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S9P6-Kojima Concrete Harvesting Activities Plans and Related Priority Research Topics in Japan R2
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Issue date:	10/04/2024
From:	Kojima M; Office of Nuclear Regulatory Research, Organization for Economic Co-operation and Development (OECD), Nuclear Energy Agency
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1 Concrete Harvesting activities / plans and related priority research topics in Japan Division of Research for Reactor System Safety Regulatory Standard and Research Department, Secretariat of Nuclear Regulation Authority (S/NRA/R)

Masa KOJIMA U.S. NRC and OECD/NEA Hybrid Workshop on International Concrete Harvesting October 4, 2024 at NRC Headquarters, Rockville, Maryland, USA

Japanese Nuclear Power Plants Fukushima Daiichi Fukushima Daini Onagawa Higashidori Hamaoka Ikata Sendai Genkai Takahama Ohi Mihama Tsuruga Shika Kashiwazaki-Kariwa Tomari Tokai Daini Tokyo Operating (BWR: 17 units)

Decommissioning (23 units)

Shimane As of October 4, 2024 2

Operating (PWR: 16 units)

Status of Operating PWR and BWR Plants

Status of Long-Term Operation Onagawa Higashidori Hamaoka Ikata Sendai Genkai Takahama Ohi Mihama Tsuruga Shika Kashiwazaki-Kariwa Tomari Tokai Daini 30 - 39 years (18 units) 0 - 29 years (10 units)

Shimane As of October 4, 2024 3

45 - 49 40 - 44 35 - 39 30 - 34 25 - 29 20 - 24 15 - 19 10 - 14 0 - 9 Operation period (years)

Operating (units) 0 2

4 6

8 10 12 0

1 1

1 3

5 10 8

4 40 - 49 years (5 units) 50 - 54 0

Review of Long-Term Facility Management Plans [1]

4 Period from the start of operation Start of the operation 30 years 40 years 50 years 60 years Long-term facility management plan for a period not to exceed 10 years Long-term facility management plan for a period not to exceed 10 years Long-term facility management plan for a period not to exceed 10 years Approval Application Approval Application Approval Application Approval Application The Review of long-term facility management plan will be verified during the review by NRA Japan.

Long-term facility management policy Inspection method and results of deteriorated condition (Special inspections are performed for applications of plants that are planned to be in operation for more than 40 years.)

Methods and results of technical evaluation of deterioration and compliance of reactor facilities with technical standards

Summary of special inspections [2]

5

Special inspections shall be conducted after 35 years from the date of the start of operation and before the beginning of the long-term facility management plan, including 40 years from the date of the start of operation.

In principle, the special inspections shall be conducted by taking core samples for testing.

Summary of special inspections (for PWR) [3]

6 Equipment and structures to be inspected Areas to be inspected Degradation events to focus on Inspection method / Inspection items Prestressed concrete reactor containment vessel Concrete Decrease in strength and shielding capacity Confirmation of strength, shielding capacity, carbonation, salt penetration, and alkaline aggregate reaction using harvested core sampling specimens, etc.

Concrete structures with safety functions Concrete structures supporting systems and equipment with safety functions Concrete structures belonging to permanent severe accident response facilities Concrete structures supporting equipment belonging to permanent severe accident response facilities Concrete Decrease in strength and shielding capacity Confirmation of strength, shielding capacity, carbonation, salt penetration, and alkaline aggregate reaction using harvested core sampling specimens, etc.

