Vol.27 No.2

研究論文

原子力バックエンド研究

Methodology Development and Determination of Solubility-limiting Solid Phases
for a Performance Assessment of Geological Disposal of High-level Radioactive andTRU Wastes
Akira KITAMURA*1

Yasushi YOSHIDA*2

Takahiro GOTO*3

Sanae SHIBUTANI*3

高レベル放射性廃棄物および地層処分相当の TRU 廃棄物の地層処分システムの性能を評価するためには，地下水や緩衝材間隙水中における放射性核種の溶解度評価が必要である．その溶解度評価のためには，溶解度を制限する固相（溶解度制限固相）を選定する必要がある．本報告では，透明性の高い選定過程が示せるように，熱力学データベースを用
いて溶解度制限固相の候補となる固相の飽和指数を算出することで溶解度制限固相を判断する選定手法を構築した．本
手法では，飽和指数が大きい固相ほど溶解度制限固相の候補になることを基本とするものの，当該固相の生成や溶解度制限が現実的であるかどうかについて，文献調査により判断することとした．併せて，わが国における最新の安全評価報告書で定義された緩衝材およびセメント間隙水組成に対し，種々の組成を類型化した上で性能評価対象元素の溶解度
制限固相を選定した．
Keywords: 高レベル放射性廃棄物，TRU 廃棄物，地層処分，溶解度，溶解度制限固相，熱力学データベース
Evaluation and estimation of solubility values are required for a performance assessment of geological disposal of high-level
radioactive and TRU wastes. Selection of solubility-limiting solid phases (SSPs) that control the solubility of radionuclides isnecessary for the evaluation and estimation of solubility values. The authors have developed a methodology for selection of the SSP
through a calculation of saturation indices (SIs) using thermodynamic database to show a transparent procedure for the selection.
Literature survey has been performed to confirm decision of the SSP from candidate SSPs which generally have larger SIs fromrealistic point of view for precipitation and solubility control. The authors have selected the SSPs for the elements of interest for thelatest Japanese performance assessment in bentonite and cement porewaters after grouping various water compositions.
Keywords: high-level radioactive waste, TRU waste, geological disposal, solubility, solubility-limiting solid phase,thermodynamic database

Introduction

1

pessimistically assumed to be soluble for the other projects thanthe Swiss and Japanese projects shown in Table 1.

1.1

BackgroundAll of the projects have been using a TDB for prediction of

Significant amount of various radionuclides are contained inradionuclide solubility (aqueous concentration limit) as shown in

high-level radioactive waste (HLW) and TRU waste packages,

Table 1. It is necessary to select a solubility-limiting solid phaseand some of them have long-lived toxicity (e.g. with half-lives(SSP) for the prediction of radionuclide solubility when using themore than 104 years), which requires isolating it from the

TDB. Selection of the SSP, however, is usually performed by an

biosphere for many hundreds of thousands of years. An

expert judgement (e.g. [3]) and is not always traceable.

international consensus has emerged that such isolation can best

Therefore the authors have developed a methodology for

be provided by disposal of the waste in geologic repositories (e.g.

selection of SSP for the HLW-PA and the TRU-PA using a TDB.

[1]), a strategy that today is pursued by most countries inpossession of nuclear waste. Latest projects for performance

1.2

Brief Review of Thermodynamic Databases(and/or safety) assessments (PAs) of geological disposal of HLW

Thermodynamic database is a set of collected numerical valuesin European and North American countries as well as Japan are

related to thermodynamic properties for substances, e.g., Gibbs

summarized in Table 1, with showing brief content of bentonite

free energy, enthalpy, entropy, heat capacity, equilibrium constantporewater compositions in reference (main or basic) cases forafter checking their internal consistency. There are some TDBs

prediction of radionuclide solubility and thermodynamic

specialized for PA of radioactive waste management.

databases (TDBs) used for the PA for HLW (HLW-PA). In

The Nuclear Energy Agency (NEA) within Organisation forcontrast, only Swiss and Japanese projects have predicted theEconomic Co-Operation and Development (OECD) initiated anradionuclide solubility for PA for TRU waste (TRU-PA) (or aninternational collaborative project on development of TDB

intermediate-level waste (ILW-PA) for some countries) (e.g. [2])(NEA-TDB) for radioactive waste management in 1984 [4].

as shown in Table 2, while all elements of interest have been

Chemical thermodynamic series (so-called “Blue Books”) havebeen published and updated for iron (Fe) [5, 6], nickel (Ni) [7],高レベル放射性廃棄物および TRU 廃棄物の地層処分の性能評価のための溶解度制限固相の選定手法の構築および選定
北村暁（kitamura.akira@jaea.go.jp），吉田泰，後藤考裕，澁谷早苗＊1 国立研究開発法人日本原子力研究開発機構
Japan Atomic Energy Agency〒319-1194 茨城県那珂郡東海村村松 4-33
＊2 株式会社 NESINESI Company Limited〒312-0005 茨城県ひたちなか市新光町 38 番地＊3 原子力発電環境整備機構
Nuclear Waste Management Organization of Japan
〒108-0014 東京都港区芝 4-1-23(Received 22 June 2020; accepted 28 August 2020)selenium (Se) [8] zirconium (Zr) [9], technetium (Tc) [10], tin(Sn) [11], thorium (Th) [12], uranium (U) [10], neptunium (Np)[10] , plutonium (Pu) [10] and americium (Am) [10], and those of
selected organic ligands [13]. All selected thermodynamic data
(Gibbs free energies, enthalpies, entropies, heat capacities andequilibrium constants) have been based on those obtained fromexperimental studies, critically reviewed, sometimes integrated
and referred to a standard state (at 298.15 K, zero ionic strength,58

December 2020

原子力バックエンド研究

Table 1 Brief content of reference (mainly bentonite) porewater compositions for interest of solubility prediction andthermodynamic databases used for a reference case in HLW-PA
Country

Project Name

SwedenSR-Site(Forsmark)Finland

Switzerland

TURVA-2012(saline)
TURVA-2012(blackish)
EN 2002
SGT-E2

FranceDossier 2005

Spain

ThermoChimie

USA

YMP-SAR

Canada
Japan

Publ.
Year
2011

pH

redox potential(Eh; mV vs. SHE)

TIC *1(mol dm3)

ref.

Nagra/PSI-TDB 01/01 [14] +NEA-TDB of Ni [7], Zr [9], Th[12], U [10] + Newly developed
Pb [15][3, 15]

ThermoChimie [16] v.7b

[17]

Nagra/PSI-TDB 01/01 [14]Nagra/PSI-TDB 12/07 [20][18, 19]
[21]

7.1

-130

0.153

7.94

-232

5.210-4

7.33

-163

1.0510-3

-193
-204
-180 –-150-179
oxidizing(fO2 = 0.2 bar)

2.8310-3
8.99410-4
7.510-4 –3.410-3
2.9510-3(2.1 ± 0.1)
10-3

ThermoChimie [16] v5.

[22]

ThermoChimie [16] v9.
data0.ymp.R2 and data0.ymp.R4
data0.yc3.R1

[16]

-200

1.110-3

ThermoChimie [16] v.7b

[24]

-280

1.710-2

JAEA-TDB (in 2014) [25]

[26]

2012
2002
2014

7.25
7.79
6.9 –
2005
7.6
2015
7.2
7.41
2008
± 0.44

the Fourth Case
2012
Study
SF-1
2015

TDB

7.0
8.4

[23]

*1Concentration of total inorganic carbon

Table 2 Brief content of cement porewater compositions for interest of solubility prediction and thermodynamic databases
used for a reference case in ILW-PA and TRU-PA
Country

Project Name

Publ.
Year

pH

SwitzerlandJapan

EN 2002
Cement PRJ.

2002
2015

13.44
13.2

Switzerland
SwitzerlandJapan

EN 2002
SGT-E2
Cement PRJ.

2002
2014
2015

12.55
12.54
12.5

Japan

Cement PRJ.

2015

11.4

Eh
TIC
(mV vs. SHE)
(mol dm3)
Region (Stage) I-430
2.0410-4-258
7.310-5
Region (Stage) II-230
9.7410-6-498
8.06410-6-240
1.210-6
Region (Stage) III-208
2.310-5

TDB

ref.

Nagra/PSI-TDB 01/01 [14]JAEA-TDB (in 2014) [25]

[27]
[28]

Nagra/PSI-TDB 01/01 [14]Nagra/PSI-TDB 12/07 [20]JAEA-TDB (in 2014) [25]

[27]
[29]
[28]

JAEA-TDB (in 2014) [25][28]

0.1 MPa). Thermodynamic data have been critically reviewed anddocumented [14, 20], while only the selected data and theirselected on the basis of the NEA’s guidelines [4], and somereferences for the ThermoChimie has been published [16].

thermodynamic values on chemical species of importance for PA

Similar TDB has also been developed in the United States [23].

have not been selected due to low reliability of the value even

Most of the PA reports by European and North American

though the data are important for PA of the geological disposal.

countries have adopted to use either Nagra/PSI-TDB [14, 20] or

The Paul Scherrer Institut (PSI) in Switzerland and National

ThermoChimie [16] as shown in Tables 1 and 2.

