Econ. Environ. Geol. 2023; 56(2): 167-183

Published online April 30, 2023

https://doi.org/10.9719/EEG.2023.56.2.167

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Review for Mechanisms of Gas Generation and Properties of Gas Migration in SNF (Spent Nuclear Fuel) Repository Site

Danu Kim1, Soyoung Jeon1, Seon-ok Kim3, Sookyun Wang3, Minhee Lee2,*

1Major of Earth and Environmental Sciences, Division of Earth Environmental System Science, Pukyong National University
2Major of Environmental Geosciences, Division of Earth Environmental System Science, Pukyong National University
3Department of Energy Resources Engineering, Pukyong National University

Correspondence to : *heelee@pknu.ac.kr

Received: February 17, 2023; Revised: March 22, 2023; Accepted: April 1, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

Gases originated from the final SNF (spent nuclear fuel) disposal site are very mobile in the barrier and they may also affect the migration of radioactive nuclides generated from the SNF. Mechanisms of gas-nuclide migration in the multi-barrier and their influences on the safety of the disposal site should be understood before the construction of the final SNF disposal site. However, researches related to gas-nuclide coupled movement in the multi-barrier medium have been very little both at home and abroad.
In this study, properties of gas generation and migration in the SNF disposal environment were reviewed through previous researches and their main mechanisms were summarized on the hydrogeological evolution stage of the SNF disposal site. Gas generation in the SNF disposal site was categorized into five origins such as the continuous nuclear fission of the SNS, the Cu-canister corrosion, the oxidation-reduction reaction, the microbial activity, and the inflow from the natural barriers. Migration scenarios of gas in porous medium of the multi-barrier in the SNF repository site were investigated through reviews for previous studies and several gas migration types including ① the free gas phase flow including visco-capillary two-phase flow, ② the advection and diffusion of dissolved gas in pore water, ③ dilatant two-phase flow, and ④ tensile fracture flow, were presented.
Reviewed results in this study can support information to design the further research for the gas-nuclide migration in the repository site and to evaluate the safety of the Korean SNF disposal site in view points of gas migration in the multi-barrier.

Keywords compacted bentonite, SNF disposal site, gas migration, multi-barrier, radioactive nuclide

사용 후 핵연료 처분장 내 가스의 발생 기작 및 거동 특성 고찰

김단우1 · 전소영1 · 김선옥3 · 왕수균3 · 이민희2,*

1부경대학교 지구환경시스템과학부 지구환경과학전공
2부경대학교 지구환경시스템과학부 환경지질과학전공
3부경대학교 에너지 자원공학과

요 약

사용 후 핵연료(SNF: spent nuclear fuel) 지하 처분장에서 발생된 가스는 처분장 내에서 자체로 이동성이 클 뿐 아니라, 처분장 내 방사성핵종 거동에도 영향을 줄 수 있다. 지하 처분장 방벽 내에서 가스-핵종 발생 및 거동 기작에 대한 연구와 가스 거동이 처분장의 안전성에 미치는 영향에 대한 연구가 처분장 건설 이전에 충분히 수행되어져야 함에도 불구하고, 처분장 다중 방벽 내 가스-핵종 거동에 대한 연구는 국내는 물론 국외에서 조차 매우 초보적인 단계이다.
본 연구에서는 지하 SNF 처분장 내 가스 발생과 거동 특성과 관련된 국내외 선행연구 결과들을 고찰하여, 가스 발생/거동 기작을 처분장의 수리지질학적 진화과정에 따라 분류하여 설명하였다. 처분장 내 가스 발생을 크게 SNF의 핵분열에 의한 방사성 가스 생성, SNF 저장 용기의 부식에 의한 가스 발생, 지하수의 산화-환원 반응에 의한 가스 생성, 미생물 활동과 천연 방벽 내 지화학적 반응에 의한 가스 생성 등 총 5가지 유형으로 구분하여 정리하였다. 처분장 다중 방벽 내 가스 거동과 관련된 선행연구자료들을 정리하여, 방벽 내 가스 거동 시나리오를 다공성 매체에서 일어나는 거동 형태에 따라, 총 4가지 형태(① visco-capillary 흐름을 포함하는 공극 내 자유상 가스 이동, ② 공극 수 내 용존상 기체로서 이류 및 확산 이동, ③ 체적팽창에 의한 거동(dilatant pathway), ④ 가압파쇄에 의한 인장 절리 흐름 등)로 구분하여 제시하였다.
본 연구를 통해 고찰한 SNF 처분장의 다중 방벽 시스템 내 가스 발생 기작과 거동 특성자료들은, 향 후 지하 SNF 처분장 내 가스-핵종 거동관련 다양한 실험 및 모델링 연구를 계획하고, 국내 건설할 처분장의 안전성을 가스 거동관점에서 평가하는데 유용하게 사용될 것으로 기대한다.

