Radiological Protection and Public Health2023

Post-Fukushima Action

Implementation at Nuclear
Installations
Human and Organisational
Factors Lessons Learnt

NE A

Human Aspects of Nuclear Safety

Post-Fukushima Action Implementation
at Nuclear Installations
Human and Organisational Factors Lessons Learnt© OECD 2023
NEA No. 7578
NUCLEAR ENERGY AGENCY
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NUCLEAR ENERGY AGENCYThe OECD Nuclear Energy Agency (NEA) was established on 1 February 1958. Current NEA
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Cover photos: Emergency exercise 1 and 2 (KINS); Validation of the filtered containment venting system (CSN).

ACKNOWLEDGEMENTS

Acknowledgements

This report is the product of a multi-year effort by a task group of the Nuclear Energy Agency (NEA)
Working Group on Human and Organisational Factors (WGHOF). The task group comprised thefollowing individuals:•

Lars Axelsson (Swedish Radiation Safety Authority [SSM]);•Yun Hyung Chung (Korea Institute of Nuclear Safety [KINS]);•

Nicolas Dechy (Institut de Radioprotection et de Sûreté Nucléaire [IRSN]);•

Cesar de le Cal Losada (Centrales Nucleares Almaraz-Trillo);•

David Desaulniers (Task Lead, US Nuclear Regulatory Commission [NRC]);•

Suzanne Dolecki (Canadian Nuclear Safety Commission [CNSC]);•

Benito Gil (Consejo de Seguridad Nuclear [CSN]);•

Lisa Hagen (CNSC);•

Carine Hebraud (Autorité de Sûreté Nucléaire [ASN]);•

Hiroyasu Ito (Japan Nuclear Safety Institute [JANSI]);•

Wondea Jung (Korea Atomic Energy Research Institute [KAERI]);•

Mohand Saïd Khemliche (IRSN);•

Jitae Kim (KINS);•Jan Kubicek (UJV);•

Ryuji Kubota (Japan Nuclear Regulatory Authority [JNRA]);•

Dhong Hun Lee (KINS);•

Salvatore Massaiu (OECD Halden Reactor Project);•

Hiroko Takada (JNRA);•

Daniel Tasset (IRSN).

The US NRC served as the lead organisation. In addition, the task group received outstanding
support from the NEA, notably from Monica Haage, Pascale Bourassa, Kamishan Martin and
Natalie Bonilla.
The WGHOF extends its appreciation to all these individuals and their organisations fortheir generosity in contributing their time and expertise to this effort.

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TABLE OF CONTENTS

Table of contents

List of abbreviations and acronyms .................................................................................................... 7
Executive summary ................................................................................................................................ 9
Chapter 1. Introduction ........................................................................................................................ 13
Motivation .......................................................................................................................................... 13
Project overview ................................................................................................................................ 13
Participating countries/organisations ............................................................................................ 14
Chapter 2. Phase 1 summary .............................................................................................................. 15
Phase 1: Information request........................................................................................................... 15
Insights from Phase 1 ....................................................................................................................... 17
Potential HOF implications and challenges ................................................................................... 18
Chapter 3. Phase 2 summary .............................................................................................................. 21
Issuance of requests for lessons learnt .......................................................................................... 21
Instructions for submitting lessons learnt .................................................................................... 21
Lessons learnt summaries and examples ...................................................................................... 24
Insights from Phase 2 ....................................................................................................................... 38
Chapter 4. Conclusions......................................................................................................................... 43
Chapter 5. Recommendations ............................................................................................................. 45
References .............................................................................................................................................. 47

List of appendices
A: Regulatory Authority Responses to the Phase 1 Information Request Summaries of Actions Taken and Questionnaire Responses Regarding Humanand Organisational Factors Addressed by these Actions ....................................................... 49
B: Responses to Phase 2 Information Request – Human and Organisational Factors
Lessons Learnt Implementing Post-Fukushima Actions ........................................................ 51

List of figures
1.
2.
3.
4.
5.
6.
7.
8.
9.

Summary of the three project phases ...................................................................................... 14
Remote Automated Gamma Monitoring Station..................................................................... 26
Sequence of expected failures and required actions in SBO scenario ................................. 27
Mobile Diesel Generator 4 x 352 kW (one per unit) ................................................................. 28
Conceptual diagram of a phased approach in accident response ........................................ 29
Safety measures to enhance third layer of defence in depth for ABWR .............................. 30
Example of improvement of external communication .......................................................... 31
MACST core cooling strategies .................................................................................................. 34
Relation between procedures .................................................................................................... 35

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TABLE OF CONTENTS

10. 3.2 MW mobile diesel generator (Korea) ................................................................................... 35
11. Validation of the filtered containment venting system (1) .................................................... 37
12. Validation of the filtered containment venting system (2) .................................................... 37
13. Applicability of lesson learnt to on-site and off-site activities ............................................. 39
14. Applicability of lesson learnt to work location ........................................................................ 39
15. Applicability of lesson learnt to job categories........................................................................ 39
16. Applicability of lesson learnt to human and organisational factors topical areas ............. 40

List of tables
1. Country participation in task implementation ....................................................................... 14
2. Summary of Phase 1 questionnaire topics and subtopics ..................................................... 15
3. List of MACST procedures .......................................................................................................... 34

