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The Effects of Impurity Composition and Concentration in Reactor Structure Material on Neutron Activation Inventory in Pressurized Water Reactor

경수로 구조재 내 불순물 조성 및 함량이 중성자 방사화 핵종 재고량에 미치는 영향 분석

  • Received : 2015.05.22
  • Accepted : 2016.01.08
  • Published : 2016.06.30

Abstract

The neutron activation inventories in reactor vessel and its internals, and bio-shield of a PWR nuclear power plant were calculated to evaluate the effect of impurity elements contained in the structural materials on the activation inventory. Carbon steel is, in this work, used as the reactor vessel material, stainless steel as the reactor vessel internals, and ordinary concrete as the bio-shield. For stainless steel and carbon steel, one kind of impurity concentration was employed, and for ordinary concrete five kinds were employed in this study using MCNP5 and FISPACT for the calculation of neutron flux and activation inventory, respectively. As the results, specific activities for the cases with impurity elements were calculated to be more than twice than those for the cases without impurity elements in stainless and carbon steel. Especially, the specific activity for the concrete material with impurity elements was calculated to be 30 times higher than that without impurity. Neutron induced reactions and activation inventories in each material were also investigated, and it is noted that major radioactive nuclide in steel material is Co-60 from cobalt impurity element, and, in concrete material, Co-60 and Eu-152 from cobalt and europium impurity elements, respectively. The results of this study can be used for nuclear decommissioning plan during activation inventory assessment and regulation, and it is expected to be used as a reference in the design phase of nuclear power plant, considering the decommissioning of nuclear power plants or nuclear facilities.

경수로 원전을 대상으로 원전 내 방사화 대상 물질인 스테인리스강, 탄소강 및 콘크리트의 불순물 정보 적용여부에 따른 방사화 핵종 재고량을 계산하였다. 본 연구에서 탄소강은 압력용기 물질에 사용되었고, 스테인리스강은 압력용기 내부 물질에 사용되었으며, 일반 콘크리트가 생체 차폐체에 사용되었다. 금속 물질에 대해서는 참고자료 1개의 불순물 함량 정보를 적용하였고, 콘크리트 물질에서는 참고자료 5개의 불순물 함량 정보를 적용하여 평가를 수행하였다. 방사화 핵종 재고량 전산해석 시 중성자속 계산에는 MCNP 전산코드를, 방사화 계산에는 FISPACT 전산코드를 각각 사용하였다. 계산 결과, 금속 물질에서 불순물을 포함한 경우가 그렇지 않은 경우보다 비방사능이 2배 이상 높았으며, 특히 콘크리트에서는 불순물을 포함한 경우가 그렇지 않은 경우보다 최대 30배 이상 비방사능이 높게 계산되었다. 방사화 핵종의 생성반응과 재고량을 분석한 결과, 금속 구조물에서는 불순물 중 Co원소와 중성자에 의해 생성되는 방사화 핵종인 Co-60이, 콘크리트에서는 불순물 중 Co, Eu 원소와 중성자에 의해 생성되는 방사화 핵종인Co-60, Eu-152, Eu-154 이 방사성폐기물 준위 결정에 큰 영향을 미치고 있음을 확인하였다. 본 연구의 결과는 원전 해체 계획 수립 시 방사화 핵종 재고량 평가 및 규제에 활용될 수 있을 뿐 아니라, 해체를 고려한 원전 또는 원자력시설의 설계 단계에서도 참고자료로 활용 될 것으로 판단된다.

Keywords

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