Transcript Early Analysis of the Fukushima Dai-ichi Fuel Pools
Explaining the Unexpected: Early Analysis of the Fukushima Dai-ichi Fuel Pools
North Carolina Health Physics Society Chapter Meeting
Raleigh, NC 6 October 2011
Andrew Sowder, Ph.D., CHP
Senior Project Manager Used Fuel & HLW Management
Fukushima Dai-Ichi: Applying Industry and Government Resources
• Substantial early engagement among DOE/EPRI/INPO/NEI/NRC
Institute of Nuclear Power Operations
• Each organization focused on its core capabilities and role
Nuclear Energy Institute
• Direct and indirect support to TEPCO/Japan • Integrated response to policy, regulatory and technical lessons learned underway
US Nuclear Regulatory Commission + Utilities, Vendors, and International Organizations
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US Department of Energy
U.S. Based Institutions - Event Response Role
Institute of Nuclear Power Operations
Coordinates industry response to operational aspects of an event
Nuclear Energy Institute
Leads industry communications to media, public, and government stakeholders and leads interface with federal government Provides technical support to industry © 2011 Electric Power Research Institute, Inc. All rights reserved.
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EPRI Role / Industry Path Forward
• Participation on “Industry Support Team” • Direct support for TEPCO by various EPRI groups – Plant Technology – Chemistry, LLW, RM – Used Fuel & HLW, FRP • The Way Forward Initiative www.nei.org/filefolder/TheWayForward_060611_FinalA2.pdf © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Industry Roles under “The Way Forward”
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Fukushima Dai-ichi Before 11 March 2011
Common Fuel Pool © 2011 Electric Power Research Institute, Inc. All rights reserved.
Units 1 - 4 6 Units 5 - 6 Dry Storage
Fukushima Dai-ichi After Tsunami
Source: TEPCO © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Fukushima Dai-ichi After Tsunami
Source: TEPCO © 2011 Electric Power Research Institute, Inc. All rights reserved.
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11 March Fukushima Dai-ichi Tsunami Strike
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11 March Tsunami Strike at Fukushima Dai-ichi
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10 Source: JNES
Early Event Analysis
• Accurate understanding essential for applying lessons learned • Early analysis drives focus on credible, significant issues • Understanding still evolving (incomplete data, many theories)
Focus for this Presentation: What role, if any, did the fuel pools play in the events at Fukushima Dai-ichi?
