The AVR reactor (German: Arbeitsgemeinschaft Versuchsreaktor) was a prototype pebble bed reactor at Jülich Research Centre in West Germany. Construction began in 1960, first grid connection was in 1967 and operation ceased in 1988. It was 15MWe, 46 MWt, and was used to develop and test a wide variety of fuels and machinery over its lifetime. AVR was the basis of the technology licensed to China to build HTR-10.
Its Helium outlet temperature was 950°C, but fuel temperature instabilities occurred during operation with locally far too high temperatures. As a consequence the whole reactor vessel became heavily contaminated by Cs-137 and Sr-90. Concerning beta-contamination AVR is the highest contaminated nuclear installation worldwide as AVR management confirmed 2001. Some contamination was also found in soil/groundwater under the reactor, as the German government confirmed in February, 2010. Thus the reactor vessel was filled in 2008 with light concrete in order to fix the radioactive dust and in 2012 the reactor vessel of 2100 metric tons will be transported about 200 meters by air-cushion sled and seven cranes to an intermediate storage.
There exists currently no dismantling method for the AVR vessel, but it is planned to develop some procedure during the next 60 years and to start with vessel dismantling at the end of the century. In the meantime, after transport of the AVR vessel into the intermediate storage, the reactor buildings will be dismantled and soil and groundwater will be decontaminated. Fuel removal out of AVR was difficult and lasted 4 years. During this procedure it became obvious that the AVR bottom reflector was broken; in its crack about 200 fuel pebbles remain captured. AVR dismantling costs will exceed its construction costs by far.
In April 2014 a report of independent experts on the AVR operation was published. This report lists hidden or downplayed events and accidents and discusses an illegal manipulation of the reactor safety system during an accident. As a consequence of the report Juelich Research Center regretted failures and scientific misbehavior with respect to the AVR.