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Technical University of Munich

Safety Systems

Section of the reactor pool. (Graphics: FRM II/TUM)

FRM II has extensive security systems. The main requirements are expressed by the following three security goals that FRM II must comply with under all circumstances:

  1. It must be possible to switch off the reactor at any time, quickly and permanently.
  2. The residual heat of the reactor – i.e. the inevitable waste heat resulting from the decay of fission products after reactor shutdown, the decay heat - must be removed safely. Immediately after shutdown it will be about 6% (1.2 MW) of the rated output, decreasing exponentially.
  3. There can be no unauthorized release of radioactivity to the environment.

These protection goals are achieved through a combination of various security mechanisms:

  1. Inherent safety features: this refers to the fact that the FRM II is constructed such that laws of nature ensure that deviations from the specified target state are intercepted. These include in the core design, for example, the negative reactivity and strong moderation of the fuel element.
  2. Passive safety features: passive safety devices require no active intervention by staff or automatically operated controls. The most important passive safety device of the FRM II is the high heat capacity of the reactor pool (700 cubic meters of water) which is capable of taking up the complete decay heat from the shut-down reactor without further action. The water would then heat up to a maximum of 80°C. The structure of the fuel element, which ensures secure retention of fission products, is also a passive safety feature.
  3. Active safety features: these require active intervention by automated systems or personnel. Should protective actions be required at short notice, these are always triggered automatically on the basis of very robust concepts. Both shut-down systems, control rod and shut-down rods, only require the presence of gravity in order to function. The residual heat can be removed passively through natural circulation without any pumps.
  4. No release of radioactivity. In addition to the measures outlined above, the multi-barrier concept provides for the safe containment of radioactive materials. These include
  • Inclusion in the fuel plates,
  • the shielding effect of the pool water,
  • the hermetic sealing of the reactor building.

Almost two thousand routine checks per year

All these facilities are inspected repeatedly in accordance with the requirements of the supervisory authority. FRM II conducts a total of almost two thousand routine checks annually, with external experts being involved as required.

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