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:
aws 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 protection system. The material properties of the turbine casing are of interest because secondary missiles could be generated if the casing fails or, alternatively, the casing could serve to arrest and contain missiles. Design speed missile generation probability should be related to disk design parameters, material properties, and the inservice volumetric (ultrasonic) disk inspection interval. Destructive overspeed missile generation probability should be related to the turbine governor and overspeed protection system's speed sensing and tripping characteristics, DRAFT Rev. 3 - April 1996 3.5.1.3-6 the design and arrangement of main steam control and stop valves and the reheat steam intercept and stop valves, and the inservice testing and inspection intervals for system components and valves. In addition, fracture toughness properties of the turbine casing material in its operational environment should be evaluated. SRP Section 10.2 provides additional information regarding inspection and testing of turbine generator components. Further information regarding turbine missile generation mechanisms and probabilities can be found in References 5, 12, and 13 and the reports cited therein.23 4. The staff believes that maintaining an acceptably small value of missile generation probability, P , by means of a suitable program of periodic testing and inspection is a 1 reliable method for ensuring that the objective of precluding generation of turbine missiles (and hence the possibility of damage to safety-related structures, systems, and components by those missiles) can be met. The NRC safety objective for turbine missiles (i.e., P should be < 10 per year per plant) is best expressed in terms of either of 4 -7 two sets of criteria applied to missile generation probability, P