Document: NUREG-0800
Document ID: 90914152-fc84-4413-a5f5-aa75efd21205
Document Type: srp
Title: TURBINE MISSILES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0636/ML063600395.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.5.1.3
CFR Part: 
CFR Title: 

Content:
or components failing to perform their safety function, P3. Stated in mathematical terms, P4 = P1 × P2 × P3. 3.5.1.3-4 Revision 3 - March 2007 In accordance with the guidance provided in SRP Section 2.2.3 and RG 1.115, the probability of unacceptable damage from turbine missiles should be less than or equal to 1 in 10 million per year for an individual plant (i.e., P4 should be < 10-7 per year per plant). Although the calculation of strike probability, P2, is not difficult in principle (i.e., a straightforward ballistics analysis), in practice it requires numerous modeling approximations and simplifying assumptions to define the properties of missiles, interactions of missiles with barriers and obstacles, trajectories of missiles as they interact with and perforate (or are deflected by) barriers, and identification and location of safety-related targets. Specific approximations and assumptions tend to have a significant effect on the resulting value of P2. Similarly, a reasonably accurate specification of the damage probability, P3, is complicated by difficulties associated with defining the missile impact energy required to render safety-related systems unavailable to perform their safety functions and with postulating sequences of events that would follow a missile-producing turbine failure. Because of the uncertainties associated with calculating P2 and P3, the staff concludes that such analyses are "order of magnitude" calculations only. On the basis of simple estimates for a variety of plant layouts, the strike and damage probability product can be reasonably assumed to fall in a range that depends on the gross features of turbine generator orientation. A. For favorably oriented turbine generators, the product of P2 and P3 tends to be in the range of 10-4 to 10-3 per year per plant. B. For unfavorably oriented turbine generators, the product of P2 and P3 tends to be in the range of 10-3 to 10-2 per year per plant. Favorably oriented turbine generators are