BEHAVIOR OF NONLINEAR SUPPORTS ON PWR COOLANT SYSTEM DURING A POSTULATED LOCA .2. EFFECTS OF STIFFNESS VARIATIONS AND CAVITY PRESSURIZATION

Part 2 of this two part paper deals with the variations in stiffness v alues of the supports and whip restraints significantly affected by un certainties in evaluating concrete embedment stiffnesses and the effec t of cavity pressurisation in the case of a Reactor Pressure Vessel (R PV) inlet or outlet nozzle break. Part 1 of the paper discussed the me thodology of the LOCA analysis of the Reactor Coolant Loop (RCL) and a sensitivity study on the method of modelling the columns supporting t he Reactor Coolant Pump and the Steam Generator. They were part of a s eries of sensitivity analyses performed to evaluate the influence of v ariations in the variables utilised as input to the primary coolant pi pe dynamic structural analyses. The stiffness variations cause variati ons in loads received at the supports or restraints, thus influencing the design and the degree of accuracy to which it is necessary to defi ne the stiffnesses. Cavity pressurisation is asymmetric pressurisation of the cavity between the RPV external surface and the primary shield wall. This generate external upthrust and lateral forces on the RPV t hus increasing RPV movements and RCL support loadings. Different block age situations impeding fluid pressure relief routes through the prima ry shield wall have been postulated due to the spalling of thermal ins ulation material. The loadings on the RCL supports and restraints as a result of increased RPV movements were analysed.