Abstract: Neutron ambient dose equivalent is one of the main objects for radiation protection survey in nuclear power plant. Estimation of neutron ambient dose equivalent strongly depends on the knowledge of the neutron distribution along with their energies. The neutron spectra and ambient dose equivalent rates, at five sites inside the containment of heavy water reactor at TQNPC, had been measured using a selfmade multisphere spectrometer. The multisphere spectrometer consists of a ³He proportional counter and nine polythene spheres with different diameters from 2.5 inch to 12 inch. Response functions of the spectrometer were calculated with the MCNP code, and were calibrated and verified by a standard ²⁵²Cf neutron source. The neutron ambient dose equivalent rates and their energy distributions at the sites were also derived from the measured neutron spectra, and the results were compared with that measured by neutron ambient dose equivalent rate meter and CR-39 trace etching detectors. The measured results can provide the relevant reference data for neutron dose survey in nuclear power plant.

Key words: Nuclear power plant, Neutron spectrum, ⁺Neutron ambient dose equivalent rate, ⁺Multisphere spectrometer