Post-Test Analysis of 10% Hot Leg Break LOCA of LSTF Using RELAP5/MOD3.2

ABSTRACT

This paper describes the post-test analysis for 10% Hot leg break LOCA carried out as a part of IAEA Coordinated Research Project on “Evaluation of Uncertainty in Best Estimate Accident Analysis” for Large Scale Test Facility of ROSA-IV in Japan. The objective of this analysis is to assess the capability to reproduce the phenomena occurring during the small break LOCA using the best estimate code RELAP5/MOD3.2 by systematically applying the procedures lead by Uncertainty Methodology based on Accuracy Extrapolation, developed at University of Pisa. The test facility nodalisation qualification is demonstrated for both ‘steady state level’ and ‘on transient level’. For the ‘steady state level’ qualification, compliance to acceptance criteria established in UMAE has been checked for geometrical details, boundary conditions and thermal hydraulic parameters. For evaluation of qualitative qualification of ‘on transient level’ five steps followed are i) Comparison between experimental and code calculation resulting time sequence of significant events ii) Identification/verification of CSNI phenomena validation matrix iii) Use of the Phenomenological Windows iv) Identification of Key Phenomena and Relevant Thermal-hydraulic Aspects v) Visual comparisons between experimental and calculated relevant parameters time trends. The steps followed have been described in details in this paper. It is concluded that most of the phenomena observed in the experiment are reproduced by the code calculation.

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