Agency for Radioactive Waste Management (ANDRA) in France

Another TDB for PA of radioactive waste management has

have developed, published and updated their own TDBs for PA ofbeen developed by Japan Atomic Energy Agency (JAEA) [25, 30,

radioactive waste management (Nagra/PSI-TDB [14, 20] and31]. This (JAEA-)TDB has been appeared as JNC-TDB in 1999

ThermoChimie [16], respectively). Both TDBs have been[32], and updated after reviewing and selecting new data. Similar

developed with using the data selected by the NEA [5-13] andto Nagra/PSI-TDB [14, 20] and ThermoChimie [16], additional

additional thermodynamic data due to insufficiency for prediction

thermodynamic data have been selected. Features of JAEA-TDB

of solubility and speciation of radionuclides using selected dataare (1) a guideline for review and selection of thermodynamic

by the NEA [5-13] only. Most of thermodynamic data selected indata has been established [30], and (2) re-review of selected data

these TDBs are equilibrium constants, and some enthalpies forby the NEA [7-13], especially for tetravalent metal ions (Zr [9],reaction have also been selected. Detail of procedure for selection

Tc(IV) [10] and actinides(IV) [10, 12]). Selection ofof thermodynamic data for the Nagra/PSI-TDB has been wellthermodynamic data other than equilibrium constants should be a59

Methodology Development and Determination of Solubility-limiting Solid Phases for a Performance Assessment of Geological
Disposal of High-level Radioactive and TRU Wastes
future task.

Neogene sedimentary,

Use of reliable TDB is important for reliable PA of radioactive–

waste management. The authors have adopted to use the latest

Two types of chloride concentration in groundwater: Low
and high,

update (at that time) of JAEA-TDB published in 2014 [25]–Two types of cement porewater: Regions I and II, andbecause of inclusion of the latest review and selection of–Four groups of TRU waste packages: Groups 1, 2, 4H andthermodynamic data and comprehensiveness of thermodynamic

4L.

data on solid phases (i.e. potential SSP). The same candidate SSPs
have been selected in the latest update of JAEA-TDB publishedIn the present study, various water compositions of interestin 2019 [31].

have been categorized to 7 groups by pH range by the authors asshown in Table 3. The composition of “bentonite porewater” is2

Procedure for Selection of Solubility-limiting Soliddefined as that of the bentonite porewater at glass/overpack

Phaseinterface (i.e. after contacting corrosion products of overpacks)
hereafter in the present study. The categorization of pH range is

2.1

Summary of Fundamental Information

based on the previous observation that four indices (pH, Eh, TIC

Before trying solubility estimation, fundamental information,and total sulfur concentration) are mainly affecting solubility ofe.g., water composition, elements of interest, applicability ofradionuclides in a water composition [34]. Furthermore, thethermodynamics to a system for radioactive waste management

composition of bentonite porewater in high pH range shown inshould be established. Furthermore, application of chemical

Table 3 has been divided into 3 groups using lower and upper

analogues, coprecipiation and formation of solid-solution, highlimits of pH and Eh values, because the range of these values istemperature conditions, correction of activities, effect of pressures,still wide for evaluation of SSPs. The combination of pH and Ehetc., should also be discussed and concluded before performing

values of divided bentonite porewater in high pH range is defined

thermodynamic calculations.

as (1) maximum pH and minimum Eh, (2) minimum pH and

Various compositions of bentonite and cement porewaters havemaximum Eh, and (3) maximum pH and maximum Eh. The

been proposed in the latest safety assessment report for Japanese

authors did not consider another combination of (4) minimum pH

geological disposal of HLW and TRU waste [33] as follows:

and minimum Eh since the combination of minimum pH (= 7.1)
and minimum Eh (= -4.1102 mV) is unlikely due to very strong–

Two types of bentonite porewater. Before and after

reducing conditions to produce hydrogen gas.

contacting corrosion products of overpacks,–

Selection of elements of interest are selected on the basis of (1)Three rock types: Plutonic, Neogene sedimentary and Pre-RNs with half-lives longer than 1 y and (2) their radioactivity

Table 3 Bentonite and cement porewater compositions for selection of SSP for PA for HLW in the NUMO-SC [33] categorized
by pH range by the authors
Waste type HLW
TRU waste
Cement porewater
Bentonite porewater
Water typeat glass/overpack interface
Region I
Region II
pH range Lower
HigherLower
HigherLower
MiddleHigherpH
6.2 ~ 6.6
7.1 ~ 9.8
12.6 ~ 12.7
13.2 ~ 13.3
11.7 ~ 11.8
12.3 ~ 12.4
12.8 ~ 12.9
Eh (mV)-(1.7~1.3)102 -(4.1~0.89)102 -(6.2~5.7)102 -(6.2~5.4)102 -(6.0~5.4)102 -(5.9~5.4)102 -(5.7~5.3)102
ionic strength (2.4~4.0)10-1 3.610-3~2.510-1 (3.7~7.0)10-1 (3.6~6.9)10-1 (0.45~2.7)10-1 (0.51~3.5)10-1 (1.6~3.5)10-1
Na (mol kg-1) (2.2~3.4)10-1 2.810-3~2.010-1 (1.4~4.8)10-1 (1.4~4.9)10-1 2.510-3~2.210-1 2.810-3~3.410-1 (1.6~3.5)10-1
Ca (mol kg-1) (0.35~1.5)10-2 1.410-5~1.610-2 (1.1~3.3)10-3 (0.75~1.2)10-3 (0.25~3.2)10-2 (0.25~3.2)10-2 (1.9~2.4)10-2
K (mol kg-1) (1.9~3.2)10-3 1.610-5~4.310-3
2.210-1
2.210-1
1.610-5~3.210-3 3.010-5~3.210-3 (0.84~3.2)10-3
-1
-3
-7
-4
-7
-7
Mg (mol kg ) (1.4~4.9)10
4.010 ~5.310 (3.8~5.1)10(2.1~3.0)10(0.73~4.5)10-6 (0.52~4.5)10-6 (2.1~2.3)10-6
-1
-4
-9
-6
-6
-5
Fe (mol kg ) (4.1~8.9)10
1.310 ~4.210 (1.2~7.5)10(0.12~2.6)10 (0.35~1.2)10-6 (0.75~3.5)10-6 (1.1~8.4)10-6
-1
-9
-7
-5
Al (mol kg ) (1.3~2.4)10(0.22~7.9)10(4.4~6.0)10(3.4~4.8)10-5 (4.5~7.1)10-6 (0.37~2.5)10-5 (1.4~1.6)10-5
-1
-4
-3
-4
Si (mol kg ) (3.1~4.6)10(0.33~1.4)10 (0.50~1.1)10 (0.65~1.5)10-4 (1.0~1.6)10-5 (1.0~3.9)10-5 (3.2~3.9)10-5-1-6-2
S (mol kg ) 4.110 ~7.710 7.210-6~7.810-2 (3.8~8.7)10-2 (1.2~2.9)10-2 (2.8~9.1)10-4 7.210-5~8.610-3 (1.7~1.9)10-3
TIC*1 (mol kg-1) (3.1~4.7)10-2 (0.12~9.1)10-3 (1.3~3.4)10-4 (1.9~5.1)10-4 (0.83~1.1)10-5 (0.82~4.9)10-5 (4.6~4.9)10-5
Cl (mol kg-1)
2.110-1(0.11~5.1)10-2 1.110-3~2.110-1 1.110-3~2.110-1 1.110-3~2.110-1 1.010-3~2.110-1 3.310-3~2.110-1-1-6
F (mol kg )6.510(1.3~5.7)10-4 6.510-6~5.710-4 6.510-6~1.910-4 6.510-6~5.710-4 6.510-6~5.710-4 6.610-6~1.910-4-1-2
B (mol kg )1.010
4.610-6~2.710-4 4.610-6~1.010-2 4.610-6~1.010-2 4.610-6~1.010-2 4.610-6~1.010-2 4.710-6~1.010-2-1-6
P (mol kg )5.910(0.65~5.6)10-6 (0.64~5.9)10-6 (5.6~6.0)10-6 (0.65~5.9)10-6 (0.65~6.0)10-6 (0.57~6.0)10-6
N (mol kg-1)
1.010-2(0.25~2.8)10-5 2.510-6~1.010-2 2.510-6~1.010-2 2.510-6~1.010-2 2.510-6~1.010-2 2.610-6~1.010-2
Br (mol kg-1)
8.010-4(0.43~3.9)10-5 4.310-6~8.010-4 4.410-6~8.110-4 4.310-6~8.010-4 4.410-6~8.110-4 4.510-6~8.110-4
I (mol kg-1)
1.810-4(3.9~7.9)10-6 3.910-6~1.810-4 3.910-6~1.810-4 3.910-6~1.810-4 3.910-6~1.810-4 4.010-6~1.910-4

60

原子力バックエンド研究
more than one thousandth of maximum radioactivity of a certain

December 2020

nitrate (NaNO3), no significant effects of SIs were found.

