Document: NUREG-0800
Document ID: dd4f84a9-8976-44c4-b631-d7c0254f4efc
Document Type: srp
Title: PROBABILISTIC RISK ASSESSMENT AND SEVERE ACCIDENT EVALUATION FOR
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1416/ML14161A594.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
ensitivity of the estimated risk to potential biases in numerical values, such as initiating event frequencies, failure probabilities, and equipment unavailabilities, (2) determining the impact of the potential lack of modeling details on the estimated risk, and (3) determining the sensitivity of the estimated risk to previously raised issues (e.g., motor-operated valve reliability). As noted in Element 1.1 of Table A-1 in Appendix A to RG 1.200, special emphasis should be placed on PRA modeling of novel and passive features in the design, as well as addressing issues related to those features, such as DI&C, explosive (squib) valves, and the issue of T-H uncertainties. 3. The following guidelines for reviewing DI&C system risk assessments are based on the lessons learned from previously accepted new reactor DI&C system PRA reviews. The review should consider the following steps, as applicable, to ensure that the risk contributions from DI&C, including software, are reflected adequately in the overall plant risk results: 19.0-31 Draft Revision 3 –November 2014 A. The level of review of the DI&C portion of the PRA may be limited due to limitations such as the lack of design details, lack of applicable data, and the lack of consensus in the technical community regarding acceptable modeling techniques for determining the risk significance of the DI&C system. The level of review should be proportional to the use of results and insights from the applicant’s DI&C risk assessment. B. The modeling of DI&C systems should include the identification of how DI&C systems can fail and what these failures can affect. The failure modes of DI&C systems are often identified by the performance of failure modes and effects analyses (FMEA). It is difficult to define DI&C system failure modes especially for software because they occur in various ways depending on specific applications. Also, failure modes, causes, or effects often are intertwined or defined ambiguously, and sometimes