In summary, PBAPS-1 is a one-of-a-kind reactor, a stand-alone design unlike any other in the United States, and the world, that results in site-specific factors that challenge decommissioning and license termination. Specifically, the special characteristics of irradiated graphite which are multi-faceted, the lack of vessel design that would support flooding to provide the standard dose and contamination protective barrier, the original materials and manufacturing methods that introduce unknown trace elements and required updates to analytical methods to support “virgin” graphite analysis all must be addressed to ensure the health and safety of the public is maintained.
These nuances of PBAPS-1 present increased risk for decommissioning activities to achieve license termination. In fact, the most closely related and only other graphite moderated HTGR in the United States, FSV, encountered radiological conditions beyond what was predicted despite following all the normal decommissioning processes and was forced emergently to re- design the plan and ultimately flood up the reactor vessel. The PBAPS-1 vessel was not designed to support flooding the cavity. The only other two experimental reactors built along with PBAPS-1 are either temporarily entombed or continue in SAFSTOR operation as their owners in Europe work to find a suitable process to manage dry decommissioning for their graphite moderated HTGRs. (Constellation Letter to the NRC, May 13, 2024)
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