Assessment of reactor vessel integrity (ARVI)

The cost-shared project ARVI (assessment of reactor vessel integrity) involves a total of nine organisations from Europe and
USA. The objective of the ARVI Project is to resolve the safety issues that remain unresolved for the melt vessel interaction
phase of the in-vessel progression of a severe accident. The work consists of experiments and analysis development. Four tests were performed in the EC-FOREVER Programme, in which failure was achieved in-vessels employing the French pressure
vessel steel. The tests were analysed with the commercial code ANSYS-Multiphysics, and the codes SYSTUS+ and PASULA, and quite good agreement was achieved for the failure location. Natural convection experiments in stratified pools have been performed in the SIMECO and theCOPOfacilities, which showed that much greater heat is transferred downwards for immiscible layers or before layers mix. A model for gap cooling and a set of simplified models for the system codes have been developed.
MVITA code calculations have been performed for the Czech and Hungarian VVERs, towards evaluation of the in-vessel melt retention accident management scheme.
Tests have been performed at the ULPU facility with organised flow for vessel external cooling. Considerable enhancement
of the critical heat flux (CHF) was obtained. The ARVI Project has reached the halfway stage. This paper presents the results obtained thus far from the project.