Wide-area surface decontamination is essential during the sudden release of radioisotopes to the public, such as nuclear accidents or terrorist attacks. A spray coating composed of a reversible complex between poly (vinyl alcohol) (PVA) and phenylboronic acid-grafted poly (methyl vinyl ether-alt-mono-sodium maleate) (PBA–g–PMVE–SM) was developed to remove radioactive cesium from surfaces. The simultaneous spay of PVA and PBA–g–PMVE–SM aqueous polymer solutions containing Cs adsorbent to contaminated surfaces resulted in the spontaneous formation of a PBA–diol ester bond-based gel-like coating. The Cs adsorbent suspended in the gel-like coating selectively removed Cs-137 from the Cs-contaminated surface. The used gel-like coating were removed from surfaces by simple water rinsing. This recovery way has advantages compared with costly incineration to remove the organic materials for final disposal/storage of the radioactive waste. Thus, our spray coating is suitable for practical wide-area surface decontamination. In radioactive tests, the hydrogel containing Cs-adsorbent showed substantial Cs-137 removal efficiencies of 96.996% for painted cement and 63.404% for cement, which are 2.33 times better than the values for the commercial surface decontamination coating agent DeconGel.

Laser scabbling has the potential to be a valuable technique capable of effectively decontaminating highly radioactive concrete surface at nuclear decommissioning sites. Laser scabbling tool using an optical fiber has a merits of remote operation at a long range, which provides further safety for workers at nuclear decommissioning sites. Furthermore, there is no reaction force and low secondary waste generation, which reduces waste disposal costs. In this study, an integrated decontamination system with laser scabbling tool was employed to test the removal performance of the concrete surface. The integrated decontamination system consisted of a fiber laser, remote controllable mobile cart, and a debris collector device. The mobile cart controlled the translation speed and position of the optical head coupled with 20 m long process fiber. A 5 kW high-powered laser beam emitted from the optical head impacted the concrete block with dimensions of 300 mm × 300 mm × 80 mm to induce explosive spalling on its surface. The concrete debris generated from the spalling process were collected along the flexible tube connected with collector device. We used a three-dimensional scanner device to measure the removed volume and depth profile.

Nuclear weapon generates huge amount of radioactive fallout which is extremely dangerous. The fallout gradually falls to the ground and then covers every surface in city and nature. A hydrogel decontamination medium has been developed to clean the surface polluted by the fallout. The hydrogel is soluble in water so the used hydrogel can be simply removed from the surface by washing. However, significant amount of waste water, containing the radioactive fallout, is generated with this process. In this respect, it is necessary to secure alternative technical options for the used hydrogel recovery. In this study, a steam-suction process was suggested for the used hydrogel recovery. Contaminated stainless steel surface, with fixed simulated fallout particles, was prepared for test. The simulated fallout particles were obtained by high-temperature treatment of a mixture of natural soil, used concrete, and Fe2O3. The hydrogel, composed of poly-vinyl alcohol and borax, was spread onto the contaminated stainless steel surface. The hydrogel was soft at first and it gradually becomes rigid with time. The used hydrogel was recovered by suction with a simultaneous steam spraying to soften the rigid gel. As a result, the clean surface of the stainless steel without the simulated fallout particles was obtained, showing the feasibility of this technique for the used hydrogel recovery.