Items for Special Inspections (for PWR) [3, 4]

7 Carbonation Strength Shielding performance Chloride penetration Alkali aggregate reaction

Water intake tank Turbine building Reactor building Reactor auxiliary building Reactor bio shield concrete

Structures for Special Inspections (for PWR) [2]

8 Structure (PWR)

Member Inspection Items related to Aged Degradation *1 Strength Shielding Performance Carbon-ation Chloride Penetration AAR

2 Reactor Building Outer Shielding Wall Yes Yes Yes Yes Yes Inner Concrete Yes Yes Yes Yes Base Mat Yes Yes Yes Control Building Outer Wall Yes Yes Yes Yes Yes Inner Wall and Floor Yes Yes Yes Yes Spent Fuel Pool Yes Yes Yes Base Mat Yes Yes Yes Turbine Building Outer Wall Yes Yes Yes Yes Inner Wall and Floor Yes Yes Yes Base Mat Yes Yes Yes Intake Structure Under Water Zone Yes Yes Yes Yes Tidal Zone Yes Yes Yes Yes Atmospheric Zone Yes Yes Yes Yes

1 YES : It is essential to check the degradation phenomenon and factors by using harvested core sampling specimens.

2 AAR : Alkali Agregate Reaction

Structures for Special Inspections (for PWR) [2]

9 Structure (PWR)

Inspection Items related to Aged Degradation Strength Shielding Performance Carbon-ation Chloride Penetration AAR Structures supporting systems and equipment with safety functions or equipment belonging to the permanent severe accident response facilities.

In the reactor containment facility Yes Yes Yes In the reactor auxiliary building Yes Yes Yes In the turbine building (including the turbine rack)

Yes Yes Yes Structures other than the above (limited to structures with safety functions, structures belonging to permanent severe accident response facilities, and structures supporting systems and equipment with safety functions or equipment belonging to permanent severe accident response facilities)

Yes Yes Yes Yes Yes

10 Structure (BWR)

Member Inspection Items related to Aged Degradation Strength Shielding Performance Carbon-ation Chloride Penetration AAR Reactor Building Outer Wall Yes Yes Yes Yes Yes Inner Wall and Floor Yes Yes Yes Yes RPV Pedestal Yes Yes Yes Primary Shield Wall Yes Yes Yes Yes Base Mat inside PCV Yes Yes Yes Base Mat outside PCV Yes Yes Yes Spent Fuel Pool Yes Yes Yes Diaphragm Floor Yes Yes Yes Control Building Turbine Building Outer Wall Yes Yes Yes Yes Yes Inner Wall and Floor Yes Yes Yes Yes Base Mat Yes Yes Yes Intake Structure Under Water Zone Yes Yes Yes Yes Tidal Zone Yes Yes Yes Yes Atmospheric Zone Yes Yes Yes Yes Structures for Special Inspections (for BWR) [2]

Structures for Special Inspections (for BWR) [2]

11 Structure (PWR)

Inspection Items related to Aged Degradation Strength Shielding Performance Carbon-ation Chloride Penetration AAR Structures supporting systems and equipment with safety functions or equipment belonging to the permanent severe accident response facilities.

In the reactor building Yes Yes Yes In buildings other than the reactor building (limited to those in which a central control room is installed)

Yes Yes Yes In the turbine building (including turbine racks)

Yes Yes Yes Structures other than the above (limited to structures with safety functions, structures belonging to permanent severe accident response facilities, and structures supporting systems and equipment with safety functions or equipment belonging to permanent severe accident response facilities)

Yes Yes Yes Yes Yes

NPPs that have already undergone special inspections Sendai ***

Takahama

Mihama

Tokai Daini **

As of October 4, 2024 12 Unit Reactor type Start of operation Operation period Takahama Unit-1 PWR 14/Nov/1974 49 years Takahama Unit-2 PWR 14/Nov/1975 48 years Mihama Unit-3 PWR 1/Dec/1976 47 years Tokai Daini BWR 28/Nov/1978 45 years Sendai Unit-1 PWR 4/Jul/1984 40 years Takahama Unit-3 PWR 17/Jan/1985 39 years Takahama Unit-4 PWR 5/Jun/1985 39 years Sendai Unit-2 PWR 28/Nov/1985 38 years The Kansai Electric Power Co., Inc.

The Japan Atomic Power Company

- - Kyusyu Electric Power Co., Inc.

