Component exposure in hypothetical accidents with very fast depressurization in a HTR module reactor

The starting event of the massive air ingress into the core of the HTR modu le reactor, classified as hypothetical incident, is the very fast depressur ization of the primary circuit. Provided that the integrity of the reactor pressure vessel is not in question, a rupture of the connecting pressure ve ssel between reactor pressure vessel and steam generator vessel is the maxi mum possible leak cross-section. In this work it is investigated whether th e components of the reactor pressure vessel are exposed by the depressuriza tion process to mechanical loads which exceed the load limits. These loads are caused by two different events, the strong momentum change of the fluid and the local pressure differences, respectively. Due to the momentum chan ge the bottom reflector receives the maximum load, whereby only 2% of the c ompressive strength of the graphite quality used there are reached. However , the load by local pressure differences is between passed volumes and in n ormal operation, not-passed volumes lead to high load values. A maximum pre ssure difference of 44.5 bar was calculated at the thermal top shield. (C) 1999 Elsevier Science S.A. All rights reserved.