The decommissioning project of the Fukushima Daiichi Nuclear Power Plant continues as an unprecedented technical challenge 14 years after the accident on March 11, 2011. This project is not merely a dismantling operation of nuclear facilities, but faces an ultra-high difficulty technical challenge unprecedented in human history: safely removing approximately 880 tons of molten nuclear fuel (fuel debris) in a high-radiation environment.
The entire project requires 30-40 years and is estimated to cost approximately 81 trillion yen. Currently, about 4,500 workers are engaged daily, with 42 prime contractors and approximately 800 cooperating companies forming a massive operational structure. While general work clothes can now be worn in about 96% of work areas, significantly improving working conditions, the technical difficulty remains extremely high.
Four Major Decommissioning Projects
1. Fuel Debris Removal (Most Important and Difficult)
Fuel debris removal is the most challenging task at the core of decommissioning. The nuclear fuel melted due to the accident, penetrated the reactor pressure vessel, and cooled and solidified at the bottom of the containment vessel, with an estimated total amount of approximately 880 tons.
Severity of Technical Challenges The first trial removal conducted at Unit 2 from September to November 2024 required 8 days to recover only 0.7 grams of fuel debris samples. At this work efficiency rate, complete removal of the remaining approximately 880 tons would theoretically take several hundred years, making realistic scheduling impossible.
The exact location, shape, and chemical properties of the debris remain unknown, requiring remote work in an extremely high radiation environment of several sieverts per hour. Current remote operation technology has limitations for precision work, and robot technology often experiences electronic equipment failures due to radiation exposure.
Prime Contractor Structure (Manufacturer-Led)
- Units 1 & 4: Hitachi-GE Nuclear Energy as primary contractor
- Units 2 & 3: Toshiba Energy Systems as primary contractor
- Construction Support: Kajima-Shimizu-Takenaka-Kumagai-Ando Hazama JV provides construction support
The trial removal at Unit 2 was conducted using remote operation equipment developed by Toshiba, with Mitsubishi Heavy Industries also participating in fuel debris removal equipment development. For future full-scale removal, consideration is underway to begin at Unit 3 in the early 2030s.
2. Spent Fuel Pool Fuel Removal
This involves safely transferring fuel assemblies stored in each unit’s spent fuel pool to secure locations. This work has relatively high technical certainty and has already achieved specific results.
Progress Status
- Unit 4: Completed December 2014 (1,535 assemblies) – Takenaka Corporation as primary contractor
- Unit 3: Completed February 2021 (566 assemblies) – Kajima Corporation as primary contractor
- Unit 6: Completed April 2025 (1,456 assemblies)
- Units 1 & 2: Currently in progress
- Unit 5: To begin after Unit 6 completion
Prime Contractor Structure (Unit-Based Distribution)
- Unit 1: Shimizu Corporation (Hitachi-GE technical support)
- Unit 2: Kajima Corporation (Toshiba technical support)
- Unit 3: Kajima Corporation (Toshiba technical support) ※Completed
- Unit 4: Takenaka Corporation (Hitachi-GE technical support) ※Completed
At Unit 1, demolition of the building cover (remaining portion) has been completed, and extensive cover installation work began in September 2021. At Unit 2, construction of fuel removal platforms and anterooms is in progress.
3. Contaminated Water and Treated Water Countermeasures
This involves countermeasures for contaminated water generated when groundwater and rainwater flowing into reactor buildings mix with radioactive materials, and management of treated water after purification processing.
Contaminated Water Generation Suppression Results Contaminated water generation in FY2024 has been suppressed to approximately 70 m³/day, achieving ahead of schedule the mid-to-long-term roadmap goal of “less than 100 m³/day by 2025.” This is due to the effects of repairing damaged roof sections, facing (mortar covering of slopes) within the site, and the land-side impermeable wall (frozen soil wall).
