Evaluation of Fast Neutron Fluence for Reactor Pressure Vessel Surveillance of Chashma Nuclear Power Plants Units 1 and 2

The energy-dependent neutron flux incident on surveillance capsule assemblies (SCAs) installed at the outer surface of the core barrel in two pressurized water reactors-Chashma Nuclear Power Plants Units 1 and 2 was evaluated. This safety study was made for the reactor pressure vessel surveillance program to determine the fast-neutron-induced radiation embrittlement of vessel materials in sections facing the core side and the upper weld positions. A total of 68 radiometric sensors were irradiated in each SCA of these two reactors, and dosimetry data were measured from radiometric sensors. Fast neutron flux (E > 1 MeV) was best estimated using the least-squares method by employing LSL-M2 package. Measured results were compared with the fast neutron flux calculated using MCNP5 at the base and weld metal sections of SCA. The results agreed within ±20% of each other in both reactors, which satisfy the regulatory acceptance criteria. Therefore, these results can be used in life assessment of reactors.