Irradiation Technology for NPP Reactor Pressure Vessel Material in 49-2 SPR

By setting up a model for the reactor core, calculation of the fast neutron energy spectrum of the position 25 cm above the bottom of the irradiation tube can be realized. Combining the results of the calculation and the multiple foil activation method measurement, the fast neutron fluence rate can be obtained by unfolding the spectrum with SANDII code. Adopting the relatively fast neutron fluence rate measurement, the distribution of the axial fast neutron fluence rate can be obtained, and, the hour-length and the scheme of the irradiation can be defined. The technique target fast neutron（E≥1 Me V） flux received by the sample reaches about 6×10¹⁹ cm^-2. For accomplishing the sample disassembly, firstly we obtained the radioactive source term of the sample by calculating with ORIGEN2 code. Then, according to the operating environment, a model was set up by MCNP code, and the gamma dose rate data in different Shielding layer thickness was obtained by calculating with the code. The comparison between the calculation result and the measurement result indicated that the shielding design was effective. This irradiation experiment completely satisfied the technique target.