The DR-2 project

DR-2 was a 5 MW tank type, water moderated and cooled research reactor, which was operated at the Risø National Laboratory from 1959 to 1975. After the close-down in1975 the DR-2 has been kept in safe enclosure until now. The aim of the DR-2 project reported here was to characterize the present state of the reactor and to determine, which radionuclides remain where in the reactor in what amounts. The first part of the reactor to be investigated was the reactor tank. The lids at the reactor top were removed, air samples taken and smear test made in the tank. Then the control rods, the magnet rods and other active components were removed from the tank, measured, cut up, and disposed of in waste drums. The beryllium reflector elements were stored in specially prepared containers. When all movable parts had been taken out, the remaining radiation field was measured by use of thermo-luminescence dosimeters. Next the hold-up tank room and the concrete cave (the igloo) in front of the thermal column were opened. They had been used as storage rooms for various components and all movable components were removed, measured and, if active, cut into waste drums. Only large and active objects remain stored in the igloo and in the hold-up tank room. A number of graphite stringers were taken out of the thermal column and their activity measured. It was a surprise to find, that the stringers contained significant 152Eu and 154Eu activity. Some of the beam plugs and irradiation tubes were extracted and reinserted after their activity had been measured. The activity of the radiation shield of the reactor was measured in three different ways: By drilling two cored holes through the shield, by thermo-luminescence dosimeter measurements in vertical tubes in the concrete shield and by measurements through an open beam hole. At the start of the project the activity in DR-2 was about 45-50 GBq. Now it is about 5-10 GBq. Based on the results of the DR-2 project it is believed that the reactor can readily be dismantled.