Design of a shield system for a hyper-pure germanium detector as a stack monitor for use in accident conditions at a nuclear power plant

Abstract

Collimator and shield configurations for two high-purity germanium detectors were designed for use during a loss of coolant accident at a boiling water reactor. The detectors will return information concerning stack releases to operators within a 15 minute time frame. Operating parameters for the stack monitors are defined by the United States Nuclear Regulatory Commission (USNRC) and a 24 hour source term generated by ORIGEN2. A lead collimator 0.4 cm in diameter, 20 cm in length for the high range detector and 2 cm in diameter, 20 cm in length for the low range detector was shown through a Monte Carlo code, MCNP4 to prevent high range detector saturation and provide enough low range detector response so good statistical data on stack releases result. A lead shield 20 cm thick was shown through MCNP4 to reduce the background radiation interference for both detectors to levels such that the detection of isotopes within the stack effluent is possible as required by the USNRC.