13 Inspection Method Inspection Items Inspection Method Strength JIS A 1108 : 2018 (Japanese Industrial Standards)

Method of test for compressive strength of concrete Shielding performance JASS 5N T-601 : 2013 (Architectural Institute of Japan)

Method for measuring dry density of concrete Carbonation JIS A 1152 : 2018 (Japanese Industrial Standards)

Method for measuring carbonation depth of concrete Chloride penetration JIS A 1154 : 2020 (Japanese Industrial Standards)

Methods of test for chloride ion content in hardened concrete AAR RREP-2018-1004 (NRA Safety Research Results Report) [6]

Example of ASR diagnosis flow for concrete structures JNES-RE-2013-2050 (JNES Research Report) [7]

Proposal of investigation methods of alkali aggregate reaction on concrete for nuclear power plant

14 Results of the Strength in Sendai Unit-1 [4, 5]

Structure Member Average Compressive Strength

( N / mm 2 )

Design Standard Strength

( N / mm 2 )

Reactor Building Outer Shielding Wall 44.7 22.1 Inner Concrete 43.0 22.1 Base Mat 36.3 22.1 Control Building Outer Wall 50.4 22.1 Inner Wall and Floor 43.4 22.1 Spent Fuel Pool 34.0 22.1 Base Mat 51.0 22.1 Turbine Building Outer Wall Steel-framed structure Inner Wall and Floor 39.7 22.1 Base Mat 44.7 17.7 Intake Structure Under Water Zone 38.5 23.5 Tidal Zone 29.9 23.5 Atmospheric Zone 45.4 23.5 Structures other than the above Fuel Oil Storage Tank Foundation for Emergency Diesel Power Generation 43.5 22.1 Fuel replacement water tank foundation 44.0 22.1

15 Results of the Shielding Performance in Sendai Unit-1 [4, 5]

Structure Member Average Density

( g / cm 3)

Average Dry Density

( g / cm 3)

Design Value

( g / cm 3)

Reactor Building Outer Shielding Wall 2.303 2.210 2.200 Internal concrete 2.363 2.261 2.200 Control Building Outer wall 2.353 2.262 2.200 Inner wall and floor 2.313 2.213 2.200

16 Results of the Carbonation in Sendai Unit-1 [4, 5]

Structure Member Carbonation Depth

( mm )

Concrete Cover

( mm )

Reactor Building Outer Shielding Wall 8.8 60 Inner Concrete 1.7 60 Base Mat 26.0 100 Control Building Outer Wall 42.2 70 Inner Wall and Floor 31.9 70 Spent Fuel Pool 36.5 70 Base Mat 36.5 70 Turbine Building Outer Wall Steel-framed structure Inner Wall and Floor 27.5 95 Base Mat 10.5 80 Intake Structure Under Water Zone 2.7 85 Tidal Zone 2.0 87 Atmospheric Zone 11.5 90 Structures other than the above Fuel Oil Storage Tank Foundation for Emergency Diesel Power Generation 1.9 70 Fuel replacement water tank foundation 28.7 70

17 Results of the Chloride Penetration in Sendai Unit-1 [4, 5]

Structure Member Chloride Ion Density ( % )

Chloride Ion Content ( kg / m 3 )

Concrete Cover

( mm )

0 20 20 40 40 60 60 80 80 100 100 120 Reactor Building Outer Shielding Wall 0.04 0.02 0.01 0.00 0.00 0.01 60 0.85 0.37 0.15 0.11 0.11 0.12 Control Building Outer Wall 0.02 0.01 0.01 0.01 0.01 0.01 70 0.37 0.22 0.12 0.12 0.13 0.13 Turbine Building Outer Wall Steel-framed structure Intake Structure Under Water Zone 0.32 0.28 0.22 0.16 0.12 0.11 85 6.73 5.93 4.55 3.38 2.62 2.22 Tidal Zone 0.57 0.43 0.30 0.25 0.20 0.14 87 12.43 9.31 6.67 5.44 4.33 3.01 Atmospheric Zone 0.07 0.08 0.06 0.05 0.05 0.05 90 1.50 1.69 1.28 1.10 1.06 1.00 Structures other than the above Fuel Oil Storage Tank Foundation for Emergency Diesel Power Generation 0.01 0.01 0.01 0.01 0.01 0.01 70 0.34 0.20 0.16 0.15 0.15 0.15 Fuel replacement water tank foundation 0.04 0.01 0.01 0.01 0.01 0.01 70 0.45 0.21 0.17 0.13 0.13 0.12

