Maintenance of the TRIGA Mark II reactor in Ljubljana and the disposal of radioactive waste

The 250 kW TRIGA Mark 33 reactor of the 'J.Stefan' Institute in Ljubljana (Yugoslavia) has been in operation since 1966. In order to improve the safety, the following improvements to the reactor's instrumentation were implemented: new scrams were introduced; warning in case of too low water level in the reactor tank, too high fuel temperature, or open door of the dry cell; new, parallel instrumentation for all four channels was put into operation; new instrumentation for measurement of the activity of the secondary water was installed; an automatic system to stop the secondary water flow when the reactor is shut down was introduced. No major events causing interruption of the reactor operation have occurred. Since the low level nuclear waste disposal facility at the reactor site, built when the reactor went critical is rather small, a new bigger facility was built with all equipment for safe temporary storage of low and intermediate level radioactive waste, generated at the reactor, as well as in hospitals and industrial operations in the Republic of Slovenia. The volume of the storage facility is 850m3 and it is partially underground. A regular monitoring programme has been carried out after the storage facility became operational