The effect of code user and boundary conditions on RELAP calculations of MTR research reactor transient scenarios

Abstract

The safety evaluation of nuclear power and re search reactors is a very important step before their construction and during their operation. This evaluation based on the best estimate calculations requires qualified codes qualified users, and qualified nodalizations. The effect of code users on the RELAP5 results during the analysis of loss of flow transient in MTR research reactors is presented in this pa per. To clarify this effect, two nodalizations for research reactor different in the simulation of the open water surface boundary conditions of the reactor pool have been used. Very different results are obtained with few choices for code users. The core natural circulation flow with the be ginning of core boiling doesn't stop but in creases. The in creasing in the natural circulation flow shifts out the boiling from the core and the clad temperature decreases be low the local saturation temperature.Ocena sigurnosti reaktora nuklearnih elektrana i istrazivackih reaktora predstavlja veoma znacajan korak pre njihove izgradnje ili tokom njihovog rada. Ova ocena zasnovana na najpreciznijim proracunima zahteva kvalifikovane programe, osposobljene korisnike i odgovarajucu nodalizaciju. U radu je prikazan uticaj korisnika na rezultate programa RELAP5 tokom analize prelaznih stanja usled gubitka strujanja u MTR istrazivackim reaktorima. Da se rasvetli ovaj uticaj koriscene su dve razlicite nodalizacije za simulaciju granicnih uslova slobodne povrsine vode u reaktorskom sudu. Dobijeni su veoma razliciti rezultati za nekoliko izbora koji su na raspolaganju korisniku programa. Prirodni kruzni tok u jezgru ne zaustavlja se vec se uvecava sa pocetkom kljucanja. Porast prirodnog kruznog toka uklanja kljucanje iz jezgra i temperatura kosuljice pada ispod lokalne temperature zasicenja.