RN, which are inorganic carbon (IC), organic carbon (OC),The authors have picked up a few candidate solid phases withchlorine (Cl), cobalt (Co), nickel (Ni), selenium (Se), strontium

high SIs since the solid phases with higher SIs are more stable.

(Sr), zirconium (Zr), niobium (Nb), molybdenum (Mo),The authors have discussed about the most suitable solid phases

technetium (Tc), palladium (Pd), tin (Sn), iodine (I), cesium (Cs),as SSP among the candidate solid phases using available

lead (Pb), radium (Ra), actinium (Ac), thorium (Th), protactinium

knowledge obtained from experimental and natural analogue(Pa), uranium (U), neptunium (Np), plutonium (Pu), americium

studies, and considering bentonite and cement porewater(Am) and curium (Cm) [33].

compositions. Note that the obtained SIs are definitely tentative.

2.2

Search of Potential Solubility-limiting Solid Phase

Results and Discussion

3

There are many potential solid phases to predict solubility of
RNs. Various types of solid phase, e.g., crystalline (abbreviation

3.1

Carbon“cr”), amorphous (“am”) and colloidal phases are proposed even

Aqueous concentration of IC has already been controlled byfor same chemical forms, e.g., UO2(cr) and UO2(am).

calcite (CaCO3) in simulated bentonite and cement porewaters

Furthermore, some solid phases could be defined neither

based on thermodynamic calculations [33]; therefore, the authors

crystalline nor amorphous; the authors show these solid phases

have selected the calcite as a SSP of IC.

with another abbreviation “s”, e.g., Pa2O5(s). As mentioned above,

No candidate SSPs for OC have been found; therefore, OC is

the JAEA-TDB [25] includes comprehensive thermodynamic

concluded to be soluble.

data (equilibrium constants in aqueous solutions) on solid phases.
It is easy to compare stability of solid phases to select potential

3.2

Chlorine

SSPs. A saturation index (SI) is defined as logarithm of ratio

No candidate SSPs for Cl have been found; therefore, Cl is

between ion activation product (IAP) and solubility product (Ksp)concluded to be soluble. Note that aqueous concentration of Cl

as follows:

may be decreased due to incorporation into cementitious materials
after formation of Friedel’s salt [36].

a IAP { A}actual{B}bactual  log 
SI  log10 10b { A}a K sp {B}eqilibrium
eqilibrium





(1)

3.3

Cobalt and Nickel

Part of the obtained SIs for Co and Ni of which chemical

for the reaction of AaBb(s) ⇄ a A(aq) + b B(aq)behavior in aqueous media are quite similar to each other, is(abbreviation “aq” shows aqueous species).

shown in Tables 4 and 5, respectively. It is found that SIs of somesulfides such as β-CoS and β-NiS and carbonates (CoCO3(cr) and

The SI is a useful quantity to determine whether the water is

NiCO3(cr)) are larger than others in bentonite porewater. However,saturated, undersaturated or oversaturated with respect to theno reliable equilibrium constants of these solid phases in aqueous

given mineral:

media, even for millerite (β-NiS) which is a naturally occurred
mineral [7, 37]. Therefore, selection of β-NiS as a SSP for nickel

SI = 0 (IAP = Ksp): saturated (in equilibrium),may be severely underestimated. Furthermore, nickel carbonate

SI < 0 (IAP < Ksp): undersaturated,(NiCO3(cr)) could be formed only under high partial pressure of

SI > 0 (IAP > Ksp): oversaturated.

carbon dioxide (CO2) [38]; therefore, it is unlikely that NiCO3(cr)forms in geological disposal conditions.

The authors have decided to calculate SIs using the PHEEQC

As a conclusion, selection of β-Ni(OH)2 as a SSP for Ni is the[35], which is the powerful geochemical calculation programs,

most likely for all conditions listed in Table 3. Similar to Ni, thesince JAEA-TDB [25] has a text file for use of the PHREEQC.

authors have selected β-Co(OH)2 as a SSP for Co.

Initial concentration of the elements of interest was tentatively set
to 110-8 mol kg-1 for the calculation of SIs.

3.4

Selenium

Preliminary thermodynamic calculations have been performed

Part of the obtained SIs for Se is shown in Table 6. Candidate

to obtain the SIs for categorized bentonite and cement porewater

SSP with the largest SI value is iron selenides such as FeSe2(cr)compositions listed in Table 3. The maximum values in eachat certain conditions and monomeric Se (Se(am, “cr, trigonal” andcategory have been chosen for the calculations because use ofmono)) at other conditions. Still there are an argument for

maximum values makes effects of redox and complexations clear.

selection of SSP for Se between FeSe2(cr) and Se(cr, trigonal);

Effect of isosaccarinic acid (ISA) for determination of SIs could

only Nagra selects Se(cr) for estimation of Se solubility for HLW

be ignored because of little contribution of the ISA at thedisposal [19, 21] while other implementations or researchmaximum of expected concentration of 110-5 mol kg-1 [33].

institutes select FeSe2(cr). The authors have selected FeSe2(cr) as

Although effect of nitrate for some cement porewater

the SSP at all conditions after reviewing the latest experimental

compositions was considered by adding 0.5 mol kg-1 of sodium

studies such as Doi et al. [39]61Methodology Development and Determination of Solubility-limiting Solid Phases for a Performance Assessment of Geological
Disposal of High-level Radioactive and TRU Wastes
Table 4 Saturation indices for candidate SSPs of cobalt
Water typepH range
α-CoSβ-Co(OH)2
β-CoS
CoCO3(cr)CoO(cr)Bentonite porewater
HigherLower(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh

-4.98
-8.16
-1.32
-3.29
-8.13

-1.16
-9.83
2.50
-9.10
-9.80

-14.33-7.09-10.67-3.32-7.06(3) Max. pH,
max. Eh-36.90-2.67-33.24-1.94-2.63

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

-1.34
-2.99
2.32
-9.54
-2.95

-11.62-2.72-7.96-10.32
-2.68

-1.16
-5.66
2.50
-11.68
-5.63

-2.82
-2.49
0.84
-9.18
-2.45

-9.88
-2.56
-6.22
-10.27-2.53

Values with bold and italic faces denotes the selected SSP and solid phases with larger SIs than the selected SSP, respectively(ditto with later Tables).
Table 5 Saturation indices for candidate SSPs of nickel
Water type

Bentonite porewater

pH range

Lower

α-NiS
β-Ni(OH)2
β-NiS
Ni3S2(cr)
Ni9S8(cr)
NiCO3(cr)NiS2(cr)

-2.90
-6.75
-2.28
-12.11-27.99-3.32-2.34

Higher(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh

0.78
-8.55
1.40
-3.47
2.79
-9.26
3.77

-12.30-5.73-11.68-32.29-104.56-3.40-19.77(3) Max. pH,
max. Eh-34.79-1.22-34.17-78.14-285.33-1.93-63.85

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

-0.43
-2.74
0.19
-0.47
-1.52
-10.73-4.09-11.54-3.31-10.92-25.47-93.17-12.34-23.53

0.78
-4.39
1.40
1.09
7.34
-11.84
-0.79

-2.07
-2.40
-1.45
-3.82
-14.67-10.53
-7.28

-9.54
-2.89
-8.92
-20.60-76.29-12.03-20.40

Table 6 Saturation indices for candidate SSPs of selenium
Water type

Bentonite porewater

pH range

Lower

β-Fe1.04Se
FeSe2(cr)Se(am)
Se(cr,trigonal)
Se(mono)CaSeO3·H2O(cr)CaSeO4·2H2O(cr)

-2.83
3.98
-0.31
0.73
0.51
-25.86-48.83

3.5

Higher(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh

-7.00
-5.56
-5.64
-4.59
-4.82
-30.72-56.75

-6.30
1.04
0.07
1.12
0.89
-19.68-40.26(3) Max. pH,
max. Eh-10.14
-4.05
-1.27
-0.23
-0.45
-4.83
-20.00Strontium and Radium

3.6

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

-4.21
-5.53
-8.20
-7.15
-7.38
-27.66-53.31

-5.55
-5.17
-6.61
-5.57
-5.79
-21.00-44.43

-3.06
-4.27
-8.04
-7.00
-7.22
-29.57-56.00

-3.97
-4.54
-7.46
-6.41
-6.64
-25.48-50.72

-5.00
-4.66
-6.63
-5.58
-5.81
-21.19-45.08

Zirconium

Both Sr and Ra belong to alkaline-earth metal group same asPart of the obtained SIs for Zr is shown in Table 9. It is foundcalcium. Part of the obtained SIs for Sr and Ra is shown in Tables

that many silicates and sulfides have larger SIs than hydroxides.