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What is a Spent Fuel Pool?
• Water-filled, stainless-steel-lined, concrete basin for storing irradiated fuel • Provides – cooling – radiation shielding – sub-critical condition • Refueling every 18-24 months in US,
12-15 months in Japan
– reactor shutdown, vessel opened, and fraction of core replaced with fresh fuel – used or spent fuel moved to pools Pool provides large thermal inertial provided, but “young” used fuel requires substantial heat removal.
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Fukushima Dai-ichi Design
Source: NEI, 2011. http://www.nei.org/filefolder/BWR_illustration_3.jpg
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Fukushima Dai-ichi Fuel Pool
Source: TEPCO © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Spent Fuel Pool Details
Pool Elevations
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Fuel Racks
Used Fuel Management at Fukushima Dai-ichi
Storage method Spent fuel pool at each reactor unit Dry cask Common pool Total Inventory as of March 2010 Total Capacity # Assemblies 3,450 408 6,291 10,149 8,310 408 6,840 15,558
Source: TEPCO © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Fukushima Dai-ichi Fuel Pool Inventories
Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Common Pool Reactor Power Level (MWt/MWe) Core Fuel Assemblies Most Recent Addition of Irradiated Fuel to Pool Irradiated fuel Assemblies in Pool Unirradiated fuel Assemblies in Pool Total Number of Assemblies in the Pool Pool Assembly Capacity Pool Decay Power (MW)
1380/460 2381/784 2381/784 2381/784 2381/784 3293/1100 400 548 548 0 548 764 March 2010 Sept 2010 June 2010 Nov 30, 2010 Jan 2010 Aug 2010 292 587 514 1,331 946 876 6,375 100 28 52 204 48 64 -
392 615 566 1,535 994 940 6,375 900 1,240 1,220 1,590 1,590 1,770 6,840
0.07
0.5
0.2
2.3
0.8
0.7
1.2
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1F4 Fuel Pool Map Indexed by Assembly Thermal Power
2 0 1 13 1 IF 0 IF 1 1 IF IF 2 1 IF IF 3 1 IF IF 4 1 IF IF A 5 1 IF IF 6 1 IF IF 7 1 IF IF 0 2 IF 12 1 IF 0 IF 1 IF IF IF 2 IF IF IF 3 IF IF IF 4 IF IF IF 2 0 5 11 1 8 0 4 1 5 4 8 2 5 4 8 3 5 4 8 4 5 4 8 5 5 8 IF 6 5 7 5 8 10 8 10 8 5 8 10 8 1 1 1 9 9 8 2 0 5 4 10 24 1 4 0 5 E F P M 5 IF IF IF 6 IF IF IF 7 IF IF IF 8 IF IF 9 IF 5 2 0 5 25 1 IF 0 5 1 5 IF 5 1 5 4 5 2 5 IF 5 3 16 IF 5 4 16 5 IF B 5 5 5 IF 6 5 5 5 2 1 0 7 5 5 5 1 8 5 5 5 2 9 5 5 5 3 4 C S 5 2 0 1 37 1 IF 0 FF 1 1 IF FF 6 2 1 IF FF 7 8 C 9 W F P M 3 1 IF FF 4 5 6 7 8 9 SBG DF DF DF DF DF DF DF DF DF DF DF DF 2 5 4 5 3 10 4 10 4 5 5 5 5 10 5 5 6 10 7 10 5 10 5 5 8 10 IF 5 9 10 2 0 FF 1 FF 10 36 1 FF 5 0 FF FF FF 2 FF 3 FF FF FF FF FF 4 IF IF IF 5 IF 6 IF IF IF IF IF 7 IF 8 9 DF