New Paradigm for Nuclear Safety
Thursday, April 25, 2013
Japan Nuclear Safety InstituteShojiro Matsuura, Chairman

In Pursuit of Improved Nuclear Safety

Copyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

Japan Nuclear Safety InstituteJapan Nuclear Safety InstituteEnsuring nuclear safety, and lessons learned from accidents

 Goal of Ensuring Nuclear Safety
To protect the general public, operators, and the environment
from the danger of radiological hazards which may result
from nuclear power generation.

In Pursuit of Improved Nuclear Safety

Copyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

Japan Nuclear Safety InstituteJapan Nuclear Safety Institute1Ensuring nuclear safety, and lessons learned from accidents●SL-1 accident●CP-1(1961)(1942)●Windscale accident●Fukushima accident●TMI accident●Chernobyl accident(1979)(1986)(2011)●September 11 attacks(2001)(1957)

Improving nuclear reactor safety
BORAX and SPERT experiments

Power Excursion
LOFT, Semiscale experiments, etc.
Accumulated radiation release accidents

Prevention measures for severe accidents andterrorism had advanced internationally,however from around 1990 these measures were notsufficiently incorporated into Japan’s nuclear power
station design and operation.

Severe accident counter measures
Counter-terrorist measures

In Pursuit of Improved Nuclear SafetyCopyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

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UK: Windscale reactor fire accident (INES: 5)(Plutonium production reactor)
Core:

15 m diameter, 7.5 m depth (horizontal type)

Fuel:

Natural U metallic fuel / Al cladding

Reactor shut down (Morning of October 7, 1957)
7 p.m. until the following morning: Nuclear heating(due to Wigner release)
Core temperature readings began to drop

Moderator: Graphite
Air cooling- For coarse control: 20 horizontal rods

Control rods:- Fine adjustment: 4 horizontal rods
- For shutting down: 16 vertical rods

Temperature during operation and temperature during Wigner
release are supposed to be measured at different locations, butwere notAt 11:05 of the following morning: Reheating → sudden
temperature increase
Control rods were inserted, but temperatures did notdecrease

5:40 a.m. October 10: High levels of radiation detected

Afternoon, October 10: Red-hot U fuel discovered

October 11: Fire extinguished through water injection(Important lesson: safe design and operation)(Wigner release)

Released I-131 from 20,000 Ci (740TBq)

Graphite accumulates energy as crystal lattice imperfections when irradiated with neutrons.
The accumulated energy is released when the graphite's temperature rises.

The reactor became sealed after
the accident

More energy is accumulated the lower the temperature when neutron is irradiated.

(2030 fuel removal plan (from NDA's website))

In Pursuit of Improved Nuclear Safety

Copyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

Japan Nuclear Safety InstituteJapan Nuclear Safety Institute3USA: SL-1 accident (INES: 4)
SL-1 (BWRs manufactured by CE)
Output: 3 MWt
Fuel:

91% enriched U fuel plates (A1 cladding)Control rods: 5 (cross-type)
Core:70 cm height

9:01 January 3, 1961 (During work to couple a control drive with control rods.)
Control rods in the center were pulled out about 67 cm. Degree of reaction approx. 3$ added.
(Criticality occurrance at around the 58 cm position)
Maximum output was 19,000 MW. Maximum pressure was 700 bar. 20% of the core melted.
Water hammer caused the reactor vessel to jump up about 2.7 m. (3 workers were killed.)

Laminated-steel shielding
Control rod drive
Concrete shield
Control rod-drive
motor
Operating-floor
Pressure vessel

Normal water level
Control rod

Thermal shield

Active core
Boral shield

Gravel shield(Site inspection after the incident)

Ground level(Core, after the incident)(Important lesson: core runaway prevention design,fuel protection design, fuel safety design)
In Pursuit of Improved Nuclear Safety

Copyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

(SL-1 cross section)
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USA: TMI-2 accident (INES: 5)
Date: March 28, 1979

Main Feed water pump trip
(Loss of feedwater)

Output: 959MWe①

Models: PWRs manufactured by Babcock and Wilcox

Auxiliary water supply failure

Reactor containment vessel
fail to close
Incorrect
reading onwater level
gauge

Water tank for fuel exchange

Pressurizer
relief valve
Pressurizer②SteamReactor shut down

Generator

Turbine(Emergency core cooling system)
Main Feed
Water Pump

Atmospheric release

Condenser
Cleaning system

Auxiliary building

Reactor Coolant Pump
Water transfer

Pressurizer release valve
stuck open

Steam generator

Manual shutdown

Effluent reservoir tank

Reactor pressure increase

Turbine building

Manual shutdownPressure relief system

Reactor pressure drop

ECCS automatic start up③、④、⑤
Condensate tank Operator shut ECCS down

Valve was closed

Core exposed,
and fuel damaged

Transfer pumpPressurizer relief tankPrimary coolant leak into C/Vs⑥Primary coolant was sent
to auxiliary buildingAuxiliary feed water supply pump