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LIST OF ABBREVIATIONS AND ACRONYMS

List of abbreviations and acronyms

ABWR

Advanced boiling water reactor

AC

Alternating current

ASN

Autorité de sûreté nucléaire (France)

CANDU

Canada Deuterium Uranium

CEZ

Czech Energy Company

CNSC

Canadian Nuclear Safety Commission

COG

CANDU Owner’s Group

CRD

Control rod drive

CSN

Consejo de Seguridad Nuclear (Spanish Nuclear Safety Council)

CSNI

Committee for the Safety of Nuclear Installations (NEA)

DAM

Diverse and mobileDC

Direct current

DG

Diesel generator

ECS

Évaluation complémentaire de sûretéEDMG

Extensive Damage Mitigation Guidelines

ELAP

Extended loss of AC power

EMC

Emergency management centre

EME

Emergency mitigating equipment

EOP

Emergency operating procedures

ERO

Emergency response organisation

ESCS

Emergency satellite communication system

FCVS

Filtered containment venting system

FEPC

Federation of Electric Power Companies

FLEX

Diverse and flexible coping strategies

FSAR

Final safety analysis report

HF

Human factors

HOF

Human and organisational factors

HOP

Human and organisational performance

HP

High pressure

HPAC

High pressure alternative cooling (pump)

HVAC

Heating, ventilation, air conditioning

HX

Heat exchanger

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LIST OF ABBREVIATIONS AND ACRONYMS

8

ICS

Incident command system

IMS

Incident management system

JANSI

Japan Nuclear Safety Institute

KAERI

Korea Atomic Energy Research Institute

KHNP

Korea Hydro and Nuclear Power Co. Ltd.

KINS

Korea Institute of Safety

LAN

Local area network

LUHS

Loss of ultimate heat sink

MACST

Multi-barrier Accident Coping Strategy

MDG

Mobile diesel generator

MOG

MACST operating guides

MUWC

Makeup water condensate (pump)MW

Megawatt

NEA

Nuclear Energy Agency

NRC

Nuclear Regulatory Commission (United States)

OECD

Organisation for Economic Co-operation and Development

OFC

Off-site centre

PCV

Pressure containment vessel

PHS

Personal handy phone system (not nuclear specific term)

PSA

Probabilistic safety assessment

R/B

Reactor building

RHR

Residual heat removal (system)

SAMG

Severe accident management guideline

SBO

Station black out

SDShut down

SLC

Standby liquid control (system)

SRV

Safety relief valve

SSM

Swedish Radiation Safety Authority

UJV

Czech Nuclear Power Engineering Company

URI

Unified RASCAL (Radiological Assessment System for Consequence Analysis)
Interface

US

United States

V&V

Verification and validation

WebEOC

Web-based emergency operating centre

WGHOF

Working Group on Human and Organisational Factors (NEA)

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EXECUTIVE SUMMARY

Executive summary

On 11 March 2011, the Great East Japan Earthquake occurred off the coast of Honshu Island,
resulting in a large tsunami causing widespread devastation across Japan and in particular at the
Fukushima Daiichi Nuclear Power Plant. In the aftermath of the Fukushima Daiichi accident,
nuclear regulators, industry organisations, and operating companies across the globe began theprocess of understanding the lessons learnt from the accident and planning actions to strengthen
preparedness and the capabilities to respond to and mitigate the effects of such extreme external
events. The actions, both within and across these plans, are diverse and include new or modified
organisations, procedures, training, and equipment. Although many of these actions leverage new
equipment or technologies, these enhancements typically continue to rely on the ability of plantstaff to make sound and timely decisions and to complete assigned actions within a limited
amount of time. As a result, human and organisational factors are central to realising the intended
benefits of the many post-Fukushima enhancements that have been implemented or remain inprogress.
The NEA Working Group on Human and Organisational Factors (WGHOF) task described inthis report began in 2016 with the following primary objectives:(1) Gathering the lessons learnt (positive and negative) related to human and organisational
factors (HOF) that are being gained from implementing the actions that many regulatory
authorities and nuclear facility operators around the world are taking to strengthen theirability to respond to events like those experienced at the Fukushima Nuclear Power Plant.
(2) Sharing these lessons learnt broadly (e.g. with nuclear facility operating companies,
technical support organisations, research institutions, and regulatory authorities) sothat they can be used to facilitate and enhance these efforts going forward.
This report addresses the second objective by including, as appendices, the submissions andlessons learnt gathered during this initiative.
The effort comprised two phases of information collection. In Phase 1, the WGHOF issued
information requests to nuclear regulatory authorities to obtain written summaries andquestionnaire responses concerning the post-Fukushima requirements and guidelines that had
been issued in their country and the actions that had been taken towards enhancing mitigationof extreme external events and management of severe accidents. In both the summaries and thequestionnaire, the focus was on the human and organisational factors of the activities,
requirements, and guidelines. The Phase 2 information request was directed towards nuclear
facility licensees and used a standardised template to elicit short summaries of HOF lessons learnt
as a result of the implementation of post-Fukushima actions.
Phase 1 of the information collection was highly successful, resulting in a compendium ofsummaries from regulatory authorities in seven countries (Appendix A) that describes thebreadth and diversity of the post-Fukushima actions, with an emphasis on the human andorganisational aspects. The summaries also point to the applicable requirements and guidelines.
Each summary is accompanied by questionnaire responses that draw the relationship between
the specific actions described in the summaries and each of ten topical areas concerning humanand organisational factors.
The Phase 1 responses indicated that in many cases the actions taken in response to the
Fukushima Nuclear Power Plant accident went beyond capabilities for response to extreme
external events to include enhancements to severe accident management and capabilities forresponse to loss of large areas of the plant due to fire or explosion. These broad-based responses
reflect the interrelated and complementary nature of these capabilities and suggest that
improvements in the flexibility and efficiency of accident mitigation may be realised through the