DF IF IF C R A 2 0 8 10 1 5 0 8 0 2 5 09 1 5 0 8 0 2 IF 1 8 08 1 10 10 0 IF 1 5 IF 10 0 1 8 8 8 1 30 2 2 8 8 10 3 5 5 IF 3 4 4 IF 5 10 5 IF 5 10 CR 5 6 6 IF 5 10 10 7 CR 8 7 8 IF 5 IF IF 10 2 5 IF 8 3 IF IF 8 4 IF 8 IF 5 IF IF 8 6 7 IF 10 8 IF 10 10 8 5 10 10 9 C R B 0 1 3 9 IF 2 0 5 8 10 23 1 10 0 IF 1 IF IF IF 2 10 IF IF 2 3 10 IF IF 4 4 10 10 IF 9 0 12 8 2 IF 22 1 9 10 0 9 5 5 10 IF IF 6 6 5 IF IF 1 IF 9 9 2 IF IF 10 3 4 5 IF IF IF 10 12 5 IF IF 12 6 7 5 IF 9 IF 12 12 7 7 5 IF IF 8 8 5 10 10 9 C R C CR 0 9 10 0 2 FF 10 35 1 FF IF 0 FF 1 FF FF FF CR 1 CR 2 2 CR 3 3 CR 4 4 FF FF FF FF FF FF FF FF FF 5 FF FF FF CR 5 CR 6 6 8 IF IF IF 9 0 1 IF IF 9 34 2 FF 1 FF FF FF 0 FF FF 2 FF FF FF 3 4 FF FF FF FF FF FF 5 FF FF FF 6 FF FF FF CR 7 7 8 8 9 7 8 FF FF FF FF FF FF 9 FF FF FF 9 IF 2 10 10 10 3 10 4 10 10 10 10 IF 0 2 IF 07 1 10 0 IF 1 10 10 IF 2 10 10 IF 3 10 4 10 10 10 IF IF 0 2 IF 06 1 IF 0 IF 0 2 IF 05 1 IF 0 IF 1 IF IF IF 2 IF IF IF 1 IF IF IF 2 IF IF IF 3 IF IF IF 4 IF IF IF 3 IF IF IF 4 IF IF IF 5 IF IF 6 10 10 7 10 IF 10 10 10 8 10 10 10 9 IF 0 2 IF 10 21 1 IF IF 0 IF 5 10 IF IF 6 IF IF IF 7 10 10 IF 8 10 10 IF 9 IF 2 0 9 10 20 1 IF IF 0 24 1 9 10 24 5 IF IF IF 6 IF IF IF 5 IF IF IF 6 4 IF IF 7 IF IF IF 7 IF IF IF 8 IF IF IF 9 IF IF IF 0 2 IF 19 1 IF 0 IF 8 IF IF IF 9 IF IF IF 0 2 IF 18 1 IF 0 IF 1 IF IF IF 2 IF IF 10 3 IF IF 4 IF IF 10 10 5 IF IF 10 6 IF 7 IF 10 10 10 10 8 IF 10 IF 9 10 0 2 FF 1 FF 10 33 1 FF FF IF 0 FF FF 2 FF FF 3 FF 4 FF FF FF FF FF FF 5 FF FF 6 FF FF FF FF 7 FF 8 FF FF FF 9 FF FF FF FF FF 2 IF 10 10 3 IF 10 4 IF 10 24 10 1 IF IF IF 1 IF IF IF 2 IF IF IF 3 IF IF IF 2 IF IF IF 3 IF 5 IF 4 IF IF IF 4 IF 5 IF 5 IF 24 10 6 IF IF 10 7 IF IF IF 5 IF IF IF 6 IF IF IF 5 IF IF IF 6 IF IF IF 7 IF IF IF 7 IF IF IF 8 IF IF IF 9 IF IF IF 0 2 FF 32 1 FF 0 FF 1 FF FF FF 2 FF FF FF 3 FF 4 FF FF FF FF FF 5 FF FF FF 6 FF FF FF 7 FF 8 FF FF FF FF FF 9 FF FF FF 8 IF IF IF 9 IF IF IF 0 2 FF 31 1 FF 0 FF 1 FF FF FF 2 FF FF FF 3 FF 4 FF FF FF FF FF 5 FF FF FF 6 FF FF FF 7 FF 8 FF FF FF FF FF 9 FF FF FF 8 IF IF IF 9 IF IF IF 2 0 8 30 1 8 0 IF 1 8 8 IF 2 8 8 IF 3 8 8 IF 4 8 8 IF 5 8 IF IF 6 8 4 IF 7 IF IF IF 8 IF IF 9 9 IF IF 9 2 0 4 45 1 IF 0 IF 1 2 IF IF 2 IF IF IF 3 IF IF IF 4 IF IF IF D 5 IF IF IF 6 IF IF IF 7 IF IF IF 8 IF IF IF 9 IF IF IF 2 0 9 53 1 0 9 1 1 9 9 9 0 2 IF 44 1 IF 0 1 1 IF IF 1 2 IF IF 1 3 IF IF 1 4 IF IF 1 5 IF IF 1 6 IF IF 1 7 IF IF 1 8 IF IF 1 9 IF IF 1 2 0 1 52 1 14 0 14 1 14 9 9 2 9 9 9 2 9 9 1 19 17 15 13 11 09 07 05 03 01 SBG SBG B G A 2 43 1 0 0 1 1 1 01 03 05 SBG SBG 42 1 0 2 0 1 1 2 0 2 2 41 1 0 2 2 2 0 2 40 1 2 0 4 2 0 4 39 1 4 0 IF 1 4 4 4 1 1 1 2 1 1 1 1 1 2 2 2 1 2 2 4 0 2 IF 38 1 0 4 4 1 2 4 4 2 2 4 4 2 1 1 2 2 1 1 