Shutdown requirements in licensing of research reactors and consequences for operation

Most countries start their nuclear life with the setup of a research reactor. Most countries have at this time no licensing authority established which can act on existing laws, rules and regulations. Thus, most countries have during this starting phase to rely on the regulations fixed by international institutions such as the IAEA (or by national institutions as the former NRC in US, which happens to take place more often from reasons below). This implies a specific responsibility for international regulations since they have to be very clear and unique. Moreover they have to be applicable to all plants they are set forth for and they have to give no unavoidable restrictions on the use of the plant. Additionally some recheck of the rules based on national rules in forth will be of help. The enrichment reduction for research reactors gave frequent cause to look at the existing IAEA-publications for research reactors. They are laid down in the safety series no. 35 edited 1971. I will only discuss here specific parts of these considerations or requirements. Since the authors' personal impressions are that the published considerations are neither that clear nor that less restrictive as necessary the subsequent discussion is carried out. One of the confusing points of the existing IAEA-regulations is the lengthy discussion of reactivity considerations for critical assemblies first, no similar separate discussion for research reactors and a second discussion titled 'control-rod considerations' under the main title 'considerations applying to critical assemblies and research reactor'. This discussion will be restricted to the latter since the critical assemblies with their timely Constance of maximum excess reactivity do not present any problem for all shut-down conditions