Operating experience with the AVR experimental power station

The AVR experimental power station, with a thermal power output of 46 MW, is the first reactor with spherical fuel elements. Its construction was begun in 1961, and in December 1967 the installation first became operational. The purpose of this paper is to present the varied experience gained during more than seven years of operation. Location of the steam generator in the top of the reactor makes possible the operation of the reactor at high gas outlet temperatures, since the region of hot gas is small and made of ceramic material. However, the activation of corrosion products leads to activity in the secondary loop, and it was therefore necessary to install a monitoring capability in the turbine hall. The biological shielding is divided into two parts. A large number of valves and other pieces of equipment are located in a radiation area between the shielding. To prevent the exposure of personnel to irradiation, operation has been interrupted several times for the purpose of changing defective equipment in this area. During recent years it has been possible to stop this kind of interruption by changing to more reliable equipment. Up to now some of the main components are still operating without any defects or changes in operational behaviour. Among these are the reflector, the blowers, the shutdown rods and the steam generator. The fuel-handling equipment permits a continuous changing of fuel while the reactor is running, but requires considerable maintenance work. Problems have occurred with all the components in this system but, except in a few cases, it was possible to perform the necessary repair work while the reactor was running. For dismantling of the components, shielding is only necessary if a fuel element is located in the defective area. The extensive need for maintenance results from the novelty of the machinery. It is not thought that these failures are characteristic of the handling of spherical fuel elements. Experience in the area of health physics has been good. The release of activity into water and into the atmosphere is low. The total exposure of personnel to radiation is about 50 man-rem/yr. In the last few years, the maximum dose for any one person was less than 2 rem/yr. Although the reactor is the first high-temperature reactor with spherical fuel elements, it has been possible to operate it with good availability of time and work. It has also turned out to be very friendly to the environment. (author)