Monitoring of nuclear reactors state in severe accidents
Accidents with multiple security system failures in light water nuclear reactors can lead to a coolant level decrease inside the reactor and may cause the core to heat up and eventually melt. Initiation of emergency measures in such an accident requires knowledge of the filling level decrease and the beginning of the meltdown. In such a scenario, the instrumentation might not or only partially available. For example, the lack of reactor state monitoring instrumentation in the Fukushima Daiichi nuclear power plant led to the state of the cores being largely unknown during the course of the accidents in 2011.
A possible solution is the development of a method for detecting the filling level decrease the beginning of a meltdown using a non-invasive measurement of the gamma ray distribution outside the reactor pressure vessel.
Such a measurement system is to be developed in this joint project with the Zittau/Görlitz University of Applied Sciences. The HZDR is performing Monte Carlo simulations for this project. The simulations will give insights into the gamma ray distribution outside the reactor pressure vessel for an operating reactor, filling level decrease and various meltdown scenarios. Further calculations will also yield the activation or the reactor pressure vessel and the distribution of fission products. A goal of these computations is to find the optimal configuration for the proposed gamma ray detector (location, detector type, arrangement).
Monte Carlo Results
Gamma fluences outside the core were computed for different core states using a simplified reactor model. Background from activation was not taken into account. Both water level decrease and core melt yield changes in the observed gamma fluence.
This Project is funded by the German Federal Ministry of Education and Research; Topic: “Nichtinvasive Zustandüberwachung von Kernreaktoren zur Detektion von Füllstandsänderungen und der Deformation des Kern, Teilthema des FuE-Programms: Grundlagenforschung Energie 2020+“ (FKZ: 02NUK018B).