주요어 압축벤토나이트, 사용 후 핵연료 지하 저장소, 가스 거동, 다중 방벽, 방사성 핵종

Article

Review

Econ. Environ. Geol. 2023; 56(2): 167-183

Published online April 30, 2023 https://doi.org/10.9719/EEG.2023.56.2.167

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Review for Mechanisms of Gas Generation and Properties of Gas Migration in SNF (Spent Nuclear Fuel) Repository Site

Danu Kim1, Soyoung Jeon1, Seon-ok Kim3, Sookyun Wang3, Minhee Lee2,*

1Major of Earth and Environmental Sciences, Division of Earth Environmental System Science, Pukyong National University
2Major of Environmental Geosciences, Division of Earth Environmental System Science, Pukyong National University
3Department of Energy Resources Engineering, Pukyong National University

Correspondence to:*heelee@pknu.ac.kr

Received: February 17, 2023; Revised: March 22, 2023; Accepted: April 1, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

Gases originated from the final SNF (spent nuclear fuel) disposal site are very mobile in the barrier and they may also affect the migration of radioactive nuclides generated from the SNF. Mechanisms of gas-nuclide migration in the multi-barrier and their influences on the safety of the disposal site should be understood before the construction of the final SNF disposal site. However, researches related to gas-nuclide coupled movement in the multi-barrier medium have been very little both at home and abroad.
In this study, properties of gas generation and migration in the SNF disposal environment were reviewed through previous researches and their main mechanisms were summarized on the hydrogeological evolution stage of the SNF disposal site. Gas generation in the SNF disposal site was categorized into five origins such as the continuous nuclear fission of the SNS, the Cu-canister corrosion, the oxidation-reduction reaction, the microbial activity, and the inflow from the natural barriers. Migration scenarios of gas in porous medium of the multi-barrier in the SNF repository site were investigated through reviews for previous studies and several gas migration types including ① the free gas phase flow including visco-capillary two-phase flow, ② the advection and diffusion of dissolved gas in pore water, ③ dilatant two-phase flow, and ④ tensile fracture flow, were presented.
Reviewed results in this study can support information to design the further research for the gas-nuclide migration in the repository site and to evaluate the safety of the Korean SNF disposal site in view points of gas migration in the multi-barrier.

Keywords compacted bentonite, SNF disposal site, gas migration, multi-barrier, radioactive nuclide

