Interfacing systems LOCA

Valve surveillance that leads to interfacing system LOCAs... 

Interfacing systems LOCA -Review surveillance procedure re isolaln u valves (b,p) -Modify procedures to depressunre PCS (p) -Revise training for ISLOCA (b.p)... 

TE = transient - -loss of electric power SE = small LOCA - -loss of electric power V = interfacing systems LOCA... 

Direct bypass of the containment (for example, due to a steam generator tube rupture or to an interfacing systems LOCA which discharges outside the containment) and failure of the containment isolation system should be addressed in the analysis. This would normally be included in the definition of the PDSs. 

The interfacing system LOCA (ISL) is presumed to result from exposing low pressure piping (design pressure 400-700 psi) of the interfacing system to high primary system pressure (about 2250 psi). The initial plant response to an ISL is the same as the response to an equivalent sized LOCA inside containment. However, RCS inventory is discharged outside containment and is not returned to the containment sump for recirculation. In addition, an ISL will provide a path, which bypasses the containment, for release of radioactive materials. 

The NRC used probabilistic risk assessment (PRA) analysis in NUREG/CR-5102 (Reference 2) to evaluate three older operating pressurized water reactors for the effectiveness of proposed requirement changes in reducing the risk of an interfacing system LOCA, and for calculating the contribution of the ISL to the overall core damage frequency estimate. 

The acceptance criterion for the resolution of GSI 105 is that the arrangement and design of systems that interconnect with the RCS and also extend beyond the containment shall be such as to minimize the probability of an interfacing system LOCA. Identification of the potential pathways for an ISL and estimation of the probable ISL frequency of occurrence shall be included in the overall plant PRA required by 10 CFR, Part 52 (Reference 3). 

NUREG/CR-5102, "Interfacing Systems LOCA Pressurized Vlater Reactors", U.S. Nuclear Regulatory Commission. 

A related issue, which also discusses the integrity of the HP to LP interface between safety-related systems is GSI 105, "Interfacing Systems LOCA".)... 

The higher radioactivity release categories are dominated by the so-called interfacing systems LOCA, where a breach of the reactor coolant... 

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