ALPS Treated Water Ocean Discharge ALPS treated water ocean discharge began on August 24, 2023, and was conducted 7 times in FY2024, with annual cumulative discharge of approximately 55,000 m³ and total tritium discharge of roughly 12.7 trillion becquerels (below the annual upper limit of 22 trillion becquerels). Marine monitoring has confirmed that all measurements have remained below WHO drinking water guidelines (10,000 becquerels/litre) and operational indicators (700 becquerels/litre).
Prime Contractor Structure (Technology Manufacturer Type)
- Existing ALPS: Toshiba Energy Systems (Toshiba equipment)
- High-Performance ALPS: Hitachi-GE Nuclear Energy (Hitachi equipment)
- Land-side Impermeable Wall: Kajima Corporation (frozen soil method, 1,500m length, 30m depth)
- Sea-side Impermeable Wall: Kajima Corporation and others (completed October 2015)
Approximately 1,000 tanks are used for storing contaminated water, with the replacement of flange-type tanks with welded-type onesreducing leakage risks.
4. Waste Countermeasures
This involves safe storage, treatment, and disposal of radioactive waste generated during decommissioning work. This field is technically relatively established, but faces serious social issues, such as securing final disposal sites.
Major Facilities and Work
- Solid Waste Storage Buildings: Multiple buildings under sequential construction, storing large waste and water treatment secondary waste
- Miscellaneous Solid Waste Incineration Facility: Incineration processing of used protective clothing, etc.
- Water Treatment Secondary Waste: Stabilization processing of sludge generated from ALPS treatment
Prime Contractor Structure (Construction Industry Distributed Type)
- Solid Waste Storage Buildings: Individual orders by Kajima, Taisei, Shimizu, etc.
- Waste Incineration Facilities: Various plant manufacturer and construction company JVs
- Water Treatment Secondary Waste Processing: Manufacturer-led by Toshiba, Hitachi, etc.
In FY2024, construction of Solid Waste Storage Building No. 11 progressed, with concrete plant installation work beginning in February 2025.
Detailed Analysis of Prime Contractor Structure
The prime contractor structure for the Fukushima Daiichi decommissioning project is a complex distribution system combining technology field-based and unit-based responsibilities. Prime contractors receiving direct orders from TEPCO number 42 companies (including manufacturers), with approximately 800 cooperating companies positioned below them in a multi-layered structure.
Role Distribution of Major Construction Companies
Five Super General Contractors System
- Kajima Corporation: Primary contractor for Units 2 & 3, land-side impermeable wall, Unit 3 fuel removal cover construction
- Shimizu Corporation: Primary contractor for Unit 1, Unit 1 building cover demolition and large cover installation
- Takenaka Corporation: Primary contractor for Unit 4 (completed)
- Taisei Corporation: Individual orders for various construction works
- Obayashi Corporation: Surrounding infrastructure development, etc.
Mid-tier General Contractors Participation
- Kumagai Gumi: Kajima JV member
- Ando Hazama: Kajima JV member
- Maeda Corporation: Various civil engineering works
Technology Distribution of Major Manufacturers
Three Nuclear Manufacturers System
- Toshiba Energy Systems: Units 2 & 3 fuel debris removal, existing ALPS, utilizing Westinghouse technology
- Hitachi-GE Nuclear Energy: Units 1 & 4 fuel debris removal, high-performance ALPS, utilizing GE technology
- Mitsubishi Heavy Industries: Fuel debris removal equipment development, remote operation technology
These manufacturers continue to handle decommissioning work for the units they were responsible for during construction, leveraging technical advantages from their detailed equipment knowledge.
Foreign Company Involvement
Rather than direct prime contractor orders, involvement occurs in three forms:
- Technology Provision: License supply and technology transfer of overseas advanced technologies
- JV Participation: Indirect participation in joint ventures with domestic companies
- Consulting: Technical advisory and specialized technical support
Technologies from Chernobyl decommissioning, French decommissioning technology, and German decommissioning experience are particularly utilised through technology provision.
Detailed Workforce Deployment
Workforce Scale Trends
The workforce at Fukushima Daiichi has undergone significant changes from the emergency response period immediately after the accident to the current stable period.
