Three Mile Island Unit 2 Key Decisions and Important Events for - - PowerPoint PPT Presentation

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Three Mile Island Unit 2 Key Decisions and Important Events for - - PowerPoint PPT Presentation

Dec 15, 2022 46 likes •210 views

Three Mile Island Unit 2 Key Decisions and Important Events for Removing the Damaged Fuel Presented at the 1st International Forum on the Decommissioning of the Fukushima Daiichi Nuclear Power Station April, 2016 Chuck Negin Washington

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TMI-2 Overview

Three Mile Island Unit 2 Key Decisions and Important Events for Removing the Damaged Fuel

Presented at the 1st International Forum on the Decommissioning of the Fukushima Daiichi Nuclear Power Station April, 2016 Chuck Negin Washington Grove, Maryland, USA charlesnegin@gmail.com

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SLIDE 2

TMI-2 Overview

Damaged Fuel and Debris

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SLIDE 3

TMI-2 Overview

Damage Examples

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SLIDE 4

TMI-2 Overview

Various Areas for Defueling

 Core Cavity  Lower Support Grid  Flow Distributor  Behind and within the Core Baffle Plates  Lower Head  Elsewhere in the Reactor Systems

Reactor Pressure Vessel Cutaway View Bottom of the Upper Core Support Assembly

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SLIDE 5

TMI-2 Overview

Defueling Progress and Key Impacts

1982-1983 Defueling Options Evaluations 1982 First Video of Core 1983 First Sample 1983 Sonar Mapping & Improved Video Mid-1984 Vessel Head Lift 1984 Defueling Method Decision Dry Canal & Mostly Manual

Vessel Defueling Progress

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Oct-85 Apr-86 Nov-86 May-87 Dec-87 Jun-88 Jan-89 Aug-89

Feb-86 Dec-1986 April-1987 Sept-1987 Oct-1985 Dec-1988 May-1989 Feb-1990 Dec-1987

Lower Grid Cutting Core Former Disassembly Lost Water Clarity

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SLIDE 6

TMI-2 Overview

Removal Methods

 Five concepts for fuel removal before visual characterization; none were used:

  • Dual Telescoping Tube, Manipulator
  • Manual Defueling Cylinder
  • Indirect Defueling Cylinder
  • Flexible Membrane
  • Dry

 Later, a remotely operated service arm, shredder, and vacuum transfer system was considered and rejected  Final method chosen was an adapted mining drill (the core bore) and manual methods

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SLIDE 7

TMI-2 Overview

Core Boring Machine

 Adapted from commercial mining drilling equipment  One of the most important machines for the project  First use with hollow core bits: 10 samples 1.8 m long x 6.4 cm diameter (figure below)  Second use with solid face bits to chew through the hard once-molten mass in the core region  Third use was assisting lower grid and instrument tubes by grinding metal (next viewgraph)

Tungsten Carbide Teeth with Synthetic Diamond

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SLIDE 8

TMI-2 Overview

Fuel Removal Tools and Equipment

 Powered Equipment

  • Core Boring Machine
  • Plasma Arc
  • Power Assisted shears
  • Bulk Removal
  • Water Vacuum and Air Lift

 Manual Controlled Equipment

  • Grippers
  • Buckets

 Some Manual Tools

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SLIDE 9

TMI-2 Overview

Work Platform

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SLIDE 10

TMI-2 Overview

Three Canister Design – 341 Shipped

60 Filter Canisters (water processing) 271 Fuel & Debris Canisters 10 Knockout Canisters (for vacuum tools)

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SLIDE 11

TMI-2 Overview

Packaging & Transport

Canister Staging in Spent Fuel Pool Transfer Cask Operations

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SLIDE 12

TMI-2 Overview

Staging & Shipping

Shipping Cask Loading the Shipping Cask

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SLIDE 13

TMI-2 Overview

Packaging, Transport, & Storage at Idaho

1986 to 1990 341 canisters of fuel & debris in 46 shipments by rail cask to the Idaho National Laboratory 1990 to 2000 Wet Storage in Spent Fuel Storage Pool 2000 – 2001 Removed from pool, dewatered, dried, and placed in dry storage

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Idaho National Laboratory Three Mile Island 3400 km

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SLIDE 14

TMI-2 Overview

Possible Remaining Fuel Particulate

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 Residual Fuel*

  • RPV: < 900 kg
  • In the Reactor Coolant System: < 133 kg
  • Criticality ruled out by analysis

 Assessment Required a Combination of*

  • Video inspection for locations
  • Gamma dose rate and spectroscopy
  • Passive neutron solid state track

recorders, activation, BF3 detectors

  • Active neutron interrogation
  • Alpha Detectors
  • Sample Analysis
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SLIDE 15

TMI-2 Overview

Events/Decisions(1)

Events/Decisions Significance Decisions for removal required visual characterization First idea of what conditions really were; complete assessment took another year; could not proceed to plan defueling without this knowledge Decision to not to install in-core shredding equipment in the vessel

  • New application for the proposed technology, concern that

failure would cause problems, relied mostly on manual manipulation with power assist

  • Allowed defueling to start earlier, knowing that overall

schedule would not be minimized. This was preferred over a 3 year development for a remote system/equipment Decision to leave refueling canal dry

  • Less depth for manually operated tools
  • Shielded work platform 2m above the reactor pressure vessel

flange

  • Reduced need for water processing
  • Dose rates were low within the refueling canal

Use of Core Boring Machine was essential

  • Samples of the fuel and debris that was melted together
  • Breaking up the crust and molten mass when manual

methods were unsuccessful

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SLIDE 16

TMI-2 Overview

Events/Decisions(2)

Events/Decisions Significance Unanticipated biological growth in water fouled filters Caused a year delay; managing water clarity is extremely important DOE to take Fuel & Debris New cask design and license Ship Fuel to Idaho by Rail and not Truck

  • Handling and shipping design and fabrication could not take

place until destination was determined

  • Allowed fuel & debris canisters to be removed from TM
  • New cask could be designed for the TMI canisters
  • Fewer shipments

Transfer to Dry Storage Long term storage stability, also allowed demolition of fuel pool at Idaho

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