Investigations of HTGR Reactor Building Response to Break in Primary Coolant Boundary

The United Kingdom government has stated that its intention is to maintain nuclear energy as a significant contributor to electricity production in United Kingdom. This is because it provides a relatively low cost, stable, and essentially emissions free source of electricity. It is complementary to "renewables" such as solar and wind. Renewables operate only intermittently (on windy days, or when the sun shines, and for example, in the UK a typical solar installation will actually generate electricity for only about 1/10 of the year.)
Until recently 'nuclear' provided approaching 30% of the country's electricity, but these plants are now reaching the end of their lives (after typically 40 or more years), and there is a need to replace them. Naturally, 50 years on, it is appropriate to replace them with more modern designs. This project is to help design some of this next generation of nuclear power stations. Britain's existing fleet of nuclear stations is largely gas cooled, and this project is to help develop the next generation of high-temperature gas cooled reactors. The particular project is to develop both experimental facilities and computational methods to understand the behaviour of the plants under the very unlikely circumstances that part of the gas circuit of the plant were to spring a leak. One of the characteristics making these new designs "advanced" is that they are extremely tolerant of this, and they will be designed such that they are essentially immune from any adverse consequences following such a leak. This project is to help to confirm and demonstrate that fact.
It is a collaborative project with United States, where essentially identical conditions apply. It will involve building a large-scale experimental facility to simulate the behaviour of a wide range of plants of this type. Measurements will be made, to determine the response of the plant to the leak. In parallel with this, computational methods will be developed to enable more detailed assessments to be made of specific actual reactor designs. These computational tools will assist with both design optimisation, and with the assessments of the plants as part of the licensing process.

This proposed joint US-UK project will have a beneficial impact on the current nuclear energy programs of both the United Kingdom and the United States. Both governments have recognized the desirability of looking beyond the current fleet of water-cooled reactors that have been with us in essentially an unchanged form for approaching half a century. Both nations have identified amongst the candidate more advanced reactors worthy of consideration various forms of high temperature gas reactors. This project will have impact by taking forward our understanding of the performance and hazards associated with this class of reactor.
Beneficiaries would be policymakers deciding upon the role and kind of nuclear energy to be employed, and following on from this, the general population will be beneficiaries if better informed decisions are able to be made.
Specifically, it will address the issue of the vulnerability of this reactor type to the ingress of oxygen into the primary circuit following a breach of the primary circuit. Such ingress could lead to oxidation of high-temperature graphite present in the primary circuit. The proposed combined programme incorporates measuring the behavior of prototypical experimental facilities that embody the main functional characteristics of a range of such reactors, and the development of modelling and prediction tools for these events, and the validation of these prediction tools against measurements.
The benefits will arise because without the ability to understand when and how these undesirable events might occur, and to be able to demonstrate reliably that they are sufficiently improbable, it would be hard for a program of deployment of such reactors to go ahead.