1 2 2 2 2 2 4 4 4 2 2 2 4 1 2 3 2 2 2 2 3 2 4 4 3 2 2 3 1 1 1 3 1 3 2 4 4 4 1 1 1 4 1 1 2 4 2 2 4 4 4 4 2 4 4 4 4 4 2 4 4 6 4 1 6 1 1 2 6 1 1 1 6 2 2 4 6 2 4 4 6 2 4 4 5 4 1 5 1 1 2 5 1 1 1 5 2 2 4 5 8 4 4 5 2 4 2 7 1 1 1 7 1 7 2 4 4 4 2 2 4 1 2 7 2 7 2 7 4 1 8 1 1 1 8 1 8 2 4 4 4 2 2 2 2 2 8 4 8 4 8 4 1 9 1 1 1 2 51 1 0 0 9 9 9 9 1 2 2 2 0 8 50 1 0 8 9 1 8 8 9 1 9 9 9 2 9 9 9 2 8 8 9 9 2 2 2 0 2 9 49 1 10 0 8 1 1 10 8 2 3 9 10 8 9 10 8 3 4 8 9 3 9 9 9 9 2 4 8 2 0 2 48 1 4 0 4 9 4 4 4 2 0 2 47 1 0 2 2 1 2 2 2 1 2 2 4 2 2 2 2 2 2 2 2 3 2 2 2 3 2 2 2 9 4 1 2 46 1 0 0 2 1 1 2 1 2 2 1 3 9 9 9 4 9 9 9 3 9 9 1 4 8 9 1 3 2 1 4 2 1 4 8 9 9 4 9 4 9 4 9 9 8 4 2 2 2 4 2 2 2 E 5 9 9 9 5 8 9 9 6 9 2 9 7 9 2 9 8 9 2 9 6 9 9 9 7 8 14 1 8 9 14 14 1 9 9 1 5 2 1 5 9 9 8 5 2 2 2 5 2 2 2 5 9 8 9 6 9 9 9 7 9 9 9 5 8 9 10 6 8 9 10 7 8 9 10 8 8 9 10 8 9 9 8 7 9 8 2 7 2 2 2 7 2 4 2 6 1 9 2 6 2 2 2 6 2 4 2 8 9 8 2 8 2 2 2 8 2 2 2 9 8 1 9 9 9 9 8 9 1 8 2 9 2 2 2 9 2 2 2 6 2 1 7 2 1 8 2 1 9 2 1 9 9 2 9 CR 9 0 2 IF 04 1 IF 0 IF 1 IF IF 4 2 IF 4 IF 3 IF 4 IF 4 IF 4 IF 5 IF IF IF 6 IF IF IF 7 IF IF IF 8 IF IF 4 9 IF 4 IF 0 2 IF 17 1 5 0 IF 1 5 IF IF 2 IF 12 IF 3 12 IF IF 4 IF IF IF 5 5 IF 12 6 IF IF 12 7 IF IF 12 8 IF IF 12 9 IF IF IF 2 0 9 29 1 9 0 9 1 9 9 9 2 9 9 9 3 9 9 9 4 9 9 9 5 9 9 9 6 9 9 9 7 9 9 9 8 9 9 9 2 0 IF 03 1 IF 0 4 1 4 IF 4 2 IF IF IF 0 2 IF 02 1 4 0 4 1 IF 4 8 3 IF IF IF 4 IF 4 4 2 4 4 8 3 IF 4 10 4 IF IF 10 5 IF IF IF 6 4 IF IF 7 IF 4 4 5 4 IF IF 6 4 IF 8 7 IF IF 10 8 4 IF 8 8 IF 4 IF 9 4 IF IF 16 2 0 12 1 12 1 0 IF IF IF IF 2 12 3 IF IF IF IF IF 9 IF IF 4 0 2 IF 15 1 IF 0 IF 1 IF IF IF 2 IF IF IF 3 IF IF IF 4 IF IF IF 4 IF IF IF 5 IF 6 IF IF 4 IF IF 5 IF IF IF 6 IF IF IF 7 IF IF IF 7 IF IF IF 8 IF IF IF 9 IF 2 0 9 IF IF 28 1 IF 0 8 1 9 8 8 2 9 8 8 3 9 8 IF 4 9 IF 8 5 IF 8 8 6 8 8 IF 7 IF 8 IF 8 8 8 8 8 IF IF 9 9 IF IF IF 0 2 IF 27 1 FF 0 FF 1 8 FF FF 2 4 FF FF 3 4 4 4 FF FF FF FF 5 IF FF FF 6 IF FF FF 7 IF 8 IF FF FF FF FF 9 IF FF FF 9 IF IF IF 9 9 9 9 0 2 12 01 1 12 0 12 1 IF IF 5 2 IF IF 12 3 IF 5 12 4 IF IF 12 5 IF 12 5 6 12 12 5 7 IF IF 12 8 IF IF 12 9 IF IF 5 0 2 IF 14 1 IF 0 IF 1 5 IF IF 2 12 IF IF 3 IF IF IF 4 IF IF IF 5 IF IF IF 6 IF IF IF 7 5 IF IF 8 IF IF IF 9 IF IF IF 0 2 FF 26 1 FF 0 FF 1 FF FF FF 2 FF FF FF 3 FF 4 FF FF FF FF FF 5 FF FF FF 6 FF FF FF 7 FF 8 FF FF FF FF FF 9 FF FF FF FF Fresh Fuel IF Irradiated Fuel DF Dummy Fuel SBG Single blade guide CR 7 CR 8 CR 5 CR 6 CR 3 CR 4 CR 1 C 0 C R D 2 Cooling time years days 365-729 730-1094 1460-1824 1825-2189 2920-3284 3285-3649 3650-4014 4380-4744 5110-5474 5840-6204 8760-9124 = = = = = = = = = = = yrs 1 9 10 2 4 5 8 12 14 16 24 © 2011 Electric Power Research Institute, Inc. All rights reserved.