Important lesson: Stochastic risk assessments andthe importance of man-machine interfaces
In Pursuit of Improved Nuclear SafetyCopyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

Radioactive material leak out throughauxiliary building's stack

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Former USSR: Chernobyl accident (INES:7)
Date:

April 26, 1986

- No containment vessels- Designed to allow easy disabling of safety systems- Positive void coefficient during low energy output

DesignOutput: 1000MWe
Model: Graphite-moderate, Light-water cooling, Boiling-water reactor(RBMK type)- Control rod pull out exceeding the regulated number- Operation with emergency core cooling systems (ECCS) off- Special tests at output lower than planned

Ruleinfraction(Important lesson: abolition of intrinsicallydangerous nuclear design,
focus on nuclear safety culture)- Non-reactor specialists in charge of operation- Special tests implemented not according to official procedure andwithout consent of the entire facility- Safety measures ill-considered

Operationmanagement

Control room: A switch to turn off safety systems
No containment vessels

25 to 26 Before dawn

Reactor conditions unstable

Fuel
Water and steam mixture
separator
Control rod

Void increase

SteamPower rise
TurbineModerator: graphite

Coolant

Primary
circulating pump

(Reactor-specific characteristics
and malfunction of emergency
shutdown systems)(Sudden steam generation)(Sudden hydrogen generation)
Numerous pressure pipes burst(1:23AM) followed by hydrogen
explosions
Turbine building fire(extinguished)Core graphite fire
(Burned for 2 weeks)

Coolant

Coolant: Water(Coolant level drops due tocoasted reactor cooling pump)

Power Excursion

GeneratorCondenser
Pressure pipe

Special testing* being done at low output

Radioactive materials frominside core releasedPumpPump

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Japan: Fukushima Daiichi accident (INES: 7)
Gigantic Earthquake
External power
supply failure

Automatic reactor shutdown
Emergency diesel generator automatic startup
Begin cooling
All AC power supply(and DC power) supply lost

Massive TsunamiCore could notbe cooledPower unable
to be restored

Vent operation failure
Fresh and saltwater injection
failureCoremeltdown
Unit 1: Hydrogen explosion at 3:36 PM on March 12

Hydrogen
explosions, etc.
In Pursuit of Improved Nuclear Safety

Copyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

Unit 2: Primary containment vessel damaged at around6:00 on March 15
Unit 3: Hydrogen explosion at 11:01 AM on March 14

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Continued: Situations at Other Nuclear Power Plants• Fukushima Daiichi Units 5 and 6, Fukushima-daini Units 1through 4, Onagawa Units 1 through 3, and Tokai-daini havebeen verified for accident prevention.
• The most important issue is that nuclear fuel was continuously
cooled until the sufficient stabilization of reactor.
These are important lessons to remember

In Pursuit of Improved Nuclear Safety

Copyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

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International Opinion on the Fukushima Daiichi Accident
Report from the American Society of Mechanical Engineers (ASME), Institute ofNuclear Power Operations (INPO), American Nuclear Society, Carnegie Institution forScience, etc.
◆This was the first large-scale, widespread release of radioactive material in the more than 50 years ofusage of light water reactors◆The cause was impact by massive tsunami waves, an extremely rare natural phenomenon thatexceeded expectations◆If using light water reactor technology of current international standards, sufficient measures can betaken to prevent accidents even like Fukushima Daiichi Nuclear Power Station, caused by unlikely
external factor accidents◆To prevent such disasters, equipment preparedness and systematic training are essential◆Despite the extremely low probability of occurrence, research into handling accidents with largescale impact must be conducted

In Pursuit of Improved Nuclear Safety

Copyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

Japan Nuclear Safety InstituteJapan Nuclear Safety Institute9Other Facts Requiring Consideration （Paradigm Shift)<Fact>
Fukushima Daiichi Nuclear Power Station was in compliance with all nuclear
regulations and facility design, construction, and operation before the accident.

We must fundamentally re-examine the old way of thinking, which regards
mere compliance to requirements made by regulatory agencies of nuclearoperators as sufficient.

In Pursuit of Improved Nuclear Safety

Copyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

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Establishment of JANSI and Efforts Going Forward< Concrete Initiatives >◆ Ensure independence from nuclear operators on technology assessments.
◆ Re-emphasize commitments from company presidents regarding improving
nuclear operators' safety measures.
◆ Hold regular meetings with all presidents to communicate to all presidents theresults of assessments concerning measures to improve safety at nuclear operators,
and provide proposals for admonishments concerning improvement, as needed.

Mission:Achieve the highest standard of safety in theworld in the nuclear energy industry.
Ceaselessly strive for excellence.

In Pursuit of Improved Nuclear Safety

Copyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

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Thank you

In Pursuit of Improved Nuclear Safety

Copyright © 2012 by Japan Nuclear Safety Institute. All Rights Reserved.

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