In-service inspection methods for low-power research reactors are described in this module. Two practical examples of an in-service inspection and maintenance task at a TRIGA reactor and at a MTR reactor are given, and a typical maintenance schedule is presented in Annex 1. The inspection methods and the maintenance schedule are based on 42 years of operation and maintenance experience of a typical 250 kW TRIGA Mark-II reactor. Although this experience is related to a TRIGA reactor, most of the ISI methods and a large part of the maintenance schedule can be applied with minor changes to other types of low power research reactors such as ARGONAUT, SLOWPOKE, and MNSR type reactors.

The useful lifetime and the safe operation of a research reactor depends on two main criteria which are

For the maintenance program of a research reactor, a maintenance schedule has to be established which lists all systems and components necessary for a safe reactor operation. These are, however, not only the direct related safety related systems and components but also auxiliary systems and components which may have an indirect effect on the safety systems or the safety of the facility. The frequency of maintenance depends on the importance of the components and also on operational experience but it will usually be at least once a year. More frequent inspections should be considered for components that show an increasing deterioration rate, require frequent corrective maintenance or are operating significantly pass their original expected lifetime.

In-service inspection (ISI) will be carried out with more sophisticated equipment using various methods described in chapter 3 (Inspection Equipment). During this ISI, one component is investigated in detail; usually an inspection report is prepared both for the operation license holder and, in many cases, also for the regulatory body. The ISI methods may vary from simple visual inspections and measurements to very sophisticated and expensive NDT inspections. The reactor type and its power level should be taken into consideration when selecting the appropriate inspection method. Typical examples of instances requiring more sophisticated inspections are the visual inspection of the reactor tank, reflector or the inspection of welds in the primary piping system by NDT methods.

The responsibility for in-service inspections is, in many cases, with the staff of the reactor operation group. Experiences with a 250 kW TRIGA reactor has shown that the manpower involved for a simple monthly ISI is about 2 man-days but a complete yearly ISI may be in the range of 14 man-days. The number of safety systems and fuel elements requiring inspection at facilities up to 1 MW are only marginally larger so the maintenance periods are similar to the 250 kW facilities. Larger, high power reactor facilities may have more systems requiring routine maintenance but often their larger staff sizes will compensate.