사용 후 핵연료 처분장 내 가스의 발생 기작 및 거동 특성 고찰

김단우1 · 전소영1 · 김선옥3 · 왕수균3 · 이민희2,*

1부경대학교 지구환경시스템과학부 지구환경과학전공
2부경대학교 지구환경시스템과학부 환경지질과학전공
3부경대학교 에너지 자원공학과

Received: February 17, 2023; Revised: March 22, 2023; Accepted: April 1, 2023

요 약

사용 후 핵연료(SNF: spent nuclear fuel) 지하 처분장에서 발생된 가스는 처분장 내에서 자체로 이동성이 클 뿐 아니라, 처분장 내 방사성핵종 거동에도 영향을 줄 수 있다. 지하 처분장 방벽 내에서 가스-핵종 발생 및 거동 기작에 대한 연구와 가스 거동이 처분장의 안전성에 미치는 영향에 대한 연구가 처분장 건설 이전에 충분히 수행되어져야 함에도 불구하고, 처분장 다중 방벽 내 가스-핵종 거동에 대한 연구는 국내는 물론 국외에서 조차 매우 초보적인 단계이다.
본 연구에서는 지하 SNF 처분장 내 가스 발생과 거동 특성과 관련된 국내외 선행연구 결과들을 고찰하여, 가스 발생/거동 기작을 처분장의 수리지질학적 진화과정에 따라 분류하여 설명하였다. 처분장 내 가스 발생을 크게 SNF의 핵분열에 의한 방사성 가스 생성, SNF 저장 용기의 부식에 의한 가스 발생, 지하수의 산화-환원 반응에 의한 가스 생성, 미생물 활동과 천연 방벽 내 지화학적 반응에 의한 가스 생성 등 총 5가지 유형으로 구분하여 정리하였다. 처분장 다중 방벽 내 가스 거동과 관련된 선행연구자료들을 정리하여, 방벽 내 가스 거동 시나리오를 다공성 매체에서 일어나는 거동 형태에 따라, 총 4가지 형태(① visco-capillary 흐름을 포함하는 공극 내 자유상 가스 이동, ② 공극 수 내 용존상 기체로서 이류 및 확산 이동, ③ 체적팽창에 의한 거동(dilatant pathway), ④ 가압파쇄에 의한 인장 절리 흐름 등)로 구분하여 제시하였다.
본 연구를 통해 고찰한 SNF 처분장의 다중 방벽 시스템 내 가스 발생 기작과 거동 특성자료들은, 향 후 지하 SNF 처분장 내 가스-핵종 거동관련 다양한 실험 및 모델링 연구를 계획하고, 국내 건설할 처분장의 안전성을 가스 거동관점에서 평가하는데 유용하게 사용될 것으로 기대한다.

주요어 압축벤토나이트, 사용 후 핵연료 지하 저장소, 가스 거동, 다중 방벽, 방사성 핵종

    Fig 1.

    Figure 1.Status of the temporary SNF (spent nuclear fuel) storage in Korea (from KHNP, 2023)(PHWR: Pressurized heavy water reactor, PWR: Pressurized water reactor).
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 2.

    Figure 2.Multi-barrier system of KBS-3 type for the SNF disposal (modified from POSIVA, 2020).
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 3.

    Figure 3.Distribution chart of fission products and crack distributed in SNF Rods (left), cross section of SNF rod (upper right), and photo of gas bubbles present on the surface of SNF rods UO2 particles (lower right) (from Ewing, 2015).
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 4.

    Figure 4.Decomposition of water molecules by X-rays and the generation mechanism of H2 (modified from Wada et al., 1995).
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 5.

    Figure 5.Structure of SNF rod iron casting support and copper canister used in the SNF repository of Finland (modified from Smart et al., 2002).
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 6.

    Figure 6.Corrosion reaction of copper canister contacted with groundwater in an oxidized environment.
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 7.

    Figure 7.Pitting corrosion from metal surface (modified from D&DCOATINGS, 2023).
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 8.

    Figure 8.H2 corrosion mechanism occurring on the metal surface and inside (modified from Ustolin, 2020).
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 9.

    Figure 9.Corrosion on surface of copper canister by dissolved O2 in groundwater (oxidized environment).
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 10.

    Figure 10.Corrosion and H2 gas generation due to reaction with sulphide ions in groundwater on the surface of copper canister (reduction environment).
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 11.

    Figure 11.H2 generation by redox reaction on the surface of cast-iron insert.
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 12.

    Figure 12.Microbial decomposition mechanisms of organic matter according to the presence or absence of sulfate (a: presence of sulfate, b: absence of sulfate) (modified from Thaue et al., 1977; Muyzer and Stams, 2008).
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 13.