7 and 8, respectively. It is found that SrCO3(strontianite) has the

Chemical behavior of these solid phases in aqueous media,

largest SSP for Sr while RaSO4(cr) has the largest SSP for radium.

however, is not clear because no experimental studies in aqueous

Since calcium forms CaCO3(calcite) which is one of the major

media have been performed [9]. The equilibrium constants havemineral components, the most likely SSP for Ra can also be its

not been selected by the NEA [9], although the equilibrium

carbonate (RaCO3(cr)) based on the chemical analogies andconstants can be easily obtained from the Gibbs free energy ofpossible formation of coprecipitates.

formation. Furthermore, estimated solubility values for Zr

Note that aqueous concentration of Ra may be decreased due

silicates and sulfides will be too low to detect with considering

to incorporation of alkaline earth minerals such as calcite

the huge SIs; therefore the estimated solubility values cannot be(CaCO3) because of a tiny amount [40].

reliable. Since experimental studies on only hydroxides and/orhydrous oxides of Zr have been performed in aqueous media, themost suitable SSP is concluded to be Zr(OH)4(am,fresh).
62

December 2020

原子力バックエンド研究
3.7

Niobium

values using the JAEA-TDB; therefore, selection of Nb2O5(s) as

Only Nb2O5(s) is the candidate SSP for Nb in the JAEA-TDB

the SSP is suitable from the pessimistic point of view.

[25]; therefore, the authors have selected Nb2O5(s) as the SSP for
Nb.

3.8

Although there is an experimental study on solubility ofcalcium

niobate(CaNb4O11·8H2O(hochelagaite))

Molybdenum

The obtained SIs for Mo are shown in Table 10. It is found thatunder

the SSP with the largest SI is MoO2(cr) for reference cases incementitious conditions, no equilibrium constants have been

bentonite porewater and CaMoO4(cr) for other cases. The

obtained but just an empirical model for predicting Nb solubility

equilibrium constant of MoO2(cr) selected in the JAEA-TDB,

has been proposed [41]. Note that the obtained experimental

however, has been just calculated from the Gibbs free energy ofvalues by Talerico et al. [41] are much smaller than the estimatedformation [42]; no reliable data on solubility of MoO2(cr) in

Table 7 Saturation indices for candidate SSPs of strontium
Water typepH range
SrCO3(strontianite)
SrSO4(celestite)

Bentonite porewater
HigherLower(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh

-4.88
-4.11

-2.48
-4.35

(3) Max. pH,
max. Eh

-4.93
-3.93

-2.58
-3.93

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

-4.18
-4.26

-4.09
-4.80

-5.25
-6.12

-4.78
-5.02

-4.83
-5.69

Table 8 Saturation indices for candidate SSPs of radium
Water typepH range
RaCO3(cr)RaSO4(cr)Bentonite porewater
Higher

Lower

(1)

-5.86
-0.94

Max. pH,min. Eh

-3.36
-1.09

(2)

Min. pH,
max. Eh

-6.00
-0.85

(3)

Max. pH,
max. Eh

-3.65
-0.86

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

-5.09
-1.03

-4.84
-1.42

-5.96
-2.69

-5.53
-1.63

-5.53
-2.26

Table 9 Saturation indices for candidate SSPs for zirconium
Water type

Bentonite porewater
HigherpH range

Lower

Ca2ZrSi3O12(cr)Ca3ZrSi2O9(cr)Na2ZrSi2O7(cr)Na2ZrSi4O11(cr)Na2ZrSiO5(cr)Na4Zr2Si3O12(cr)Zr(OH)4(am,fresh)
ZrO2(mono)
ZrS1.5(cr)ZrS2(cr)
ZrS3(cr)ZrSiO4(cr)91.74-28.36-4.04
7.12-10.42-13.04
-2.81
0.96
55.71
63.99
64.58
5.26

(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh

99.27
-8.19
2.37
13.69
-4.09
-0.30
-2.57
1.19
65.71
75.19
78.20
5.57

100.21-24.13
-2.29
9.82
-9.15
-10.02
-2.57
1.19
39.12
43.38
35.94
5.97

(3) Max. pH,
max. Eh120.61
-8.73
2.30
13.61
-4.16
-0.45
-2.57
1.19
-4.08
-10.62-39.66
5.57

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

97.43
-1.86
0.58
3.76
-1.81
0.20
-2.69
1.09
54.86
61.02
57.38
1.39

100.08
-2.14
-0.40
1.08
-1.95
-0.93
-3.25
0.53
37.38
39.37
27.41
-0.01

95.80
-2.76
-1.17
2.68
-3.89
-3.64
-2.73
1.03
59.49
66.70
65.15
1.67

98.80
-0.73
-0.89
2.29
-3.29
-2.77
-3.36
0.41
51.02
56.40
51.22
0.71

100.43
-0.28
-1.79
-0.01
-3.49
-3.86
-3.89
-0.12
39.34
41.91
31.07
-0.51

Table 10 Saturation indices for candidate SSPs for molybdenum
Water type

Bentonite porewater

pH range

Lower

CaMoO4(cr)Mo(metal)
MoO2(cr)-3.36-28.99-1.10

Higher(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh-3.06-26.07-4.32-3.27-37.07-4.41(3) Max. pH,
max. Eh-3.27-58.68-15.21
63

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher-4.16-33.20-10.67-4.80-41.04-14.09-2.75-28.93-7.97-2.88-33.76-10.41-3.09-38.78-12.75

Methodology Development and Determination of Solubility-limiting Solid Phases for a Performance Assessment of Geological
Disposal of High-level Radioactive and TRU Wastes
aqueous media under geological disposal conditions have been

respectively), the estimated solubility values are too small tofound. In contrast, solubility product of powellite (CaMoO4(cr))

detect. Experimental solubility values for Pd-OH-Cl system arehas been determined by Felmy et al. [43] and Grambow et al. [44]well interpreted by assuming the SSP of Pd(OH)2(am) [47].

Furthermore, geochemical modelling for Mo leaching from a

Therefore, the authors have selected Pd(OH)2(am) as the SSP.

mine site showed that powellite is closest to mineral saturation
3.11 Tinand solubility control on aqueous Mo, with wulfenite (PbMoO4)
and other Mo minerals playing a much lesser role [45]. Therefore

The obtained SIs for Sn is shown in Table 13. Cassiterite

the authors have selected CaMoO4(cr) as the SSP at all conditions.

(SnO2) is the most stable solid phase and the solubility of
SnO2(cassiterite) is smaller than that of SnO2(am) [48]. Solubility

3.9

Technetium

values from oversaturation direction, however, are wellinterpreted with assuming SnO2(am) as SSP [11, 48]. Therefore

Part of the obtained SIs for Tc is shown in Table 11. It is foundthat the solid phase with the largest SI is TcO2(cr). The

the authors have selected SnO2(am) as SSP.

equilibrium constants of Tc(cr) and TcO2(cr), however, are not
3.12 Iodine

selected by the NEA [10] but just estimated from the Gibbs freeenergy of formation in JAEA-TDB [26]. Furthermore, thePart of the obtained SIs for I is shown in Table 14. Althoughestimated solubility of Tc(cr) and TcO2(cr) are too small to detect,KI(cr) is the most stable solid phase, calculation of solubility of I

and the experimental solubility measurements of hydrous Tc(IV)using the KI(cr) as SSP has not been well converged in theoxide fit to a thermodynamic calculation with SSP ofthermodynamic calculation due to changing pH and Eh of water

TcO2·1.6H2O(s) [46]. Therefore, the authors have selectedcomposition drastically and very large concentration limit of I.

TcO2·1.6H2O(s) as the SSP at all conditions.

Therefore the authors did not select any SSPs for I, and I isconcluded to be soluble. Note that aqueous concentration of I may

3.10 Palladium

be decreased due to incorporation into cementitious materials
after formation of ettringite, monosulfates, etc [49].

The obtained SIs for Pd is shown in Table 12. Althoughmonomeric Pd(cr) and Pd(s) are more stable than amorphous andcolloidal Pd hydroxides (Pd(OH)2(am) and Pd(OH)2(colloidal),Table 11 Saturation indices for candidate SSPs for technetium
Water typepH rangeTc(cr)
TcO2(cr)
TcO2·1.6H2O(s)Bentonite porewater
Lower

Higher(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh

-1.26
3.65
-0.35

5.59
4.36
0.36

(3) Max. pH,
max. Eh

-5.42
4.26
0.27

-21.49-1.01-5.00

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

2.89
2.44
-1.57

-2.13
1.84
-2.17

5.35
3.33
-0.67

2.37
2.75
-1.25

-0.80
2.25
-1.75

Table 12 Saturation indices for candidate SSPs for palladium
Water typepH rangePd(cr)
Pd(OH)2(am)Pd(OH)2(colloidal)
Pd(s)Bentonite porewater
Lower
15.20
-5.29
-6.46
11.91

Higher(1)

Max. pH,min. Eh

22.60
-0.95
-2.12
19.31

(2)

Min. pH,
max. Eh

17.16
-0.93
-2.10
13.87

(3)

Max. pH,
max. Eh

11.75
-0.95
-2.12
8.46

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

18.60
-4.57
-5.74
15.31

17.53
-3.43
-4.60
14.24

17.72
-6.23
-7.40
14.43

17.68
-5.07
-6.24
14.39

17.33
-4.09
-5.26
14.04

Table 13 Saturation indices for candidate SSPs for tin
Water type

Bentonite porewater

pH range

Lower

SnO(cr)SnO2(am)
SnO2(cassiterite)-12.93-1.58
1.01

Higher(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh-11.29-3.01-0.42-15.34-1.60
0.99(3) Max. pH,
max. Eh-22.16
-3.02
-0.43
64