18 IF 1 2 4 5 8 9 10 12 14 16 24
3.60 kW 1.12 kW 0.55 kW 0.40 kW 0.30 kW 0.24 kW 0.23 kW 0.22 kW 0.21 kW 0.20 kW 0.19 kW 0.16 kW
Understood: Hydrogen Explosions in Units 1 and 3
Zr + 2H 2 O → ZrO 2 + 2H 2 + energy
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Unexpected: 15 March Unit 4 Damage
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Source: Air Photo Service Co. Ltd., Japan 20
Early Focus on 1F Unit 4 Pool
BEFORE
• Damage to Unit 4 reactor building unexpected – Unit 4 reactor was offline for maintenance – Defueled ~100 days before earthquake/tsunami • Full core offload in fuel pool – youngest, hottest fuel (2.3 MW decay heat load in 1F4 pool vs. <1 MW in other pools) – most reactive fuel (first cycle for BWR) – other pools less challenged
AFTER
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March 16: Grave Statements from US Officials
http://abcnews.go.com/Business/wireStory?id=13150227 © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Rampant Speculation on Cause of Unit 4 Damage
• Hydrogen gas from spent fuel in pool from high temp reaction of steam w/ Zr cladding after loss of water
Zr + 2H 2 O → ZrO 2
• Hydrogen gas from :
+ 2H 2 + energy
– radiolysis (radiation induced breakdown of H 2 O) – other sources in Unit 4 – Unit 3 shared piping or other connectivity • Other combustible gas in Unit 4 • Combustion of soot from lube oil fire Venting of hydrogen gas from Zr oxidation in Unit 1 and 3 cores implicated in explosions of those units.
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Early Information for Unit 4 Assessment
• 15 March - Unit 4 explosion at day 4 (<< nominal time for boil off) • Ongoing venting of Unit 1 – 3 containments • Increasing flow of dose rate and environmental data 3/17 dose rates: – early exposure readings in vicinity of Unit 4 building • 87.7 mSv/hr at 100 m el. – contamination of sea water near plant – low (near ambient) Pu soil concentrations onsite • 400 mSv/hr near Unit 3 • Unconfirmed reports of water in pool west wall • Initial water spray from ground level on 20 March • 100 mSv/hr near Unit 4 • Water additions via concrete pump boom on 22 March • 12 April – Water sample collected, water temp (90 ºC) & level (2 m above fuel), dose rate measured prior to filling* *Reported to be “several dozens” of mSv/hr above refueling floor – consistent with water above fuel.
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Lots of Unfiltered Information
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Milestone: 13 April 2011 Water Analysis Data for Unit 4 Pool
Unit 4 fuel pool water analysis Unit 2 fuel pool water analysis © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Data Source: TEPCO
Reported Water Additions to 1F4 Consistent with Evaporation – Not Leakage TEPCO concludes on 4/28 fuel pools not leaking based on daily evaporation rates of 140 to 210 tons (kiloliters) of water daily that match water additions.
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Milestone: Underwater Images of Unit 4 Pool Conditions
• No damage to storage structure • No major fuel damage Source: TEPCO © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Closing in on Cause for Unit 4 Damage
• Visual evidence of fuel, racks, and pool integrity does not support catastrophic pool drainage and Zr oxidation event • Other Unit 4 sources of hydrogen or other combustible material not considered significant or credible • Unit 3 as source of hydrogen remains most credible suspect – timing of Unit 3 & 4 events – hydrogen role in Units 1 & 3 damage – shared vent stack and piping – consistent failure of venting – 16 May TEPCO analysis Source: Air Photo Service Co. Ltd., Japan Hydrogen from Unit 3 currently most credible theory.
