Molybdenum-99 (Mo-99) and, its daughter, technetium-99m (Tc-99m) are the most commonly used medical isotope covering more than 85% of the nuclear diagnostics. Currently, majority of Mo-99 supplied in the market is fission-based Mo-99 produced by the fission of U-235 in research reactors. In spite of substitutive production schemes, fission-based Mo-99 is the major source for its significant advantages of high specific activity and large production capacity. The new research reactor (KJRR) is under construction in Gijang, Busan, Korea. The project is aiming 2,000 Ci/week Mo-99 production. For the objective, KAERI has been developed Mo-99 production process using HANARO. Weekly production of 2,000 Ci (100,000 Ci/yr, 6-day calibration) Mo-99 can cover 100% domestic needs, as well as 20% of international demand. However, overall cost for the fission-based Mo-99 production is continuously increasing. Previously, the most Mo-99 producers used weapon-grade highly enriched uranium (HEU) targets. Recently, the use of HEU in private sector is limited for non-proliferation. As a result, major Mo-99 producers are forced to convert their targets from HEU to low enriched uranium (LEU, 19.75% U-235 enrichment). The conversion of Mo-99 target caused waste issue. It is not only because of the 50% less yield in production, but also increment of the radioactive waste by 200%. Therefore, designing optimal radioactive waste treatment strategy for fission-based Mo-99 production is becoming more important than ever. During the process, irradiated LEU targets are dissolved in alkaline solution in hot cells. Fission products other than Mo-99 removed from the solution via series of separation steps. Then Mo-99 is eluted and purified to meet international standard as an active pharmaceutical ingredients (APIs). Radioisotopes of xenon (Xe) and krypton (Kr) generated from the fission of U-235 during the irradiation of the target in the research reactor. Then, the radioactive gas released during the process. The emission of radioactive noble gas from the medical radioisotope production facility can be controlled via delayed release through large charcoal beds. KAERI developed compact xenon adsorption module with chilled carbon column to meet 5 GBq/ day of CTBTO recommendation. Small volume of chilled charcoal can satisfy the guideline, replacing massive gas tank system. Therefore, development of optimized radioactive gas treatment system for the Mo-99 production is one of the essential piece for the successful construction, licensing and operation of the KJRR project.

As part of the third ATM Challenge, we performed a series of atmospheric dispersion simulations for routine releases of Xe-133 from ordinarily operating nuclear facilities such as Medical Isotope Production Facilities (MIPFs), Nuclear Power Plants (NPPs), and Research Reactors (RRs) in the Northern Hemisphere using our ATM, Lagrangian Atmospheric Dose Assessment System (LADAS), with Numerical Weather Prediction (NWP) data produced by the Korea Meteorological Administration (KMA). The simulation time period is 6 months, from June to November in 2014, and we used the stack emission data except for CNL (Canada) and IRE (Belgium) in accordance with the scenario of the third ATM Challenge 2019. In addition, the simulations were done individually for all MIPFs, NPPs, and RRs. We utilized 3-hourly KMA’s Unified Model Global Data Assimilation and Prediction System (UM-GDAPS) data with 0.35°×0.23° horizontal resolution as input meteorological fields and extracted hourly time series results for Xe-133 activity concentrations with few different resolutions such as 0.5°×0.5°, 0.35°×0.23°, and 0.1°×0.1° at several IMS stations in the Northern Hemisphere which were in normal operation in 2014. Considering previously reported values of daily Xe-133 release amounts for CNL and IRE, measured signals at some IMS stations (such as CAX17, DEX33, SEX63, and USX75) were well reproduced from the simulation results.

북한은 2017년 9월 3일 풍계리 핵실험장에서 6차 지하 핵실험을 단행하였다. 이전에 수행했던 핵실험들과 달리 풍계리 핵 실험장 주변에서 몇 차례의 유발지진이 발생하였고 이로 인해 지하에 갇혀 있던 방사성제논이 대기 중으로 방출되는데 영향을 끼쳤을 것으로 예상된다. 본 연구에서는 북한의 6차 핵실험 이후에 발생한 유발지진을 고려하여 핵실험으로 발생한 방사성제논의 몇 가지 방출 시나리오에 따른 대기확산 모의실험을 본 연구진이 개발한 LADAS (Lagrangian Atmospheric Dose Assessment System) 모델에 기상청의 수치예보자료를 적용하여 수행하였다. 방사성제논의 가능한 검출 위치와 시간을 찾기 위해, 1일 간격 및 1주일 간격의 지연방출뿐만 아니라 유발지진으로 유출된 지연방출 시나리오도 설정하였다. 포괄 적핵실험금지조약기구(Comprehensive Nuclear-Test-Ban Treaty Organization)에서 운영중인 전세계관측망(International Monitoring System)과 원자력안전위원회의 133Xe 탐지 결과는 유발지진으로 유출된 방사성제논의 방출 시나리오에 따른 모의실험의 결과와 대체로 부합되었다.