SHAFT BREAK REVIEW RESPONSIBILITIES Primary- Reactor Systems Branch (RSB) Secondary- None

The events postulated are an instantaneous seizure of the rotor or break of the shaft of a reactor coolant pump in a pressurized water reactor (PWR) or recircu-lation pump in a boiling water reactor (BWR). Flow through the affected loop is rapidly reduced, leading to a reactor and turbine trip. The sudden decrease in core coolant flow while the reactor is at power results in a degradation of core heat transfer which could result in fuel damage. The initial rate of reduction of coolant flow is greater for the rotor seizure event. However, the shaft break event permits a greater reverse flow through the affected'loop later during the transient and, therefore, results in.a lower core flow rate at that time. This SRP section is intended to cover both of these accidents. The review is conducted with radioactivity releases and with the postulated initial and long-term core and reactor conditions'that are pertinent to the rotor seizure or broken shaft events, the methods of thermal and hydraulic analysis, the postulated sequence of events including time delays prior to and after pro-tective system actuation,-the assumed reactions of reactor system components, the functional and operational characteristics of the reactor protection system in terms of how it.affects the sequence of events, and all operator actions required to secure and maintain the reactor in a safe condition. The results of the appilcant's analyses are reviewed to assess fuel damage and to ensure that values of pertinent system parameters are within expected ranges for the type and class of reactor under review. Fuel damage is assessed by the methods described in SRP Section 4.2 (Ref. 13). The system parameters that are evaluated include: core flow and flow distribution (including hydraulic instabil-ities), channel heat flux (average and hot), minimum critical heat flux rati