Research and development for the VHTR by high-temperature helium gas loops

Extensive research programmes on further development of the Multi-Purpose Very High-Temperature Gas-Cooled Reactor (VHTR) are being carried out by the Japan Atomic Energy Research Institute (JAERI). Several types of loop facilities, both out-of-pile and in-pile, have been or will be installed in JAERI for tests such as dynamic flow tests, heat transfer experiments and irradiation tests. The in-pile helium gas loop, OGL-1, which is nearing completion, will be used for (a) irradiation test beds for fuels and structural materials, (b) study of the transport properties of gaseous fission products, and (c) gaining experience in the construction and operation of the loop facility which will be useful for later VHTRs. A series of development studies has been successfully carried out for the construction of OGL-1, which will circulate about 10000C helium at high pressure as primary coolant. The five main development studies are described in the paper. Out-of-pile high-temperature helium gas loop facilities have been operated to carry out dynamic flow tests of components and heat transfer experiments of VHTR fuel elements as well as to study the prevention of helium permeation and to study the behaviour of a thermal insulation material at very high temperature. Investigations to develop techniques of preventing helium flow laminarization in a fuel channel, which can result in a decrease of the heat transfer coefficient, were conducted with the HTGL facility. Evaluation of the heat loss and the hot spot factor formed in the VHTR core and piping system were carried out. (author)