Concrete radioactive waste is divided into surface-contaminated concrete and activated concrete, and although the generation rate varies depending on the operating conditions of the nuclear power plant, it is reported that the amount of surface-contaminated concrete generated is greater. It is reported in the ‘US-NRC Inventory Report’ that 99% of radionuclides in surface-contaminated concrete are distributed within 1 mm of the surface. Since concrete radioactive waste accounts for a large amount of generation after metal radioactive waste, it is necessary to reduce the amount of radioactive waste disposal by applying appropriate treatment techniques to surface-contaminated concrete. In this study, a similar contamination environment work space with the size of 5.4 (W) × 3.6 (L) × 2.5 (H) [m] in which concrete specimens can be fixed on the wall and floor was established. And an integrated decontamination equipment was verified the automation performance for ‘location accuracy’, ‘radioactive contamination level measurement’ and ‘concrete surface laser scabbling’. It was confirmed that the average was 8.3 [mm] in the evaluation of the ‘location accuracy’ for the remote control and movement of the integrated decontamination equipment. For performance verification of ‘radioactive contamination level measurement’ and ‘laser scabbling’, it were used that size of 30×30×8 [cm] ordinary concrete specimens and concrete radioactively contaminated with Co-60 below the regulatory exemption concentration. ‘Radioactive contamination level measurement’ is measured as much as the set range, divied and display the measured values in different colors on the map of the control program. Ordinary concrete specimens are 0.066~0.089 μ Sv/hr, and contaminated concrete specimens are 0.107~0.121 μ Sv/hr, and it was confirmed that they are expressed in different colors on the map. For ‘laser scabbling’, the performance according to the laser scabbling speed and reproducibility with ordinary concrete specimens was verified. As a result, a weight change of up to 1.48 kg was confirmed. Contaminated concrete specimens were subjected to a direct method using a surface contamination detector and an indirect method using a smear paper to measure surface contamination before and after scabbling, and the debris generated after scabbling was analyzed using HPGe.

A large amount of concrete radioactive waste is generated during the decommissioning of nuclear facilities, including nuclear power plants, and it is expected that the radioactive waste management expenses will be huge. In order to reduce the concrete radioactive waste, a decontamination or removal process is required, but working on concrete may present a risk of worker exposure in a high-radioactive space. Therefore, in this study, a remote control integrated decontamination equipment that can reduce concrete radioactive waste and ensure the safety of workers during the concrete decontamination process in a high-radioactive space was developed. The integrated decontamination equipment consists of remote movement, automatic surface contamination measurement, automatic surface decontamination and debris/dust removal systems. The remote movement system generates ‘mapping data’ of topographic features for the work space and ‘location data’ that coordinates the location of the integrated decontamination equipment through LiDAR (Light Detection and Ranging) sensor and SLAM (Simultaneous Localization And Mapping) technique. The user can check the location of the integrated decontamination equipment through ‘location data’ outside the work space, and can move it by remote control through wired/wireless communication. The automatic surface contamination measurement system uses a radiation detector and an automatic measurement algorithm to generate ‘surface measurement data’ based on the measurement distance interval and measurement time set by the user. ‘Surface measurement data’ is combined with ‘location data’ to create a visualized map of radioactive contamination, and users can intuitively realize the location and degree of contamination based on the map. The automatic surface decontamination system uses a laser and an automatic removal algorithm to decontaminate the concrete surface. Concrete debris and dust generated during this process were collected by the debris/dust removal system, minimizing waste generation and radiation exposure due to secondary pollution. The integrated decontamination equipment developed through this study was applied with technologies that reduced radioactive concrete waste and ensured the safety of workers. If technology verification and on-site applicability review are performed using concrete specimens simulating nuclear power plant or similar environments, it is reasoned to contribute to the domestic and overseas decommissioning industry.

핵연료 운반용 실린더의 재사용을 위한 용기세척공장의 제염공정에 대한 성능을 평가하기 위하여 Na2CO3 + H2O2 혼합용액의 조합을 약간 달리한 2회의 시험을 실행하였다. 각 시험은 모두 일련의 5 단계에 걸쳐 실시되었다. 우라늄 제염의 주 화학종은 Na4UO2(CO3)3 로 식별되었다. 그리고 첫 단계에서의 세척액은 물이었으며, 이 단계에서 50% 이상의 우라늄이 제염되었다. 그 이후로는 단계가 더해 갈수록 우라늄의 제염양은 지수함수적으로 감소하는 경향을 나타내었으며, 화학양론적으로 제거된 우라늄에 비하여 투여된 Na2CO3 의 양은 과다함을 나타내었다. 이러한 결과들에 의하면, 공정최적화를 통하여 Na2CO3 의 투여량 감축, 세척폐액의 감량, 제염단계 축소 등을 꾀할 수 있을 것으로 판단된다.