18 Results of the AAR in Sendai Unit-1 [4, 5]

Structure Member Stage of Progression Delayed-Expansion Reactive Minerals Reactor Building Outer Shielding Wall ii: No reactive

Inner Concrete i: No reactive

Base Mat i: No reactive

Control Building Outer Wall i: No reactive

Inner Wall and Floor ii: No reactive

Spent Fuel Pool ii: No reactive

Base Mat

Turbine Building Outer Wall Steel-framed structure Inner Wall and Floor ii: No reactive

Base Mat

Intake Structure Under Water Zone ii: No reactive

Tidal Zone ii: No reactive

Atmospheric Zone ii: No reactive Cryptocristalline quartz Microcristalline quartz Structures other than the above Fuel Oil Storage Tank Foundation for Emergency Diesel Power Generation ii: No reactive

Fuel replacement water tank foundation ii: No reactive

19 Structure Member Stage of Progression

Delayed-Expansion Reactive Minerals Reactor Building Outer Shielding Wall ii: No reactive

i: Reaction rim in aggregates Light-weight (Latency)

No reactive ii: Gel seepage in cement pastes Light-weight (Latency)

No reactive iii: Cracks and gel filling in aggregates Light-weight (Latency)

No reactive iv: Cracks and gel filling in cement pastes Medium (Progress and Acceleration Periods)

Reactive v: Gel filling in air bubbles in cement paste Pronounced (Accelerated and Deteriorated Phases)

Reactive Reaction Rim Reaction Rim Reaction Rim AAR Gel Reaction rim formation and gel seepage were observed at most of the inspected locations.

Conditions for alkali aggregate reaction were minor.

AAR Gel Results of the stereo microscope in Sendai Unit-1 [5]

20 Structure Member Stage of Progression Delayed-Expansion Reactive Minerals Intake Structure Atmospheric Zone ii: No reactive Cryptocristalline quartz Microcristalline quartz Reaction Rim Rhyolite Cement paste Cryptocrystalline quartz and Feldspar Plagioclase Single nicole Orthogonal nicole In some parts of the "intake structure", delayed dilatant reactive minerals (cryptocrystalline quartz and microcrystalline quartz) were observed in the -part of the marine sand, the rhyolite.

As a result of the accelerated expansion test (*1), the possibility of delayed expansion was judged to be low. Other than rhyolite, no retarded expansion reactive minerals were observed.

1: The accelerated concrete core expansion test in 1N NaOH solution at 80 degrees for 4 weeks was conducted in 2022. Compared to the judgment criteria (*2) (expansion rate of less than 0.1% in 21 days), the expansion rate was about 0.069% after 28 days of immersion.

2Katayama et al: Alkali-aggregate reaction under the influence of deicing salts in the Hokriku district, Japan (2004)

Results of the polarizing microscope in Sendai Unit-1 [5]

21 Research using waste materials from Hamaoka Unit-1 [8, 9]

Objective:

To develop a rational integrity evaluation method that minimizes building damage by making full use of nondestructive testing methods and analytical evaluation methods.

Research on the use of the decommissioning plant of Hamaoka Unit-1 organized by CEPCO*

CEPCO: Chubu Electric Power Co., Inc.

22 Verification of non-destructive testing method The applicability of nondestructive testing methods will be examined to see if they can be used as a substitute for concrete strength testing without core sampling.

Verification of evaluation method by numerical analysis The applicability of a numerical analysis method based on a database will be examined to see if it can be used as a substitute for concrete strength without the need to examine concrete strength by core sampling.

