The 5th International Forum on the Decommissioning of the Fukushima Daiichi Nuclear Power Station

Efforts to Ensure Safety in Decommissioning （No. 3)

Safety and Challenges in Decommissioning
November 1, 2021
Tatsuya Taminami
Executive Vice President
Fukushima Daiichi Decontamination &Decommissioning Engineering Company
Tokyo Electric Power Company Holdings, Inc.
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0. Table of Contents

1. What is "Safety" in decommissioning?
2. Difficulties and challenges in decommissioning
2-1. Different basic concepts for ensuring safety2-2. Unestablished system for ensuring safety
2-3. Difficult environment for developing safety awareness
2-4. Projects requiring trial and error

3. Moving forward with safer decommissioning©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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1. What is "Safety" in decommissioning?
Decommissioning is a “Risk reduction activity” in itself
・Operating reactors: Insufficient safety state→ Low-risk state can be achievable by shutdown
・1F: Stagnation in decommissioning work can lead to slowing down in risk reduction
or lead to increased risk
→ Decommissioning work is “Effort to improve safety”: However, individual tasks may be associated with significant risk
→ Work needs to be forwarded even in high-risk conditions and environments→ Some short-term risk needs to be tolerated to reduce mid-to-long term risk

Looking at decommissioning from a safety perspective,
decommissioning is the work to reduce long-term risk of theplant continually while continuing to minimize the risk of
individual tasks and plant at that time, sometimes tolerating
short-term risk

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22. Difficulties and challenges in decommissioning
The concept of "Safety" has the same meaning in decommissioning
and operating, however, the approach to "Safety" differs significantly.
→Understanding this difference is critical in “Safe decommissioning”
2-1. Different concepts for ensuring safety→ What to take care of
2-2. Unestablished safety assurance system→ What is enough2-3. Difficult environment for developing safety awareness→ Environment where workers are less aware of nuclear safety
2-4. Projects requiring Trial & Error→ Agile response ⇔ Doesn’t tolerate failure©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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2-1. Different concepts for ensuring safety
Difficulty ①

There is no template of “What to take care of”

In normal reactors
・There are some basic concepts for ensuring safety.

・Examples of basic concepts for ensuring safety:

・Defense in-depth
Occurrence prevention-Escalation prevention-Mitigation
・Five layers of walls
Pellet - Cladding tube - RPV - PCV - Reactor building

・Fail safe
SCRAM mechanism, HE proof©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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2-1. Different concepts for ensuring safety
Difficulty ①

There is no template of “What to take care of”

At 1F
・Defense in depth

Using custom-ordered and general-purpose products(makes difficult to keep defense in depth)

・Five layers of walls

Pellet - Cladding tube - RPV - PCV - Reactor building
Only PCV is barely remaining

・Fail safe

⇔Human error directly leads facility shut-down

The design is not necessarily well-balanced, and “What to takecare” have to be determined on a case-by-case basis.
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2-1. Different concepts for ensuring safety
Effort to address the Difficulty ①
・Most challenges are “Application problems”→ “Thinking skills” is required, especially “Thinking skills as anorganization”→ Proven results from other industries shall be adopted without being
persisting nuclear safety
・One failure could lead serious consequences→ Understanding the importance of each equipment and device
・Defense in depth: Within the sequence of “Occurrence prevention-Escalation
prevention-Mitigation”, “occurrence prevention” is usually the most important.
→ Quality management to prevent failure is important→ “Quality improvements” for facilities that have been constructed in ahurry after the accident are still in progress©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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2-1. Different concepts for ensuring safety(Reference)
Examples of experience facing challenges in quality management

・Malfunctions in equipment for fuel removal from Unit 3・Operation error of the emergency shutdown button for thecontainment vessel gas management system
・Leaks from the waste storage container

・Damage to the exhaust filter in the HIC transfer device©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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2-2. Unestablished system for ensuring safety
Difficulty ②

There is no standard for “What is enough”

In normal reactors
・There is a standard for ensuring safety.

・Examples of standards for securing safety:
・Importance classification guideline
・Safety design guideline/safety assessment guideline
・Design basis accidents
・Seismic standard(design basis ground motion, seismic class classification)・Exposure assessment methods©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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2-2. Unestablished system for ensuring safety
Difficulty ②

There is no standard for “What is enough”

At 1F
・There is no “Standard for securing safety.”
・What is “Safety critical equipment”?
・Should there be redundancy in systems?
Is emergency power necessary?
・What are transients and accidents should be assumed?
・How much quality management requirement should be made?
・Which systems should have LCO?

