Computer codes validation for conditions of core voiding

Abstract of the technical paper presented at:
14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-14)           
Toronto, Ontario, Canada
September 25-29, 2011

Prepared by:
Aleksandar Delja and Pat Hawley
Canadian Nuclear Safety Commission (CNSC)
Ottawa, Ontario, Canada

Abstract

Void generation during a loss of coolant accident (LOCA) in a core of a CANDU reactor has a specific importance because of its strong coupling with reactor neutronics. The use of dynamic behaviour and computer code capability to predict void generation accurately in the temporal and spatial domain of the reactor core is fundamental for the determination of CANDU safety.

As a part of regulatory assessment and resolving identified generic issues (GI), and in an effort to build independent thermal hydraulic computer codes for the CNSC, a series of validation exercises were done in the CNSC using different computer codes for the evaluation of the void generation phenomena. In their assessment, the Canadian industry used the RD14M test facilities for code validation. The validation exercises for the Canadian computer codes TUF and CATHENA have been done.  Recently, the CNSC has had access to the computer code trACE, and given the potential to use this code in CANDU applications, a validation exercise for this code has also been done by the CNSC.

The paper presents the validation exercise of void generation for a selected RD14M test for the trACE computer code. The accuracy of the obtained results is discussed and compared with previous validation assessments that were done using the CATHENA and TUF codes.

The presented work provides important elements of safety evaluation for CANDU reactors using computer codes. It quantifies the accuracy of each code applied in the assessment, and also presents the differences in the results which can then be used in code and model modifications. The results obtained from this exercise are important for code uncertainty evaluation as they are used to evaluate realistic computer codes that are being used in safety and safety margin assessments. 

Keywords: Thermalhydraulics, safety, code development, code validation, etc.

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