초록 ▼

○ PyroGreen은 사용후핵연료 전량을 관리기간 300년 내의 안전성, 핵안보성 및 핵비확산성을 갖는 중준위폐기물로 제염. 달성된 제염계수는 U 및 TRU에 대해 20,000, Cs 및 Sr에 300, Tc 및 I에 50, Zr 피복관내 TRU 및 Cs에 각각 67 및 7이며 이를 실험 및 모델로 입증함

○ 핵심개발기술은 불화염 기반 산화물 직접전해환원법, 용융결정화 정제공정, 불화염 기반 Zr 전해정련공정, Bi 기반 악티나이드 고성능 제염 공정, 저유실 제염 용기, 민감 물성 도출용 제일원리 원자모델, 공정성능해

○ PyroGreen은 사용후핵연료 전량을 관리기간 300년 내의 안전성, 핵안보성 및 핵비확산성을 갖는 중준위폐기물로 제염. 달성된 제염계수는 U 및 TRU에 대해 20,000, Cs 및 Sr에 300, Tc 및 I에 50, Zr 피복관내 TRU 및 Cs에 각각 67 및 7이며 이를 실험 및 모델로 입증함

○ 핵심개발기술은 불화염 기반 산화물 직접전해환원법, 용융결정화 정제공정, 불화염 기반 Zr 전해정련공정, Bi 기반 악티나이드 고성능 제염 공정, 저유실 제염 용기, 민감 물성 도출용 제일원리 원자모델, 공정성능해석용 멀티스케일모델, 정상 및 사고 시나리오의 안전-안보-비확산 평가법, 및 중준위폐기물 유리화 공정임

○ 실험-공정해석-원자모델 삼위일체 검증으로 PyroGreen 공정 목표 제염계수 충족함을 한국원자력연구원 참여하에 국내-국제검증 완료함

○ 핵변환-분리 분야 세계 최고권위자로 구성된 PyroGreen 국제검증위원회(PGIF)의 2년간 심층평가 받음. PGIF 최종검증보고서는 사용후핵연료 전량 중준위화로 300년 관리 후 안전성, 핵안보성 및 핵비확산성 충족함을 실험실 규모로 확인하고, 실증규모 연구를 권고하며, 본 고준위처분장 불필요화 기술의 혁신성, 실용성 및 필요성을 높이 평가하고 공동연구를 희망함

(출처 : 보고서 요약서 3p)

Abstract ▼

The management of Spent Nuclear Fuel (SNF) and/or High Level Waste (HLW) from reprocessing has become one of major challenges of all countries that have produced nuclear electricity. Disposal of SNF and/or HLW has been delayed by the opposition of general public in most countries due to uncertaintie

The management of Spent Nuclear Fuel (SNF) and/or High Level Waste (HLW) from reprocessing has become one of major challenges of all countries that have produced nuclear electricity. Disposal of SNF and/or HLW has been delayed by the opposition of general public in most countries due to uncertainties with the long-term safety and environmental impact on biosphere outside repositories. PyroGreen technology to eliminate SNF is motivated to avoid potential future safety and proliferation problems with the geologic disposal of SNF/HLW. The significant future risk has been identified in this study based on Markov chain process modeling caused by the increasing likelihood of clandestine plutonium mining and inadvertent human intrusion especially in countries with high population densities. Based on the magnitude of long-term safety and security challenges with direct disposal of SNF and reprocessed HLWs it has been concluded that it is necessary to develop innovative partitioning and transmutation technology to eliminate them. An innovative partitioning technology designated as PyroGreen has been developed to this end by advancing the current pyrochemical technology of the Korea Atomic Energy Research Institute, Korea. This study is aimed at demonstrating the viability of eliminating SNF/HLW leaving behind only wastes that can resolve potential problems, by means of independent expert review process by domestic evaluation and international evaluation, respectively.

The development of PyroGreen technology can improve public acceptance to the waste disposal approaches in countries with high population densities where it can be very difficult to find a disposal site for SNF and/or HLW that can meet requirements for radiological safety criteria for both normal scenario involving the leaching-migration of long-living radionuclides as well as human intrusion scenarios. Paucity of human knowledge on natural phenomena and human behaviors over unprecedented long period for adequate decays casts serious doubts on the assurance for radiological safety, nuclear safeguards and security of future generations.

