ITER REFERENCE ACCIDENTS

Reference accidents are selected to envelope possible accident sequenc es to confirm the adequacy of ITER's safety design. Analyses of ITER r eference accidents were carried out starting from postulated initiatin g events (PIE) to all consequential failures including environmental r eleases, if any. In case of plasma control malfunctioning, up to 3.3 G W of fusion power can be reached transiently, however, no radiological consequence is expected from those transients. Assuming multiple firs t wall pipe failures, the pressure suppression system limits the maxim um pressure within the vacuum vessel to below 0.5 MPa. Long-term decay heat removal is assured by the vacuum vessel cooling system operating in natural circulation. In case of ex-vessel coolant loss with contin ued plasma burn, the plasma facing components can potentially reach la rge temperatures. This is avoided by the fusion power shutdown system that terminates plasma burn. A small in-vessel coolant leak with failu re of one vacuum vessel penetration line and several confinement optio ns are investigated to show compliance with release limits. Failures i n the magnet system are analyzed and their impact on other systems suc h as damage to neighboring confinement barriers are investigated by po stulating air, water and helium ingress into the cryostat. Failures in the tritium plant are analyzed to demonstrate the adequacy of confine ment. Radioactive releases for all reference accidents are shown to be well below conservatively defined design guidelines. (C) 1998 Publish ed by Elsevier Science S.A. All rights reserved.