The increase of occupational radiation exposure(ORE) due to the increase of the operational period at existing nuclear power plant and also the publication of the new version of ICRP recommendation(ICRP publication No. 60) for radiological protection require much more strict reduction of radiation build-up in the nuclear power plant. The major sources of the radiation, i.e. the radioactive corrosion-products, are generated by the neutron activation of the corrosion products at the reactor core, and then the radioactive corrosion products are transported to the outside of the core, and accumulated near the steam generator side at PWR. Major radioactive corrosion-products of interest in PWR are $Cr^{51}, Mn^{54}, Co^{58}, Fe^{59}$ and $Co^{60}$. Among them $Co^{58}$ and $Co^{60}$ are known to contribute approximately more than 70% of the total ORE. Thus our main concerns are focused on predicting the transport and deposition of the Co radionuclides and suggesting the optimizing method which can minimize and control the ORE of the nuclear power plant. It is well known that Co-source is most effectively controlled by pH-solubility radiation control, and also some complex computer codes such as CORA and PACTOLE have been developed and revised to predict the corrosion product behavior. However these codes still imply some intrisic problems in simulating the real behavior of corrosion products in the reactor because of 1) the lack of important experimental data, coefficients and parameters of the transport and reactions under actual high temperature and pressure conditions, 2) no general theoretical modelling which can describe such many different mechanisms involved in the corrosion product movements, 3) the newly developed and measured behavior of the corrosion product transport mechanism. Since no sufficient and detailed information is available from the above-mentioned codes(also due to propriority problems), we concentrate on developing a new computer code, CP-TRAN(Corrosion Product TRANsport), which can predict the corrosion product and radioactivity transport within the primary coolant system, and also can be utilized for the computer simulation with actual plant data of currently operating Korean nuclear power plants to predict the transport of the radionuclides. In this study, the following problems will be updated, improved and compared with the already existing codes: 1) development and analysis of recent mechanistic modelling of corrosion product deposition, 2) application and modification due to the temperature kinetic effect, 3) separation of the effect of Fe, Co, Ni and Mn solubility rather than Fe solubility alone, and 4) consideration of Ni activation and recoil process.
By applying the above updated and improved mechanisms, the corrosion product behavior in PWR of currently operating Korean unclear power plants has been simulated. In addition, the evaluation of particulate transport, independent solubility data of major radionuclides and acute nodalization were included and extended. Then, with the developed computer code, we have evaluated and analyzed the activity and corrosion product build-up controlled by many parameters such as pH, composition of metal, and auxiliary system performance.
여러 가지 자료들을 통해 작업자 방사선 피폭이 부식 생성물의 이동 메카니즘들에 의해 일어남이 밝혀지고 ICRP 권장 작업자 피폭 제한치가 년간 5 rem 에서 2 rem으로 대폭 하향 조정됨에 따라 부식 생성물의 제어와 예측을 위한 모델링과 컴퓨터코드의 필요성이 대두되었지만 국내의 경우에 있어 사용할 수 있는 코드들이 제한되어있고 또한 사용 가능한 코드에 있어 여러 가지 미비점들이 지적되고 있어 새로운 코드의 개발이 필요하게 되었다.
본 연구는 위와 같은 필요성을 만족시키고자 PACTOLE과 CRUDSIM을 근간으로 하여 새로운 컴퓨터 코드를 개발하는데 그 목표를 두고 새로운 모델을 설정하고 또한 최근의 연구 결과를 응용하여 CP-TRAN을 개발하였으며, 그 평가를 논리적으로 가장 유사한 형태이며 비교적 그 사용 결고자료들이 비교적 풍부한 CORA의 결과와 비교하였다.
장시간 및 단기 운전에 있어, 짧은 시간의 경우, 이정 범위내에서 운전 조건들에 민감한 결과를 보였으나 장시간 운전시에는 비교 대상 값들과 일치를 보였다. 또한 화학적 조건을 고 pH로 함에 따라 뚜렷한 방사능 준위의 저감을 볼 수 있었으며 여러 가지 경우에 있어 코드의 결과가 실제 발전소데이터나 비교 코드의 값들과 일치함을 알 수 있어 본 연구에서 설정한 비대류 모델의 적합함을 입증할 수 있었다.