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

-16.70-8.03-5.44-20.11-9.23-6.64-14.03-6.15-3.56-16.44-7.36-4.77-18.78-8.36-5.77

December 2020

原子力バックエンド研究
Table 14 Saturation indices for candidate SSPs for iodine
Water type

Cement porewater
Region I

Bentonite porewater

pH range

Lower

CaI2(cr)I2(cr)
KI(cr)
NaI(cr)3.13 Cesium-41.23-38.80-12.48-13.64Higher(4) Max. (5) Min. (6) Max.
pH,
pH,
pH, Lower
min.
max.
max.
Eh
Eh
Eh
-41.01-41.20-41.20-41.97-48.24-37.40-37.40-53.68-12.91-12.96-12.96-10.64-13.81-13.85-13.85-13.49

Region II

HigherLower

MiddleHigher

-42.52-52.67-10.41-13.46-40.67-52.65-12.42-13.77-40.76-52.65-12.43-13.59-40.97-52.32-12.42-13.583

No candidate SSPs for Cs have been found; therefore, Cs is2saturation index

concluded to be soluble.
3.14 Lead
Part of the obtained SIs for Pb is shown in Table 15. Galena(PbS) is the most stable solid phase in most cases. The solubilityof PbS(galena), however, is below detection limit (< 10-7 mol dm3) at pH = 8.6 [50]. No solubility data at room temperature on

1

Am(OH)3(cr)AmCO3OH･0.5H2O(cr)0-2other lead compounds of which the SI is larger than-3

PbCO3(cerrusite) and Pb(OH)2(am) listed in Table 15. Cerrusite

-4
10.0

is a naturally occurred mineral and its solubility and stability haveAm(OH)3(am)-1

AmCO3OH(am)10.5

been investigated [51]. Therefore, the authors have selected
PbCO3(cerrusite) or Pb(OH)2(am) as the SSP of Pb.

Fig.1

11.0
pH

11.5

12.0

Saturation index of candidate SSPs of americium forplutonic rock-type bentonite porewater as a function

3.15 Actinium, Americium and Curiumof pH

Actinium (Ac), Am and Cm are trivalent and chemicallysimilar to each other in geological disposal conditions. Kitamura
3.16 Thorium

et al. [52] applied the selected thermodynamic data for Am to
those for samarium (Sm), Ac and Cm after confirming anPart of the obtained SIs for Th is shown in Table 18. Althoughapplicability of chemical analogy among these elements.

ThO2(cr) is the most stable solid phases, there are no reliable

Part of the obtained SIs is shown in Table 16 for Am and Cm,solubility data on ThO2(cr) at room temperature; therefore, theand in Table 17 for Ac of which crystalline solid phases cannot

NEA has not been selected the equilibrium constant for solubility

be formed because of instability of solid phase of Ac due to itsof ThO2(cr) [12]. Furthermore, the preparation of water-free

own α-radioactivity. Although the most stable solid phase is

crystalline actinide(IV) dioxide (AnO2(cr)) requires heating

phosphate (MPO4(am,hydr), M: Ac, Am and Cm), the expected

above 700 °C [54], and radiolytic amorphization and hydration on

solubility values are too small to detect [53]. Therefore, theAnO2(cr) surface cannot be ruled out [55]. Therefore the authors

authors have eliminated MPO4(am,hydr) from candidate SSPs

accepted the discussion by the NEA [12] and selected ThO2(am,and have selected crystalline and amorphous hydroxidesaged) as the SSP due to requirement for assessing long-term(M(OH)3(cr) (M: Am and Cm) and Ac(OH)3(am), respectively),

behavior of Th migration.

and amorphous and crystalline mixed carbonate-hydroxide
compounds(MCO3OH·0.5H2O(cr)and3.17 Protactinium

AcCO3OH(am),respectively).

The obtained SIs for Pa is shown in Table 19. The authors have

Saturation index of these solid phases of Am as a function of

selected the pentavalent Pa oxide (Pa2O5(s)) as the SSP under all
conditions.

pH is shown in Fig.1 for plutonic rock-type bentonite porewater.
It is interesting that the most appropriate SSP changes from

3.18 Uranium

AmCO3OH·0.5H2O(cr) to Am(OH)3(cr) at pH around 10.9, andfrom the AmCO3OH(am) to the Am(OH)3(am) at pH around 10.4.

Part of the obtained SIs for U is shown in Table 20. Although

The authors have concluded that change of SSP as a function ofthere are many candidate SSPs for U, most of them may not be

pH was reasonable; therefore the authors have selected

appropriate to select as the SSP, because some of them are not

MCO3OH·0.5H2O(cr) and AcCO3OH(am) as the SSP in bentonite

formed in aqueous media from oversaturation directions (e.g.,porewaters, while that is M(OH)3(cr) and Ac(OH)3(am) as the

CaU6O19·11H2O(cr) and K2U6O19·11H2O(cr)), and the estimated

SSP in cement porewaters.

solubility values are too small to detect even if the possible
65Methodology Development and Determination of Solubility-limiting Solid Phases for a Performance Assessment of Geological
Disposal of High-level Radioactive and TRU Wastes
Table 15 Saturation indices for candidate SSPs for lead
Water type

Cement porewater
Region I

Bentonite porewater

pH range

HigherLower

Pb(cr)
Pb(OH)2(am)Pb5(PO4)3Cl(chloro_pyromorphite)
PbCl2(s)PbCO3(cerrusite)
PbHOCl(cr)PbHPO4(s)PbO(red,litharge)
PbO(yellow,massicot)
PbS(galena)
PbSO4(anglesite)(1) Max. pH, (2) Min. pH, (3) Max. pH, Lower
min. Ehmax. Ehmax. Eh

-9.87
-9.87
-3.02
-6.87
-2.18
-4.87
-5.01
-9.50
-9.78
-1.34
-4.19

-8.21
-11.28-34.59-15.86-7.73-10.07-13.33-10.90-11.182.74-12.38-11.16
-8.77
-0.82
-7.97
-2.18
-4.87
-4.64
-8.40
-8.68
-10.66-3.96-13.92-6.14-8.46-10.74
-2.59
-4.94
-8.04
-5.77
-6.05
-35.02-6.73

Region II

HigherLower

MiddleHigher

-9.13-9.61-56.13-20.03-14.38-11.32-20.65-9.23-9.51-13.16-17.89-3.40-6.87-32.72-14.24-10.06-7.05-15.18
-6.49
-6.77
2.99
-13.73-5.55-7.82-43.23-16.41-11.69-8.62-17.85
-7.45
-7.73
-2.80
-14.72-7.82-8.75-52.26-18.34-13.63-10.05-20.07-8.38-8.66-10.72-17.29-5.75-8.44-45.83-17.66-12.17-9.55-18.20
-8.06
-8.34
-1.44
-15.03

Table 16 Saturation indices for candidate SSPs for americium and curium
Water typepH range
M(OH)3(am) *M(OH)3(cr)MCO3OH(am)MCO3OH·0.5H2O(cr)MPO4(am,hydr)
NaM(CO3)2·5H2O(cr)Bentonite porewater
Lower

Higher(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh

-8.19
-6.89
-3.67
-1.47
1.55
-1.55

-2.67
-1.37
-2.31
-0.11
0.14
-1.30

(3) Max. pH,
max. Eh

-6.93
-5.63
-3.52
-1.32
2.06
-2.20

-2.71
-1.41
-2.34
-0.15
0.25
-1.38

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

1.28
2.58
-5.63
-3.44
-3.62
-8.71

1.30
2.60
-6.66
-4.47
-4.88
-10.16

1.18
2.48
-5.20
-3.00
-2.27
-8.90

1.27
2.57
-5.78
-3.58
-3.89
-9.38

1.29
2.59
-6.77
-4.57
-5.16
-10.87*M: Am or Cm

Table 17 Saturation indices for candidate SSPs for actinium
Water typepH range
Ac(OH)3(am)AcCO3OH(am)AcPO4(am,hydr)

Bentonite porewater
Lower

Higher(1) Max. pH,
min. Eh(2) Min. pH,
max. Eh(3) Max. pH,
max. Eh

-2.64
-2.27
0.17

-6.93
-3.52
2.07

-2.67
-2.31
0.29

-8.18
-3.66
1.55

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

1.28
-5.63
-3.62

1.30
-6.66
-4.88

1.18
-5.20
-2.27

1.27
-5.78
-3.89

1.29
-6.77
-5.16

Table 18 Saturation indices for candidate SSPs for thorium
Water typepH range
ThO2(am,aged)
ThO2(am,fresh)
ThO2(cr)ThOF2(cr)Bentonite porewater
Lower
-2.07
-2.87
4.67
-2.77

Higher(1)

Max. pH,min. Eh

-0.26
-1.06
6.48
-3.40

(2)

Min. pH,
max. Eh

-0.83
-1.63
5.91
1.42

Max. pH,
max. Eh

(3)

-0.34
-1.14
6.40
-3.49

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

0.91
0.11
7.65
-8.06

0.91
0.11
7.65
-10.21

0.90
0.10
7.64
-6.28

0.90
0.10
7.64
-7.49

0.82
0.02
7.56
-9.50

3.19 Neptunium

formation in aqueous media (e.g., β-UO2+x, UO2+x(cr) andUSiO4(cr). Therefore the authors have selected UO2(am) as thePart of the obtained SIs for Np is shown in Table 21. Although

SSP for U.

