Document: NRC Regulatory Guide
Document ID: c7a40fcc-fc9d-4eb2-ad86-f9f5b0f04c82
Document Type: regulatory_guide
Title: Plant-Specific, Risk-Informed Decisionmaking:  Technical Specifications (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1920/ML19206A489.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.177
CFR Part: 
CFR Title: 

Content:
eating only part of the failure rate as time related when this is not the case underestimates the test-limited risk; therefore, such a breakdown of the failure rate should be justified through data or engineering analyses. In addition, sometimes only the failure probability (i.e., the component unavailability, q) may be provided without giving a failure rate. In such a case, the effect of a change in the SF cannot be evaluated unless the component test interval previously used for “T” is used to convert the unavailability, q, in terms of λ and “T.” When the breakdown between time-related and cyclic demand-related contribution is unknown, all failures can be assumed to be time related to obtain the maximum test-limited risk contribution. In summary, the data required for measuring a change in risk with a change in the SF are a breakdown of the failure probability of the component into its time-related and demand-related components, the proposed SF, and the out-of-service time for surveillance testing of the component. A-2.3.6 Test-Caused Transients To evaluate and identify the test-caused transients risk (typically defined as RC), transient events, as well as those caused by a test, should be identified. In most cases, this requires reading through the description of transients that have occurred and noting those caused by the test. When reduced SFs are allowed, the resulting reduction in test-caused transients per unit time tends to cause decreases in risk because there are fewer adverse effects of testing over that longer test interval (which, however, will be partially or wholly balanced by increases in RD that are caused by the longer time period before detection and correction of failures). The transient events are obtained from the following plant operating data: a. Performance indicator reports: These reports list the number of reactor trips and safety system actuations at each plant, the date of the events, and the numbers of the relevant licensee