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EXECUTIVE SUMMARY

enhancements to, and integration of, these programmes. The Phase 1 responses revealed that theplanned enhancements in each country included the addition of new and additional equipment
for accident mitigation. While the approaches varied from country to country in terms of relativeemphasis on installed vs portable equipment, nearly all the enhancements to mitigation
capabilities relied on human action to effect the mitigation strategies. These Phase 1 results
confirmed the importance of understanding the HOF associated with these enhancements andthe potential value of HOF lessons learnt during the development, validation, and deployment ofthese enhancements.
Phase 2 of the information collection produced a compendium of 40 lesson learnt submissions(Appendix B) describing specific implementation activities that had been undertaken and theinsights gained in the process. These submissions bring to life the actions and requirements
described in responses to the Phase 1 information collection, including some of the challenges
that were encountered and overcome in the process. One limitation of the Phase 2 responses wasthat they frequently focused on the action that was taken without substantive discussion ofrelated HOF lessons learnt during implementation. Additionally, given the small sample size oflessons learnt and because respondents selected the lessons learnt to submit (i.e. the sample issmall and non-random), the reader is cautioned against inferring that the sample is representativeof the population of all HOF lessons learnt through implementation of post-Fukushima actions.
Nevertheless, the Phase 2 results suggest some possible themes.
Nearly all the lessons learnt were characterised by the submitters as applicable to on-site
response in comparison to roughly half being characterised as applicable to off-site activities.
The results suggest a greater emphasis on on-site activities, such as prevention of core damage,relative to mitigation of off-site consequences from radiological releases. The distribution is not
surprising when viewed from a perspective that it is preferable to prevent an accident than
mitigate its consequences. By contrast, it was interesting to find that when considering plant
locations to which the lessons learnt applied, the preponderance were applicable to theemergency operations facility. A smaller number were applicable to the main control room,
technical support centre, and other local control stations, though among these other locations
the number of applicable lessons learnt were roughly equal. These results would seem tounderscore that whereas under design-basis emergency operations the main control room isthe focal point, under conditions of response to extreme external events and severe accidents,
a much broader range of plant facilities and locations become prominent in the response.
A similar pattern was observed when examining the applicability of lessons learnt to job
categories, with other categories of personnel being the subject of lessons learnt as often, andin some cases more often, than main control room operators. Examining the lessons learnt by
the topic addressed, it emerged that the lessons learnt were most often applicable to mitigation
strategies, emergency response facilities, and emergency response plans. Other procedures andguidelines, communications, and training were also commonly identified as topics addressedby the lessons learnt
In light of the information collected in Phases 1 and 2, this report discusses the central roleof human and organisational performance in mitigating extreme external events and the
management of severe accidents. The report also addresses the importance of validating theability to perform these actions, and the challenges associated with performing such validations
with fidelity to the conditions likely to be present during such events. The report concludes withfour recommendations:
1. Explore the contents of Appendix A and use the information as a resource(e.g. identification of alternative tools, methods, and strategies) to inform current andfuture efforts pertaining to the mitigation of extreme events and management of severe
accidents. Additionally, the report proposes a systemic human, technology andorganisation (HTO) approach to implementing post-Fukushima actions such that theinteractions of humans, technology and organisational factors are considered in an
integrated manner, as it could prove useful in gaining the full benefit of these efforts.
2. Explore the contents of Appendix B to gain a deeper understanding of the material in
Appendix A, consider the human and organisational factors of response to extreme
external events and severe accidents, and assess the applicability of the lessons learnt
to their efforts and capabilities for event mitigation and accident management.

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EXECUTIVE SUMMARY

3. Undertake initiatives that target the challenges associated with validating the actions
required of individuals and organisations for the mitigation of extreme external eventsand severe accidents, with the aim of developing innovative and practical solutions andsharing these solutions broadly. Efforts are recommended to enhance validation for suchactions at both the elemental and integrated levels.
4. Pursue initiatives, such as the effort documented in this report, that facilitate theidentification and broad dissemination of insights and best practices for the HOF aspectsof mitigating extreme external events and managing severe accidents.

