Figure 2 1 shows a typical location for an out of core neutron sensor In this example, the sensor is also outside the reactor vessel The figure also shows the magnitude of the neutron flux, the gamma exposure rate, and the temperature in the out of core location typical of a boiling-water or pressurized-water reactor during operation at rated power

In today’s power reactors the neutron flux inside the core boundary is always greater than 1011 neutrons cm’2 sec”1 Consequently, it is current practice to define an out of-core sensor as one that is not exposed to a neutron flux greater than 1011 neutrons cm” sec” The tern perature and gamma exposure rate are not involved in this definition Both the temperature and the gamma exposure rate in Fig 2 1 are at least an order of magnitude less in out of core locations than they would be within the core

boundary. An out-of-core sensor, however, can be located inside the reactor pressure vessel, e. g., in the region of the thermal shield, provided the neutron flux does not exceed 10 neutrons cm-2 sec-1 .