HLW produced from conventional Partitioning and Transmutation (P&T) approach is not significantly safer than existing SNF/HLW, although the reduction of repository footprint can marginally save the risk of human intrusion.

PyroGreen technology presented herein from lab-scale experiments and connecting models is dodged on the fact that there are success experiences with ILW repositories that require only a few hundred years for institutional control. The U.S. Waste Isolation Pilot Plant in Carlsbad, New Mexico is an outstanding proof as brought to public attention by the U.S. Blue Ribbon Commission for America’s Nuclear Future. The WIPP as an Greater Than Class C Low Level Waste (ILW in IAEA classification) repository has been licensed, publically accepted, constructed and operated with safety, security and safeguards criteria satisfied for both normal and breakout scenarios after a few hundred tears of the institutional control period even with non-negligible quantities of long-living actinides. Building new ILW repositories can publically accepted considering the technical confidence and the fact that ILW are and will be produced from medical and manufacturing industries in large quantities. This contrasts technically and even politically to the case of SNF/HLW repositories.

The present research group has arrived at the conclusion that PyroGreen approach to eliminate SNF/HLW has been proven its lab-scale viability and has adequate potential for industrialization in the future with justifiable risk and benefits. This study is based on the assumption that the viability of innovative partitioning is vital to a central question that if SNF and HLW can be decontaminated into the cleanliness standards of ILW by the innovative partitioning, transmutation and disposal (APTAD) system.

Therefore, this report describes scientific and technical evidences for the viability of an innovative partitioning technology that we designated as PyroGreen.

PyroGreen is an indigenous pyrochemical partitioning technology that is designed to decontaminate all HLW streams from SNF recycling as well as from P&T only to leave ILW that meets the acceptance criteria of the U.S. WIPP. The WIPP has proved adequate safety margin to both migration dose and human intrusion risk. Required Decontamination factors (DFs) for PyroGreen to decontaminate SNF into the WIPP waste standards are determined to be 20,000 for TRU, 50 for both Tc, I, 300 for both Cs and Sr and 67 for TRU in Zr hull.

In this report, the technical feasibility of achieving the DF goals and hence of satisfying key disposal criteria including safety, security and safeguards has been assessed by a combination of available lab-scale experimental data and computer modeling. Since the start of the second period of this project in 2014, PyroGreen flowsheet has been modified to employ fluoride salt in Zr-electrorefining and SNF direct reduction processes while keeping eutectic chloride salts in most processes. The flowsheet has been compared on the repository performance in this viability study with respect to the Korean P&T scenario of KIEP-21 based on the pyroprocessing technology of KAERI that is designed to remove 99.9% of TRU from SNF, i.e, DF of 1,000.

PyroGreen flowsheet has been advanced from KAERI’s pyroprocessing flowsheet by replacing liquid cathode materials from cadmium with bismuth and by introducing fluoride salt for oxide used fuel reduction and Zr-hull decontamination as well as salt zone refining for salt recycling with enhanced removal of Cs and Sr. The head-end processes including SNF chopping and voloxidation are taken from KAERI’s flowsheet as granted because they are already demonstrated in KAERI’s DUPIC program. The use of bismuth liquid cathode enables advanced stripping of actinides while retaining fission products in salts, leading to the development of PyroRedSox process. PyroRedsox as the key element of the PyroGreen process transfers U, TRU and rare earth (RE) elements in molten salt into liquid Bi cathode by reductive electrolysis. At the second stage, RE elements are electrochemically oxidized or via the titration with BiCl3. By PyroRedSox, it is shown to achieve PyroGreen DF goals on TRU.

Bismuth like cadmium produces intermetallics with actinides, making the production of pure plutonium difficult, providing inherent proliferation-resistance. For the institutional assurance of proliferation-resistance, this report suggests a multilateral approach to both R&D and industrialization of PyroGreen using active nuclear fuels.

The introduction of LiF salt was necessary to achieve adequate electro-reduction of used oxide pellets for achieving DF goals for fission products. Zr-hull electrorefining and recovery of trace actinides can facilitate drastic volume reduction of PyroGreen ILW by recycling decontaminated zirconium for nuclear applications. In Zr-hull electrorefining, the chopped cladding is decontaminated and Zr is recovered by electrochemical reactions in the LiCl-KCl molten salt. This process would considerably decrease the volume of the final wastes.

