Assessment of the ''deterministic realistic method'' applied to large break LOCA analysis

Electricite de France (French Electrical Utility) presented a new method, called ''deterministic realistic method'' (DRM) for the safety analysis of large break loss of coolant accident (LB LOCA). In principle, the method relies on the use of the CATHARE GB code, in association with the statistical evaluation of the peak clad temperature with a high probability level (95%) for the verification of the safety criterion. However, in order to have a simpler methodology, Electricite de France defines the 'DRM evaluation model': this model consists in applying penalties on initial conditions and boundary conditions as well as on certain CATHARE GB code models, in such a manner as to obtain, by a single calculation, an evaluation of the peak clad temperature covering the peak clad temperature resulting from statistical method. Some insufficiencies concerning the statistical approach, both in its elaboration and its justification were identified by the assessment of the method. As far as the 'DRM evaluation model' is concerned, the Institut de Protection et de Surete Nucleaire has concluded that this model provides a conservative evaluation of peak clad temperature, independently of the proposed statistical method. (orig.)