“Earthquake Resilience Nuclear Facilities” Pacific Rim Forum, University of California Berkeley, June 8, 2015

Perspectives on the safety ofnuclear facilities
Yoshiaki Oka
Professor Emeritus, the University of Tokyo
Chairman, Japan Atomic Energy Commission

The views expressed here are of my own and do not necessarily reflect those of JAEC nor the government1

Outline
1. Basic safety issues
2. Lessons learned and recommendation derived
3. Examples for potential countermeasures and technologies tobe applied
4. Improvement of nuclear safety in Japan
5. Mitigation of social and mental effects of the people affected

Reference of 1‐3: Y.Oka and. D.Bittermann, “Chapter 12, Implications and Lessons for
Advanced Reactor Design and Operation”, Reflections on the Fukushima Daiichi Nuclear
2Accident, Jan 2015 Springer

The levels and the main means of action for thedefense‐in‐depth safety concept
INSAG10
Goallevel
1
Prevention of abnormal operationand failures

Main means of action
Conservative design and high quality
in construction and operation

2

Control of abnormal operation andfailures

Control, limiting and protection systems
and other surveillance features

3

Control of accidents within thedesign basis

Engineered safety features andaccident procedures

4Control of severe conditions
including prevention of accident
progression and mitigation of theconsequences of a severe accident

Complementary measures andaccident management

5

Mitigation of the radiologicalconsequences of significant external
release of radioactive material

Offsite emergency response3

Safety Culture• INSAG‐4 definition: Safety culture is that assembly ofcharacteristics and attitudes in organizations and individuals
which establishes that as an overriding priority, nuclear
plant safety issues receive the attention warranted by theirsignificance.
• NRC definition: A good safety culture in a nuclear installation
is a reflection of the values, which are shared throughout alllevels of the organization and which are based on the belief
that safety is important and that it is everyone’s
responsibility.
4

TEPCO Fukushima‐Daiichi NPP accident

NRA (2013) New regulatory requirement for Light‐ water nuclear power plants outline‐ August 2013
Nuclear Regulatory Authority, http://www.nsr.go.jp/english/e_news/data/13/0912.pdf

5Natural hazards
Lessons:
The safety systems did not lose function by the earthquake. The
height of the tsunami was, however, underestimated.
Recommendation:
It is necessary to develop imagination of natural hazards and its
combinations that may potentially cause severe accidents.

6

Emergency power supply
Lessons
The external power of the TEPCO Fukushima Daiichi plants was lostby the failure of transmission lines by the earthquake. The emergency
DGs and some batteries were flooded. Both AC and DC power werelost. The capacity of the remaining batteries was exhausted. The
safety systems and instrumentation systems lost their functions.
Recommendation
It is necessary to enhance the reliability of both AC and DC power
supply against external events and provide sufficient power in case of
severe accidents. Incase that they are lost, alternative power supplies
need to be provided for the plant.
7Loss of heat sink
Lessons• Loss of ultimate heat sink is the important lesson of the accident aswell as loss of emergency power. Damage of seawater pumps by
the tsunami caused multiple failures of functioning pumps and heatexchangers that need cooling for operation and dumping heat intothe sea.
Recommendation• Provision of protective measures like e.g. bunkering of importantcomponents and/or alternative cooling devices as well as the water
source is necessary.
8Hydrogen detonation
Lessons• The reactor building of unit 1,3 and 4 were destroyed by hydrogendetonation. The building of unit 2 was not destroyed, because theblow‐ out panel of the reactor building dropped down by thedetonation of unit1.The hydrogen detonation of the unit1 building
scattered the debris on the site and made preparation of securing
activities of unit 2 and 3 difficult.
Recommendation• The provision against hydrogen leakage at severe accidents shouldbe elaborated and the respective measures should be performed.
9Measurement at severe accidents
Lessons• Important reactor parameters such as water level, pressure andtemperature was not able to be measured due to the loss of DC
power after the tsunami. The water level, the most important safetyparameter of LWRs was measured erroneously after core melt downbecause of the change of the reference water level by evaporation.
Recommendation• Important reactor parameters as well as radiation level, radioactivity
and hydrogen concentration in PCV need to be measured for
management of severe accidents
10Recommendations and requirements derived fromlessons learned
New regulatory requirements and improvements in Japan• Enforcement of resistance against earthquake and tsunami• Reliability of power supply• Measures to prevent core damage by postulating multiple failures• Measures to prevent failure of containment vessel• Measures to suppress radioactive material dispersion• Strengthen command communication and instrumentation• Consideration of natural phenomena in addition to earthquakes and tsunamis, forexample volcanic eruptions, tornadoes and forest fires• Response to intentional aircraft crashes• Consideration of internal flooding• Fire protection
11