Chronological Changes
- Around 2013: Approximately 3,500 people/day
- 2015 (Peak): Approximately 7,000 people/day (contaminated water countermeasure construction expansion period)
- 2018-2019: Monthly approximately 8,800-9,500 people (registration basis)
- 2024: Approximately 4,530 people/day (March data)
- 2025: Approximately 4,500 people/day (May estimate)
Annual Total Person-Count
- FY2024: Approximately 190,000 entries/year (total entry count)
Regional and Corporate Composition
Regional Employment Structure
- Fukushima Prefecture Employment Rate: Approximately 70% (April 2024)
- Hamadori Region Residents: Approximately 90% of Fukushima Prefecture workers
- Workers from Outside Prefecture: Approximately 30%
Corporate Size Composition
- TEPCO Employees: Several hundred scale
- Prime Contractors: 42 companies (each ranging from dozens to hundreds)
- Cooperating Companies: Approximately 800 companies (each ranging from several to dozens)
Estimated Corporate Workforce
While specific corporate workforce data is not publicly available, based on project scale and role distribution, the following estimates can be made:
Major General Contractor Groups
- Kajima Corporation: Estimated 500-800 people/day (Units 2 & 3 + frozen soil wall)
- Shimizu Corporation: Estimated 300-500 people/day (Unit 1 primary contractor)
- Takenaka Corporation: Estimated 200-300 people/day (continuing peripheral work after Unit 4 completion)
Manufacturer Groups
- Toshiba Energy Systems: Estimated 200-400 people/day (Units 2 & 3 + ALPS)
- Hitachi-GE Nuclear Energy: Estimated 200-400 people/day (Units 1 & 4 + ALPS)
- Mitsubishi Heavy Industries: Estimated 100-200 people/day (development and technical support)
Small and Medium Cooperating Companies
- 800 companies sharing remaining approximately 2,500-3,000 people
- Average 3-4 people per company
However, these figures vary significantly with construction progress and seasonal factors, with significant changes expected as fuel debris removal becomes full-scale.
Fundamental Project Management Issues
Management Difficulties with Technical Uncertainty
The Fukushima Daiichi decommissioning project is a unique project fundamentally lacking the “predictability” that conventional project management methods assume. Particularly for fuel debris removal, removal methods must be determined without an accurate understanding of debris conditions, creating aconstant risk of significant divergence between plans and actual work.
Problems with Multi-layered Subcontracting Structure
The complex contract structure of 42 prime contractors and 800 cooperating companies creates the following serious problems:
- Dispersed and Ambiguous Responsibility and Authority: Unclear decision-makers when technical judgment is required
- Delayed and Distorted Information Transmission: Information not accurately transmitted from field to headquarters
- Technical Succession Difficulties: Unestablished mechanisms for technology and experience succession in the 30-40 year long-term project
Contradiction Between Safety Requirements and Efficiency
Extremely high safety requirements make it virtually impossible to improve schedule management accuracy in environments where work must be suspended for even minor risks. Previous schedule delays have been primarily due to cautious approaches for safety assurance rather than technical difficulties, and this trend is expected to continue.
