Current status of the MELCOR nodalization for Atucha- I nuclear power plant

This paper presents the status of the model with MELCOR 1.8.4. Code, which is being developed for ATUCHA-I nuclear power plant. The specific objective is to analyze severe accident progression in Atucha-I. Atucha-I has a particular design (prototype); the specific features are laid in both Reactor Pressure Vessel and Containment. This nuclear power plant has been designed and built by SIEMENS A.G. of Erlangen, Germany and is a nuclear power plant with a heavy pressure water reactor (HPWR) which is fueled with natural uranium. The reactor uses heavy water as coolant and moderator and it is refueled on line. The thermal power is of 1170 Mw, with nominal output electrical power of 357 Mw. The reactor coolant system has two parallel loops, each of them having a circulation pump, a vertical steam generator with U- tubes and the necessary connecting pipes. One of the loops has a pressurizer with safety valves. Both primary system and the accumulators within the emergency core coolant system are enclosed in a containment building. The containment safety system consists of several basic sub-systems: the concrete containment, the steel containment, the containment isolation system and the reactor building annulus air extraction system. Two accidental sequences will be considered: Station Blackout (high-pressure scenario) and LB-LOCA (low-pressure scenario); up to now the model is being improved under a Station Blackout accidental sequence. (author)