이 연구에서는 플라즈마 제염 기술의 실용화를 위해 , , 등의 반응성 플라즈마 기체를 이용하여 원자력 시설의 주요 오염원인 코발트 핵종에 대한 표면 제염 모의실험을 수행하였다. 디스크 형태의 금속코발트에 대하여 시편 표면 온도를 변수로 플라즈마 식각 실험을 수행한 결과 반응율은 에서 기체의 경우 그리고 와 기체의 경우 각각 과 이었으며, 이들 반응의 활성화에너지는 각각 39.4 kJ/mol, 42.1 kJ/mol, 116.0 kJ/mol이었다. 이와 함께 AES (Auger Electron Spectroscopy)를 이용하여 반응 생성물 성분 분석 결과 이들 반응의 주요 반응 기구는 코발트의 불화 반응임이 밝혀졌다. 이 연구를 통해 확보된 의 금속 표면 식각율은 주요 반도체 공정의 식각율을 뛰어넘는 높은 식각율로 플라즈마 제 염 기술의 실용화를 앞당길 수 있는 고무적인 결과라 할 수 있을 것이다.

원자력발전소가 폐로 단계에 도달하게 될 경우, 다량의 방사성물질 및 폐기물이 발생한다. 특히, 해체 시 발생되는 콘크리트 폐기물은 경제적, 환경적 측면을 고려해서 재사용, 재활용, 처분 등이 관리방법 중 가장 적합한 방법을 선정해야 한다. 원자력시설의 해체 시 발생하게 되는 콘크리트 폐기물은 80%이상을 차지하고 있으며, EC(European Commission)의 보고서에 의하면 2060년까지 원자력 시설의 해체에 따라 유럽에서만 약 500만 톤의 콘크리트 폐기물이 발생할 것으로 예상하고 있다. 이러한 막대한 양의 콘크리트 폐기물에 대해 프랑스, 일본, 벨기에 등에서는 이미 콘크리트 폐기물의 제염 및 저감에 대한 연구가 심도 있게 진행 중에 있으며 프랑스의 경우에는 실험적인 연구를 거쳐서 상용화 수준에 다다른 실정이다. 콘크리트 폐기물은 원자력시설에 제한적으로 재활용이 가능하며, 방사성 폐기물의 저장 및 기반시설의 건설, 방사성 폐기물 처리에 사용되는 콘크리트 고화체, shielding block, backfiller 등으로 사용되고 있다. 해체 콘크리트 폐기물은 용적오염과 표면 오염으로 이루어져 있으며 대부분 표면으로부터 약 1∼10mm 두께로 오염되어 있어 기계적 처리 방법을 통해 방사성 폐기물로서 처리되어야 한다. 방대한 양으로 발생되는 콘크리트 해체폐기물을 자체처분 하거나 재활용한다면 처분 대상 폐기물량의 감소로 인한 처분 비용의 절감 및 처분 안전성의 증대뿐만 아니라 자원의 재활용성을 증대시킨다는 점에서 매우 긍정적인 측면을 나타낸다. 원자력시설의 콘크리트 제염기술로는 물리적 방법을 사용한 제염기술이 주로 사용되며 이를 다시 세분화 하면 표면제염기술과 표면파쇄제염으로 구분된다. 방사성 콘크리트의 물리적 표면제염 공정 및 장치 선정시에는 오염확산 및 작업자의 방사능 피폭 최소화, 제염 폐기물의 최종 처리방법, 제염 작업 최적화를 위한 최단, 최소 작업과 장소, 대상, 목적 등을 고려하여 제염기술이 선정되어야 한다. 이는 곧바로 방사능 구역에서의 작업자의 안전성 향상 및 해체비용 절감과 직결되기 때문이다. 그러나 원자력이라는 특수한 상황에서는 최적의 기술 선정시 경제적인 측면 보다는 안전성에 바탕을 두고, 주위 환경이 오염을 최대한 억제하는 방법에 초점을 맞추어야 할 것이다.