NpO2(cr) is the most stable solid phases, the authors did not selectthe NpO2(cr) as the SSP, similar to ThO2(cr). Therefore theauthors have selected NpO2(am) as the SSP for Np.
66

December 2020

原子力バックエンド研究3.20 Plutonium

3.21 Comparison of Selected Solubility-limiting Solid
Phases with Those Selected by Other Safety

Part of the obtained SIs for Pu is shown in Table 22. Potential

Assessments

redox states of Pu under geological repository conditions are 3
and4.

AlthoughPuO2(cr),

and

Pu

(III)

phosphates

The selected SSPs in the present study have been listed and(PuPO4(am,hydr) and PuPO4(s,hyd)) are candidate SSPs for Pu,

compared with those selected in other PA reports for HLW

the authors did not select these solid phases as the SSP as

disposal in European and North American countries in Table 23.

discussed in section 3.16 and 3.15, respectively. Therefore the

The authors have not taken any information about SSPs from theauthors have selected PuO2(am) as the SSP for Pu.

Dossier 2005 [22] and the safety analysis report for Yucca

Table 19 Saturation indices for candidate SSPs for protactinium
Water type

Bentonite porewater

pH range

Lower

Pa2O5(s)PaO2(cr)

0.68
-7.28

Higher(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh

2.07
-5.05

1.38
-8.12

(3) Max. pH,
max. Eh2.07-10.48

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

2.10
-5.23

2.10
-6.33

2.08
-4.85

2.08
-5.45

2.09
-6.11

Table 20 Saturation indices for candidate SSPs for uranium
Water typepH range

Bentonite porewater
HigherLower

β-UO2.25
β-UO2.3333
CaU6O19·11H2O(cr)K2U6O19·11H2O(cr)NaUO3(cr)UO2(am)UO2(cr)UO2.25(cr)UO2.6667(cr)UO2CO3(cr)USiO4(cr)(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh

0.26
-0.63
31.98
25.82
-8.49
-5.24
1.92
0.27
-3.91
-7.00
1.80

2.64
1.50
39.10
31.84
-3.87
-2.09
5.07
2.65
-2.81
-11.06
5.03

0.08
-0.61
42.73
35.56
-7.79
-6.01
1.15
0.09
-3.09
-6.48
1.51

(3) Max. pH,
max. Eh

-5.62
-5.86
38.19
31.03
-9.45
-13.06
-5.91
-5.61
-6.55
-11.19-5.95

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

3.68
2.57
51.89
50.14
0.50
-1.14
6.02
3.69
-1.61
-17.02
1.90

0.86
-0.07
45.53
44.39
-1.14
-4.52
2.64
0.87
-3.51
-19.23
-2.32

5.07
3.89
56.24
49.63
0.51
0.44
7.60
5.08
-0.54
-15.67
3.82

4.00
2.92
56.29
49.76
0.52
-0.93
6.23
4.01
-1.12
-16.52
2.12

2.06
1.09
51.46
45.15
-0.57
-3.20
3.95
2.07
-2.50
-18.47-0.85

Table 21 Saturation indices for candidate SSPs for neptunium
Water type

Bentonite porewater

pH range

HigherLower

NaNpO2CO3·3.5H2O(cr)NpO2(am)
NpO2(cr)(1) Max. pH, (2) Min. pH, (3) Max. pH,
min. Ehmax. Ehmax. Eh

-8.63
-1.75
8.61

-9.30
0.24
10.59

-6.92
-0.42
9.94

-4.01
0.14
10.49

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

-12.41
1.01
11.37-11.72
1.01
11.37-13.43
1.00
11.36-12.73
1.01
11.36-12.56
1.01
11.36

Table 22 Saturation indices for candidate SSPs for plutonium
Water typepH range
PuCO3OH·0.5H2O(cr)PuO2(am)PuO2(cr)
PuPO4(am,hydr)
PuPO4(s,hyd)

Bentonite porewater
Lower
-1.54
-2.32
3.39
1.47
1.28

Higher(1) Max. pH, (2) Min. pH,
min. Ehmax. Eh

-1.40
0.43
6.14
-1.15
-1.34

-1.91
-0.39
5.32
1.48
1.29

(3) Max. pH,
max. Eh

-6.84
0.43
6.14
-6.44
-6.63
67

Cement porewater
Region I

Region II

Lower

HigherLower

MiddleHigher

-6.48
2.84
8.55
-6.66
-6.85

-8.63
2.84
8.55
-9.05
-9.24

-5.55
2.83
8.54
-4.82
-5.01

-6.82
2.83
8.54
-7.13
-7.32

-8.50
2.84
8.54
-9.09
-9.28

Methodology Development and Determination of Solubility-limiting Solid Phases for a Performance Assessment of Geological
Disposal of High-level Radioactive and TRU Wastes
Mountain repository (YMP-SAR) [57]. Also the authors havethermodynamic database was useful for showing a morecompared the selected SSPs in the Swiss PA reports for TRU

transparent procedure for the selection than expert judgements.

waste disposal as shown in Table 24. It is interesting that the

The selected SSPs were similar to those selected in PA reports inselected SSPs are similar to each other for most elements, but

European and North American countries for most elements, butthere are discrepancies for selection of SSP in some elements suchthere are discrepancies for selection of SSP in some elements. The

as Co, Ni, Se, Sr, Mo, Sn, Ra, Am and Cm. It is difficult to discuss

authors believe our selected SSPs are the most suitable forthe discrepancies because there is lack of information for

performance assessment of the Japanese geological disposal

selection of SSPs in other PA reports. The authors believe oursystem of HLW and TRU waste through determining SIs andselected SSPs are the most suitable for PA of the Japanese

discussion through experimental and natural analogue studies.

geological disposal system of HLW and TRU waste throughAcknowledgement

determining SIs and discussion through experimental and natural
analogue studies.

The present study has been performed in the collaborative
4

Conclusions

project between Nuclear Waste Management Organization ofJapan (NUMO) and JAEA.

Selection of solubility-limiting solid phases (SSPs) that control
References

the solubility of radionuclides has been performed for theelements of interest for the performance assessment (PA) inmodeled bentonite and cement porewaters. It was found that[1]

determination of saturation indices of candidate SSPs using a

Nuclear Energy Agency (NEA) within Organisation for
Economic Co-Operation and Development (OECD):

Table 23 Selected SSPs for HLW disposal in PA reports
Country
Project
Name
Ref.

SwedenSR-Site(Forsmark)[3, 15]Finland
TURVA-2012(saline/blackish)[17]

Switzerland

Switzerland

EN 2002

SGT-E2

IC

CaCO3 (calcite)

CaCO3 (calcite)

CaCO3(s)

OC
Cl
Co
Ni
Se

––
––
––
β-Ni(OH)2
FeSe2(s)

Sr
Zr
Nb
Mo
Tc
Pd
Sn
I
Cs
Sm
(Eu)
Pb

[19]

(no SSPs)––(no SSPs)(no SSPs)––
CoCO3(s)Ni(OH)2(s)NiCO3(cr)FeSe2(s)Se(cr)(no SSPs) <saline>
sorption onto
SrSO4(celestite) SrSO4(celestite)bentonite<blackish>
Zr(OH)4(am,aged) Zr(OH)4(am,aged)
ZrO2(s)
Nb2O5
Nb2O5(s)Nb2O5(s)––MoO2(tugarinovite)
MoO2(s)TcO2·1.6H2O
TcO2·1.63H2O(s)TcO2·1.6H2O(s)Pd(OH)2(s)Pd(OH)2(s)Pd(OH)2(precip.)SnO2(am)
SnO2(am)
SnO2(cassiterite)––(no SSPs)(no SSPs)––(no SSPs)(no SSPs)
SmCO3OHSmOHCO3(s)EuCO3OH(s)·0.5H2O(cr)PbCO3(s)––2PbCO3·Pb(OH)2(s)Ra

RaSO4(cr)(Rax,Ba1-x)SO4(Ba,Ra)SO4(ss)

Ac

––

––

analogous to Am

Th
Pa
U
Np
Pu

ThO2(am,aged)
Pa2O5(s)UO2(am,aged)
NpO2·2H2O
Pu(OH)4(am)NaAm(CO3)2·5H2O(s)ThO2·2H2O(am)Pa2O5(s)UO2·H2O(am)NpO2·2H2O(am)PuO2·2H2O(am)NaAm(CO3)2·5H2O(s)ThO2(s)Pa2O5(s)UO2(s)
NpO2(hyd,am)
PuO2(hyd,aged)

Cm2(CO3)3(s)analogous to Am

analogous to Am

Am
Cm

AmCO3OH(cr)

68

Spain
ThermoChimie[16]