Construction of a new evaluation method for the integrity of concrete structures Development of Concrete Database Strength, specific gravity, static and dynamic modulus of elasticity, moisture content, formulation estimation, carbonization depth, alkali aggregate reaction, etc.

Research using waste materials from Hamaoka Unit-1 [8, 9]

23 Hamaoka Core sampling locations Outer wall of containment vessel RPV pedestal MS Tunnel Spent fuel pool Reactor building inner wall Reactor building outer wall Foundation mat Reactor well section Floor slab One side of the inner wall of the building Interior wall joints, etc.

Unit Reactor type Electrical output Start of operation End of Operation Hamaoka Unit-1 BWR 540 MWe 17/Mar/1976 30/Jan/2009 Research using waste materials from Hamaoka Unit-1 [8, 9]

24 Research using waste materials from Hamaoka Unit-1 [10]

In the concrete wall (1.5 m thick) in the general area away from the reactor containment vessel, the interior was about 1.5 times stronger than the outer part.

In the biological shielding wall exposed to high temperatures and radiation, the interior was about twice as strong as the outer part.

The strength increase was shown to be related to the distribution of moisture in the concrete. Microstructural observations using an electron microscope revealed that calcium hydroxide produced by the hydration reaction of cement reacts with minerals (alkali feldspars) present in the sand in the concrete to form a substance called calcium aluminosilicate hydrate.

Analysis of biological shielding walls and pedestals (the lower part of the reactor pressure vessel), which are exposed to relatively high temperatures during power plant operation, revealed the formation of tobermorite, a type of rock mineral, which increases chemical stability and strength.

25 Japan's International Contributions NRA Japan publishes results and details of special inspections on its website.

See refs. 4-5, refs. 11-19 CEPCO introduces its research results on ICIC (International Committee on Irradiated Concrete). [8]

See refs. 20-27

26 Reference

1. The 7th study team on safety regulation of aged power reactors, Document 2-2, "Overall picture of the regulatory system to ensure the safety of power reactors that have been in operation for a long period of time", pp. 9-10, 19 June 2023.

https://www.nra.go.jp/data/000436842.pdf https://www.nra.go.jp/disclosure/committee/yuushikisya/koukeinenka/120000001_00006.html

2. NRA rules for commercial power reactors, "Examination criteria for long-term facility management plans for commercial power reactors", 30 August 2023.

https://www.nra.go.jp/data/000451732.pdf https://www.nra.go.jp/law_kijyun/law/jitsuyou_kisoku.html

3. The 5th study team on safety regulation of aged power reactors, Document 1-3, "Special inspections", pp. 10-13, 19, 26 April 2023.

https://www.nra.go.jp/data/000428259.pdf https://www.nra.go.jp/disclosure/committee/yuushikisya/koukeinenka/120000001_00004.html

4. The 1107th review meeting on the conformity of nuclear power plants to the new regulation standards, Sendai Unit-1 and 2, Document 2-4-1, 24 January 2023.

https://www2.nra.go.jp/data/000418095.pdf https://www2.nra.go.jp/disclosure/committee/yuushikisya/tekigousei/power_plants/300002593.html

27 Reference

5. Hearing on the application for the extension of the operation period of Sendai nuclear power plant (extension of the operation period of reactors Unit-1 and 2),

The detailed explanation of the special inspections, Document 4, Document 10, Document 16, Document 22, 10 October 2023.

6. NRA safety research report, Development of technical knowledge for licensing reviews of lifetime extension and aging management: 3.2 Study on ASR (Alkali Silica Reaction) of concrete structures, RREP-2018-1004, Fig.3.8 Example of ASR diagnosis flow for concrete structures, p. 28, November 2018.

https://warp.da.ndl.go.jp/info:ndljp/pid/11203941/www.nsr.go.jp/data/000253084.pdf https://warp.da.ndl.go.jp/info:ndljp/pid/11203941/www.nsr.go.jp/activity/anzen/seika/anzen_houkoku.ht ml

