MINET [Momentum Integral NETwork] analysis of MHTGR [Modular High Temperature Gas-Cooled Reactor] moisture-ingress transient

The transient which involved a steam-generator tube leak and the ingress of moisture into the primary coolant system of the standard Modular Modular High Temperature Gas-Cooled Reactor (MHTGR) is analyzed by using the MINET (Momentum Integral NETwork) computer code. The analysis provides detailed information on the effect of power excursion on transient system pressures and temperatures. It is concluded that during the short term transient period the moisture ingress presents no threat to the integrity of the fuel elements and does not lead to pressures which would cause relief valve opening and fission product release