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          NRC Library  Document Collections  NUREG-Series Publications  Publications Resulting from International AgreementsAssessment of RELAP5/MOD3.3 against Single Main Steam Isolation Valve Closure Events at the Krško Nuclear Power Plant (NUREG/IA-0223)

On this page: Publication Information AbstractDownload complete document NUREG/IA-0223 (PDF - 1.01 MB)Publication Information **Manuscript Completed:**November 2003**Date Published:**April 2010 **Prepared by:** Iztok Parzer, Borut Mavko Jožef Stefan Institute Jamova cesta 39 SI-1000 Ljubljana, Slovenia A. Calvo, NRC Project Manager **Published by:** Office of Nuclear Regulatory Research  U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Availability Notice Abstract Recently, the last frozen version of RELAP5/MOD3.3 was released, before the code will be merged with another best estimate thermal-hydraulic system code (TRAC) into an integrated thermal-hydraulic code. Therefore, it is of utmost importance to assess models built using the RELAP5/MOD3.3 code against real plant transients before the code merger. The paper presents the RELAP5/MOD3.3 analysis of two abnormal events that occurred at the Krško Nuclear Power Plant in September 1995 and January 1997, before replacement of the steam generators (SGs) in 2000. The events resulted from the sudden closure of a main steam isolation valve (MSIV). In the September 1995 event, a malfunction in the MSIV in SG-1 caused inadvertent valve closure. In the January 1997 event, the valve stem in SG-2 was broken, also causing sudden valve closure. Researchers obtained valuable plant data from these real plant transients and performed the RELAP5/MOD3.3 code assessment. The analyses used a full two-loop plant model, developed at the Jožef Stefan Institute in Ljubljana, Slovenia. The model assumed old Westinghouse D4-type SGs with preheaters. It assumed that 18-percent of the U-tubes were plugged in both SGs. 
      
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