Examples for potential countermeasures andtechnologies to be applied• External events• Design of buildings, systems and components• Severe accident issues

12External events
General approach
Common countermeasures proposed for all external events are:• Develop an approach to regulate hazards from extreme natural phenomena• Periodically redefine and reanalyse the natural event design basis
External events in most cases lead to a combination of initiating events like e.g.
earthquake and tsunami or earthquake and fire. Such combined effects have tobe systematically considered for the design.
One proposal is as follows:• Extending even further the in‐depth safety approach to any type of hazards, inparticular external ones, and accounting for any mode of combination of them;• Systematically include the design extension conditions (beyond design basisaccidents) in the defence‐in‐depth approach at the design stage.
13

Need for future studies and development(external events)• Development of approaches to natural hazard definition, techniques anddata, and development of guidance on natural hazards assessments,including earthquake, flooding and extreme weather conditions;• Development of guidance on the assessment of margins beyond the designbasis and cliff‐edge effects for extreme natural hazards;• Development of a systematic approach to extreme weather challenges and amore consistent understanding of the possible design mitigation measures;• Development of the approach for assessment of the secondary effects ofnatural hazards, such as flood or fires arising as a result of seismic events;• Enhancement of PSA for natural hazards and development of methods todetermine margins and identify potential plant improvements;• Overall enhancement of PSA analysis, covering all plant states, external
events and prolonged processes, for PSA levels 1 and 2.
14

Earthquake• It is proposed from several organizations to increase theseismic design criteria for the evaluation and assessment ofbeyond design external events.
• In Japan NRA strengthened the examination of active faults.
The basic earthquake ground motion (EGM) should bedetermined taking the three dimensional undergroundstructures which may amplify the EMG. The safety‐classstructures and buildings should not be built on the activefaults. Strengthening the seismic design of the plants isconducted after the approval of NRA.
15

Tsunami
Actual Japanese NRA requirements• The standards set by the Japanese NRA define a “Design BasisTsunami” as one which exceeds the largest ever recorded. It requires
protective measures such as seawalls. The standards also require“structure, systems and components (SSCs)” for tsunami protective
measures to be classified as class S, the highest seismic safetyclassification to ensure that they continue to prevent inundations
even during earthquakes.
• The examples of multi‐ layered protection measures against tsunami
are installation of a seawall to prevent site inundation andinstallation of water‐ tight doors to prevent the flooding of buildings.
16

Seawall to prevent site inundation

NRA (2013) New regulatory requirement for Light‐ water nuclear power plants outline‐ August
17
2013 Nuclear Regulatory Authority, http://www.nsr.go.jp/english/e_news/data/13/0912.pdf

Design of buildings, systems and components
1. Sites with more than one reactor• Strict separation of safety related systems and components• Provision of a plant arrangement which prevents common cause failures forsafety related systems and components
2. Off‐site and on‐site electricity supply
In case of an external event like an earthquake, the off‐site electricity
supply is very difficult or even impossible to maintain. The way to substituteoff‐site electricity supply is mainly to provide mobile power supply systems
or addition of diesel generators or other power sources like e.g. gas turbines.
These components must be protected against external events by bunkering
or e.g. located at positions which cannot be affected by e. g. tsunami waves.
18

