Application of a graded approach to support the NRU Reactor U-2 experimental loop return to service

This year marked over 60 years of safe operation during which the National Research Universal (NRU) at the Canadian Nuclear Laboratories (CNL) supported a wide range of applications including, testing of fuels and materials under typical power reactor conditions in two experimental loops (U-1 and U-2). Both experimental loops had been taken out of service several years ago. CNL applied a graded approach to successfully return one of these loops, the U-2 Loop to service. The graded approach applied a risk informed methodology commensurate to the potential risk posed by the operation of the U-2 Loop, without compromising safety. The work enabled the U-2 Loop to remain operational until the NRU reactor was permanently shut down earlier this year, generating valuable data that will be used in development of advanced nuclear fuels and materials. This paper describes the graded approach employed by CNL that supported the U-2 Loop Return To Service (RTS). The use of graded approach is articulated to support development of safety and licensing cases for Small Modular Reactor (SMR) projects. (author)