Recently, BNS (Best System) developed a system for evaluation and classification of soil and concrete wastes generated from nuclear power plant decommissioning. It is composed of various modules for container loading, weight measurement, contamination evaluation, waste classification, stacking, storage and control. The contamination evaluation module of the system has two sub modules. One is for quick measurement with NaI (Tl) detector and the other is for accurate measurement with HPGe detector. The container used at the system for wastes handling has capacity of 100 kg and made of stainless steel. According to the measurement result of Co-60 and Cs-137, the waste is classified as waste for disposal or waste for clearance. Performance of the system was demonstrated using RM (Reference Material) radiation source. This year, necessity of system improvement was suggested due to revised operation requirements. So, the system should show throughput of more than 1 ton/hr and Minimum Detectable Activity (MDA) of less than 0.01 Bq/g (1/10 of criteria for regulatory clearance) for Co-60 and Cs-137. And soil waste become main target of the system. For this, the container used for soil waste handling should have capacity of 200 kg. As a result, material for the container need to be changed from stainless steel to plastic or FRP (Fiber Reinforced Plastics). And large area detector should be introduced to the system to enhance processing speed of the system. Additionally, container storage rack and conveyor system should be modified to handle 200 kg capacity container. Finally, moving path of the container will be redesigned for enhanced throughput of the system. In this paper, concept development of the system was suggested and based on that, system development will be followed.

In the decommissioning site of Korean Research Reactor 1&2 (KRR-1&2), according to Low and Intermediate-level Radioactive Waste Disposal Acceptance Criteria of the Korea Radioactive Waste Agency (WAC-SIL-2022-1), characteristics of radioactive waste was conducted on approximately 550 drums of concrete and soil waste for a year starting from 2021. Among them, 50 drums of concrete waste transported and disposed to Gyeongju LILW disposal facility at the end of 2022. For the remaining approximately 500 drums of concrete and soil waste stored on-site, they were reclassified into two categories: permanent disposal grade and clearance grade. This classification was based on calculating the sum of fractions (SOF) per drum for each radionuclides. The plan is to dispose of around 200 drums in the permanent disposal grade and about 300 drums in the clearance grade by the end of 2023. Since concrete and soil decommissioning wastes are generated in large quantities over a short period with similar origins, they were grouped within five drums as suggested by the acceptance criteria. Mixed samples were collected from each group and used for radionuclide analysis. When utilizing mixed samples, three distinct samples are collected and analyzed for each group. The maximum value among these three radionuclide analysis results is then uniformly applied as the radionuclide concentration value for all drums within that group. Radioactive nuclides contained in similar types of radioactive waste with similar origins can be expected to have some statistical distribution. However, There has been no verification as to whether the maximum value among the three mixed samples exists within the statistical distribution or if it deviates from this distribution to represent a different value. In this study, we confirmed characteristics of radionuclide concentration distribution by examining and comparing radionuclide concentration distributions for radioactive wastes drum grouped for nuclear characteristic among 50 concrete wastes drum disposed in year 2022 and 500 concretes & soils drum scheduled for disposal (clearance or permanent disposal) in year 2023. In particular, when comparing tritium to other nuclides, it was observed that the standard deviation for the distribution of maximum values was approximately 318 times larger.

During decommissioning and site remediation of nuclear power plant, large amount of wastes (including radioactive waste) with various type will be generated within very short time. Among those wastes, soil and concrete wastes is known to account for more than 70% of total waste generated. So, efficient management of these wastes is very essential for effective NPP decommissioning. Recently, BNS (Best System) developed a system for evaluation and classification of soil and concrete wastes from the generation. The system is composed of various modules for container loading, weight measurement, contamination evaluation, waste classification, stacking, storage and control. By adopting modular type, the system is good for dealing with variable situation where system capacity needs to be expanded or contracted depending on the decommissioning schedule, good for minimizing secondary waste generated during maintenance of failed part and also good for disassemble, transfer and assemble. The contamination evaluation module of the system has two sub module. One is for quick measurement with NaI(Tl) detector and the other is for accurate measurement with HPGe detector. For waste transfer, the system adopts LTS (Linear Transfer System) conveyor system showing low vibration and noise during operation. This will be helpful for minimizing scattering of dust from the waste container. And for real time positioning of waste container, wireless tag was adopted. The tag also used for information management of waste history from the generation. Once a container with about 100 kg of soil or concrete is loaded, it is moved to the weight measurement module and then it transfers to quick measurement module. When measured value for radioactivity concentration of Co- 60 and Cs-137 is more than 1.0 Bq/g, then the container is classified as waste for disposal and directly transferred to stacking and storage rack. Otherwise, the container is transferred to accurate measurement module. At the accurate module, the container is classified as waste for disposal or waste for regulatory clearance depending on the measurement result of 0.1 Bq/g. As the storage rack has a sections for disposal and regulatory clearance respectively, the classified containers will be positioned at one of the sections depending on the results from the contamination evaluation module. The system can control the movement of lots of container at the same time. So, the system will be helpful for the effective nuclear power plant decommissioning in view of time and budget.

