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TVA Nuclear Safety Initiatives After Fukushima

IEEE Nuclear Power Engineering Committee Winter 2012Joe D. Williams

General Manager Design EngineeringTVA Nuclear Power Group

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• The Fukushima Daiichi Event• What Made Fukushima Daiichi

Different?• TVA Lessons Learned from

Fukushima Daiichi– Site Considerations– Regional Events Considerations

• TVA’s Commitment to Safe Nuclear Power

TopicsTopics

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The Fukushima Daiichi EventThe Fukushima Daiichi Event

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• March 11 @ 1446 – 9.0 earthquake strikes

– Epicenter is at sea ~200 km north of Fukushima– Design basis earthquake for the plant was 8.2– Seismic monitors initiate automatic shutdown on 11 reactors

• Fukushima Daiichi, Fukushima Daini, Onagawa and Tokai • All subsystems work as designed but offsite power is lost

– Emergency Diesel Generators start and load as designed– Core cooling systems are started to remove the decay heat

• March 11 @ 1545 – Tsunami hits Fukushima Daiichi

– All Emergency Diesel Generators are flooded and incapacitated

– Station batteries last 1-8 hours– DC is exhausted, core cooling and spent fuel pool cooling

are lost4

Sequence of EventsSequence of Events

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Tsunami at Fukushima DaiichiTsunami at Fukushima Daiichi

Emergency diesels and electrical boards

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• Wide area loss of grid– Simultaneous trip of multiple units and plants– Nuclear, fossil and hydro plants lost – Instant drop in grid capacity: 52,000 to 31,000

MW• Workforce was impaired or unable to respond• Communication with support organizations

impaired • Access to drawings, procedures and data impaired• Leads to loss of assets and radiation releases

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Results of Quake and Tsunami Results of Quake and Tsunami

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What Made Fukushima Daiichi Different?What Made Fukushima Daiichi Different?

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• Onsite– Beyond design basis event

• Tsunami was 42’ versus 17’ feet expected– Breached the seawall– Flooded ground floor and basement elevations– Flooded the switchyard and relay house– Impaired EDGs, batteries and board rooms

– Some units were in outage• Hot fuel was in the spent fuel pool

– Loss of core and spent fuel cooling• Decision to vent H2 was delayed• Loss of facility and large radiation release

Factors Which Made a DifferenceFactors Which Made a Difference

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• Offsite– It was a regional disaster– Multiple plants and units effected– Widespread loss of the grid– Impaired response

• Infrastructure breakdown– Transportation– Communication

• Loss of workers, their families and homes

Factors Which Made a DifferenceFactors Which Made a Difference

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• Fukushima Daiichi offsite power provided at 275 kV and 500 kV

– Having only HV and EHV offsite connections slowed restoration times

• Offsite power restoration times per TEPCO– U1 - 13 days– U2 - 15 days– U3 - 11 days– U4 - 18 days– U5 - 11 days– U6 - 11 days

Factors Which Made a DifferenceFactors Which Made a Difference

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TVA Lessons LearnedTVA Lessons Learned

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1. Protect the public and the environment2. Preserve the asset

Characteristics of success– Provide motive power to critical plant components

• For core and spent fuel pool cooling• Keep temperature in the spent fuel pool under 200oF

– Get all reactors to cold shutdown– No fuel damage– No radiation releases– Address vulnerabilities to ‘stacked’ events– Must be able to handle regional events

TVA Lessons Learned - Definition of SuccessTVA Lessons Learned - Definition of Success

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• Its all about power– Need to extend battery life

• Add dedicated diesel generators in-plant (no transport)– Add more large portable diesel generators (LPDGs)

• Both onsite and remote– For motive power and battery recharging

• Seismically harden onsite storage shelters– Seismically harden the switchyards

• Avoids potential fires – From tipping of transformers and breakage of bushings

• Facilitates restoration of offsite power

• Diversify means to refill the spent fuel pool– With and without AC power

• Timely H2 venting is critical13

TVA Lessons Learned – OnsiteTVA Lessons Learned – Onsite

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• Station batteries– TVA coping time for SBO is 4 hrs

• Achieved with some load shedding

– Extended coping dictates Battery DGs (BDGs) must be permanently installed in their needed location

– BDGs be sized to power chargers plus one channel of load

– BDGs will backfeed electrical boards through a dedicated welding receptacle

• Portable battery carts– Motive/control power for devices– Easily transported– Procedure controlled – Operators trained

TVA Lessons Learned – Onsite (Batteries)TVA Lessons Learned – Onsite (Batteries)

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• TVA planning assumes all installed EDGs will be lost

• Provide multiple connection points for LPDGs

– Connection points must be widely spaced and above flood elev– Use modified ground trucks to backfeed boards

• LPDG placement must consider:– Access, especially for flood– Storage, transport (limits size), connection and refueling– Must consider seismic aftershock durability– Match generation voltage to plant grid

• Eliminates interposing transformer

TVA Lessons Learned – Onsite (LPDGs)TVA Lessons Learned – Onsite (LPDGs)

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• Restoration of offsite power is crucial– “Lost but recovered in 5 hrs at Fukushima Daini”

• No significant issues– Only “momentarily lost” at Onagawa

• Closer to the epicenter than either Fukushima plant• No significant issues

– Offsite power at both plants helped contain events• Site elevations also played a role