    Figure 13.Transportable path of gas generated in the SNF repository.
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Fig 14.

    Figure 14.Evolution process of the SNF repository and the gas generation mechanism for each evolution stage.
    Economic and Environmental Geology 2023; 56: 167-183https://doi.org/10.9719/EEG.2023.56.2.167

    Table 1 . Generation and consumption of H2 from the natural barrier origin.

    MechanismReaction formulaReferences
    GenerationConsumption
    Radiation decomposition of water moleculesH2O → 2H· + O·
    2H· → H2
    Vértes et al. (2003)
    Serpentinization of olivine6Mg1.8Fe0.2SiO4 + 8.2H2O →
    1.8Mg(OH)2 + 3Mg3Si2O5(OH)4 + 0.4Fe3O4 + 0.4H2
    McCollom et al. (2016)
    Oxidation of H22H2 + O2 → 2H2O(almost impossible)Delos et al. (2010)
    Sulfate reduction4H2 + 2H+ + SO42- →H2S + 4H2OHao et al. (1996)
    Methane synthesis reaction of Fischer-TrophschCO2 + 4H2 → CH4 + 2H2OBougault et al. (1993), Schoell (1988), Sherwood et al. (1993), Whiticar (1990)
    Acetic acid generation / carbonate reduction2CO2 + 4H2 → CH3COOH + 2H2ODelos et al. (2010)

    Table 2 . Generation and consumption of CH4 from the natural barrier origin.

    MechanismReaction formulaReferences
    GenerationConsumption
    CH4 generation / carbonate reductionCO2 + 4H2 → CH4 + 2H2ODelos et al. (2010)
    CH4 generation by FermentationCH3COOH → CH4 + CO2
    Methane synthesis reaction of Fischer-TrophschCO2 + 4H2 → CH4 + 2H2OBougault et al. (1993), Schoell. (1988), Sherwood et al. (1993), Whiticar. (1990)
    Low-grade metamorphismC + 2H2 → CH4Delos et al. (2010)
    Oxidation of CH4CH4 + 2O2 → CO2 + 2H2O
    Sulfate reduction / CH4 oxidationCH4 + SO42- → HCO3- + HS- + H2OHao et al. (1996)
    Iron reduction / CH4 oxidation8Fe3+ + CH4 + 2H2O → 8Fe2+ + 8H+ + CO2Delos et al. (2010)

    Table 3 . Microbial decomposition mechanism in anaerobic environment.

    MechanismReaction formulaGenerative energy (ΔGo : kJ/reaction)References
    Sulfate reduction reaction4H2 + SO42– + H+ → HS– + 4H2O-151.9Thaue et al. (1977)
    Acetate– + SO42– → 2 HCO3– + HS–-47.6
    Propionate + 0.75SO42- → Acetate- + HCO3- + 0.75HS- + 0.25H+-37.7
    Butyrate- +0.5SO42- → 2Acetate- + 0.5HS- + 0.5H+-27.8
    Lactate- + 0.5SO42- → Acetate- + HCO3- + 0.5HS--80.2
    Acetic acid generation reactionPropionate- + 3H2O → Acetate- + HCO3- + H+ + 3H2+76.1
    Butyrate- + 2H2O → 2Acetate- + H+ + 2H2+48.3
    Lactate- + 2H2O → Acetate- + HCO3- + H+ + 2H2-4.2
    CH4 Generation reaction4H2 + HCO3- + H+ → CH4 + 3H2O-135.6
    Acetate- + H2O → CH4 + HCO3--31.0
    Self-acetic acid production reaction4H2 + 2HCO3- + H+ → Acetate- + 4H2O-104.6
    Lactate- → 1.5Acetate- + 0.5H+-56.5

    KSEEG
    Apr 30, 2024 Vol.57 No.2, pp. 107~280

    Stats or Metrics

    Share this article on

    • kakao talk
    • line

    Related articles in KSEEG

    Economic and Environmental Geology

    pISSN 1225-7281
    eISSN 2288-7962
    qr-code Download