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INTRODUCTION

Chapter 1. Introduction

Motivation
Extreme external events (e.g. floods, earthquakes) that can significantly challenge a nuclear
facility’s operational safety have, fortunately, been rare. The same can be said for severe
accidents at nuclear facilities. However, this means that opportunities to learn from such
events have been limited. Although the challenge of having few opportunities to learn fromlarge scale events is certainly preferable to the alternative, it should not be dismissed orunderestimated. The mitigation of these events, relative to design-basis accidents, depends
on operators’ manual actions and decisions, which are taken in highly challenging
environmental and operational conditions. It is clear that providing the training and support
necessary for personnel to be effective in these unique and challenging conditions will be
critical to success in mitigating these events.
Following the accident at Fukushima Daiichi, nuclear regulatory authorities and operatingcompanies in many countries established plans to assess and, as warranted, enhance theircapabilities to mitigate the consequence of extreme external events and severe accidents. The
NEA Working Group on Human and Organisational Factors (WGHOF) recognised that theassessments, audits, validation tests, exercises, and drills conducted as part of theimplementation of these mitigation capabilities represented a unique and significant
opportunity to gain insights that can be used to help industry learn about the challenges andmost effective means to implement such capabilities. Seizing upon this opportunity, the
WGHOF undertook the task of aggregating and disseminating internationally the lessons
learnt from these activities with the objective of accelerating the accumulation of such
experience and consequent industry learning.

Project overview
The WGHOF’s main mission is to improve the understanding and technical basis for treating
human and organisational factors in the nuclear industry in order to support the safety
performance of nuclear installations and improve the effectiveness of regulatory practices inmember countries. In keeping with the WGHOF’s mission, this effort to collect anddisseminate lessons learnt focused on the human and organisational factors (HOF) associatedwith mitigation of extreme external events and severe accidents. The project was conductedin three phases:•

Phase 1: The WGHOF task team requested regulatory authorities in seven countries in
Europe, North America and Asia to provide information concerning post-Fukushimarequirements, guidelines and implementation schedules that regulatory authorities issued
or endorsed to improve the HOF elements of responding to extreme external events andsevere accidents (i.e. those involving significant core damage). The intention was to gather
the background information that the task team would require to: (1) formulate the Phase 2
solicitation for lessons learnt, (2) time the issuance of the solicitations given the countryspecific implementation schedules, and (3) understand the lessons learnt provided by eachparticipating country in the context of the requirements, guidelines, and schedules thatwere applicable to the source of the lessons learnt.

•

Phase 2: The WGHOF issued information requests to operating companies in the sevencountries that participated in Phase 1. The requests to operating companies were for the
HOF lessons learnt during their implementation of post-Fukushima actions for the
mitigation of extreme external events and management of severe accidents. The

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INTRODUCTION

requests included a standardised template to summarise and submit the lessons learnt
and participation was voluntary. Although responses identified the country of origin,
respondents were requested to redact any information identifying sites.
•

Phase 3: The task group analysed the lessons learnt to develop this report.

The three phases of the project are graphically summarised in Figure 1.

Figure 1. Summary of the three project phases
Phase 1: Request to regulatory authorities
Requirements

Guidelines

Implementation schedules

Phase 2: Periodic requests to plant operating companies
Validations

DrillsExercises

Training

Other

Phase 3: Analysis of collective lessons learnt
Analysis

Insights

ThemesParticipating countries/organisations
Participation in this WGHOF task was voluntary. Table 1 summarises the countries/organisations
that participated in Phases 1-3 based on the availability of resources. The objective was for eachcountry to participate in both Phase 1 and Phase 2 of the information collection to facilitate
understanding of the lessons learnt in the context of national action plans, requirements andguidance. This objective was achieved with the exception of two countries that participated inonly one of the two information collection phases.

Table 1. Country participation in task implementation
Country

Phase 1: Survey ofrequirements, guidelines andimplementation schedules

Phase 2: Collectionof human and organisational
factors lessons learnt

Phase 3: Reportdevelopment

Canada

X

X

X

X

X

Czech RepublicOECD Halden
Reactor Project*

X

X

X

France

X

X

X

Japan

X

X

X

Korea

X

X

X

Spain

X

X

X

SwedenX

United States

X

X

X

The OECD Halden Reactor Project participated by providing technical support to the task group.

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PHASE 1 SUMMARY

Chapter 2. Phase 1 summary

Phase 1: Information request
The Phase 1 request to regulatory authorities specifically requested that they:•

provide a brief summary of actions taken in their country since the accident at the
Fukushima Daiichi Nuclear Power Plant to improve mitigation capabilities for extreme
external events and severe accidents; and•respond to a questionnaire regarding specific human and organisational factors that may
have been addressed by these actions.

Respondents were asked to provide in the summary of actions an overview level perspectiveon the scope of actions taken, the objectives of these actions, and any important interrelationships among these actions or between these actions and the pre-existing requirements
and guidelines. The objective of the summary was to create a narrative context that helps
understand the responses that the regulatory authority provided.
The objective of the questionnaire was to understand which actions described in theregulatory authority’s summary of actions were intended, or are expected, to improve the abilityof individuals and organisations to respond to extreme external events or severe accidents.
Each item in the questionnaire requested the regulatory authority to describe actions taken in
their country in one of ten main topic areas. The ten main topic areas were developed and selectedby the task group with the aim of covering the spectrum of topics where actions may have been
implemented to address the human and organisational challenges presented by extreme external
events and severe accidents. For each main topic area, the questionnaire included several subtopics. The subtopics were provided as prompts or suggestions for specific information to beconsidered when developing a response. Table 2 summarises the ten main topic areas andsubtopics of the questionnaire. For any changes described in a topical area, the regulator was
asked to state their implementation schedule (either required or estimated, as applicable) and list
any opportunities for gaining relevant HOF lessons learnt (e.g. related assessments, validations,
audits, inspections, training, drills, and exercises).

