The neutron source is built for the research with neutrons. There is no interest in the generation of electricity by nuclear fission. A neutron source is not characterized by the total power, resp. the nominal thermal power, which means a high number of produced neutrons per second. But it is characterized by a high density, resp. a high flux of available neutrons. This is decisive for research with neutrons is based on interaction of neutrons with the matter to be analyzed and the interaction depending on the flux of the neutrons.

Because of economic and some other reasons the nominal thermal power of neutron sources is very small. Regarding FRM II the nominal thermal power is 20MW of the reactor core and 4MW due to installations responsible for the functionality of the reactor. Therefore the total power of a neutron source is a fraction of the total power of a nuclear plant. The reactor core of FRM II is very small, it is a compact core, but its power density is much bigger than the power density of nuclear plants: The power density of FRM II is bigger than 1MW per litre nuclear volume. Temperature and pressure of the cooling medium water is very small for there is no interest in generating electricity.

The existing neutron sources for research with neutrons can be specicified according to their different usage. Often they are designed to meet different requirements of usage at the same time:

• The first research neutron sources were built for analysing new nuclear fuel and studying radiation damage by means of fast neutrons. But FRM II hasn't been built to meet these requirements.
• Neutron sources are built for they provide excellent possibilities for isotope production and doping usage.
• Beam-tube neutron sources are of actual interest in science. Normally slow neutrons are guided to experiments by means of beam-tubes and neutron guides for adequate inquiries.