Security barrier

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In nuclear technology , the term safety barrier refers to various technical measures that are intended to prevent nuclear fuel and its fission products from escaping into the environment. The multiple barrier principle is used as part of the 'defense in depth' principle in order to be able to retain the substances if one or more barriers fail.

The following components are specifically designated as safety barriers in light water reactors:

1. the nuclear fuel UO ₂ itself
2. the cladding tube
3. the primary cooling circuit
4. the security container

UO ₂ (and also MOX ) is a ceramic material that includes most of the fission products. Exceptions are fission products that arise on the surface, noble gases and the elements iodine and cesium , which are mobile at the prevailing temperatures and can diffuse out of the fuel.

The cladding tube is a gas-tight barrier that safely encloses the entire contents when intact. Radioactive substances that get into the cooling water if individual cladding tubes fail are removed from the cooling water by means of cooling water treatment.

The primary cooling circuit consists of the reactor pressure vessel and the main coolant lines as well as the steam generators (pressurized water reactor) or turbines and condenser (boiling water reactor), the latter being decoupled from the reactor in the event of an accident in order to prevent radioactive leaks from the turbines.

As a gas-tight shell, the containment encloses the primary cooling circuit and withstands pressures that are expected in the event of an accident. However, the containment can have a leak rate of the order of 0.25% by weight per day.

The behavior and handling of failing safety barriers is the subject of deterministic safety analysis.

Individual evidence

1. ↑ http://www-pub.iaea.org/MTCD/publications/PDF/Pub1013e_web.pdf , p. 8
2. ^ The Radiochemistry of Nuclear Power Plants With Light Water Reactors, Karl-Heinz Neeb, p. 111ff
3. ↑ http://www.lsa.ethz.ch/education/vorl/snpp_slides_12/01_Nuclear_Safety_Problem_handout.pdf , p. 13