Table 2. Summary of Phase 1 questionnaire topics and subtopics
No.

Topic

Subtopics

1.

Mitigation strategies (for maintaining or restoring core cooling, containment, and spent fuel pool cooling capabilities)
a. Development of new mitigation strategies
b. Modification of current mitigation strategies
c. Assessment and/or integration of the whole set of mitigation strategies (e.g. Extended Damage
Mitigation Guidelines, FLEX Guidelines, Severe Accident Guidelines, Emergency Operating Guidelines,etc.).
d. Addition of new procedures/guidelines for newly installed systems or components or new mobile
equipment for improving mitigation capabilities
e. Changes, if any, in strategy design, implementation, use and adherencef.

Other actions related to mitigation strategies

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PHASE 1 SUMMARY

Table 2. Summary of Phase 1 questionnaire topics and subtopics (cont’d)
No.

Topic

2.

Other procedures and guidelines (to manage other elements of event or emergency response not directly supporting
the implementation of mitigation strategies)
a. Modification of procedures and guidelines
b. Changes, if any, in procedure design, implementation, use and adherencec. Other changes or additions to procedures and guidelines
Staffing
a. Assessment of staffing needs (numbers and roles)
b. Changes in plans and measures to augment on-site staffingc. Other actions related to staffing
Organisational structures, communication, decision making authorities, and safety culture
a. Changes, if any, in the command and control organisations for accident management, including single andmultiple source term response, if applicableb. Others changes to organisation structures, co-ordination protocols, and guidance for decision making andcommunications (both internal and external). (Note: Communications equipment is addressed separately
in topical area 6)
c. Changes, if any, in the requirements or guidelines for promoting healthy safety culture
Personnel qualification and training
a. Changes in job qualification requirements to address the need for new technical and non-technical (e.g. formanaging the unexpected, stress management) knowledge and abilities
b. Changes in training programme content to address new knowledge and ability needsc. Changes in training programme structure (e.g. instruction/assessment methods or frequency)
d. Other changes to personnel qualifications or training
Plant instrumentation, controls, human-system interfaces, and communications equipmenta. Addition or modifications to plant instrumentation and control to improve the usability or availability of
information to plant staff and their ability to take control actions (e.g. spent fuel pool instrumentation,
containment venting)b. Addition or modifications to plant communications capabilities (on-site/internal communications andcommunication with off-site individuals/organisations)c. Other changes to plant or equipment human-system interfaces to improve human performance reliability
Portable equipment/tools, protective gear, and work environments

3.

4.

5.

6.

7.

8.

9.

10.

16

Subtopicsa. Provision of additional portable plant equipment or hand tools to support reliable human performanceb. Design of portable plant equipment or hand tools to support reliable human performance (e.g. plug andplay pipe connections, portable and installed equipment painted with some specific colour, equipment
needed during a station blackout identified with fluorescent labels)c. Provision of additional protective gear or modifications to protective gear to support reliable humanperformanced. Modifications to work environments to support reliable human performance (e.g. emergency lighting,flood protection)e. Other changes to plant equipment/environments to support reliable performance of mitigation actions
Work planning, technical support, and emergency response facilities
a. Design and implementation of new or modified on-site facilities
b. Design and implementation of new or modified off-site facilities
c. Changes to other facilities not previously addressed
Emergency response
a. Changes in emergency response plans or implementation methods
b. Changes in the drills or exercises of the emergency response planc. Other changes to emergency response plans
Extended (longer-term) response
a. Additions or modifications to plans or capabilities to address on-site staff physiological needs (e.g. food,water, sleep, hygiene) over the duration of time required to achieve a safe/stable plant stateb. Additions or modifications to plans or capabilities to address on-site staff psychological needs (e.g. fatigue/
stress management, contact with families) over the duration of time required to achieve a safe/stable plantstatec. Additions or modifications to plans or capabilities to relieve/augment on-site staff (e.g. communication,transportation, site access)d. Other additions or modifications to extended response plans

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The questionnaire requested the regulatory authorities to describe any actions by theregulatory authority or industry organisations in their country. Actions to be described included,
but were not limited to, requirements, recommendations, demands for information orassessments, guidelines, and regulatory oversight. The directions also stated that the scope ofindividual and organisational performance to consider when listing actions in the responses
should include, but was not limited to, actions by: (1) control room operators, (2) equipment
operators or other field personnel installing/operating equipment in the field, (3) personnel toprevent or mitigate adverse effects of the environment (e.g. external flooding), (4) personnel inwork control centres, technical support centres, emergency operations facilities or like facilities,(5) personnel in emergency response organisations or like organisations managing off-siteradiological responses, (7) personnel in off-site organisations (e.g. local police, fire, medical
personnel), (8) senior officials with decision making authority for site responses under conditionsof extreme external events and severe accidents. The directions also noted that the time period
to be considered for the individual/organisational actions should include the onset of the event
through maintaining the plant in a safe/stable state, prior to the initiation of recovery actions.