28 Reference

9. Shizuoka prefecture disaster prevention and atomic energy science council, 10th specialist subcommittee for verification of nuclear economy, etc., 3rd nuclear energy subcommittee meeting in JFY 2015, "Status of decommissioning of Hamaoka NPP units 1 and 2 and research on the adoption of government-subsidized projects utilizing the decommissioning plant", 30 March 2016.

https://www.pref.shizuoka.jp/_res/projects/default_project/_page_/001/030/310/shiryou2_280330.pdf https://www.pref.shizuoka.jp/bosaikinkyu/genshiryoku/genshiryokukaigibunkakai/1030310.html

10. Nuclear industry newspaper, "Nagoya university and others use Hamaoka Unit-1 to increase the strength of concrete", 17 November 2020.

https://www.jaif.or.jp/journal/japan/5400.html

8. Research using concrete from Hamaoka Unit-1, Concrete edition, Techno fair 2020 https://www.chuden.co.jp/resource/seicho_kaihatsu/kaihatsu/techno/techno_webtenzikai2020/techno_w ebtenzikai2020_04_2.pdf https://www.chuden.co.jp/seicho_kaihatsu/kaihatsu/techno/techno_webtenzikai2020/web_safety_08.html

7. JNES Research Report, Proposal of investigation methods of alkali aggregate reaction on concrete for nuclear power plant, JNES-RE-2013-2050, February 2014.

https://warp.da.ndl.go.jp/info:ndljp/pid/10207746/www.nsr.go.jp/archive/jnes/content/000127228.pdf https://warp.da.ndl.go.jp/info:ndljp/pid/10207746/www.nsr.go.jp/archive/jnes/gijyutsu/seika/re_report_20 13.html

29 Reference

13. The 340th review meeting on the conformity of nuclear power plants to the new regulation standards, Mihama Unit-3, Document 2-4-1, 15 March 2016.

https://warp.da.ndl.go.jp/info:ndljp/pid/11235834/www.nsr.go.jp/data/000143523.pdf https://warp.da.ndl.go.jp/info:ndljp/pid/11235834/www.nsr.go.jp/disclosure/committee/yuushikisya/tekig ousei/power_plants/00000124.html

14. Hearing on application for approval of extension of operation period (Mihama Unit-

3) (45), Document 1, 2 November 2016.

https://www.nra.go.jp/data/000169345.pdf https://www.nra.go.jp/disclosure/committee/yuushikisya/untenkikanencho/meeting/mihama3.html

11. The 251st review meeting on the conformity of nuclear power plants to the new regulation standards, Takahama Unit-1 and 2, Document 1-4, 21 July 2015.

https://warp.da.ndl.go.jp/info:ndljp/pid/11235834/www.nsr.go.jp/data/000115461.pdf https://warp.da.ndl.go.jp/info:ndljp/pid/11235834/www.nsr.go.jp/disclosure/committee/yuushikisya/tekig ousei/power_plants/00000058.html

12. Hearing on the application for approval of extension of operation period (Takahama Unit-1 and 2) (52), Document 4, 16 June 2016.

https://www.nra.go.jp/data/000154282.pdf https://www.nra.go.jp/disclosure/committee/yuushikisya/untenkikanencho/meeting/takahama12.html

30 Reference

17. The 1182nd review meeting on the conformity of nuclear power plants to the new regulation standards, Takahama Unit-3 and 4, Document 1-7, 5 September 2023.

https://www2.nra.go.jp/data/000447398.pdf https://www2.nra.go.jp/disclosure/committee/yuushikisya/tekigousei/power_plants/300002664.html

18. Hearing on the application for approval of the extension of the operation period of Takahama Power Plant (extension of the operation period of reactors Unit-3 and 4) and the application for approval of changes to safety regulations (technical evaluation of the aging of reactors Unit-3 and 4, etc.), Document 15, Document 16, 5 December 2023.

https://www.nra.go.jp/data/000463761.pdf https://www.nra.go.jp/data/000463762.pdf https://www.nra.go.jp/disclosure/committee/yuushikisya/untenkikanencho/meeting/takahama34.html

