Upper plenum temperature calculations: comparison of TRANSURANUS with a 2–D model under steady–state conditions

The model for the evaluation of the upper plenum temperature (pressure) of the TRANSURANUS code is further developed to predict with better accuracy the role played by this parameter under steady–state and accident conditions (LOCA, RIA), rather than providing this parameter on input. At present, for the gas contained in the upper plenum volume, the code has a “low temperature” and a “high temperature” model. The former assumes that the plenum temperature coincides with the coolant temperature while the latter adopts a weighted value of the cladding inner temperature and the fuel central temperature evaluated in the uppermost zone of the fuel stack. To refine the accuracy of the code predictions, the adopted strategy was to improve the description of the plenum volume sub–system by means of 2–D models.. For this purpose, both a transient heat transfer model and a FEM model by using the commercial software COMSOL Multiphysics were developed. In addition, ENEA implementated in TRANSURANUS the FRAPCON–3 plenum temperature model for comparison with the two other models. The paper presents the comparison of the code results for a PWR fuel pin under steady–state conditions. In addition, thanks to the capability of the code to account for the change in the plenum gas composition, preliminary calculations on the effect of fission gas release on the plenum temperature are also presented. Finally, we discuss the plenum spring gamma heating and the clad–to–coolant heat transfer coefficient under transient conditions in the light of the FK–1 test (NSRR) and the results published in the open literature.

CALABRESE Rolando;  SCHUBERT Arndt;  VAN UFFELEN Paul;  VLAHOVIC Luka;  GYORI Csaba; 

2014-12-09

Nuclear Society of Slovenia

JRC90253

https://publications.jrc.ec.europa.eu/repository/handle/JRC90253,