Safety circuit development at Brookhaven National Laboratory

FROM the time of the earliest nuclear reactors, it has been considered of primary importance that they be protected against an uncontrolled rise in temperature, whether this rise be due to a corresponding uncontrolled rise in neutron level or to a failure of the cooling system. While it is claimed that some types of reactor are intrinsically safe from this kind of accident, it is likely that until a solid background of experience has been acquired, all nuclear reactors will continue to be protected by devices which ¿scram¿ them when such devices foresee a dangerously high temperature. But temperature-sensing devices are too slow, as well as too insensitive at low levels to provide protection during startup. Therefore neutron-sensing devices are used. The present paper will be limited to discussing that part of the safety system which senses neutrons. Similar principles are applicable as well to other portions of the safety system, such as those which sense temperature, coolant flow, etc.