Abstract
The application of Loviisa Nuclear Power Plant (NPP) operating license extension for 20 years was submitted to the Ministry of Trade and Industry of Finland on November 1, 2006. For the application a great number of different studies, analyses, clarifications etc. were needed to show to the authorities that the plant can be operated safely for another 20 years. The main tool in the safety analysis work was APROS (Advanced PROcess Simulator) simulation software, which has been developed in Finland during the past 20 years. This paper deals with the cold leg loss-of-coolant accidents (LOCA) which were analyzed using APROS. The break size was between 140 - 260 cm2. Models with different descriptions of the core region were applied in the analyses. The first model had an average core with one flow channel and separate hot rods modeled in isolated sub channels. In the second phase the hot rod was implemented in a hot fuel assembly and so called hot channel analyses taking boundary conditions from the previous analyses were run. Finally the analysis was carried out using a special Loviisa large break LOCA analysis model in which the core is divided into seven parallel channels. All three analyses resulted in a qualitatively similar peak cladding temperature behavior but the maximum value of cladding temperature depended on the model which was used. This paper presents the results of these analyses focusing on the behavior of fuel cladding temperature. The paper also explains why the peak cladding temperature behavior depends on the core model.
