The Berlin research reactor

Operation reactor BER II: Neutrons for research on condensed matter

The Berlin research reactor (Berlin Experimental Reactor) is a 10MW swimming pool reactor that uses low enriched uranium (LEU). The reactor core contains 25 standard fuel assemblies and six special fuel assemblies with control rods. It is enclosed by a beryllium reflector to ensure an optimal link between beam tubes and core.

There are six beam tubes to supply neutron scattering experiments with thermal neutrons in the first experiment hall directly around the reactor pool. Furthermore there is one special beam tube which contains a Cold Source which feeds eight neutron guides with cold neutrons for experiments in the second experimental hall.

Main part of the BER II is the reactor pool which consists of two aluminum tanks with 3,5m in diameter and 11m in height. They are filled with 200m³ demineralized light water. The primary cooling circuit is completely within the reactor pool. Therefore no shielding against N16 is necessary and a loss of cooling because of a leakage in the primary circuit cannot occur. The cooling water is sucked by three pumps through the core and in case of a shut down two valves in the primary circuit are opened by gravitation force. The beginning natural convection is high enough to remove the afterheat from the fuel assemblies. Therefore there is no need of active cooling and therefore even a total station blackout does not lead to an emergency situation.
Also the shutdown system for BER II provides passive safety: in the event of a mal-function the control rods drop into the reactor core alone under the action of gravity and so put the reactor out of operation.

The BER II typically is operated in cycles of two weeks followed by one week for safety tests, maintenance, refueling etc. In addition, there are longer scheduled maintenance periods to enable more extensive inspections and refurbishments of the reactor components.