ICHMT DIGITAL LIBRARY ONLINE

ISSN 961-91393-0-5

Year 1995

• 1Heat and Mass Transfer in Severe Nuclear Reactor Accidents Proceedings of International Symposium - 22 -26 May, 1995, Kusadasi, Turkey

708 pages

Volume price - $176.00

H. Plank
Siemens AGKWU

H. Weisshaupl
Siemens AGKWU

Any device for mitigation of coremelt accidents must be suitable for a wide range of possible scenarios. Frequently the design of mitigative measures is based on a few enveloping scenarios. Because it is on the one hand difficult to specifly an enveloping scenario for a particular mitigation measure and on the other hand the question, which possible accident progression events should be covered and which one belong to the residual risk cannot be solved by choosing enveloping scenarios this work presents two alternative methods with respect to characteristic in-vessel scenarios. The first one is a comprehensive MAAP3.0B study, where the selection of the scenarios is based on the results of a probabilistic safety analysis. In this way on the one hand more than 80% of all coremelt scenarios could be analyzed by a limited number of calculations and on the other hand likelihood distributions of some key results (e.g. begin of melting, slumping, RPV-failure, hydrogen mass, mass and temperature of melt at slumping) could be generated. The second method uses the accident progression event tree (APET) method to generate characteristic coremelt groups at the time of vessel failure and their estimated likelihoods. One key question for coremelt stabilization outside the RPV is the fraction of fuel rods which have been relocated into the lower head at the time of vessel failure. While it follows from the comprehensive study that this fraction is at least 85%, the APET method gives a somewhat lower value: ≥80% with a likelihood of 77% and <80% with a likelihood of 23%.

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