DS397 Saf Use Mod RRs with NUSSC comments 18-06-2010

should be given to provide the means for placing the experiment in a safe condition withoutinvolving the reactor shutdown system.4.3. In addition to the normal reactor operations, such as startup, steady state andshutdown, other situations should be considered for their effects on the experiments ormodifications. These conditions include unscheduled shutdowns followed by immediaterestart, maintenance, extended shutdowns, fuel changes, low power operation, coreconfiguration changes and failure of electric power and other utilities. Also the design basisaccidents of the research reactor should be considered for their effects on the experiments ormodifications. Similarly, the effects of all states of experiments or modifications on thereactor should be considered.4.4. The interfaces between nuclear safety and nuclear security should be considered aspart of the design process. These interfaces should be considered in such a way that theimpacts of safety on security and the impacts of security on safety are taken into account fromthe design stage and an appropriate balance is achieved.SPECIFIC CONSIDERATIONSReactivity4.5. If the experimental device or a modified system, or its failure, can lead to an increasein the reactivity of the reactor, the experimental device or modification should be designed soas to limit the positive reactivity effects to those which can safely be accommodated by thereactor control and shutdown systems.4.6. If modification of the reactor control and shutdown systems is necessary toaccommodate an increase in the reactivity of the reactor core, then this modification should betreated as a separate modification with major safety significance and implemented before theoriginal proposed modification or experiment is implemented.4.7. The reactivity worth of an experiment or reactor modification should be determinedfor all situations (e.g. insertion of the experiment into the reactor core, removal and potentialfailure modes). A calculated, or otherwise determined, reactivity worth should usually bechecked by measurement, using a critical experiment procedure or an equivalent method. Thedesign basis accident for the reactor should also be considered in the evaluation. Thereactivity worth of experiments or modified systems should be within the approvedoperational limits and conditions.16