The study for activation evaluation on activated structures in nuclear power plant with 40 years operation history

Abstract Reactor pressure vessel internal, reactor pressure vessel and bio-shield are one of the activated structures in nuclear power plant. Especially, reactor pressure vessel internal which is irradiated by neutrons for several decade of years to the level of 1E + 11 ∼ 1E + 13 neutrons/cm2.sec is highly activated one and specific activity for some nuclide is to the level of ∼1E + 09 Bq/g. In case of reactor pressure vessel, neutron flux level is 1E + 09 ∼ 1E + 11 neutrons/cm2.sec and specific activity is to the level of ∼1E + 06 Bq/g, so, it could be classified as low activated region. Bio-shield can be divided into two parts – very low activated and clearance regions, and neutron flux and specific activity in very low activated region are ∼1E + 08 neutrons/cm2.sec and ∼1E + 01 Bq/g. Separation between two regions in bio-shield is determined by the factors of impurities’ kind and quantity included in it. Major activated nuclides in those structures are Ni-63, Fe-55, Co-60, Ni-59, Mn-54, H-3, C-14, etc. through neutron capture reaction – (n, γ), (n, p), (n, 2n), and (n, α). Activation evaluation for structures in nuclear power plant is performed using MCNP and ORIGEN codes.