Molten salt reactor experiment begins at Petten

Irradiation tests on a mixture of lithium and thorium fluoride salts are under way at the High Flux Reactor at Petten in the Netherlands. The results will yield new data on the safe operation of molten salt reactors.

Irradiation tests on a mixture of lithium and thorium fluoride salts are under way at the High Flux Reactor at Petten in the Netherlands. The results will yield new data on the safe operation of molten salt reactors (MSRs).

Molten salt reactors use fuel dissolved in a molten fluoride or chloride salt. As an MSR fuel salt is a liquid, it functions as both the fuel (producing the heat) and the coolant (transporting the heat away and ultimately to the power plant). This means that such a reactor could not suffer from a loss of coolant leading to a meltdown. The basic technology is not new - it was first demonstrated at Oak Ridge National Laboratory in the 1960s, where a 7.4 MWt test reactor, the Molten Salt Reactor Experiment (MSRE), operated from 1965 to 1969.

The High Flux Reactor (Image: NRG)

The Nuclear Research and Consultancy Group (NRG) said it is conducting research into molten salt reactors as part of a nuclear research program funded by the Ministry of Economic Affairs. The research is being carried out in collaboration with the Joint Research Centre (JRC) of the European Commission in Karlsruhe, Germany.

JRC has developed fuel comprising lithium and thorium fluoride salts. NRG started an irradiation in the High Flux Reactor of samples of this fuel on 10 August. The irradiated samples will be investigated by JRC in their laboratories.

The irradiation is being carried out to investigate the stability of the salt mixture during and after irradiation, the evolution of fission gases and the effect of the salt on surrounding materials.

The experiment was originally planned to start last year, but because of a lack of experience with molten salt irradiations at NRG, additional research was carried out to ensure safe operation under all circumstances.

Project manager Irene Bobeldijk said, "Safety is of overriding priority at NRG. We have used an extra year to investigate different scenarios in which safety and/or quality of the experiment could be compromised. Now that we know that the design of the irradiation facility is adequate, we can start the experiment."

She added, "It has been some time since a similar molten salt fuel has been irradiated. Our research can contribute to the renewed interest by providing well-founded data."

Much of the interest today in reviving the MSR concept relates to using thorium (to breed fissile uranium-233), where an initial source of fissile material such as plutonium-239 needs to be provided. There are a number of different MSR design concepts, and a number of interesting challenges in the commercialisation of many, especially with thorium.

Researched and written
by World Nuclear News