Nuclear fission of uranium inside the fuel element produces radioactive fission products. FRM II has three barriers to prevent the release of radioactivity:

• The specially treated fuel plates lock in the radioactive fission products during nuclear operation.
• In case of a heavy accident the fuel element can get damaged. Next barrier to prevent the release of radioactivity is the water inside the reactor pool.
• Besides its function as a container for the experimental equipment the reactor building is the last of three barriers to prevent radioactive emission.

These three barriers enable the plant to cope with extreme and very unlikely accidents in addition to fulfilling the legal safety requirements at all circumstances.