes does not need to affectpreviously agreed-upon milestones for final closing of the tanks. Infact, if new technologies become available, they may speed up tankcleanup and closure, possibly leaving less waste behind.
The Savannah River Site also faces what DOE calls a crisis inthe amount of compliant tank space available to store waste fromongoing operations at the site, including tank cleanup itself. Tanksare considered compliant if they have a secondary containment system,so that they are essentially tanks within tanks; noncompliant tankshave no second wall or only a partial one. A certain amount ofcompliant space also must be reserved for an emergency, such as a tankleak.
The committee agreed that the lack of compliant space is amajor problem, but questioned DOE's plans for freeing up space inexisting tanks. DOE plans to use a physical separation process toremove radioactivity from some salt wastes, and then grout andpermanently store those wastes in on-site vaults. But the committeenoted that while waste from this process represents only 8 percent ofthe volume of radioactive waste to be generated during salt-wasteprocessing, the waste contains 80 percent to 90 percent of theradioactivity projected to be in the vaults. Chemical processes thatcan remove more radioactivity from salt wastes are scheduled to beginin 2007 and 2009. Until then, DOE should consider other options forpreserving or better utilizing its limited compliant tank space, suchas setting aside carefully selected nonleaking, noncompliant tanks foremergency storage, or reducing waste streams to compliant tanks.
In a follow-up report expected early next year, the committeewill further evaluate environmental risks at the Savannah River Siteand examine DOE's plans for managing radioactive tank wastes at sitesin Idaho and Washington state.
The study was sponsored by the U.S. Department of Energy. TheNational Research Council is the principal operating arm of theNational Academy of Sciences and the National Academy of Engineering.It is a private, nonprofit institution that provides science andtechnology advice under a congressional charter. A committee rosterfollows.
Copies of TANK WASTES PLANNED FOR ONSITE DISPOSAL AT THREE DEPARTMENTOF ENERGY SITES: THE SAVANNAH RIVER SITE will be available from theNational Academies Press; tel. 202-334-3313 or 1-800-624-6242 or on theInternet at HTTP://WWW.NAP.EDU. Reporters may obtain a pre-publication copy from the Office of News and Public Information (contacts listed above).
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