APPLICATIONS OF EX-VESSEL NEUTRON DOSIMETRY IN CHINA PRESSURIZED-WATER REACTOR POWER PLANTS

Ex-vessel Neutron Dosimetry (EVND), which may be installed in cavity annulus between reactor vessel outer wall and the biological shield, along to the beltline region of the reactor vessel in the pressurized-water reactor power plants, can be applied to meet the followings objectives, 1. Determine azimuthal and axial gradients of fast neutron exposure over the beltline region of the reactor. 2. Provide measurement capability sufficient to allow the determination of exposure parameters in terms of both neutron (E > 1.0 MeV) fluence and iron displacements per atom (dpa). 3. Provide a long-term monitoring capability for the beltline region of the reactor vessel. 4. Verify the in-vessel surveillance capsule neutron fluence measurements and evaluate the neutron fluence at the extension life end of the reactor pressure vessel if there is changes in the fuel design and fuel cycles. Compared with the in-vessel surveillance capsule, EVND method, which also uses multiple foil sensor sets for neutron spectrum measurements, has the following advantages: 1. Flexible in installation positions, 2. Easy in installation operations, 3. Flexible in monitoring period selection, 4. Low cost than in-vessel surveillance capsules. From 2010 to 2012, State Nuclear Power Plant Service Company(SNPSC), as one of the designated users of technology transfer from Westinghouse Electric Company (WEC), had organized some engineers to learn EVND technology from WEC. After that, we designed and built our own training facilities to simulate the real working process and working environment, to support EVND installation training, to reduce the installation and replacement time. We also verified that EVND method was good enough to working in light water reactor system through verification testing. From 2013 to 2017, SNPSC and WEC worked together to support one China PWR power plant to install EVND and then replace it at 2015 and replaced again at 2017. Comparisons of measurements and calculation results showed that it was one successful application in China PWR power plant and we believe that results of this application will support PWR power plants life extension in China.