Paris, 4 November 1996
On 9 October 1996 the first large-scale test involving the melting of real core
material of a light water reactor was successfully carried out in the Rasplav
facility in the Russian Research Centre at the Kurchatov Institute in Moscow.
This experiment was performed within the framework of the first OECD Nuclear
Energy Agency (NEA) sponsored project set up in Russia in the area of nuclear
safety. The project addresses overheating of the reactor vessel under severe
nuclear accident conditions. It has been designed to ensure that the results
generated will be of relevance to the reactors operating in NEA Member countries
as well as to Russian-designed pressurised water reactors (VVER). Furthermore,
the project is applicable to both current and future reactor designs.
During the test, core material was heated to 2700C. The test vessel was cooled externally in a controlled manner to simulate external cooling of the vessel in a severe accident. All measuring and engineering systems functioned normally during the experiment. It is the first time that a large mass of core material has been heated up to such high temperatures under controlled conditions. The test results confirmed the technical feasibility of conducting further large scale tests with such core material compositions. The post-test examination will consist of sectioning the solidified material and performing metallographic examination to determine the details of test performance, along with a comparison of the temperature measurements with the pre-test thermal analysis.
The Rasplav Project brings together 14 NEA Member countries and Russia in the first Agency-sponsored joint nuclear safety project to be carried out in a non-Member country. The participating Russian organisations are the Russian Research Centre 'Kurchatov Institute', the Russian Federation Ministry of Atomic Energy and the Ministry of Science and Technology Policy. Rasplav is a major international nuclear reactor safety undertaking being carried out over three years. The experimental work is carried out in the Kurchatov Institute, the analytical work is done in the Institute of Nuclear Safety, and design work and some testing work is done by other organisations in the Moscow region.
Rasplav is the latest link in a chain of international projects aimed at refining strategies for maintaining the integrity of reactor pressure vessels in the highly improbable event of a core meltdown. Retaining the integrity of the reactor pressure vessel for such accidents, which are estimated to have a probability of occurrence of less than 1 in 10,000 years per reactor, will help prevent the release of radioactive material to the environment.
A background note on the Rasplav project is attached.
News Media Contact:
The Rasplav project is concerned with behaviour of the lower head of the reactor
pressure vessel during severe accidents leading to core meltdown. The Rasplav
project may be regarded as a successor to the OECD Three Mile Island (TMI)
Vessel Investigation Project which was completed in 1993. That project was set
up to examine and assess the condition of the actual TMI lower head and thus
offered a unique opportunity to study a severe accident in a commercial nuclear
power plant. However, in order to better understand and model the complex
phenomena taking place during interaction of molten fuel with the reactor vessel
lower head, it is also necessary to reproduce this interaction in a controlled
environment where the governing parameters can be varied over the range of interest.
This is the main aim of the Rasplav project.
During a core melt accident, the core debris will relocate to the bottom of the
reactor vessel. In the absence of any cooling of this debris, the heat generated
would eventually overheat the reactor vessel, which would fail, thereby releasing
the corium (molten core material) to the lower containment. There is interest in
two aspects of the issue. First, for existing reactors, when external cooling may
not be practicable, there is a desire for a better understanding of the phenomena
and of the time before the molten fuel penetrates the vessel and discharges to
the reactor containment, to assist in the development of severe accident
management strategies. Secondly, for future designs where external cooling in
severe accidents is being considered at the design stage, and for some existing
reactors, there is a need for a better understanding of the complex interactions to
demonstrate that cavity flooding is a viable accident management option.
The Rasplav project uses prototypical materials (real core material components and vessel steel) in large quantities and at temperatures representative of a core meltdown accident. This assists in understanding the chemical reactions, which are very complex, and contributes to understanding the natural convection processes. The design of this main integral test facility is a model of the reactor vessel, filled with 200kg corium, in the form of a slice through the lower head. The corium is electrically heated with graphite induction heaters in the planar side walls, protected from the corium by layers of tantalum and tungsten. The vessel section is cooled by water.
There are supporting smaller scale experiments to study material properties and chemical interactions, and to investigate the technological aspects of the larger Rasplav experiment. These have supplied necessary design information for Rasplav.
Several molten fuel structural experiments are carried out in the Rasplav programme. The technical objectives include:
The information from Rasplav complements the database obtained from other experiments and projects that provide information related to vessel failure, such as the OECD TMI Vessel Investigation Project, and the European Union sponsored the Melt-Vessel Interaction Project.
The following OECD countries with nuclear power programmes participate: Belgium, Canada, Finland, France, Germany, Italy, Japan, Republic of Korea, the Netherlands, Spain, Sweden, Switzerland, the United Kingdom and the United States.
The budget is $6.9 million in total, over a three year period. The project started on the 1st of July 1994.