이상의 결과를 종합하면, 평가대상 토양을 증류수로 20배 희석하여 200rpm 으로 30분간 진탕한 후 PDA (감자추출배지)와 혼합하여 121℃에서 20분간 살균한 후 Coriolus hirsutus (MKACC 50560) 균을 접종한다. 접종완료 후 25℃에서 5일간 배양한 후 균사 생장을 측정하여 담자균의 균사 생장률 (목적토양에서의 균사생장/PDA 에서의 균사생장×100)을 계산한다. 이 기준에 따라 균사생장률이 60%이상이 되면 대상 토양은 작물 생육에 적합한 토양이라고 추정할 수 있다. 이러한 방법은 토양의 건전성 평가를 위한 신속한 간이검사를 통하여 소량의 시료를 가지고 단기간 내 대량 분석을 가능하게 하여 토양 건정성 평가의 기초 자료로 사용될 수 있다고 사료된다.

중금속으로 오염된 토양과 광미는 지하수 및 생태계에 추가적으로 피해를 발생시킨다. 이러한 독성 금속의 축적은 식물의 성장억제 및 인체의 발달이상, 발암과 같은 다양한 질병의 원인이 된다. 오염된 토양에서 중금속을 정화하는 방법으로는 고형화/안정화, 토양세척, 토양경작법 등과 같이 다양한 방법이 있다. 하지만 부지 및 오염특성에 따라 적절한 방법을 사용해야 한다. 적절한 방법 중 하나는 오염된 토양의 고형화/안정화이다. 본 연구의 목적은 오염된 토양 및 광미 내 존재하고 있는 중금속을 고형화/안정화 공법을 적용하여 정화하는 방법을 제안하는데 있다. 본 연구에서는 오염토양 내 중금속을 고형화/안정화 시키고 강도 증진을 위해 MICP 토착미생물과 산업폐기물인 굴패각, 폐석고를 배합하여 고화제로 사용하였다. 국내의 중금속 오염토양과 광미에서 MICP 토착미생물을 분리하였고 균체 지방산 분석을 통하여 동정을 진행하였다. 각각의 시료에서 분리한 균주를 동정한 결과 가장 많이 유사성을 보이는 균주는 Brevibacillus centrosporus 와 Bacillus megaterium 이었다. 또한 MICP 토착미생물의 최적 성장 조건을 도출하였으며, 산업폐기물과 MICP 토착미생물의 최적 배합비를 적용한 공시체의 일축압축강도 분석을 진행하였다. 그 결과 28일 경과 후 일축압축강도는 미국 EPA 폐기물처리 표준 기준을 만족하였으며, 위해성 평가를 위한 TCLP, SPLP 분석 결과 미국 EPA 기준을 만족하였다.

The purpose of this study was to suggest feasible disposal methods for heavy-metal-contaminated soil or mine tailings through solidification/stabilization. To improve the compressive strength and enhance the heavy-metal stabilization after solidification/stabilization, we used the industrial wastes (oyster shell powder and waste gypsum) and indigenous bacteria as immobilization agents. Three indigenous bacteria were isolated from each heavy-metal-contaminated soil or mine tailing site, and the bacteria were identified by cellular fatty acid composition analysis. The results of cellular fatty acid composition analysis showed that the closest strains of these bacteria are Brevibacillus centrosporus, Lysinibacillus sphaericus, and Bacillus megaterium. To the best of our knowledge, this research was the first report of biomineralization by Brevibacillus centrosporus. As a result of mixing additives with the optimum mixing ratio suggested in this study, the compressive strengths of specimens were satisfied in accordance with the US Environmental Protection Agency (EPA) waste treatment standard after 28 days of aging. Additionally, the results of the Toxicity Characteristics Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure (SPLP) analysis showed the successful immobilization of heavy metals after 28 days of specimen formation for solidification/stabilization.