NuclearReactor_ZLFR.exe - eine vereinfachte Online-Simulation des Zittauer Lehr- und Forschungsreaktors
The ZLFR in Zittau is a self-construction of the former University of Engineering (Ingenieuhochschule Zittau), which was successfully used for educating students and also for research projects. It was commissioned in 1979 and switched of in 2005. The reactor was a so-called critical assembly (or zero-power reactor), in which a controlled chain reaction was kept running at a very small thermal power. Students were allowed to control the reactor in the presence of examined reactor personnel. They were able to perform a lot of interesting experiments, as it can be seen at the link above.
The computer simulation works quite similar to the simple reactor core model. Please, read the corresponding instruction. The biggest difference from most of the power reactors is the possibility to shut-down the reactor by a quick moderator drainage. If this is activated at close-to-nominal power, one can see how the neutrons escape in an avalanche towards the top and how the reactor immediately becomes sub-critical. The moderator drainage system was an alternative for a safety shut-down beside the safety rod and the three control rods.
Such an emergency shut-down cannot be applied in power reactors that use the same water both as moderator and for the cooling. The drainage would terminate the cooling of the fuel, while the decay heat continues to be produced even after the stop of the chain reaction. This would lead to a core melt-down. Some reactors have liquid moderators, that is different from the coolant. There a moderator drainage system can be used, as for example at the Canadean reactor type CANDU, which uses Heavy Water as moderator.