Theoretical Aspects of the Field Radiological Monitoring System for a Reactor Accident, (I)

Abstract

Fundamental principles for designing the ideal field montoring network have been studied from the viewpoint of monitor detecting capability.The detecting capability is specified by a radius of orbicular "detecting domain" such that the radjoactive cloud flowing into the domain gives an exposure-rate above the alarm level to the detector; for example, 100 m for a cloud-gamma detector at 2 km downwind, 400 m for a cloud-concentration monitor at lkm downwind, assuming a radioactive cloud that inflicts a dose of 100rems to the thyroid of a child staying for lOhr at the point of maximum concentration.The ideal distribution of detectors are obtained by adjoining their detecting domains so as to surround the reactors, keeping a outlying distance from the reactors, i. e., 1.8km, to retain complete capability for detecting a radioactive cloud, and to eliminate the direct gamma radiation assuming the 106Ci of fission products confined in the reactor in an accident. In the neighborhood of reactors, film-dosimeters or TLD are advisable instead of the y-monitors.The concept of detecting domain is also applicable to the evaluation of the probability of detecting a radioactive cloud by a deficient monitoring network, composed of insufficient number of field monitors.