A1 NPP Decommissioning, Slovakia. Annex A.I-6

The first pilot NPP in the former Czechoslovakia was A1, which was built at Jaslovske Bohunice near the town of Trnava. An NPP with a capacity of 143 MW(e), it was commissioned in 1972 and operated with interruptions until 1977. A KS-150 reactor with natural uranium as fuel, D2O as moderator and gaseous CO2 as coolant was installed in the plant. The first serious accident associated with refuelling occurred in 1976, when a locking mechanism at a fuel assembly failed. The core was not damaged during that accident and after reconstruction of the damaged technology channel, the plant resumed operation. The second serious accident (level 4 according to the International Nuclear Event Scale) occurred in 1977, when a fuel assembly overheated, causing release of D2O into the gas cooling circuit. This accident was attributed to human error during replacement of a fuel assembly. Subsequent rapid humidity increase in the primary system resulted in damage to fuel elements in the core, and the primary system was contaminated by fission products. Internal reactor structures were also damaged. Radioactive contaminants penetrated into parts of the secondary system by leaking through steam generators. The radiation impact on and around the plant site was below specified limits for both events. Based on a technical and economic study of the difficult equipment repairs needed to restore plant operation, and also due to the policy decision to discontinue further construction of gas cooled reactors in the former Czechoslovakia, a decision was made in 1977 to terminate plant operation. The decision to proceed with the A1 plant decommissioning was issued in 1979. Beginning in 1981, decommissioning proceeded with disassembly of equipment from the secondary system (process equipment in the machine hall, turbines with auxiliaries, feed water tanks, diesel generator station, pumps, cooling towers, electric equipment). At the same time, other systems were disassembled, which included turbine generators with auxiliaries, gas systems, oil systems and other equipment and systems in the main production building and in nearby buildings