15. The 555th review meeting on the conformity of nuclear power plants to the new regulation standards, Tokai Daini, Document 1-5-1, 8 March 2018.

https://warp.da.ndl.go.jp/info:ndljp/pid/12348280/www2.nra.go.jp/data/000222521.pdf https://warp.da.ndl.go.jp/collections/info:ndljp/pid/12348280/www2.nra.go.jp/disclosure/committee/yuus hikisya/tekigousei/power_plants/00002051.html

16. Hearing on application for approval of extension of operation period (Tokai Daini)

(51), Document 4, 5 November 2018.

https://www.nra.go.jp/data/000252495.pdf https://www.nra.go.jp/disclosure/committee/yuushikisya/untenkikanencho/meeting/toukaidai2.html

31 Reference

19. Hearing on the application for approval of the extension of the operation period of Takahama Power Plant (extension of the operation period of reactors Unit-3 and 4) and the application for approval of changes to safety regulations (technical evaluation of the aging of reactors Unit-3 and 4, etc.), 22 Document Document 23, September 27, 2023.

https://www.nra.go.jp/data/000452559.pdf https://www.nra.go.jp/data/000452560.pdf https://www.nra.go.jp/disclosure/committee/yuushikisya/untenkikanencho/meeting/takahama34.html

20. I. Maruyama, J. Ryme, A. Aili, S. Sawada, O. Kontani, S. Ueda, R. Shimamoto, Long-term use of modern portland cement concrete: The impact of Al-tobermorite formation, Materials & Design, vol. 198, 109297 (2021).

https://doi.org/10.1016/j.matdes.2020.109297

21. J. Ryme, I. Maruyama, R. Shimamoto, A. Tachibana, Y. Tanaka, S. Sawada, Y.

Ichikawa, O. Kontani, Long-term material properties of a thick concrete wall exposed to ordinary environmental conditions in a nuclear reactor building: The contribution of cement hydrates and feldspar interaction, Journal of Advanced Concrete Technology, vol. 17, pp. 195-215 (2019).

https://www.jstage.jst.go.jp/article/jact/17/5/17_195/_pdf/-char/ja

32 Reference

22. A. Aili, I. Maruyama, G. Geng, S. Umeki, K. Sumitani, S. Sawada, S. Ueda, Y. Umeki, Micro Xray diffraction and elemental study on Altobermorite formation in aged modern concrete, Journal of the American Ceramic Society, vol. 105, issue 11, pp.

6924-6937 (2022).

https://doi.org/10.1111/jace.18624

23. A. Aili, I. Maruyama, Y. Umeki, K. Yokokura, Impact of aggregate-cement paste reaction forming Al-tobermorite on ion transport in aged concrete, Transport in porous media, vol. 151, pp. 243-261 (2024).

https://doi.org/10.1007/s11242-023-01998-2

24. K. Yokokura, H. Wada, O. Kontani, I. Maruyama, S. Manager, N. Civil, S. Manager, K.

Corporation, Concrete strength evaluation of massive concrete structures based on the data obtained from decommissioning nuclear power plant, 24th international conference on structural mechanics in reactor technology, SMiRT-24, pp. 209-218, Busan, Korea (2017).

25. K. Yokokura, O. Kontani, S. Sawada, I. Maruyama, Compressive strength of massive concrete structure members increasing from the surface to the inside, 27th international conference on structural mechanics in reactor technology, SMiRT-27, Yokohama, Japan, Tu.1.H-04 (2024).

33 Reference

26. Nagoya university, Do as the romans: power plant concrete strengthens with time, 8 January 2021.

https://architexturez.net/pst/az-cf-214556-1607606477 https://en.nagoya-u.ac.jp/research/activities/news/2021/01/do-as-the-romans-power-plant-concrete-strengthens-with-time.html

27. News On Research / Academia, Rare mineral that improves the long-term performance of concrete, The international information center for civil engineers, 5 February 2021.

https://www.thecivilengineer.org/index.php/news/rare-mineral-that-improves-long-term-concrete-performance

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