The many years of HTR physics experience of the Dragon Project have seen great progress in the development of reactor physics to meet the special requirements of HTRs.

Because of the international character of the Project there has always been a very close collaboration by the Project’s physics team with the national groups. The policy has been to meet the requirements of the Dragon Reactor with its constantly changing layout of experiments as well as power reactor studies by getting the best methods and programmes where available, adapting and developing them, and originating within the Project programmes and programme systems only where suitable alternatives did not exist.

In this way a very close collaboration with the various organizations of the Dragon Signatory Countries was built up and very good contacts between the Project and centres in the U. S.A. established.

The Dragon Countries Physics Meetings (DCPM) were set up and have now been running for some years, involving research centres, industry, utilities and regulatory bodies in the Project’s Signatory Countries. The purpose of these meetings has been the exchange of information at the forefront of development and many bi- and tri-lateral collaborations on the theoretical as well as the experimental research and development side have been initiated.

It was, therefore, only natural that the Project should initiate and sponsor the writing of a book on the present state of HTR physics at a time when the HTR is entering the nuclear energy market and interest in it will widen on many fronts, at industry and university research levels, not only with respect to its use as a heat source for electricity generation, but, looking ahead, also as a source of very high-temperature heat for industrial processes.

The challenge of steadily increasing requirements, of high complexity, on the experimental side and demands for high accuracy has been met successfully over the years. The present state is characterized by the fact that the physics of the HTR is now so well understood and so well checked against experiments that present-day require­ments and demands for designing and commissioning HTRs can be adequately met.

The further development of the HTR to realize its potential as a source of heat at very high temperatures, and also the prospects which it offers to achieve high conversion ratios, requires continuing physics studies and progress in methods. In particular, higher accuracies in the predictions of temperatures and their gradients, as well as fast neutron doses and burn-ups over the lifetime of fuel elements will be wanted, since these are main features which have to be considered in the fuel and fuel

element endurance and performance, and determine to a great extent the release of fission products.

Present and future requirements seen together make clear that it is now the right time to survey what has been achieved and compile what is now fully available and will form the basis and starting point of any further progress.

Winfrith, Dorset July 1975 H. Gutmann

Head of Physics Branch, OECD High Temperature Reactor Project (DRAGON)

ACKNOWLEDGEMENTS

Thanks are due to the Chief Executive of the Dragon Project and to Dr. P. J. Marien for their continuous support, as well as to the Members of the Staff of the Dragon Project Physics Branch, to Dr. A. T. Butland and Mr. P. B. Kemshall of the United Kingdom Atomic Authority, and to all scientists who indirectly contributed to this work by discussing their methods and results at the Dragon Countries Physics Meetings.

The Author also wishes to thank the Commission of the European Communities for permission to publish this book