Skip to main content

Assessment of reactor vessel integrity

Deliverables

The ARVI (Assessment of Reactor Vessel Integrity) project involved a total of nine organisations from Europe and USA. The objective of the ARVI project was to resolve the safety issues that remained unresolved for the melt vessel interaction phase of the in-vessel progression of a severe accident. The top-level objectives were to provide the data and the models to assess: - The feasibility of promulgating the in- vessel melt retention (IVMR) scheme in current and future plants or in its absence. - The time available before vessel failure in which emergency accident management measures could terminate the accident within the vessel. The second level objectives were to determine: - The mode and location of vessel failure. - The melt discharged to the containment. - The effectiveness of the gap cooling. - The critical heat flux for external cooling of the lower head. - The effects of melt stratification. - To apply the data and models for design of IVMR for some specific plants. The work consisted of experiments and analysis development. The modelling activities in the area of structural analyses were focused on the support of EC-FOREVER experiments as well as on the exploitation of the data obtained from those experiments for modelling of creep deformation and the validation of the industry structural codes. Work was also performed for extension of melt natural convection analyses to consideration of stratification, and mixing (in the CFD codes). Other modelling activities were for: - Gap cooling CHF. - Lower head dynamic loading due to steam explosion inside. - Simple models for system code. Finally, the methodology and data could be applied to design of IVMR severe accident management scheme for VVER-440/213 plants. The work was broken up into five packages. They were divided into many tasks, which were performed by different partners. The work consisted of experiments and analysis development. The major experimental project was EC-FOREVER in which data was obtained on melt pool natural convection and lower head creep failure and rupture. The EC-FOREVER experiments were the first in the world in which vessels, containing heated melt, and the lower head wall maintained at prototypic accident conditions, were ruptured. Additional tests were made in which the melt pool was flooded with water to determine the potential for in-vessel coolability. The results obtained from the experiments were related to the following main issues: - The effectiveness of gap cooling. - Multiaxial creep laws for different vessel steels. - Effects of penetrations. - Mode and location of lower head failure. - Data for validation of computer codes. Two other experimental projects were also conducted. One was the COPO experiments project, which was concerned with the effects of stratification and metal layer on the thermal loads on the lower head wall during melt pool convection. The second experimental project was conducted at ULPU facility, which provided data and correlations of CHF due to the external cooling of the lower head. The modelling activities in the area of structural analyses focused on supporting the EC-FOREVER experiments. These were exploited to validate the industrial structural codes. Work on the melt pool turbulent natural convection analyses through Computational Fluid Dynamics was performed, which essentially determined the stratification and mixing process. Other modelling activities were on the gap cooling model for CHF and simple models for system code. Finally, the methodology and data have been applied to design of IVMR severe accident management scheme for VVER-440/213 plants.