Canadathe Fourth
Case Study
[56]
CaCO3
(calcite)
––
––
––
––
FeSe2(s)[21]
CaCO3(calcite),––
FeCO3(siderite)––––(no SSPs)––
CoCO3(spherocobaltite)––
NiCO3(cr)––Se(cr)––
ion exchange
equilibria on––––montmorillonite
Zr(OH)4(s)––Zr(OH)4(am, aged)
Nb2O5(s)Nb2O5(s)Nb2O5(s)CaMoO4(powellite) MoO2(s)MoO2
TcO2·1.6H2O(s)––TcO2·1.6H2O
Pd(OH)2(s)––Pd(OH)2(s)SnO2(am)––
SnO2(am)
AgI(s)––––(no SSPs)––––
SmCO3OH––––·0.5H2O(cr)PbCO3(s)PbCO3(s)PbCO3(s)(Ba,Ca,Ra)SO4––
RaSO4(s)(ss)
analogous to––––Am
ThO2(am,hyd,aged) ThO2(aged) ThO2(aged)
Pa2O5(s)––Pa2O5(s)UO2(am)UO2·2H2O(am)UO2(am)NpO2(am,hyd) NpO2·2H2O(am)NpO2(am)PuO2(am,hyd)––
PuPO4NaAm(CO3)2 AmCO3OH AmPO4·xH2O·5H2O(s)(am)(am)
analogous to
––
––
Am

Japan
SF-1,
present[26], present
CaCO3(calcite)(no SSPs)(no SSPs)β-Co(OH)2
β-Ni(OH)2
FeSe2(cr)SrCO3(strontianite)
Zr(OH)4(am,fresh)
Nb2O5(s)CaMoO4(cr)TcO2·1.6H2O(s)Pd(OH)2(am)SnO2(am)(no SSPs)(no SSPs)
SmCO3OH·0.5H2O(cr)PbCO3(cerrusite)(Rax,Ba1-x)CO3 <SF-1>
RaCO3(s)<present>
AcCO3OH(am)ThO2(am,aged)
Pa2O5(s)UO2(am)NpO2(am)PuO2(am)
AmCO3OH·0.5H2O(cr)CmCO3OH·0.5H2O(cr)December 2020

原子力バックエンド研究
Table 24

Selected SSPs in PA reports under cementitious
conditions

Country
Project
Name
Ref.

Switzerland

Switzerland

EN 2002

SGT-E2[27]

IC

CaCO3(s)

OC
Cl

Co
Ni
Se
Nb

––
(no SSPs)
Ca(OH)2(s) /CaCO3(s) /CaF2(s)Co(OH)2(s)Ni(OH)2(cr)
CaSeO3(s)(no SSPs)Mo

CaMoO4(cr)

Tc
Pd
Sn
I
Cs
Sm
(Eu)
Pb
Ra
Ac
Am
Cm
Np
Pa
Pu
Sr
Tc
Th
U
Zr

TcO2·1.6H2O(s)Pd(OH)2(precip.)CaSn(OH)6(s)(no SSPs)(no SSPs)Ca

Eu(OH)3(am)Pb(OH)2(s)RaSO4(s)analogous to Eu
Am(OH)3(am)analogous to Am
NpO2(am,hyd)––PuO2(hyd,aged)
SrCO3(s)(no SSPs)ThO2(s)(no SSPs)
ZrO2(s)W.: Chemical Thermodynamics of Nickel. Elsevier,
Amsterdam (2005).

Japan
Cement PRJ,
present[28], present[8]Olin, Å., Noläng, B., Osadchii, E. G., Öhman, L.-O., Rosén,
E.: Chemical Thermodynamics of Selenium. Elsevier,
Amsterdam (2005).

[29]
calcite, strontianite,
Al,Fe-moncarbonate CaCO3(calcite)
solid solutions––(no SSPs)(no SSPs)(no SSPs)
portlandite, CSH,
calcite, calcium- CaCO3(calcite)
aluminate-phases
Co(OH)2(s,rose)β-Co(OH)2
Ni(OH)2(theophrastite)
β-Ni(OH)2
CoSe2(cr)FeSe2(cr)(no SSPs)
Nb2O5(s)powellite
CaMoO4(cr)(CaMoO4(s))
TcO2·1.6H2O(s) TcO2·1.6H2O(s)Pd(OH)2(s)Pd(OH)2(am)CaSn(OH)6(precip)
SnO2(am)
AgI(s)(no SSPs)(no SSPs)(no SSPs)
Sm(OH)3
Sm(OH)3(cr)(am,cr)Pb(OH)2(pr)Pb(OH)2(am)(Ra,Ba)SO4(ss)RaCO3(cr)analogous to Eu Ac(OH)3(am)Am(OH)3(am)Am(OH)3(cr)Cm(OH)3(am,coll.)
Cm(OH)3(cr)NpO2(am,hyd)NpO2(am)
Pa2O5(s)Pa2O5(s)PuO2(am,hyd)PuO2(am)
SrCO3(strontianite) SrCO3(strontianite)
TcO2·1.6H2O(s) TcO2·1.6H2O(s)ThO2(am,hyd,aged) ThO2(am,aged)
UO2(am)UO2(am)ZrO2(baddeleyite) Zr(OH)4(am,fresh)[9]

Brown, P. L., Curti, E., Grambow, B., Ekberg, C.: Chemical
Thermodynamics of Zirconium. Elsevier, Amsterdam(2005).

[10] Guillaumont, R., Fanghänel, T., Neck, V., Fuger, J., Palmer,
D. A., Grenthe, I., Rand, M. H.: Update on the Chemical
Thermodynamics of Uranium, Neptunium, Plutonium,
Americium and Technetium. Elsevier, Amsterdam (2003).
[11] Gamsjäger, H., Gajda, T., Sangster, J., Saxena, S. K., Voigt,
W.: Chemical Thermodynamics of Tin. OECD, Paris (2012).
[12] Rand, M., Fuger, J., Grenthe, I., Neck, V., Rai, D.: Chemical
Thermodynamics of Thorium. Elsevier, Amsterdam (2008).
[13] Hummel, W., Anderegg, G., Puigdomènech, I., Rao, L.,
Tochiyama, O.: Chemical Thermodynamics of Compounds
and Complexes of U, Np, Pu, Am, Tc, Se, Ni and Zr withselected Organic Ligands. Elsevier, Amsterdam (2005).
[14] Hummel, W., Berner, U., Curti, E., Pearson, F. J., Thoenen,
T.: Nagra / PSI chemical thermodynamic data base 01/01.
Technical Report 02-16, National Cooperative for the
Disposal of Radioactive Waste in Switzerland (Nagra)(2002).
[15] Grivé, M., Domènech, C., Montoya, V., García, D., Duro,L.: Determination and assessment of the concentration
limits to be used in SR-Can – Supplement to TR-06-32. R10-50, SKB (2010).
[16] Grivé, M., Duro, M., Colàs, E., Giffaut, E.: Thermodynamic
data selection applied to radionuclides and chemotoxic
elements: An overview of the ThermoChimie-TDB. Appl.
Geochem. 55, pp.85-94 (2015).

Geologic Disposal of Radioactive Waste in Perspective.
[2][17] Wersin, P., Kiczka, M., Rosch, D.: Safety case for theOECD, Paris (2000).

disposal of spent nuclear fuel at Olkiluoto – Radionuclide

Swedish Nuclear Fuel and Waste Management Co. (SKB):

solubility limits and migration parameters for the canister

Radionuclide transport and dose calculations for the safety

and buffer. POSIVA 2012-39, Posiva Oy (2014).

assessment SR-PSU. TR-14-09 (2014).
[3][18] Curti, E., Wersin, P.: Assessment of porewater chemistry in

Duro, L., Grivé, M., Cera, E., Gaona, X., Domènech, C.,
Bruno,J.:

Determination

andassessmentofthe bentonite backfill for the Swiss SF/HLW repository.

theTechnical Report 02-09, Nagra (2002).

concentration limits to be used in SR-Can. TR-06-32, SKB[19] Berner, U.: Project Opalinus Clay – Radionuclide(2006).
[4]Östhols,

concentration limits in the near-field of a repository forE.,

Wanner,

H.:

TDB-0

–

The

NEA

spent fuel and vitrified high-level waste. Technical Report

thermochemical data base project. OECD, available online

02-10, Nagra (2002).

at http://www.oecd-nea.org/dbtdb/guidelines/tdb0new.pdf[20] Thoenen, T., Hummel, W., Berner, U., Curti, E.: The(2000).
[5]

PSI/Nagra chemical thermodynamic database 12/07.

Lemire, R., Berner, U., Musikas, C., Palmer, D. A., Taylor,

Arbeitsbericht NAB 14-49, Nagra (2014).

P., Tochiyama, O.: Chemical Thermodynamics of Iron (Part[21] Berner, U.: Solubility of radionuclides in a bentonite

1). OECD, Paris (2013).
[6]

environment for provisional safety analyses for SGT-E2.

Lemire, R. J., Palmer, D. A., Taylor, P., Schlenz, H.:

Technical Report 14-06, Nagra (2014).

Chemical Thermodynamics of Iron (Part 2). OECD, Paris[7][22] National Agency for Radioactive Waste Management(2013).

