Radiation Environment about the Nerva Reactors

This paper describes the neutron and gamma dosimetry measurements made by the Westinghouse Astronuclear Laboratory (WANL) during the low and high power NRX-A2 and NRX-A3 (NERVA) reactor tests. Measurements were made in an effort to: 1) more clearly define the radiation environment about the reactor; 2) determine more accurately the leakage radiation per watt of reactor power for both a low and high power reactor; and, 3) verify analytical techniques employed for predicting gamma ray and neutron environment. Measurements made about the reactor with various resonance and threshold neutron detectors and gamma dosimeters are illustrated. Calculated values are presented to give a comparison to the measured values. It was concluded that further neutron experimental data are required to reduce uncertainties in the calculations and to provide a better definition of changes in neutron leakage for low versus high power NERVA reactors. Also, gamma exposure rates are needed for a high power run in order to evaluate changes in external gamma levels for low versus high power.