Assessment of RELAP5/MOD3 Version 5m5 using inadvertent safety injection incident data of Kori Unit 3 Plant

This report discusses an inadvertent safety injection incident which occurred at Kori Unit 3 in September 6, 1990 was analyzed using the RELAP5/MOD3 code. The event was initiated by a closure of main feedwater control valve of one of three steam generators. High pressure safety injection system was actuated by the low pressure signal of main steam line. The actual sequence of plant transient with the proper estimations of operator actions was investigated in the present calculation. The asymmetric loop behaviors of the plant was also considered by nodalizing the loops of the plant into three. The calculational results are compared with the plant transient data. It is shown that the overall plant transient depends strongly on the auxiliary feedwater flowrate controlled by the operator and that the code gives an acceptable prediction of the plant behavior with the proper assumptions of the operator actions. The results also show that the solidification of pressurizer is not occurred and the liquid-vapor mixture does not flow out through pressurizer PORV. The behavior of primary pressure during pressurizer PORV actuation is poorly predicted because the actual behavior of pressurizer PORV could not be modelled in the present simulation.