(ANDRA):

Gamsjäger, H., Bugajski, J., Gajda, T., Lemire, R. J., Preis,

Phenomenological evolution of a geological repository.
69

Dossier

2005

Argile–Tome:Methodology Development and Determination of Solubility-limiting Solid Phases for a Performance Assessment of Geological
Disposal of High-level Radioactive and TRU Wastes
ANDRA (2005).
[23] Sandia

National

for preliminary investigation stage (3) – Progress report on
Dissolved

NUMO-JAEA collaborative research in FY2013. JAEA-

concentration limits of elements with radioactive isotopes.

Laboratories(SNL):

Research 2014-030 / NUMO-TR-14-05 (2014) (in

ANL-WIS-MD-000010 Rev. 06, US Department of Energy

Japanese).

(US-DOE) (2007).

[35] Parkhurst, D. L., Appelo, C. A. J.: Description of input and[24] Nuclear Waste Management Organization of Canada(NWMO):

Pre-project

reportonadaptive

examples for PHREEQC version 3 – A computer programphasedfor speciation, batch-reaction, one-dimensional transport,

management – Used fuel repository conceptual design andand inverse geochemical calculations. U. S. Geologicalpostclosure safety assessment in crystalline rock. TR-2012-

Survey Techniques and Methods, Book 6, Chap. A43, 497

16 (2012).

p. (2013).

[25] Kitamura, A., Doi, R., Yoshida, Y.: Update of JAEA-TDB:[36] Hirao, H., Yamada, K., Takahashi, H., Zibara, H.: Chloride

Update of thermodynamic data for palladium and tin,binding of cement estimated by binding isotherms ofrefinement of thermodynamic data for protactinium, andhydrates. J. Adv. Concrete Technol. 3(1), pp.77-84 (2005).

preparation of PHREEQC database for use of the Brønsted-[37] Thoenen, T.: Pitfalls in the use of solubility limits for

Guggenheim-Scatchard model. JAEA-Data/Code 2014-

radioactive waste disposal: The case of nickel in sulfidic

009, JAEA (2014).

groundwaters. Nucl. Technol. 126(1), pp.75-87 (1999).

[26] JAEA Radioactive Waste Processing and Disposal Research[38] Gamsjäger, H., Preis, W., Wallner, H.: Solid-solute phase

Department: Preliminary assessment of geological disposal

equilibria in aqueous solutions XIV. Thermodynamic

system for spent fuel in Japan – First progress report on

analysis of the solubility of hellyerite in water. Monatsh.

direct disposal –. JAEA-Research 2015-016 (2015) (inChemie 132 (3), pp.411–415 (2001).

Japanese).

[39] Doi, R., Uchikoshi, K., Beppu, H.: The FeSe2(cr) solubility[27] Berner, U.: Project Opalinus Clay – Radionuclide

determined by solubility experiments of Se co-existing withconcentration limits in the cementitious near-field of an

Fe. J. Nucl. Sci. Technol. 53(10), pp.1554-1562 (2016).

ILW repository . Technical Report 02-22, Nagra (2002).

[40] Yoshida, Y., Yoshikawa, H., Nakanishi, T.: Partition[28] JAEA: Project on advanced assessment technology

coefficients of Ra and Ba in calcite. Geochem. J. 42(3),development for impact of cement on geological disposal

pp.295-304 (2008).

system for long-lived radioactive waste. Technical report[41] Talerico, C., Ochs, M., Giffaut, E.: Solubility of Nb(V)submitted to Ministry of Economy, Trade and Industry ofunder cementitious conditions: Importance of Ca-niobate.

Japan in FY 2014 (2015) (in Japanese).

Scientific Basis for Nuclear Waste Management XXVIII[29] Berner, U.: Solubility of radionuclides in a concrete(Mat. Res. Soc. Symp. Proc Vol. 824), (Hanchar, J. M.,

environment for provisional safety analyses for SGT-E2.

Stroes-Gascoyne, S., and Browning, L. ed.) San Francisco,Technical Report 14-07, Nagra (2014).

U.S.A., April 13-16, 2004, CC8.31 (6 p.) (2004).

[30] Kitamura, A., Fujiwara, K., Doi, R., Yoshida Y., Mihara, M.,[42] Kitamura, A., Kirishima, A., Saito, T., Shibutani, S.,

Terashima, M., Yui, M.: JAEA thermodynamic database forTochiyama, O.: JAEA thermodynamic database for

performance assessment of geological disposal of high-performance assessment of geological disposal of high-level radioactive and TRU wastes. JAEA-Data/Code 2009-

level and TRU wastes: Selection of thermodynamic data of024, JAEA (2010).

molybdenum.

[31] Kitamura, A.: Update of JAEA-TDB: Update of

JAEA-Review

2010-010(2010)(inJapanese).

thermodynamic data for zirconium and those for[43] Felmy, A. R., Rai, D., Mason, M. J.: The solubility ofisosaccahrinate, tentative selection of thermodynamic data

CaMoO4(c) and an aqueous thermodynamic model forfor ternary M2+–UO22+–CO32- system and integration with

Ca2+-MoO42--ion-interactions. J. Solution Chem. 21, pp.525

JAEA’sthermodynamic

databaseforgeochemical-532 (1992).

calculations. JAEA-Data/Code 2018-018, JAEA (2019).

[44] Grambow, B., Muller, R., Rother, A.: Determination of[32] Yui, M., Azuma, J., Shibata, M.: JNC thermodynamic

molybdate mean ionic activity coefficients for the

database for performance assessment of high-levelassessment of radionuclide mobility. Radiochim. Acta 58/59,

radioactive waste disposal system. JNC TN8400 99-070,

pp.71-77 (1992).

Japan Nuclear Cycle Development institute (JNC) (1999).

[45] Morin, K. A., Hutt, N. M.: Geochemical characterization of[33] Nuclear Waste Management Organization of Japan

molybdenum leaching from rock and tailings at the Brenda(NUMO): NUMO safety case report – Development of Pre-

Minesite, British Columbia. Proceedings of the 1999

siting SDM-based Safety Case – (Draft for external review).

Workshop on Molybdenum Issues in Reclamation (Price, W.

NUMO-TR-18-03 (2018) (in Japanese).

A., Hart, B., and Howell, C. ed.) Kamloops, U.S.A.,[34] Shibata, M. et al.: Enhancement of the methodology of

September 24, 1999, pp.76-85 (1999).

repository design and post-closure performance assessment[46] Rard, J. A., Rand, M. H., Anderegg, G., Wanner, H.:
70

原子力バックエンド研究
Chemical Thermodynamics of Technetium. Elsevier,
Amsterdam (1999).
[47] Rai, D., Yui, M., Kitamura, A.: Thermodynamic model for
amorphous Pd(OH)2 solubility in the aqueous Na+–K+–H+–
OH−–Cl−–ClO4−–H2O system at 25 °C: A critical review. J.
Solution Chem. 41(11), pp.1965-1985 (2012).
[48] Rai, D., Yui, M., Schaef, H. T., Kitamura, A.:
Thermodynamic model for SnO2(cr) and SnO2(am)solubility in the aqueous Na+–H+–OH−–Cl−–H2O system. J.
Solution Chem. 40(7), pp.1155-1172 (2011).
[49] Toyohara, M., Kaneko, M., Ueda, H., Mitsutsuka, N.,
Fujihara, H., Murase, T., Saito N.: Iodine sorption onto
mixed solid alumina cement and calcium compounds. J.
Nucl. Sci. Technol. 37(11), pp.970-978 (2000).
[50] Uhler, A. D., Helz, G. R.: Solubility product of galena at
298 °K: A possible explanation for apparent supersaturationin nature. Geochim. Cosmochim. Acta 48, pp.1155-1160(1984).
[51] Taylor, P., Lopata, V. J.: Stability and solubility
relationships between some solids in the system PbO-CO2H2O. Can. J. Chem. 62, pp.395-402 (1984).
[52] Kitamura, A., Fujiwara, K., Yui, M.: JAEA thermodynamic
database for performance assessment of geological disposalofhigh-level

and

TRU

wastes:Refinementofthermodynamic data for trivalent actinoids and samarium.
JAEA-Review 2009-047, JAEA (2010).
[53] Rai, D., Felmy, A. R., Fulton, R. W.: Solubility and ion
activity product of AmPO4·xH2O(am). Radiochim. Acta
56(1), pp.7-14 (1992).
[54] Neck, V., Kim. J. I.: Solubility and hydrolysis of tetravalentactinides. Radiochim. Acta 89(1), pp.1-16 (2001).
[55] Kim, J. I., Kanellakopulos, B.: Solubility products ofplutonium(IV) oxide and hydroxide. Radiochim. Acta 48(3-4), pp.145-150 (1989).
[56] Duro, L., Montoya, V., Colàs, E., García, D.: Groundwater
equilibration and radionuclide solubility calculations.
NWMO TR-2010-02, NWMO (2010).
[57] U. S. Department of Energy (US-DOE): Yucca Mountainrepository license application: Safety analysis report.
DOE/RW-0573 (2008).

71

December 2020