What are some nuclear reactor simulation codes

Criticality

In a nuclear power plant, some of the energy that is released when atomic nuclei are split is used to generate electricity. During nuclear fission, a neutron meets an atomic nucleus. This splits into two new, smaller atomic nuclei, releasing energy. Among other things, new neutrons are released in the process.

Some of these neutrons are lost - for example through absorption; the remaining neutrons can in turn trigger further nuclear fission. If further nuclear fission occurs in this way, one speaks of a chain reaction.

In nuclear technology, criticality is understood to mean the state of a nuclear reactor or a fissile material system in which a chain reaction takes place that is self-sustaining at constant power. This assumes that there is a balance between the formation rate, the loss and the neutrons that trigger new fission in the nuclear reactor. A constant number of splits ensures a constant release of energy.

The parameter that describes this state is also referred to as the multiplication factor k. Here k corresponds to the ratio of the number of neutrons of two successive generations. If k = 1, one speaks of a critical arrangement. A critical arrangement is the normal state in nuclear reactors. If the number of neutrons of the next generation is smaller than the current one, one speaks of a subcritical arrangement (k <1). If the number of neutrons of the next generation is larger than the current one, it is a supercritical arrangement. A supercritical condition can e.g. B. lead to high uncontrolled energy release in the event of accidents and should therefore be avoided.

GRS work on the topic of criticality
The phenomenon of criticality as part of reactor physics plays a central role in the safe operation of a nuclear power plant. Security-related issues relating to criticality are therefore examined both in research and in the assessment by GRS.

In addition, criticality safety must also be guaranteed in the manufacture, transport, storage and disposal of nuclear fuels. Here, for example, GRS is developing a computer program to simulate relevant processes in a geological repository for spent nuclear fuel. In addition, GRS is the publisher of an internationally recognized collection of information and data on criticality security, the “Handbook on Criticality”.