There are no standards or precedents for “What is enough”, andeverything has to be determined on each system©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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92-2. Unestablished system for ensuring safety
Example: Redundancy in the reactor injection pump
CST reactor injection pump
凡
既設FT

例

建屋内

PT

Pump that is currently being used to injectwater into the reactor

屋外(Other reactor injection pumps are backup)

仮設

既設・仮設取合い

FT

PT

原子炉注水系（注水中ライン）

復水貯蔵
CSTタンク

2号機 CST炉注水ポンプ

原子炉注水系（補給水）
原子炉注水系（他号機）

Permanent highground reactor
injection pumpPI

原子炉注水系（非常時用）

Reactor injectionpump in the T/B

2号機 タービン建屋内
炉注水ポンプ

処理水より

2号機

Source of water for Units 1 & 3

1,3号機へ

原子炉注水系

Unit 2

FIPI

FI

PI

Treated
処理水water
バッファbuffer
タンク
tank

処理水より

補給用

1～3号機共用

消防車
FIPI

FI
1号機
To Unit2

給水系配管（消火系より）
3号機
To Unit
3

給水系配管
FI

常用高台炉注水ポンプ

ＦＤＷ(B)
Injectionline

FI

Filtrate
ろ過水タンクtank

PIRawwater
原水地下underタンク
groundtank

復水補給水系配管
1号機
To Unit2

炉心スプレイ系配管(B)

ＣＳ(B)system injection line

消防車

消防車

1～3号機共用

1～3号機共用

3号機
To Unit3

残留熱除去系配管～復水補給水系配管～消火系配管
非常用高台炉注水ポンプ
送Emergency high groundreactor injection pump

水口

2号機
原子炉圧力容器

Current injection line
Permanent reactor
injection system
Emergency reactor
injection system©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

Pure
純水タンク
watertank

PI

1号機
To Unit2

消火系配管等へ

消防車

FI

3号機 3
To Unit海※非常時

補給用設置

純水タンク脇炉注水ポンプ

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Injection pump at the sideof the pure water tank10

2-2. Unestablished system for ensuring safety
Effort to address the Difficulty ②
Establishing standards suitable for the actual situation at 1F・Importance classification of decommissioning facilities

・Approach to seismic design (Fukushima Earthquake, 2/13/2021)
・Quality management for important procurement items(based on experience of fuel removal from Unit 3)

Flexibly review standards in accordance with progress in decommissioning
・LCO related to injection (see next slide)
The followings need to be clarified in accordance with progress in fueldebris retrieval
・Scope of events that should be assumed (definition of accident events)

・Criteria for assessing impact (1 mSv/y at surrounding site, 5 mSv/accident)©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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2-2. Unestablished system for ensuring safety
Example of reviewing standards in accordance with progress indecommissioning- LCO related to reactor injection -• Continuous water injection: Require constant injection → Allow temporarysuspension• Injection water amount: 4.5 m3/h→0.9 m3/h (Unit 1)

Changes in “the amount of water necessary for reactor cooling”•Increase in injection water amount: 1.0 m3/h→1.5 m3/h→3.0 m3/h
•Power source: A dedicated DG for the pump is required. →No DG requirement©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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2-3. Difficult environment for developing safety awarenessDifficulty ③Environment where workers do not develop an awareness of nuclear safety

In normal reactors

・・Through routine tasks and learning about the nuclear power plantsystem, workers can “naturally” obtain knowledge of “nuclear safety”.
・Clear concept of not exposing the surrounding public to radiation risk
・Existence of a clear source of risk: "core“ (especially in a critical state)・Straight-forward accident scenarios where risk is faced
・Existence and awareness of the basic concepts of and standards forensuring safety©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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2-3. Difficult environment for developing safety awarenessDifficulty ③
Environment where workers do not develop an awareness of nuclear safety

At 1F
・Environment where workers do not naturally develop an awareness of nuclear safety
・Nuclear safety ≒ Do not expose the surrounding public to radiation risk

・There were no people in the surrounding area (for a while after the Accident).
・Risk sources are distributed across the station.
(fuel debris, spent fuel, waste from water treatment, contaminated rubble, etc. )・Plant potential energy that could cause an accident is significantly lower.

