WOSUB : a subchannel code for steady-state and transient thermal-hydraulic analysis of BWR fuel pin bundles.

Abstract

The WOSUB-codes are spin-offs and extensions of the MATTEO-code [1]. The series of three reports describe WOSUB-I and WOSUB-II in their respective status as of July 31, 1977. This report is the first in a series of three, the second of which contains the user's manual [2] and the third [3] summarizes the assessment and comparison with experimental data and various other subchannel codes. The present report introduces the drift-flux and vapor diffusion models employed by the code, discusses the solution method and reviews the constitutive equations presently built into the code. Wherever applicable, possible exteriors of the models are indicated especially with due regard of the findings presented in [3]. Overall, the review of the model and the package of constitutive equations demonstrate that WOSUB-I and II constitute true alternatives for BWR bundle and PWR test bundle calculations as compared to the commonly applied COBRA-IIIC, and COBRA-IIIC/MIT codes which were primarily designed for PWR subchannel and core calculations, respectively. In fact, the incorporation of the drift flux and the vapor diffusion pro- cesses into a subchannel code has to be cdnsidered.a major step towards a more basic understanding and a well balanced engineer- ing approach without the extra burden of a true two-fluid two- phase model. Recommendations for improvements in the various areas are indicated and should serve as guidelines for future develop- ment of this code which in light of the encouraging results pre- sented in [3] seems to be highly warranted. The WOSUB-code is still in the stage of evolutionary development. In this context, the review reflects the achieve- ments as of July 1977.