Corporate Business Scope Matrix
Legend
- ★★★: Primary contractor/core role
- ★★☆: Important role/technical support
- ★☆☆: Partial participation/cooperation
- ー: No involvement/unknown
Construction and Civil Engineering Companies
| Company | Fuel Debris Removal | Spent Fuel Removal | Contaminated/Treated Water | Waste Management | Notes |
| Kajima Corporation | ★☆☆ | ★★★ (Units 2&3) | ★★★ (Frozen wall) | ★★☆ | Units 2&3 primary, frozen impermeable wall construction |
| Shimizu Corporation | ★☆☆ | ★★★ (Unit 1) | ★☆☆ | ★☆☆ | Unit 1 primary, building cover demolition |
| Takenaka Corporation | ★☆☆ | ★★★ (Unit 4 completed) | ー | ★☆☆ | Unit 4 completed, continuing peripheral work |
| Taisei Corporation | ー | ★☆☆ | ★☆☆ | ★★☆ | Individual construction work orders |
| Obayashi Corporation | ー | ★☆☆ | ★☆☆ | ★☆☆ | Surrounding infrastructure development |
| Kumagai Gumi | ★☆☆ | ★☆☆ | ★☆☆ | ★☆☆ | Kajima JV member |
| Ando Hazama | ★☆☆ | ★☆☆ | ★☆☆ | ★☆☆ | Kajima JV member |
| Maeda Corporation | ー | ★☆☆ | ★☆☆ | ★☆☆ | Individual civil engineering orders |
Manufacturer Companies
| Company | Fuel Debris Removal | Spent Fuel Removal | Contaminated/Treated Water | Waste Management | Notes |
| Toshiba Energy Systems | ★★★ (Units 2&3) | ★★☆ (Units 2&3 tech support) | ★★★ (Existing ALPS) | ★★☆ | Unit 2 trial removal conducted, Westinghouse technology |
| Hitachi-GE Nuclear Energy | ★★★ (Units 1&4) | ★★☆ (Units 1&4 tech support) | ★★★ (High-performance ALPS) | ★★☆ | GE technology utilization, fuel handling equipment |
| Mitsubishi Heavy Industries | ★★☆ (Equipment development) | ★☆☆ | ★☆☆ | ★☆☆ | Debris removal equipment development, remote operation technology |
| IHI | ★☆☆ | ★☆☆ | ★☆☆ | ★★☆ | Mechanical equipment and piping work |
| Kawasaki Heavy Industries | ★☆☆ | ★☆☆ | ★☆☆ | ★☆☆ | Special machinery and robotics |
IT and Systems Companies
| Company | Fuel Debris Removal | Spent Fuel Removal | Contaminated/Treated Water | Waste Management | Notes |
| TIS Chiyoda Systems | ★★☆ (Schedule management) | ★★☆ (Schedule management) | ★★☆ (Schedule management) | ★★☆ (Schedule management) | Oracle Primavera P6, integrated project management |
| TIS | ★☆☆ (Parent company support) | ★☆☆ (Parent company support) | ★☆☆ (Parent company support) | ★☆☆ (Parent company support) | IT infrastructure and system development |
| Chiyoda Corporation | ★☆☆ (Parent company support) | ★☆☆ (Parent company support) | ★★☆ (Technical support) | ★★☆ (Technical support) | Plant technology and design |
Electric Power and Energy Companies
| Company | Fuel Debris Removal | Spent Fuel Removal | Contaminated/Treated Water | Waste Management | Notes |
| TEPCO Holdings | ★★★ (Project owner) | ★★★ (Project owner) | ★★★ (Project owner) | ★★★ (Project owner) | Overall coordination and ordering party |
| Kansai Electric Power | ★☆☆ (Technical cooperation) | ★☆☆ (Technical cooperation) | ★☆☆ (Technical cooperation) | ★☆☆ (Technical cooperation) | Decommissioning experience and technology provision |
| Chubu Electric Power | ★☆☆ (Technical cooperation) | ★☆☆ (Technical cooperation) | ★☆☆ (Technical cooperation) | ★☆☆ (Technical cooperation) | Hamaoka decommissioning experience utilization |
Specialized and Cooperating Companies (Major Companies Only)
| Company | Fuel Debris Removal | Spent Fuel Removal | Contaminated/Treated Water | Waste Management | Notes |
| Atox | ★★☆ (Remote technology) | ★★☆ (Remote technology) | ★☆☆ | ★★☆ | Nuclear specialist, remote operation and robotics |
| Toso Mirai Tech | ★★☆ | ★☆☆ | ★☆☆ | ★☆☆ | Local company, Unit 3 debris work |
| Clear Pulse | ★☆☆ | ★☆☆ | ★☆☆ | ★★☆ | Decontamination and environmental technology |
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