(Operating reactor: Low frequency, high impact→1F: High frequency, low impact)
・Workers have got “used" to abnormal situations(seeing a damaged reactor building every day, exposed to high dose on daily basis, working inhighly exposed areas, experience in the environment ‘speed is the priority’ just after theAccident)

Awareness of nuclear safety needs to be deliberately established.
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2-3. Difficult environment for developing safety awareness・The work environment has improved significantly since just after the accident.
・Worker exposure dose has fallen significantly.
Changes in worker personal exposure dose (month)
TEPCO
employees
Contractor
workers

March 2011

June 2021 Average
0.32 mSv/month(provisional)(reference)
Dose limit

1.67 mSv/month(Monthly average of the dose
limit of 100 mSv/five years)©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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2-3. Difficult environment for developing safety awarenessIn the world, the annual dose is around 10.1 person・Sv even at the highest plant.
1F workers are still exposed to three times the exposure dose of a BWR plant withthe highest dose rate in the world.

40
27.02

Fukushima
Daiichi20

Total dose (person・Sv／2 year-average)

10.10©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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Ringhals(3)Oskarshamn(1)Olkiluoto(2)Gundremmingen(1)Monticello(1)Cooper(1)Hope Creek(1)Clinton(1)Cofrentes(1)FitzPatrick(1)Columbia(1)Harris(3)Limerick(2)Grand Gulf(1)Forsmark(3)Leibstadt(1)Susquehanna(2)River Bend(1)Dresden(2)Penly(3)Peach Bottom(2)Tarapur(2)Brunswick(2)Quad Cities(2)2.70Nine Mile Point(2)Browns Ferry(3)Fermi(1)

Laguna Verde(2)0Fukushima
福島第一(6)
Daiichi4.00 3.60

LaSalle(2)10Kuosheng(2)30FY2019 27. 20 person・Sv
FY2020 26. 84 person・Sv

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2-3. Difficult environment for developing safety awareness

Efforts to address the Difficulty ③・Mechanisms to increase awareness of nuclear safety
Established the Safety and Quality Office (in April 2020), Design Review
Meetings, Risk Management, Nonconformance Management,
Safety Culture Monitoring Meetings

・Introducing built-in gate processes to work
・Use of reviews by external organizations
WANO, IAEA, JANSI,TEPCO Nuclear Reform Monitoring Committee,
Nuclear Safety Oversight Office・Others
10 Traits, Safety Improvement Proposal Competitions.

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2-3. Difficult environment for developing safety awareness
Example: Use of risk maps

・Nuclear safety risk map・PJ implementation risk map

・Decommissioning CP risk map

Large

・Operation maintenance risk map
132Impact

48A514109615

11B
7Small1216Low©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

13Probability
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High18

2-4. Projects requiring Trial & Error

Other characteristics of 1F related to nuclear safety
・”Stop & Cool & Contain” and “Stop→Cool→Contain”
・Nuclear fuel materials that are not sealed (exposed)
・Work and timeline that make setting goals difficult(Decades without “operation → outages→ startup”. Ambiguous goals)

・Accumulation of immature technologies(Unproven technology, prototype, general-purpose items, andcustom-ordered items)
・Areas that need trial and error ⇔ Culture that does not tolerate failure
・Difficulties in understanding the entire risk under the PJ system(Optimizing for each project rather than the entire)

・Equipment/facility documents are not fully developed.

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3. Moving forward with safer decommissioning

Different ways of thinking and approach are necessary
・No standards→ A lot of room to think and decide for oneself
・Habits built from old ways of thinking→ Necessary for a shift in mindset, high expectations for the post-3.11 generations
・Different challenge than in nuclear power plants→ Importance of learning widely from the experience of others, including overseas

・Agile approach (Trial & Error, Lead and Learn, PDCA, social receptiveness to DLTG)→Perspective of the local community/society and information provision in advance,
Decommissioning Information and Planning Office・Maintaining motivation→ SDGs, adopting cutting edge technologies in the field despite the “backwardfacing” image of 1F work (robots and remote operation technology)©Tokyo Electric Power Company Holdings, Inc. All Rights Reserved.

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