Nuclear Safety Regulation:

Before and after Fukushima*

Shridhar Chande, India

International Conference on Effective Nuclear Regulatory Systems:

Sustaining Improvements Globally, Vienna 11-15 April 2016

*Accident at the Fukushima Daiichi NPP

• The main lesson from the Accident at Fukushima Daiichi

NPP

• Changes in Defence in Depth and other requirements

for Nuclear Safety

• Impact of the revised requirements on the safety of new

plants

• Can good regulations alone ensure safety?

• Robust National Nuclear Safety System - Institutional

Strength in Depth (A proposal from INSAG)

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The main lesson from the Accident at

Fukushima Daiichi NPP

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• More than 160 000 people were evacuated from their homes.

• Consequently, nobody received any significant amount of

radiation

• Many of them, still continue to stay in provisional housing, away

from home. They may not be able to return for several more years

• Many are suffering from health issues emanating from uncertainty,

anxiety, depression and discrimination

• It is reported that about 1600 have died during this period due to

non-radiological health effects

• The accident has caused enormous economical, societal and

psychological impact on Japanese people

Though nobody has received any significant radiation

dose, the displacement of large number of people for prolonged

period is not acceptable to the society

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• Protecting people from radiation alone is not the only focus

of safety of NPPs

• It is essential to ensure that under any circumstances there

is no need to relocate the public for prolonged periods

• Hence the focus of safety must shift from

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Protect people and the environment from the

harmful effects of radiation

The necessity for off-site protective actions to mitigate radiological

consequences should be limited or even eliminated&

As a consequence, the safety objectives of the nuclear power

plant can be restated as

In order of priority

• A nuclear accident should be prevented

• If an accident takes place it should be prevented from

progressing to a Severe Accident (SA)

• In case it develops in to a SA, its consequences should be

mitigated so as to

– Prevent/minimise and delay the radioactive releases, and

– Ensure that no urgent or long term protective actions are needed

in the public domain

• An accident involving early or large releases should be

practically eliminated

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1. New nuclear power plants are to be designed, sited, and

constructed, consistent with the objective of preventing

accidents in the commissioning and operation and, should an

accident occur, mitigating possible releases of radionuclides

causing long-term off site contamination and avoiding early

radioactive releases or radioactive releases large enough to

require long-term protective measures and actions.

2. Comprehensive and systematic safety assessments are to be

carried out periodically and regularly for existing installations

throughout their lifetime in order to identify safety

improvements that are oriented to meet the above objective.

Reasonably practicable or achievable safety improvements

are to be implemented in a timely manner.

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• The most important safety principle used in design and operation of

NPPs is the Defence in Depth philosophy to guard against human

and equipment failure.

• Defence in Depth involves building of multiple levels of safety, such

that if one level fails the subsequent level prevents progression of

the event, limiting consequences.

• Each level has redundant and diverse safety systems to make it

robust and reliable. The levels are made independent to the extent

possible, to avoid common cause failures

With proper defence in depth in place, an accident with such

consequences as in Fukushima shouldn’t have happened

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All offsite and onsite power supplies were lost due to tsunami flooding. This disabled all normal and back up systems needed for cooling the reactor.

A common cause failure of all the three levels of

defence in depth for prevention due to

flooding

Accident management guidelines could not be implemented as no instruments were working and there was no power supply. Total darkness and debris in the plant areas made access difficult.

A failure of the fourth level of defence again due to flooding and its consequences

The essential lesson here is to strengthen the defence in depth,

both at Level 3, for the prevention of accident; and

at Level 4, controlling the progression and mitigating the

consequences of the accident

Change in Defence in Depth and other

requirements for Nuclear safety

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• This level deals with the postulated set of design basis accidents

(DBA) for which the plant is designed

• The essential means to deal with the DBA are inherent or

conservatively designed engineered safety features

• Improve the robustness of preventive measures and avoid their

common cause failures by use of redundancy, diversity, physical

separation and functional independence

• Change in the radiological acceptance criteria to be consistent with

the revised safety objectives

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Earlier Criteria

Prevent significant off-site releases to keep public dose within the specified limit (100-250 mSv, allowing due credit for protective measures)

