The development of interim guidance on systems interactions

The Office of Nuclear Reactor Regulation is developing interim guidance to direct the systematic evaluations of LWRs for adverse systems interactions. The guidance establishes a three-step review process and provides basic definitions, deterministic safety criteria, a classification of the types of adverse systems interactions, and descriptions of the formal methodology applicable for disciplined evaluations including the ranking of interactions by their relative importance to safety. The guidance provides for accommodating lessons learned from operating experience and relates systems interactions to human errors and probabilistic risk assessments