Insights from Phase 1
The responses from each country to the Phase 1 information request are provided as Appendix A
to this report. As noted in Table 1, seven countries responded to the Phase 1 information request.
Each respondent addressed the breadth of the information request noting the requirements or
guidelines that had been established and the actions that had been undertaken or were plannedfor each of the ten topical areas identified in the Phase 1 request. The responses were provided in
narrative form with the exception of the response from CNS for Spain, which elected to provide
its response in the form of presentation slides.
As stated in Fukushima Daiichi Nuclear Power Plant Accident, Ten Years On: Progress, Lessons, andChallenges (NEA, 2021), comprehensive reviews have been undertaken across NEA countries toevaluate the safety and robustness of nuclear power plants, including their capacity to withstandmajor incidents beyond the existing design-basis capabilities for external hazards. Althoughdiverse approaches and methods were used for the reviews, individual NEA member countries
reached many similar conclusions regarding the needed safety improvements and enhancements.
A shared insight is the need for diversity of equipment, enhancements in the robustness of safetyfunctions, and continuing efforts to improve organisational behaviour. Common activities haveincluded a focus on plant and process improvements to mitigate the potential impact of external
hazards. Areas under examination include: i) reassessment of external hazards; ii) improvementof the robustness of the electrical systems; iii) an enhancement of the robustness of the ultimate
heat sink (UHS); iv) protection of the reactor containment system, v) protection of spent fuel inspent fuel pools (SFPs); vi) reinforced capability to rapidly provide diverse equipment andassistance from on-site or off-site emergency preparedness facilities; vii) reinforced safety culture,including human and organisational factors in decision making during emergencies; viii)
continued safety research; and ix) consideration of events that could affect all the reactors at asingle site simultaneously (multi-unit events).
The working group reviewed the responses to the Phase 1 information request and foundthat the responses from the sample of countries participating in this WGHOF initiative wereconsistent with the general characterisation provided by the NEA in its 2021 report. Additionally,
the WGHOF task group made the following observations, based upon the Phase 1 responses,
with respect to: (1) the scope of the events addressed by the post-Fukushima actions; (2) thegeneral characteristics of measures that were being taken; and (3) the types of personnel actions
that are being used to mitigate extreme external events and severe accidents.

Scope of events addressed•

all address impact of extreme external events (some including new phenomena);•

many address multiple unit events;•

many update severe accident management guidance;•some add capabilities/guidance for extensive damage/loss of large areas of the plant.

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PHASE 1 SUMMARY

Characteristics of response•

all include the addition of new equipment for accident mitigation;•

responses vary with respect to relative emphasis on installed vs portable equipment;•

all result in numerous revised and additional procedures/guidelines for event response;•

all include augmentation of personal protection equipment;•

most include an assessment of staffing adequacy and capability for staff augmentation;•

most include the addition of pre-staged equipment off-site;•

most update/augment emergency response organisations and facilities;•some include measures to improve management of stress;•

nearly all significant enhancements to response capabilities depend on human action.

Types of actions•

selecting event mitigation/accident management strategies;•

securing emergency power sources;•

implementing load shedding;•securing makeup/injection water;•transporting, connecting, and operating portable equipment;•cooling and refuelling of portable equipment;•

monitoring/maintaining fuel pool water levels;•

removing debris to establish access/transport pathways;•

maintaining control room habitability;•

providing supplies and accommodations to maintain worker fitness;•fighting large area fires;•supplementing response with off-site personnel, equipment and supplies;•

suppressing off-site radioactive release;•assessing multiple source term release;•carrying out containment venting;•limiting dose to personnel accessing irradiated fuel bays.

Given the number and diversity of actions being undertaken in the countries participatingin this initiative, a detailed accounting of the specific actions is beyond the scope of thissummary report. However, such details are available in the Phase 1 responses provide by eachparticipating country, which may be found in Appendix A.

Potential HOF implications and challenges
The objective of this effort was to understand the HOF implications and challenges of
implementing the post-Fukushima actions. To that end, the task group observed that the Phase 1
responses confirmed that the preponderance of enhancements to mitigation capabilities for
extreme external events and severe accidents depend on human actions, rather than installed,
passive or automated, engineered safety features. Whereas this approach leverages the flexibility
and adaptability of humans, the effectiveness and reliability of these actions is likely to bechallenged by stressors that may be new or more intense, in comparison to those experienced
under normal operations or even design-basis accident conditions. It is also noted that the humanactions required for these new strategies are not limited to simple manual tasks, but in some cases
require complex analysis and decision making, cognitive tasks that can be vulnerable to stressors(e.g. time pressure, incomplete/inconsistent information, threat of death or injury) likely to bepresent during such events.

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PHASE 1 SUMMARY

The challenges presented by extreme event conditions to human performance were thefocus of Human Performance under Extreme Conditions with Respect to a Resilient Organisation (NEA,
2015). In that report, extreme conditions are characterised as having one or more of thefollowing event attributes:•

unexpected, not covered by training or procedures;•

beyond design basis, loss of safeguards and safety barriers;•

dynamic, rapidly changing, escalating or accumulating;•insufficient and unreliable information;•complex and potentially long-term duration;•

challenging to the organisation (on-site and off-site);•

potential adverse health consequences including loss of life.