Revised Criteria

Only minor radiological impact in the public domain that does not necessitate any off-site protective measures. (dose limited to only a few mSv, without any credit for off site protective measures)

• Level 4 (earlier called BDBA conditions)addresses the accident

conditions that exceed the design basis either due to multiple

failures or severity of the PIE and are called Design Extension

Conditions (DEC), implying that they are to be considered in the

design process

• This level requires provision of additional safety systems/features,

which are different from those used for more frequent accidents and

capable of functioning under the expected severe accident

conditions

• DECs are categorised as follows

– DEC without core melt

– DEC with core melt

• Accident conditions leading to early or large radioactive releases are

to be practically eliminated

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Defence in

depth level

Objective Radiological Criteria

Level 4A

DEC without core

melt

Arrest

progression of

accident

(Same as Level 3, except use

of best estimate methods

permitted)

Level 4B

DEC with core melt

Mitigate the

consequences

of severe

accident

Protective measures limited in time and area to be sufficient, with adequate time being available to implement. No significant offsite contamination

SA involving early

or large releasesTo be practically eliminated

• Level 4 earlier called BDBA had the objective to limit

off-site releases as low as reasonable achievable

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• Strengthening the different levels of defence in depth and their independence

• Conservative consideration of external hazards and sufficient margins

• Strengthening the reliability of heat sink

• Strengthening the emergency power supply

• Ensuring the safety of spent fuel storage under accident conditions

• Enabling the use of non-permanent equipment

• Provision of emergency response facilities

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• Rigorous implementation of Periodic Safety

Reviews*

• Improving the Emergency preparedness

• Strengthening the Accident Management

provisions and plans

*Vienna Declaration on Nuclear Safety

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Impact of Revised Requirements

on the safety of new plants

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Dose Criteria for Public (Indian example)Pre-Fukushima Post-Fukushima*

Plant State Dose Limits at

EZ boundary

Normal operation 1 mSv/year

Anticipated

Operational

occurrences

1 mSv/year

Design Basis

Accidents

100mSv

Beyond design

basis accidents

No limit

Plant State Dose targets at exclusion zone

boundary

Normal operation 1 mSv/year

Anticipated

Operational

occurrences

1 mSv/year

Design Basis

Accidents

20 mSv/year following the event , no

need for offsite protective measures

Design Extension

Conditions

without Core melt

No need for offsite protective

measures except control on food or

agriculture limited to small area &

time. Dose Target same as for DBA

Design Extension

Conditions with

Core melt

No permanent relocation of

population. The offsite Interventions

to be limited in area and time

Conditions giving rise to large or early releases

have to be practically eliminated 18

*AERB safety code on

Siting of Nuclear Facilities

AERB/NF/SC/S (2014)

Pre Fukushima Post Fukushima*

CDF For new NPPs

< 10E-5/RY

For new NPPs

• <10E-6/RY for internal events,

power and shut down states

• <10E-5/RY for internal events and

external hazards together

LERF For new NPPs

< 10E-6/RY

For new NPPs LER to be practically

eliminated (LERF <10E-7)

*As per new AERB safety code on

Design of NPPs based on LWR technology

AERB/NPP-LWR/SC/D (2015)

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Design CDF LERF

EPR 7.1x10E-07/RY 7.7x10E-08/RY

AP1000 5x10E-07/RY 6x10E-08/RY

VVER ~10 E-07/RY ~10E-08/RY

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• These CDF values are typically two orders of magnitude

better than most currently operating NPPs

• Even if severe accident stage is reached, the radiological

consequences will be limited in area and time (No

urgent need for protective actions in the public

domain and no long-term impact on the society)

• With LERF values well below 10E-7/RY, large or early

releases can be considered as practically eliminated

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Can good regulations alone ensure

safety?

