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

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Keim, Elisabeth Hertlein, Roland Ilg, Ulf Ko¨nig, Gu¨nter Schlu¨ter, Norbert Widera, Martin
Copyright Year	2008
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.
Sponsorship	Pressure Vessels and Piping
Starting Page	679
Ending Page	686
Page Count	8
File Format	PDF
ISBN	9780791848296
DOI	10.1115/PVP2008-61188
e-ISBN	0791838285
Volume Number	Volume 6: Materials and Fabrication, Parts A and B
Conference Proceedings	ASME 2008 Pressure Vessels and Piping Conference
Language	English
Publisher Date	2008-07-27
Publisher Place	Chicago, Illinois, USA
Access Restriction	Subscribed
Subject Keyword	Leakage Water Fracture mechanics Reactor vessels Plumes (fluid dynamics) Brittle fracture Irradiation (radiation exposure) Flanges Systems analysis High temperature Steel Pressure Stress Transients (dynamics) Design Emergency core cooling systems Nozzles Coolants Safety Pressurized water reactors Thermal stresses Accidents Cylinders Low temperature
Content Type	Text
Resource Type	Article

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