• Benefits of the grid– Much “stiffer” than diesel generator power– High capacity compared to need– High reliability compared to diesel power– Eliminates logistical problems of fuel resupply– Onsite distribution must be available for any benefit of grid

• Not enough consideration has been given to regional events

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TVA Lessons Learned – OffsiteTVA Lessons Learned – Offsite

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• Restoring existing lines– Daiichi had 275 and 500 kV

lines– Having only HV and EHV

connections delayed restoration– Offsite power “available” 11-18

days after the quake/tsunami

• Consider new emergency lines

– Mobile transformers may be needed to connect with the plant power system

• Difficult transport if highway infrastructure is damaged

– Local distribution voltage can be erected faster than HV/EHV

• Lesson learned for all plants

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TVA Lessons Learned – Offsite (Grid)TVA Lessons Learned – Offsite (Grid)

Offsite power restoration at Fukushima Daiichi in

full dress-out

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• April 27, 2011

TVA’s Regional Event – Tornado StormTVA’s Regional Event – Tornado Storm

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Red is tornado, blue is high wind and yellow is hail.226 tornadoes in 24 hrs; left 330 dead, 230 in AL alone

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TVA’s Regional Event – Tornado StormTVA’s Regional Event – Tornado Storm

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• Several plants off-line including all 3 units at Browns Ferry

• 350 transmission structures damaged or destroyed including:

– All 500 kV lines in N. AL and N. MS– One of two 161 kV offsite lines to

Browns Ferry• Remaining line had limited

capacity• Plant remains on EDGs for five days• 108 lines out of service• 128 customer connections broken• 850,000 customers without power

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TVA’s Regional Event – Tornado StormTVA’s Regional Event – Tornado Storm

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• 4,000 workers • 24/7 task• Within 5 days

– 121 of 128 distributors and direct-serve customer connections were restored

• Last 500-kV line was restored June 30th

• $39M in repairs• $95M for replacement

power

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TVA’s Regional Event – Lessons LearnedTVA’s Regional Event – Lessons Learned

• Communication assets need upgrading• Chattanooga Emergency Center needs

hardening• Multi-unit events need to be part of standard

drills• Drills must involve Nuclear and Transmission• Emergency warning sirens need alternate

power source• Reliability of existing rented temporary diesel

generators needs improvement• Evaluating installation of some offsite feeders

underground

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Other Regional Events - FloodingOther Regional Events - Flooding

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Flood levels are categorized as a near impossible flooddue to rainfall/dam failures event (substantially greater than a 10,000-year flood)

Sequoyah and Watts Bar are designed to have the structures and systems capable for cooling the fuel during this event TVA is evaluating options to harden sites Berms and Dikes Making structures water-tight to higher elevations

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• Potential initiator of regional event– Higher frequency event than DBE– Could cause widespread loss of

grid– Could damage critical

transformers– Short duration needing fast

response• TVA actions

– Evaluating transformer susceptibilities

• Developing monitoring and response strategies

– Scripting plant operator responses to grid alert

Regional Events - Geomagnetic StormsRegional Events - Geomagnetic Storms

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• Offsite Power is Crucial• Switchyards should be hardened

– Including fire protection– Seismically anchor transformers, breakers etc

• Procure spare mobile power transformers– In case onsite units are destroyed/damaged

• Stock spare HV/EHV bushings– Most vulnerable element

• Need structured offsite power restoration strategies with transmission provider

• Black-start switchyards and relay rooms must also be hardened

Regional Events - SeismicRegional Events - Seismic

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• Identify transmission lines to black-start units– Don’t rely on those with river crossings

• Long restoration times– Consider distribution level feed from local utility– Stockpile tower steel, line conductor and

insulators– Evaluate required logistics (storage,

transportation etc)• Joint Nuclear and Transmission activities

– Relocate emergency centers to common structure

Regional Events – The GridRegional Events – The Grid

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TVA Commitment to NuclearTVA Commitment to Nuclear• Established 1934• 88,000 square miles

– Parts of seven states• Generation and

transmission– No distribution

• Approx 33,000 MW– 11 fossil plants, 59 units– 29 power dams, 117

units– 20 non-power dams– 1 pumped storage plant

• 4 units– 3 nuclear plants

• 6 operating units

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• Nuclear power is safe and being made safer– This is a learning industry

• It makes sense for the environment– No greenhouse gases– Minimizes dependence on widespread strip

mining• Permanent siting of spent fuel remains a national

policy issue– Interim on-site storage is current policy

Why a Nuclear Future?Why a Nuclear Future?

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Nuclear Power’s Increasing RoleNuclear Power’s Increasing Role

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A More Balanced Power SupplyA More Balanced Power Supply

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• Westinghouse PWR• 1,180 MW• Construction halted

1985– Restarted 2007

• Expected online in 2013

Watts Bar Unit 2Watts Bar Unit 2

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• B&W PWR• 1,260 MW• Deferred in 1988• Board approved U1

completion Aug 2011

• Online by ~ 2020

Bellefonte 1Bellefonte 1

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• 125-megawatt reactors would be built in groups• Could replace aging coal units and use existing

sites and transmission• “Passive” safety design w/underground

containment• 4 to 5-year fuel cycle• mPower group plans to demonstrate this

technology by 2020 near Oak Ridge, TN

Small Modular ReactorsSmall Modular Reactors

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Timeline for New ProjectsTimeline for New Projects

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Questions?Questions?

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