Acceptable Seismic Risks at Nuclear Facilities

The paper investigates the potential impacts of the transition to the requirements per DOE Order 420.1B and the criteria promulgated by the new DOE-STD-1189 on the current practice for seismic design of Structures, Systems, and Components (SSCs). The review addresses the modification of the prescribed unmitigated radiological dose consequence methodology provided in ANSI/ANS 2.26-2004 by the new DOE-STD-1189-2008. Captured in the investigation is the issue of how a facility designed and constructed in accordance with these procedures may comply with requirements for protection of worker and public safety identified by the Nuclear Regulatory Commission (NRC) in 10 CFR Part 70 . The new ANSI/ANS Standards provide criteria and guidance to select Seismic Design Category (SDC) and Limit State (LS) for the structures, systems, and components (SSCs) important to safety. An unmitigated consequence analysis considering the uncertainties in estimating failure and the safety consequences of the failure may be performed to determine the SDC and the Limit State, which then are used to establish the level of Peak ground Acceleration (PGA) and design response spectra. The SDC selection is based on the objective of achieving acceptable risk to the public, the environment and workers from seismic induced events. Unmitigated consequence analysis is a procedure that has been used by the DOE for the purpose of incorporating safety in design and operation of its nuclear facilities. The concept is also used in 10 CFR 70, the U.S. Nuclear Regulatory Commission (NRC) regulation that applies to fuel cycle facilities.