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• External hazards, in particular Tsunami, had not been reassessed in a systematic and comprehensive manner

• Operating experience (in plant as well as around the world) indicated vulnerability of safety systems to flooding. This did not lead to any significant safety upgrades

• Periodic Safety Reviews also did not lead to any safety upgrades based on current safety requirements

• Accident management guidelines were neither comprehensive nor up to date. Operators were not trained and hence were not prepared for implementing the guidelines

• Regulatory inspections were not adequately structured to verify safety or identify new safety issues

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The IAEA Fukushima report concludes

• All stake holders, namely, the NPP people, Regulators

and the concerned Government Agencies believed (and

even mutually reinforced the belief) that the nuclear

plants in Japan are adequately safe and a severe

accident is unlikely. Consequently, essential safety

upgrades were not implemented

• None of the organisations or their staff challenged the

level of safety. There was an air of complacency all

round which was detrimental to safety culture

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• The regulations need to be implemented with rigour and

sincerity by the Industry

• The Regulatory Body has the responsibility to verify and

ensure proper implementation of all safety regulations by

the Industry

• Individuals and organisations need to continuously

challenge and re-examine the prevailing assumptions

about nuclear safety and the implications of their

decisions and actions that could affect nuclear safety

• It is essential to promote and continuously strengthen

safety culture.

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Robust National Nuclear Safety System:

Institutional Strength in Depth

(A proposal from INSAG)

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• The National Nuclear Safety System (NNSS) comprises

of all those players who can/should influence nuclear

safety. These include the nuclear industry, the regulators,

the national/international nuclear safety bodies, the

national Governments and other stake holders such as

public and media

• Its main function is to develop, assess, review and

continuously improve nuclear safety, which is also an

important element of nuclear safety culture

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• The main principle of the NNSS proposed by INSAG is

the Strength in Depth approach, a concept derived from

Defence in Depth for nuclear safety itself.

• The main features of this approach are

� Multiple layered approach

� Independence of layers

� Diversity, redundancy and separation of functions

• These features should prevent failure of the entire

system either due to single failure or common mode

multiple failures

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• Level 1 : A strong nuclear industry, who has the

primary responsibility for safety

• Level 2 : A strong nuclear regulator, with a

responsibility to oversee and ensure that the nuclear

industry maintains the desired level of safety

• Level 3 : Strong set of stakeholders, includes those

who can get affected and also those who can influence

the safety at policy level

Transparency and Effective Communication are the primary

requirements for these levels to function effectively

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Sub Levels Essential elements/Mechanisms

1.1 Licensee/Operator Maintain and improve

• Knowledge, Competency and

Resources

• Internal review and audit

• Worker involvement

• Vibrant Safety Culture

1.2 National/Regional

Nuclear Industry

Peer pressure and guidance

1.3 International Industry Peer reviews / guidance

( such as WANO, Owners Groups e.g.

CANDU, BWR etc.)

1.4 International

Organisations

Peer reviews

(such as IAEA OSART)

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Sub Levels Essential elements/mechanisms

2.1 Regulatory

Authority

Maintain/improve

• Technical and Regulatory competence

• Independence and legal authority

• Organisation, structure and procedures

• Accountability to the Governing Body

2.2 External Technical

Experts/Expert

Groups/standing

panels

Consultation and advice

• Policy issues, high level principles

• Special topics (e.g. Seismic hazards, PSA,

Digital C&I)

2.3 International

standards

Guidance and bench marking

• IAEA safety standards

• WENRA reference levels etc.

2.4 International

Organisations/

Conventions

Peer Reviews

• Convention on Nuclear Safety

• IAEA IRRS

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Stakeholders Means of

communication

(by Industry and

Regulator)

Essential Elements

• Local Government

• National

Government/Parliament

• Public and Media

• NGOs and Special

Interest Groups

• Neighbouring countries

(if likely to be affected)

• World community

• Routine information

and reports

• Special issues and

events reports

• Response to request

for information

• Routine/Special

meetings

• Openness and

transparency

• Effective

communication

• Industry/ Regulator

Leadership and

initiative

• Safety Culture

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• Openness and transparency

• Effective communication

Across all layers

• Competence and resources

• Leadership and initiative

• Vibrant Safety Culture• Questioning Attitude

• Willingness to listen, explain, adopt/change where necessary

• Desire to learn, improve and excel

• Safety : topmost priority under all circumstances

For Industry and the

Regulator

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• In the post Fukushima era, with the revised

regulations, the nuclear plants are expected to

be significantly safer

• However, rigorous implementation of the

regulations, continuous vigilance together with

high level of safety culture can alone ensure

accident free operation of nuclear installations

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Thank you for your attention

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Contact : chandes@gmail.com