The effects that such extreme conditions can have on human performance are well
documented in the human factors literature. For example, NUREG/CR-5680, The Impact ofEnvironmental Conditions on Human Performance, provides a compendium of such information
applicable to nuclear power plant workers (NRC, 1994a). Volume 1 of the NUREG is a handbook
for use by inspectors to help them assess the potential impact (e.g. decreased dexterity,
impaired vision, hearing loss, memory deficiency) of specific environmental conditions on
licensee personnel performance. The technical basis is summarised in Volume 2, which
includes a comprehensive review of the technical literature. Similarly, NUREG/CR-6127, The
Effects of Stress on Nuclear Power Plant Operational Decision Making and Training Approaches to Reduce
Stress Effects, examined the effects of stress in nuclear power plant settings, with a particularfocus on the context of severe accident management (NRC, 1994b). The report notes that thefollowing types of impairments in performance have been identified:•a narrowing and shift in attentional focus;•

a reduced working memory capacity;•

time pressure effects, in one of these two forms;•

speed-accuracy trade-offs;•

incomplete task processing;•

impaired crew communication patterns.

More recently, Laarni (2019) provided a systematic review of the effects of cognitive heuristics
among operations and maintenance personnel in nuclear power plants.
Laarni notes that these heuristics may sometimes foster resilience and adaptability indemanding situations but may also lead to cognitive biases and errors.
The literature on human performance under extreme conditions and stressors, such as thereports described above, can help inform our view of the post-Fukushima actions that have beentaken to improve accident mitigation capabilities, including the specific measures that have been
implemented to mitigate potential adverse effects on human performance. In this regard, we notethat the aforementioned NEA report (NEA, 2015), NUREG/CR-6127 (NRC, 1994b), and Laarni (2019),
each address methods for mitigating such adverse effects and thereby improving the performanceand resilience of plant personnel under challenging operational conditions.
A final observation is that operating companies in many countries implemented a broad
range of measures, instituting changes in facilities, equipment, procedures, training, andorganisational structures. Although such multi-faceted approaches are commendable, the large
number and complexity of changes at each facility introduces the potential for unintended
consequences due to deficiencies in the analysis, specification, or implementation of thechanges and unforeseen interactions of these elements. Accordingly, we propose that asystemic human, technology and organisation (HTO) approach to implementing these changes,
in which the interactions of humans, technology and organisational factors are considered in
an integrated manner, could prove useful in gaining the full benefit of these
efforts. The NEA report Human and Organisational Performance in Nuclear Installations provides afull discussion of the systemic approach, including a view of nuclear facilities as HTO systems
and application case studies of the systemic approach (NEA, 2022).

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PHASE 2 SUMMARY

Chapter 3. Phase 2 summary

Issuance of requests for lessons learnt
The Phase 2 requests to operating companies for examples of lessons learnt were issued
between May 2019 and February 2020. The date of the issuance varied from country to country,
based largely on availability of resources to issue and respond to the request. The request
described the objective of the information collection, provided an overview of the three phasesof the project, and included instructions and a template (described in the section below) for
submitting the lessons learnt. The request also noted the lessons learnt would be compiled ona country basis and that any site-identifying information would be redacted.

Instructions for submitting lessons learnt
The instructions stated that the lessons sought were those gained while implementing postFukushima actions that can contribute to the efficiency and effectiveness of complying withrequirements and implementing guidance (i.e. accelerate the learning curve) to enhance
mitigation capabilities for extreme external events and severe accidents. The instructions also
noted that potential sources of and opportunities for such lessons learnt include:•

Stress tests, assessments, drills, exercises or validation efforts that resulted in identifying
ways to improve mitigation capabilities for extreme external events and severe accidents.

•

Instances when guidance from the regulatory authority was limited or not applicable,
and additional site-specific guidance or alternative guidance/methods were developed
to meet the need.

•

Instances when initial attempts to meet regulatory requirements did not fully achieve
the intended outcome and subsequent changes or exceptions to the accepted method
resulted in improved outcomes.

•

Any area where the endorsed guidance was used but it was possible to use an innovative
approach to compliance or meet the new safety objectives.

•

Any modifications to facilities, equipment, programmes, procedures, or training not
specifically identified in the regulatory authority’s requirements or guidance but
implemented to enhance capabilities for response to and mitigation of extreme external
events.

To aid operating companies in identifying candidate activities that may have produced
lessons learnt, the instructions included example categories. The example categories were thesame as those provided to regulatory authorities in Phase 1 and which are summarised in
Chapter 2, Table 1 of this report.
The instructions also included a ten-question template that was to be used for summarisingand submitting a lesson learnt in a standardised format. The response template is reproducedon the following pages as exhibit 1.

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PHASE 2 SUMMARY

Exhibit 1
1.

Concisely describe the lesson learned noting the challenge and how it was resolved or overcome(i.e. describe a success story). See Note 3 at the end of this form for guidance on the level of detailto provide.

2.

List the names of any files that you are submitting with this form to supplement your description of
the lesson learned (e.g. photo, diagram, report). If none, please type, "not applicable".

3.

Briefly describe the obtained or anticipated benefits of this insight/resolution (e.g. performance,
safety improvement, cost reduction).

4.

This lesson learned has implications for (you may check both.): On‐site Response (Mitigating Event) Off‐site Response (Protective Actions for Public)
5.

