Evaluation criteria and procedure for nuclear power plant temporary loads/temporary conditions

Operating nuclear power plants frequently encounter temporary loads/temporary conditions in plant normal operation and maintenance (O and M). The most obvious examples are installation of temporary shielding and scaffolding, or removal of certain supports, to facilitate plant refueling and maintenance outage activities. Short-term operability calls such as those due to snubber failures or unanticipated transients also create temporary loads/temporary conditions. These temporary situations often generate loads that are outside the original plant design basis. Consequently, separate evaluations are needed to ensure that plant structures, systems and components (SSCs) maintain their integrity and functionality while these temporary loads are active. Also, the temporary structures and components need to be evaluated to ensure their integrity during the temporary duration of use. Three types of approaches are normally adopted either individually or in combination to perform needed evaluations: relax the design allowables, use a more refined analysis model but retain the design basis acceptance criteria, or offset temporary loads by eliminating or reducing part of the design basis loads based on short duration considerations. This paper reviews temporary loading/temporary condition issues and the current industry criteria and procedures proposed in dealing with these issues. Where appropriate, regulatory positions on temporary loads/temporary conditions aremore » discussed.« less