Numerical prediction of heat transfer and pressure tube/calendria tube deformation during a contact boiling test

Abstract of the technical paper presented at:
PHWR Safety 2014 / CANSAS-2014
Ottawa, Ontario
June 23–26, 2014

Prepared by: A. Tanase, A. Delja, A. Oussoren, J. Szymanski
Canadian Nuclear Safety Commission
Ottawa, Ontario, Canada

Abstract

Assessment of fuel channel integrity during large break LOCA requires adequate prediction of the thermal-mechanical behavior of the fuel channel behavior following possible contact between the Pressure Tube (PT) and the Calandria Tube (CT). Analytical models are developed to estimate moderator subcooling requirements to prevent channel failure following contact. Such models need to be validated against experimental data.

In 2012 IAEA prepared a new International Collaborative Standard Problem (ICSP) on "HWR Moderator Subcooling Requirements to Demonstrate Backup Heat Sink Capabilities of Moderator during Accidents". The purpose of ICSP is to provide contact boiling experimental data to assess computer codes capabilities in simulating this event. The following are the main phenomena simulated by codes:

• radiation heat transfer to the pressure tube
• pressure tube deformation or failure
• pressure tube to Calandria tube heat transfer
• calandria tube to moderator heat transfer
• calandria tube deformation or failure

CNSC staff is participating in this ICSP, and has developed its own simulation code. Most of the models and correlations implemented in the code are the same as those built into the CATHENA thermalhydraulics code developed by the Canadian industry and used for this application.

The paper summarizes CNSC staff approach for these numerical calculations, and presents results obtained for the thermal and mechanical behavior of both PT and CT during this transient. Results were also produced for channel deformations in the similar test series of CT Strain Contact Boiling (CSCB).