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TEPCO 16 May 2011 Theory for Source of Hydrogen in Unit 4
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30 Source: TEPCO
TEPCO 16 May 2011 Theory for Source of Hydrogen in Unit 4 (cont’d)
Source: TEPCO © 2011 Electric Power Research Institute, Inc. All rights reserved.
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1F4 Emergency Gas Treatment System – Post Accident Configuration
Source: TEPCO 27 August 2011 © 2011 Electric Power Research Institute, Inc. All rights reserved.
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June 15: The Correction
http://abcnews.go.com/US/wireStory?id=13845733 © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Interim EPRI Assessments
• Fukushima Dai-ichi Fuel Pool Criticality Assessment • Summary of fuel pool evolution following loss of cooling – preliminary gap analysis – calculation of time required to evaporate 1F fuel pool water inventory for key scenarios – identifying important scenarios and mitigating factors • Evaluation of proposed scenarios directly implicating Unit 4 pool in hydrogen generation – from cladding oxidation in blocked fuel channels experiencing DNB in a pool with water level above fuel – from enhanced radiolysis in high radiation fields in a fuel pool at or near boiling © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Early EPRI Criticality Assessment for Fukushima Dai-ichi Fuel Pools
• A spent fuel pool criticality event remains highly unlikely in damaged Fukushima Dai-ichi spent fuel pools.
– includes the extreme case of the introduction of water to a dry fuel pool – total fuel inventory present in the form of rubblized fuel pellet fragments lying at the bottom of the pool •
Primary objective for mitigation of drained fuel pool at Fukushima should be covering spent fuel pool with water to reduce the dose to workers.
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Fuel Pool Evolution Following Loss of Cooling
Stage
1 2 3 4 5 6 7
Sequence
Nominal condition of pool: 30 45 ° C, normal water level Pool water temperature gradually approaches water boiling point Boiling of pool water: Boiling begins in racks where hottest fuel assemblies are stored; pool water level gradually decreases towards top of fuel assemblies’ levels Gradual uncovering of fuel assemblies Thermal ramping of fuel rods in the presence of water (water level above rack base plate).
Thermal ramping of fuel rods in the absence of water (pool water below rack base plate). • The level of water at which temperatures start ramping up will depend on decay heat and assumed heat transfer mechanisms, including boiling heat transfer at the submerged fuel rod-water interface. •
GAP: More realistic assessment of the transition point from sufficient to insufficient axial cooling as a function of rack and assembly design and decay heat
.
Dispersal of fuel materials © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Estimated Time Margins for 1F Pools Based on Simple Calculations
Unit
1 2 3 4
Time to Uncovering Top of Fuel (days)
250 35 88 7.6
Time to Uncovering 50% Fuel Length (days)
350 50 120 11
NOTE: For Unit 4, additional inventory from refueling cavity and D/S pit could provide up to 14 days of additional margin .
Assumes: Initial Pool Temp = 35 °C Initial sloshing removes 1.5 m of water inventory D/S Pit 20' x 49' Refueling Cavity r = 20' Fuel Pool 32.5' x 40' © 2011 Electric Power Research Institute, Inc. All rights reserved.
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TEPCO 20 June 2011 Theory for Evolution of 1F4 Fuel Pool Water Inventory following LOCA
• Refueling well and D/S pit were flooded and interconnected. • Spent fuel pool gate was in place.
• Following evaporation of pool inventory, leakage from adjoining refueling cavity provided an alternative source of makeup water
D/S
ピット
D/S
ピット © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Early EPRI Evaluation of Scenarios Implicating Fuel Pool in Unit 4 Explosion
• Hydrogen generation from cladding oxidation in pool with water covering fuel due to localized departure from nuclear boiling (DNB) in debris-blocked fuel channels
Hydrogen from zircaloy cladding oxidation not likely for pool levels covering at least half the fuel height
• Hydrogen from water radiolysis in 1F4 storage pool (fuel offload)
Bounding production rate calculations indicate insignificant H 2 production relative to building volume to cause explosion (<<1% in gas mixture)
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Status of Unit 3 Fuel Pool
14 March: Unit 3 explosion
Source: NHK Source: TEPCO; Video image obtained 8 May 2011 Source: Air Photo Service Co. Ltd., Japan © 2011 Electric Power Research Institute, Inc. All rights reserved.
