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Brittle Fracture Safety Analysis of German RPVs Based on Advanced Thermal Hydraulic Analysis

[+] Author Affiliations
Elisabeth Keim, Roland Hertlein

AREVA NP GmbH, Erlangen, Germany

Ulf Ilg

EnBW Kernkraft GmbH, Philippsburg, Germany

Günter König

EnBW Kernkraft GmbH, Neckarwestheim, Germany

Norbert Schlüter

Kernkraftwerke Lippe-Ems GmbH, Lingen, Germany

Martin Widera

RWE Power AG, Essen, Germany

Paper No. PVP2008-61188, pp. 679-686; 8 pages
doi:10.1115/PVP2008-61188
From:
  • ASME 2008 Pressure Vessels and Piping Conference
  • Volume 6: Materials and Fabrication, Parts A and B
  • Chicago, Illinois, USA, July 27–31, 2008
  • Conference Sponsors: Pressure Vessels and Piping
  • ISBN: 978-0-7918-4829-6
  • Copyright © 2008 by ASME

abstract

During the design stage of the today operating German PWRs, one major design target was to manage the materials ageing behavior of the ferritic reactor pressure vessel (RPV) steel in oder to prevent a brittle fracture of the RPV under all possible loads. Very conservative thermal hydraulic input data were used in this context for the assessment of loss of coolant accidents. Today more realistic thermal hydraulic analyses based on large scale experimental results are available as well as more sophisticated fracture mechanics methods to assess postulated flaws. Using these tools an additional joint analysis of six German PWR RPVs is performed. A fully representative spectrum of all possible large and small break loss of coolant accidents is investigated. Locations of interest are the irradiated RPV core beltline region as well as those regions with negligible irradiation but higher loading, like the RPV MCL nozzles and the flange to cylinder transition area. The thermal hydraulic work comprises global system analyses with subsequent local analysis considering mixing phenomena like plume forming below the injecting nozzles. Dependent on the location of the postulated flaw (core or nozzle region), the postulated leak size is differing. In the core weld region medium leak sizes (100 to 200 cm2 ) with subsequent injection into the cold leg lead to dominating loading, whereas in the nozzle the small leak sizes (3 to 20 cm2 ) with injection into the hot leg are more important. This is due to the higher pressure at smaller leak sizes and the larger thermal stresses caused by the high temperature of the nozzle flange and the low temperature of the injected ECCS-water. But independent of the number of transients it turned out that all load paths of the postulated flaws and the investigated leak sizes show a similar behavior. As the result of this additional joint safety analysis of six German PWR RPVs with different injection modes, a brittle fracture of all RPV regions can be excluded with sufficient safety margin.

Copyright © 2008 by ASME

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