Protective functions of the experimental multi-purpose high-temperature gas-cooled reactor

Protective functions of the experimental multi-purpose high-temperature gas-cooled reactor being developed in JAERI were appraised in safety features of the operational protection system for events during normal operation at regular and frequent intervals and also the reactor protection system for unplanned events during abnormalities. Described are the plans of protection for the total plant system according to the current standards and criteria, setting of the actual safety systems in design safety limits, and protection sequences for normal operation occurences and unplanned abnormal events. Along this line, the requirements of reactor safety design are expounded. In planning the protection systems, a set of limiting safety consequences is established for the respective categories of events. The consequences restrict the process variables and design parameters by normal operating value, process safety limit and design safety limit, with the protection sequences. Concerning functions of the operational protection system, control rod withdrawal sequence and sequential control manners for reactor start and normal shut-down were studied, and for the reactor protection system, protection sequences were examined by simulation analysis of the events. Then, the sequences in detail were applied in transients of the reactor plant. In conclusion, 1) capacity of the auxiliary cooling system must be larger than in the first conceptional design, and 2) installation of a pony-motor in the intermediate loop (secondary loop) are necessary. (auth.)