Dismantling of Biological Agricultural Reactor Netherlands (BARN)

The Biological Agricultural Reactor (BARN) was built in 1962 by government order through the Institute for Atomic Science in Agriculture (ITAL) in the Netherlands. The idea to build this nuclear reactor especially for biological research purposes was grown out of the first international conference about peaceful application of atomic energy hold in 1955. The construction composed of a basin reactor with light water as moderator and cooling medium. Up to 90% enriched Uranium was used as fuel. The maximal power was 100 kW. The reactor was used for research in the field of plant reproduction and other biological research. Mainly because of disappointing scientific results in 1978, 15 years after the start, the decision was made to terminate the reactor process following by dismantling. Alternative techniques proved to give comparative results at lower costs. In the decision making process political considerations played an important role. Prior to dismantling the reactor the 26 fuel elements were removed. Beside the uranium-235 each element contains about 1.3 TBq of fission and activation products. In 1982 the elements were shipped tot the Savannah River Plant in United States. An extensive analyze was carried out to map out the activation products on basis of neutron flux data, radiation history and composition of the materials. Results of this study was used to predict the dose rate of the different activated items and consequently to reduce risks of handling the items. For several reasons (e.g. control of building, knowledge of the plant) in 1996 a project has been initiated to remove all the active materials form the building and to recover the place to the original state, i.e. forest. High radioactive items with large dimensions were transferred to the so-called 'hot cells' of the ECN and were cut into small pieces. Finally all the activated material was brought to the COVRA for end storage. Parts of the basin construction were highly activated and were removed with a diamond saw with remote control. The remaining less activated concrete (<10 Bq/g) was recovered during the final demolition in 1999. During the different steps of dismantling registered radiological workers carried out all operations, involving a certain radiation risks. During the removal of the fuel elements no significant dose was received. The maximal individual dose (whole body dose equivalent) received during disposal of the activated items and the removal of the activated tubing was 0.45 mSv. The collective dose was 1.36 man-mSv. The real activity of the irradiated items was more then 10 times lower compared to the predicted values. By using remote techniques the received personal dose was minimal. Also the environmental dose consequence was minimal. Soil (-water) samples were analyzed by gammaspectrometric methods to determine possible contamination. (author)