Fast neutron exposure evaluation using the ex-vessel neutron dosimetry system

The Code of Federal Regulations, Title 10, Part 50, Appendix H, requires that the neutron dosimetry be present to monitor the reactor vessel throughout its plant life. The Ex-Vessel Neutron Dosimetry Systems which consist of sensor sets, radiometric monitors, gradient chains, and support hardware have been installed for Korean nuclear power plants after a complete withdrawal of all six in-vessel surveillance capsules. The systems have been installed in the reactor cavity annulus in order to characterize the neutron energy spectrum variations axially and azimuthally over the beltline region of the reactor vessel. In addition, stainless steel gradient chains are used in conjunction with the encapsulated dosimeters to complete the mapping of the neutron environment between the discrete locations chosen for spectrum determinations. Cycle specific neutron transport calculations were performed to obtain the energy dependent neutron flux throughout the reactor geometry including the dosimetry positions. Comparisons between the calculations and measurements were performed for the reaction rates of each dosimetry sensor and the results show good agreements. (author)