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Development of a Dynamic Event Tree for a Pressurized Water Reactor Steam Generator Tube Rupture Event

Chun-Chang Chao, Chin-Jang Chang

Nuclear Technology

Volume 130 / Number 1 / April 2000 / Pages 27-38


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The DPRA-SGTR computer program was written to develop a dynamic event tree for the analysis of a steam generator (SG) tube rupture (SGTR) event. Using the dynamic event tree, a full-scope understanding of the possible responses of a plant following an SGTR event and the related actions with the emergency operating procedures (EOPs) can be analyzed. RELAP5/MOD3.2 was linked to DPRA-SGTR to calculate the thermal-hydraulic response of a Westinghouse three-loop pressurized water reactor at the Maanshan nuclear power plant. One SG tube with a double-ended break was postulated at the beginning of the accident. The plant thermal-hydraulic behaviors, status of the mitigation systems, and operator actions following the EOPs were explicitly modeled in the postulated SGTR. A total of 131 sequences were generated after an SGTR event. Among the 131 sequences, 91 sequences with a frequency sum of 8.5 × 10-6 were stopped either because of low-occurrence frequency (<1 × 10-12) or because the preset mission time was reached (30 000 s after initiating the event). Seven out of the 91 sequences with a frequency sum of 6 × 10-9 were intentionally stopped as a fatal error occurred when RELAP5 was calculating the thermal-hydraulic response.

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