13 April – Unit 3 pool reported to be “full”
40 Data Source: TEPCO
Status of Units 1 & 2 Fuel Pools
• No video or photographic images of either pool • Unit 2 pool had 2 nd highest thermal load (0.5 MW) • Unit 2 water additions start 3/20 Source: Air Photo Service Co. Ltd., Japan © 2011 Electric Power Research Institute, Inc. All rights reserved.
41 Data Source: TEPCO
Units 1 - 4 Summary as of 16 August 2011
Source: TEPCO
Physical Status Loading of SFPs, # assemblies Heat Loads in March, estimated SFP Volume in m 3 SFP Rack Material Fuel Burnup Estimate of Fuel Damage Temperature of SFP Date closed loop cooling in service Volume of seawater injected early on Evaporation rate before cooling set up Unit 1
Roof collapsed on operating floor and SFP Used 292 New 100 180 kW 1020 Unknown; but well <10 tons/day
Unit 2
Roof intact; operating floor condition unknown Used 587 New 28 620 kW 1425 Aluminum & Boral Most recent S/D 9/27/10 Aluminum & Boral Most recent S/D 11/18/10 Aluminum & Boral Most recent S/D 9/23/10 likely none, believed always covered Current 36 C Est. peak <80 C. 8/10/11 Using original HX with new secondary system none likely none, believed always covered Alternate SFP Cooling system Some mechanical damage from fallen debris Current 38 C Current 33 C Peak of 80 o C. o C 5/31/11 6/30/11 Alternate SFP Cooling system 90 tons 4,560 tons SS 304 Most recent S/D 11/29/10. All assemblies in SFP.
<1% based on water sample on 4/12/11 Current 45 C. Peak >90 7/31/11 700 tons o C. Alternate SFP Cooling system 21 tons/day
Unit 3 Unit 4
Roof and structure destroyed; debris in pool, exposed concrete Roof structure damaged; debris in pool. Support beams installed July.
Used 514 New 52 (32 MOX) 540 kW 1425 17 tons/day
Used 1,331
New 204 2,300 kW 1425 72 tons/day © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Units 1 - 4 Summary as of 16 August 2011
• Structure reinforcement of Unit 4 pool completed • Hydrazine has been added to Units 2, 3, 4 for corrosion concerns • Boric acid has been added to Unit 3 for pH purposes • A truck-mounted desalination unit is being planned for CL- reduction; movable between units; not in service as of 8/15/11 • Unit 3 water sample of 5/9/11 showed CL- at 2,400 ppm and pH 11.2
• ND - Not Detectable Source: TEPCO © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Status of Fuel in Dry Storage and Common Pool
• 17 March - While also inundated with water, TEPCO confirms integrity of dry storage casks and building • 18 March - TEPCO confirms stability of common fuel pool Source: TEPCO © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Broader Picture: Event Analysis ► Understanding ► Lessons Learned
• U.S. plant features and operating practice have evolved in light of operating experience and knowledge • Still early in Fukushima recovery phase • Event analysis remains incomplete • Implications for U.S. plant design and operations not fully understood • Post-Fukushima: – vulnerabilities identified and corrected – mitigation strategies developed for credible beyond design basis hazards © 2011 Electric Power Research Institute, Inc. All rights reserved.
Mitigation 45 Design Basis Accidents Post 9/11 or B.5.B Mitigation Strategies Fukushima Strategies TMI Modifications IPE / IPEEE and PRA Modifications
Post-Fukushima R&D Path Forward
• Verify current understanding • Identify and address gaps – Risks posed by external hazards – Severe accident progression, including combustible gas control – Monitoring and instrument needs – Radiological releases and paths – Fuel pool phenomena and relative risk – Integration and execution of mitigation actions • Establish and preserve pedigreed Fukushima accident knowledge base © 2011 Electric Power Research Institute, Inc. All rights reserved.
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Together…Shaping the Future of Electricity
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