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:
d operating speed and (b) failure of the overspeed protection system. Failure of turbine rotors 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 rotors 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. The missile generation probability at the design speed should be related to rotor design parameters, material properties, and the intervals of inservice examinations of disks. The missile generation probability at the destructive overspeed should be related to the speed sensing and tripping characteristics of the turbine governor and overspeed protection system, the design and arrangement of main steam control and stop valves, the reheat steam intercept, reheat stop valves, and the inservice testing and inspection intervals for system components and valves. In addition, the turbine casing material in its operational environment should be evaluated for fracture toughness properties. SRP Section 10.2 provides additional guidance regarding inspection and testing of turbine generator components. Further information regarding turbine missile generation mechanisms and probabilities can be found in NUREG-1048, NRC Memorandum from E. Jordan to W. Russell, and Letter from C. Rossi (NRC) to J. Martin (Westinghouse Electric Corporation). 3. The staff believes that maintaining an acceptably low missile generation probability, P1, by means of a suitable program of periodic testing and inspection is a 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