Document: NUREG-0800
Document ID: 29fa664a-a42c-4ff0-8ae1-3798f7f23c23
Document Type: srp
Title: TURBINE MISSILES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070373.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.5.1.3
CFR Part: 
CFR Title: 

Content:
t of P and P tends to be in 2 3 the range of 10 to 10 per year per plant. -4 -3 b. For unfavorably oriented turbine generators, the product of P and P tends to be 2 3 in the range of 10 to 10 per year per plant -3 -2 Favorably oriented turbine generators are located such that the containment and all, or almost all, safety-related structures, systems, and components outside containment are excluded from the low-trajectory hazard zone described in Regulatory Guide 1.115. Because of inadequate data, controversial assumptions, and modeling difficulties as described above, the staff accepts a product of strike and damage probabilities of 10 per -3 year per plant for a favorably oriented turbine and 10 per year per plant for an -2 unfavorably oriented turbine. The staff does not encourage applicants to calculate P , P , 2 3 or their product. The suggested values represent the staff's best estimate of the product of P and P , based on the results of calculations performed at NRC and elsewhere (Refs. 2 3 5 and 14).22 3. Operating experience indicates that turbine disks crack (Refs. 6, 11, and 12), turbine stop and control valves fail (Refs. 7, 10, and 12), and disk ruptures can result in the generation of high-energy missiles (Refs. 9 and 12). Analysis (Refs. 7 and 8) indicates that missile generation can be modeled and the probability of generation can be strongly influenced by a suitable program of periodic inservice testing and inspection. In general, two modes of turbine disk failure can result in turbine missile generation: (a) rotor material failure at approximately the rated operating speed and (b) failure of the overspeed protection system. Failure of turbine disks at or below the design speed (nominally, 120% of normal operating speed) can be caused by small flaws or cracks that grow to critical size during operation. Failure of the turbine disks at destructive overspeed (about 180% to 190% of normal operating speed) can result from failure of the overspeed