Goals on decontamination factors (DF) to meet the WIPP Waste Acceptance Criteria and the achievable DF from this viability study for PyroGreen are summarized in Table 1. By utilizing experimental data and benchmarked computer models, achievable DF for U and TRU is found to be about 100,000 or five times higher than the goal. It is shown that DF for Cs can meet its goal of 300 by the demonstrated recovery 98% of Cs in voloxidation followed by 90% of residual Cs through salt zone refining.

DF for Sr can reach as high as 2,500 compared with its goal of 300 by recovering 99.6% of Sr in carbonization process followed by 90% additional recovery via zone refining. Zr hull electrorefining is also shown to meet its decontamination goals. The final RE wastes from PyroredSox are vitrified by using dedicated glass composition to meet the WIPP waste acceptance criteria.

Since PyroGreen requires very high decontamination factors it is necessary to limit hide-out within the facilities and leakages of important element out of all process lines. Hide-out can be recovered by periodic decontamination of all metallic surface based on past experiences with ITU experimental facilities. Hide-out into non-metallic surfaces can be minimized by surface treatment of porous ceramic crucibles by using new materials developed in this work. Leakage through crucible discharge can be reduced by the prevention of cracking and fracture of pyrochemical apparatus by employing an isothermal operation scheme for the electrorefiner. All additional hide-out and leakages during transfer between processes are expected to be recoverable during clean-up and materials accounting within heavily-shielded hot-cell with negative pressure requirement, based on past laboratory experiences.

PyroGreen waste is shown to meet WIPP requirements both on alpha-emitter concentration and heat density of waste packages and the safety characteristics of PyroGreen ILW geologic repository satisfies biosphere dose criteria of ROK and IAEA, as compared in Table 2 from both deterministic and probabilistic simulation using GoldSim®.

In summary, results of this PyroGreen viability study utilizing both lab-scale experiments and advanced computer simulations showed that the goals on decontamination factor can be reached to meet the WIPP waste standards radiological safety limits as well as nuclear security limits even in the event of clandestine human intrusion. The viability study has been made specifically for the Korean PWR SNF P&T scenario, called KIEP-21.

KAERI’s pyroprocessing with the goal of 99.9% TRU removal for burning recovered TRU in sodium fast reactors assumes that HLW streams with reduced footprint can significantly expand the capacity of a geologic repository where SNF from CANDU will have to be directly disposed of.

Both HLWCANDU SNF can be decontaminated by PyroGreen to leave only ILW that meet the WIPP standards. During this viability study it was also understood that the characteristics of all new processes of PyroGreen is within the reach of technical capability in the scale-up of conventional pyroprocess being developed worldwide.

(출처 : SUMMARY 16p)

목차 Contents

• 표지 ... 1제 출 문 ... 2보고서 요약서 ... 3요 약 문 ... 5SUMMARY ... 16CONTENTS ... 21목차 ... 22표목차 ... 23그림목차 ... 25제 1 장 연구개발과제의 개요 ... 33 제 1 절 연구개발의 목적 및 필요성 ... 33 제 2 절 연구개발의 최종 목표 ... 44 제 3 절 연구개발의 방법 ... 48제 2 장 국내외 기술개발 현황 ... 57 제 1 절 국외 기술개발 현황 ... 57 제 2 절 국내 기술개발 현황 ... 73제 3 장 연구개발수행 내용 및 결과 ... 80 제 1 절 Direct Oxide Reduction ... 80 제 2 절 고발열성 Cs 및 Sr 분리를 위한 용융결정화 공정(Zone Refining) ... 88 제 3 절 지르칼로이 피복관 전해정련 ... 118 제 4 절 폐용융염 내 악티나이드 분리공정 (PyroRedSox) ... 128 제 5 절 전해제련용 액체금속 반응용기 소재 기술 개발 ... 156 제 6 절 PyroGreen 중준위폐기물 유리화 공정 ... 169 제 7 절 Ab-initio 및 멀티스케일 전산모델 ... 176 제 8 절 방사성폐기물의 지질학적 처분 장기 안전성 평가 ... 202 제 9 절 방사성폐기물 심지층 처분의 핵확산저항성 평가 ... 214제 4 장 목표달성도 및 관련분야에의 기여도 ... 222제 5 장 연구개발결과의 활용 계획 ... 226제 6 장 연구개발과정에서 수집한 해외과학기술정보 ... 228제 7 장 참고문헌 ... 231연구성과(연구사업지원시스템 입력성과) ... 241끝페이지 ... 246