Water reactor top flange radiation dose is reduced - by annular neutron shield and water gamma shield

摘要

A shielding arrangement for reducing the neutron flux and gamma radiation near the flange of a nuclear pressure vessel comprises an annular plate of neutron-absorbing material in the space between the vessel and the biological shield and an annular pond of water, above a bellows seal, to absorb gamma radiation. The annular plate may be below or above the bellows seal or below the duct penetrations into the vessel. The plate is pref. 10 cm thick, of monalite. The water level is pref. at the top of the vessel top closure plate. The water may also serve as coupling medium for ultrasonic inspection of the wall face (edge face) of the flange, in which case it is at least as high as the top of the flange. Instead of two separate neutron and gamma shields, a single ring of serpentine concrete, absorbent to both types of radiation may be used.