https://re.public.polimi.it/bitstream/11311/1020691/1/rev_A%20Dynamic%20safety%20margin%20characterization%20approach%20in%20support%20of%20IDPSA.pdf

A dynamic probabilistic safety margin characterization approach in support of Integrated Deterministic and Probabilistic Safety Analysis

Effects of RCP trip when recovering HPSI during LOCA in a Westinghouse PWR

Instrumentation needs for the detection of inadequate core cooling are discussed, and a review of reactor coolant inventory tracking systems (RCITS) is presented. RCITS installation experience is considered, and attention is given to operating experience, accuracy, and procedures. It is noted that the addition of inadequate core cooling accident monitoring instrumentation to all PWRs (pressurized water reactors) is nearing completion after more than eight years. The response of and acceptance by the utilities have been largely positive, with only a few holdouts. It is concluded that the systems developed, while not providing the precision that might be desired, are sufficient to provide vital information for accident avoidance and recovery. In addition, unexpected benefits for normal operation have resulted, and operator acceptance and confidence have been good. >

/pdf/post-implementation-review-of-inadequate-core-cooling-3lov5ab9uv.pdf

Post-implementation review of inadequate core cooling instrumentation

Presented are experimental results on the general performances of core exit thermocouples (CETs) to detect core overheat for accident management (AM) action by using the Large-Scale Test Facility (LSTF) of the ROSA Program of the Japan Atomic Energy Agency. The LSTF is a full-height, full-pressure, and 1/48-volumetric-scaled model of a 4-loop pressurized water reactor (PWR). This study was motivated by a significant delay in the time and temperature rise of the CETs from core heat-up during a vessel top head small break loss-of-coolant accident (SBLOCA) test. A certain delay in time and temperature rise of the CETs was also observed in various SBLOCA and abnormal transient tests. Such CET performances are derived from thirteen LSTF tests as follows: (1) general CET performances are obtained in the form of equations including cases under limited influences of water fall-back from hot legs, (2) the major reason for the delay is the interaction of three-dimensional steam flows with low-temperature structures...

Reliability of Core Exit Thermocouple for Accident Management Action during SBLOCA and Abnormal Transient Tests at ROSA/LSTF

Instrumentation needs for detection of inadequate core cooling. Studies of the Three Mile Island accident identified the need for additional instrumentation to detect inadequate core cooling (ICC) in nuclear power plants. Industry studies by plant owners and reactor vendors supported the conclusion that improvements were needed to help operators diagnose the approach to or existence of ICC as well as to provide more complete information for operator control of safety injection flow to minimize the consequences of such an accident. In 1980, the US Nuclear Regulatory Commission (NRC) required further studies by the industry and described ICC instrumentation design requirements that included human factors and environmental considerations. On December 10, 1982, NRC issued to Babcock and Wilcox (B and W) licensees orders for Modification of License and transmitted to pressurized water reactor licensees Generic Letter 82-28 to inform them of the revised NRC requirements. The instrumentation requirements include upgraded subcooling margin monitors (SMM), upgraded core exit thermocouples (CET), and installation of a reactor coolant inventory tracking system. NRC Regulatory Guide 1.97, which covers accident monitoring instrumentation, was revised (Rev. 3) to be consistent with the requirements of item II.F.2 of NUREG-0737.

T.L. Hauang

Papers

Instrument accuracy in reactor vessel inventory tracking systems