Bunkered emergency feed building for recent
German PWRs

• Recent German PWRs are equipped with a second fourfold emergency power
supply (emergency diesel sets). These second emergency cooling systems cancool the reactor core (via steam generators) as well as the fuel element pool

Source : Y.Oka and. D.Bittermann, “Chapter 12, Implications and Lessons for Advanced Reactor Designand Operation”, Reflections on the Fukushima Daiichi Nuclear Accident, Jan 2015 Springer

19Passive components andsystems using natural forces

20

Passive containment cooling system (AP1000)
1: Core,2: PRHR,
3: IRWST,
4: Gutters,
5: CV,
6: Louvers,
7: PCCWST,
8: Atmosphere

Source: Vereb F, Winters J, Schultz T, Cummins E, Oriani L (2012) The AP1000 nuclear power plant innovative features forextended station blackout mitigation , Proceedings of ICAPP’12, Chicago USA, June 24‐28, 2012, paper 12063
21

Passive Safety Systems (ESBWR)

Barrett A. J. and Marquino W (2012) ESBWR response to extended station blackout andloss of all AC power, Proceedings of ICAPP’12, Chicago, USA, June 24‐28, 2012)22

Mitigation measures against
severe accidents

23

Hydrogen mitigation
Passive auto catalytic recombiner

Source : Y.Oka and. D.Bittermann, “Chapter 12, Implications and Lessons for Advanced Reactor Designand Operation”, Reflections on the Fukushima Daiichi Nuclear Accident, Jan 2015 Springer

24

Containment venting systems
Venturi scrubber

Source : Y.Oka and. D.Bittermann, “Chapter 12, Implications and Lessons for Advanced Reactor Designand Operation”, Reflections on the Fukushima Daiichi Nuclear Accident, Jan 2015 Springer

25Melt stabilization measures

In‐ vessel retention

Ex‐ vessel retention

AP‐1000

VVER‐1200

Core catcher concept
EPR, ATOMEA,European ABWR (no needof separate spreading chamber)

Source : Y.Oka and. D.Bittermann, “Chapter 12, Implications and Lessons for Advanced Reactor Designand Operation”, Reflections on the Fukushima Daiichi Nuclear Accident, Jan 2015 Springer

26

Safety improvement in Japan
1. Established independent nuclear regulatory agency (NRA)
2. Started voluntary safety improvement by utilities/ industries

27Voluntary Safety Improvement Mechanism in US Industry
Common Goal：Nuclear Safety Improvement
Researchoutsourcing

DOE（Department of Energy）

PublicCongress

Providing information,
Public relations activities
Recommendations/explanations

Budget /Quota

Propose legal regulationand safety goals

Adapted from METI

Report result ofsafety researchElectricUtilities

EPRI（Electric PowerResearch Institute）（Nuclear EnergyInstitute）

Compileopinions

NRC※INPO : Institute of Nuclear Power Operations
NEI : Nuclear Energy Institute
EPRI : Electric Power Research Institute
NRC : Nuclear Regulatory Commission
PRA : Probabilistic Risk Assessment

NEI

Jointresearch

Reasonable andscientific discussionof regulation（Nuclear RegulatoryCommission）

Joint Research

Reportoperationdata

INPO
Peer review,advice,recommendations

Information exchange (Independentand supplementary）（referred to the reference material of the Second Meeting Working
Group on Voluntary Efforts and Continuous Improvement ofNuclear Safety, Advisory Committee for Natural Resources andEnergy April 23, 2013 ）（Institute of Nuclear
Power Operations）

WANO（World Association of NuclearOperators）

28

Japanese effort for Voluntary Safety Improvement

JANSI（Japan Nuclear Safety Institute）
NRRC（Nuclear Risk Research Center）
Japanese Nuclear Industry
Electric Utilities：the Federation of Electric Power Companies of Japan, 9utilities, Japan Nuclear Fuel Limited, Central Research Institute of ElectricPower Industry etc…
Manufacturers：Mitsubishi Heavy Industries, Ltd., Hitachi, Ltd., Toshiba
Corporation, The Japan Electrical Manufacturers’ Association, fuelmanufacturers etc…
Japan Atomic Industrial Forum, Inc.(JAIF) etc.

