Alisa (Access to Large Infrastructures for Severe Accidents) is the outcome of two financially independent projects—one in Europe, the other in China—that include experimental programmes of a similar scale and which are accessible to both parties. The selected large-scale experiments focus on R&D issues relating to the management of severe accidents in reactors, such as the ones currently operated in Europe and Asia.
Studies have been conducted into priority research issues like early damage of the core, the late phase of fission product retention in the vessel bottom, fuel-coolant interaction outside the vessel and hydrogen behaviour in the containment.
"Alisa gave our teams access to large infrastructures in China and, in return, the Chinese were able to work on KROTOS and VITI, for example, in the CEA center of Cadarache, and on other facilities in Europe. Alisa has led to the cross-fertilization of Chinese and European research expertise to maximise human and financial resources, learn from each other and disseminate the results to society at large. Our aim is not only to understand the physical context of a severe accident, but also to strengthen our knowledge to enable us to mitigate its consequences", explains Christophe Journeau of the CEA Nuclear Energy Division and project coordinator for the CEA.
A total of 12 experiments were conducted as part of the project. They produced large-scale data on the behaviour of corium, the material combining fuel, fuel cladding and reactor core structure materials that is created in the event of a meltdown accident.
The primary objective of the teams involved in the project is to understand how a partial or total core meltdown would affect reactor safety and how to reinforce accident management procedures.
They have worked on complex technical questions such as the cooling strategy of a degraded core through additional water supply, in-vessel melt retention, spread limitation within the containment, and measures to neutralise the hydrogen that could potentially build up in the containment.