Resolution of Generic Safety Issues: NMSS-0002. Significant Quantities of Fixed Contamination Remain in Krypton-85 Leak-Detection Devices after Venting ( NUREG-0933, Main Report with Supplements 1–34 )
This issue was identified1700 by NMSS after several cases were reported where licensees found residual contamination remaining in some components of Krypton-85 handling systems after the standard decommissioning process. The staff's concern was that systems released as "cleaned" under existing decommissioning procedures could still contain the residue and be released into the scrap stream for later reuse. Although the incidents only involved Krypton-85, the concern extended to all gas handling systems that subject a radioactive gas to vacuum/pressure cycling.
During cleaning and decommissioning of some gas handling systems, a varnish-like residue was found on the inside of some of the system components (storage tank and compressors). This residue is not easily removed by commonly used solvents; however, it can be removed by exposing the internal surfaces of the components and scraping the residue. Due to the low levels of gamma radiation emitted by Krypton-85 and the robust construction of the storage tanks and other components, the presence of the residue is not detectable by measurements from the outside of the components.