Three Mile Island Unit 2
Defueling- Safety & Risk Reduction
Process Experience: Core Drilling
Machine Evolution
Fukushima Forum
3 July 2017
Lake H. Barrett
Lake@Lbarrett.com
L. Barrett Consulting LLC

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Three Mile Island Experience• Light Water Power Reactor Core Melt Accident– 1979: 38 Years ago– 14 Year $1B Decontamination/Defueling Project• Similar & Different Than Fukushima Daiichi (1F)
– TMI Major but Less Technically Severe Accident– Similar Technical/Management/Social-Political
Challenges• Many Lessons Are Applicable• TMI Was Safely Accomplished & 1F Can Be Also
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Three Mile Island Units 1 &2
March 28, 1979

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Three Mile Island Unit-2 Accident
March 28, 1979
04:00 Relief Valve fails toclose

Operators
Believe
ReactorOverfilled andTurn Off
Injection
Pumps

Core is uncovered Fueloverheats/fails/~50% Melt

650,000 gallons of highly
radioactive water collects
L. Barrett Consulting
4LLC

TMI Core Damage Sequence~120 Min Core UncoversDamage Starts
800C Burst (~06:00)~150MinCore Cladding
Oxidize ~1800C(~06:30)
L. Barrett Consulting LLC~226 Min Core
Melted ~2700C(~07:30)
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TMI Decontamination andDecommissioning (D&D) Approach• Prompt Safe & Cost Effective Cleanup– Control, Contain, Reduce Risks, Stabilize• Clear End State Focus: Defuel Damaged Core
• Expect Surprises– Monitor, Self-Learn, Adapt, Succeed• Keep Simple– Adapt Proven Technologies As Much As Possible• Work Safely From Outside In– Step-wise with Constant Feedback Evolution• Always: Think, Learn, Create, Improve
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TMI D&D Organizations• General Pubic Utilities Nuclear (GPUN)Owner/Licensee-Responsible for D&D Work
• US Nuclear Regulatory Commission– Delegated Authority to New TMI Program Office (TMIPO)• US Department of Energy (DOE)– Provided Federal R&D Assistance (GEND) to:– Allowed DOE Laboratories to Independently Support NRC
on Specific NRC Tasks, e.g.

• Nuclear Industry– Supported GPUN
– EPRI Technical Support– Nuclear Contractors• Bechtel National and Others– Bechtel and GPUN Organizations Integrated Together– US Navy & Academic Advisors for Review and AssistanceGroupsL. Barrett Consulting LLC

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Safety-Risk Reduction Focus• Safe Prompt Defueling to Place Damaged
Fuel/Radioactive Materials Into Safe
Engineered Containers– Time at Risk In Un-Designed Post Accident
Condition Was Important Risk Reduction Factor– Control & Containment of Radioactive Material• High Activity Waste Container Safety– New Safety Issues, e.g. Hydrogen Generation

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Safety Review Process• Stepwise Evolutionary Process– GPUN Safety Evaluation For Each Major D&D Step
• DOE Safety Support to GPUN

– USNRC Review/Approval• Risk Informed On Site Reviews• Within Bounds of NRC Programmatic Environmental
Impact Statement• Safety Analysis for D&D Operations Within Bounds ofNormal Reactor Accident Risk

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9Core Drilling Machine Evolution• Beginning- Phase 1: Data Recovery R&D Core
Stratification Sampling Machine Tool
– 1980-86– DOE/INL Lead & GPUN Support• Phase 2: Core Mass Breakup Machine Tool
– 1986– GPUN Lead & DOE/INL Support• Phase 3: Steel Structure Cutting Machine Tool
– GPUN Lead & DOE/INL Support– 1987-1988
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10Drilling Machine Evolution
Core Sampling
For Analysis/LearningCore Mass BreakingDefuelingCore Support
Structure Removalfor Lower
Defueling AccessCore Breaking Bit
Drilling OperationCore Boring Sampling

Broken Core Center Fragment
Analysis Results

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Core Plate Segment 13

Phase 1 Core Bore Sample Evolution• 1980-82: Developing Sampling NeedsDiscussions• 1981-83: DOE/INEL Evaluates Adapting
Geologic Core Sampling Drilling Technology• 1984: Core Sampling Via Core Drilling Safety
Discussions (GPUN, DOE, NRC)
• 1985-August: GPUN Safety Submittal to NRC• 1986-June: NRC/TMIPO Approval SER• 1986-July: NRC Procedure Approvals &Operations
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Safety Issues Evaluated• Release of radioactivity,• Criticality,• Boron dilution,• Hydrogen evolution,• Pyrophoricity,• Fire protection,• Decay heat removal,• Reactor vessel integrity,• Instrumentation interference,• Heavy load drops,• Ability to maintain control even if there was a reactor vesselleak,• Occupational exposures• There not being an Unreviewed Safety Question
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Phase 2: Core Mass Breakup Drilling Evolution• 1985-86: GPUN Adopted the Drilling Machineas a defueling tool to break up core mass
based on positive team experience. Safety
Discussions with all.
– NRC Safety concerns regarding drilling forces onReactor Vessel Instrument Guide Tube Integrity• 1986-July: GPUN Safety Submittal to NRC• 1986-July:NRC/TMIPO Approval SER– With Vessel Integrity Location Limitations
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Phase 2: Defueling Core Mass Breakup Tool-2
1986-September: GPUN Provides Safety
Analysis for Guide Tube Safety
1986-October: NRC Approves Drilling over
Wider Area
1986-October: NRC Approves Procedures andDrilling Began.
1986-November: 409 Drill holes Breaks Up
Central Core Mass Successfully.
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Phase 3: Lower Core Structure
Cutting Tool Evolution• 1986-1987: With Good Experience With
Drilling Machine, GPUN/EG&G adapts it anddiscusses with NRC for cutting steel
structures for lower fuel access.
• 1987-October: GPUN Safety Submittal for
Cutting LCSA.
• 1988-January: NRC approves withdimensional controls• 1988 January: NRC approved procedures andGPUN cutting begins sequentially andsuccessfullyL. Barrett Consulting LLC

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Summary of Safety Lessons• Constant Onsite Risk Informed Focus• Adaptive Learning with Safety Hold Points• Sequential GPUN and NRC Safety Evaluations
Built on Previous Experiences• Early Safety Design Basis Criteria Was
Important• Constant Effective Communications Between:– Scientists/Developers– Licensee Engineers/Operators– Regulators
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