Core Exit Temperature (CET) Effectiveness in Accident Management of Nuclear Power Reactor

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The Task on the Core Exit Temperature (CET) thermocouple effectiveness in Accident Management (AM) was initiated based on a discussion held by the NEA’s Committe on the Safety of Nuclear Installations (CSNI) Working Group on Analysis and Management of Accidents (WGAMA) in September 2007. The discussion focused on results of the test 6-1 performed in the frame of the OECD ROSA/LSTF project simulating a vessel head small break loss-of-coolant accident (SBLOCA) under an assumption of total failure of the high pressure injection (HPI) system. The test had to be terminated prematurely to avoid excessive overheating of the core. It was noted that core uncovery had started well before CET thermocouples indicated superheating and the temperature increase rate in the core was higher than shown by the CET. The results suggested that the response of the CET thermocouples could be inadequate to initiate the relevant AM actions. Moreover, examples of CET response in other tests, for example, LOFT, PKL and LSTF, seemed to confirm this observation.

To address this issue, the CSNI approved a WGAMA activity in December 2007 with the ojectives to review and consolidate background knowledge of CET application in AM and to provide conclusions and recommendations for possible further work.