29

Structure of Japan Nuclear Safety Institute (JANSI)

Source: JANSI HP http://www.genanshin.jp/english/association/establishment.html

30Structure of the Nuclear Risk Research Center (NRRC)

31（Source: N20’s presentation Material, Hirobumi KAYAMA, “the Current Nuclear Energy Policy” as of November 3, 2014）

Mitigation of mental and social
impact of the people affected32• Acute healtheffect occurs
abovethreshold(high) dose.
• Linear non‐thresholdmodel (linearhypothesis) isused forestimating
latent healtheffect (cancer)
at low dose

Potential Damage to Health

Health effect of low level radiation

2.4 mSv
Average Yearly Exposure
from Natural Causes

Source:A.E. Waltar

Reliable
Database

Known
Adverse Effects

No known
Adverse Effects

CA

Area ofControversy

100 mSv
B

Dose Causing Observable
Adverse Health Effects

Radiation Dose [mSv]33

Health implications of radiation exposure of the
public resulting from FDNPS accident(UNSCEAR 2013 Report, Appendix E)• “No discernible risk”: An increased incidence of effects is unlikely.
Consequences are small relative to the baseline risk and uncertainties.
• The most important health effects would appear to be on mental and social
well‐being as a consequence of the evacuation and their displacement tounfamiliar surroundings, and the fear and stigma related to radiation
exposure. For example more than 50 hospitalized patients died either
during or soon after the evacuation, probably because of hyperthermia,dehydration or deterioration of underlying medical problems. Upward of
100 elderly people may have died in subsequent months.
• Understanding full heath impact of accident forms an important context for
the Committee’s commentary.
34
UNSCEAR: United nations scientific committee on the effects of atomic radiation

“Maintaining health” should be the goal
• Order of “sheltering” made most people escape from their homes, but those
weak in disaster (single elderly people, patients etc.) were left and separated
from outside area.
• Displacement worsen health of the evacuees. No working (farming) increases
instability of legs, sugar disease, fatness, osteoporosis• Displacement for avoiding low level of radiation exposure increased otherhealth risks. It is effective, only when other risks do not increase.
• Lack of exercise and fatness increase cancer risk 1.2 times, equivalent to 100‐
200mSv of exposure.
• Telling only “radiation” risk increased fear of “radiation”. Radiation risk is apart of cancer risk. It is a part of health risk.
• “Maintaining health” should be the goal for avoiding mental and social healtheffects of nuclear accidents.
Source: Sae Ochi, Energy review pp7‐10, April 2015,(in Japanese)

35

Lessons of risk communication and managementof nuclear accidents• LNT model is a hypothesis, not a scientific fact. But it assumes that risk
is NOT zero. Start to tell “no risk” was a wrong way, failed andincreased fear of radiation in Fukushima. It is logically impossible toprove “zero risk”. Start to tell “Cancer risk of radiation exposure is NOTzero” looks a good way of risk communication.
• Telling various cancer risks in human life and its uncertainty at low
exposure is the way. Cancer risk of low radiation exposure is within theuncertainty.
• Comparing various cancer risks such as radiation, chemicals, etc. isnecessary, but will be not enough to manage mental and social effects.
• “Maintaining health” is good goal for managing the problems andtaking actions at severe nuclear accidents.
36

Thank you for your attention

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