This lesson learned has implications for performance in the following plant locations. Check all that
apply.

 Main Control Room
 Remote Shutdown Panel/Facility
 Other Local Control Station/Field
 Activities Technical Support Center Emergency Operations Facility
 Other (Please specify.) _______________________
6.

This lesson learned has implications for personnel in the following job categories. Check all that
apply.

 Control Room Operators
 Field Operators
 Maintenance Technicians Health Physicists/Radiation Protection/Chemistry Other Emergency Response Organization Personnel
 Security
 Other (Please specify.) _______________________
7.

This lesson learned concerns (check all that apply.): Mitigation Strategies
 Other Procedures and Guidelines
 Staffing

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PHASE 2 SUMMARY Organizational Structures
 Communication
 Decision-making Authorities Safety Culture Personnel Qualifications
 Training Plant Instrumentation/Controls Human-System Interfaces
 Communications Equipment
 Work Planning Technical Support
 Emergency-response Facilities
 Emergency-response Plans
 Extended Longer-term Response Other (Please specify.) _______________________
8.

This lesson learned was identified during: Initial Analysis/Development of the Action
 Validation
 Training
 Drill/Exercise
 Audit/Self-assessment
 Other (Please specify.) _______________________
9.

The events described in this lesson learned occurred in what country and between what months
and years?
E.g. France from May 2009 to July 2009

10. Please write the name of the person who completed this Lessons Learned Report and provide thedate. Kindly note that the name of the individual/organization contributing the lesson learned will
not be made public.
E.g. Jane Doe on 17 May 2019

Note 3: When providing your description of the lesson learned, please be concise yet provide a level of detailsufficient for a reader to evaluate the potential applicability to their facility and the benefit to be gained by
implementing the lesson learned. These details likely include:- the requirement, guidance, or need that was addressed- the action/method taken- the insight gained/results achieved that are the basis for the lesson learned
Types of information that you do not need to provide are site-specific details (e.g. equipment/ component
identifiers), instead use generic terms. The amount of text necessary to provide these and other relevant
details will vary according to the complexity of the circumstance, but generally should not be more than acouple paragraphs. If helpful, you may include supplemental files (e.g. photos, diagrams, reports) with yoursubmission and list these in Section 2 of this form.

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PHASE 2 SUMMARY

Lessons learnt summaries and examples
As noted in Table 1, the task group received submissions from seven countries in response to thePhase 2 information request. Collectively, these countries submitted 40 lessons learnt reports. In
addition, Japan submitted an integrated summary of actions implemented in Japan. Theirsummary addresses each of the ten topical areas addressed in Table 2. The information gathered
through these submissions is provided in a standardised format in Appendix B of this report. The
following subsections provide overviews of the submissions provided by each country. In addition,
each section highlights a specific submission in a more detailed discussion.

CanadaIn response to the Phase 2 request for information, the Canada Deuterium Uranium (CANDU)
Owners Group (COG) provided eight Fukushima lessons learnt summary sheets. COG is anindustry group that represents all owners of CANDU reactors. Of the eight responses, seven relatespecifically to the broad recommendation to “enhance emergency response capability”. The
responses provided are from Canadian nuclear power plants and Canadian Nuclear Laboratories.
The following is a listing of the topics submitted:
1. Emergency Management Centre (EMC).
2. Emergency Mitigating Equipment (EME).
3. Incident Management System (IMS).
4. Public alerting systems.
5. Remote Automated Gamma Monitoring System.
6. Emergency Satellite Communication System (ESCS).
7. Unified RASCAL (Radiological Assessment System for Consequence Analyses) Interface(URI).
8. Web Emergency Operating Center (WebEOC).
To highlight the work done in the Canadian industry, implementation of the remote
automated gamma monitoring system will be described in further detail. This illustrates how
the actions taken by licensees relate specifically to the recommendations made by the CNSC
Fukushima Task Force (CNSC, 2011) and address one of the lessons learnt from the Fukushima
event.

Remote automated gamma monitoring:
In Phase 1, the CNSC reported on the Fukushima Task Force Recommendations (CNSC, 2011).
There were four broad categories:•

strengthen reactor defence in depth;•enhance emergency response capability;•

improve the regulatory framework and processes;•

enhance international co-operation.

Within each of these broad categories, there were a number of recommendations supported
by several actions for each, with closure criteria identified. Licensees were requested to respondto the first two, with the second two being actions undertaken by the CNSC in response to the
Fukushima accident.
The Fukushima event highlighted the need to improve emergency response capabilities.
This included, but was not limited to, upgraded emergency response facilities, sharing of data
between organisations, improved communications capabilities, and public alerting systems.

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PHASE 2 SUMMARYWith respect to the implementation of Remote Automated Gamma Monitoring (Appendix B,
Lesson Learnt: CA-05 Remote Automated Gamma Monitoring System) the requirements can betraced to CNSC’s Phase 1 submission for Canada (Appendix A, Canada).

 Recommendation 5 – Update Emergency Facilities and Equipment
Action A.5.3 – Licensees should install automated real-time station boundary radiation
monitoring systems with backup power sources and communication systems. This action has
Human and Organizational Performance (HOP) closure criteria expectations.

 Action Item A.5.3.1 – Develop a plan/schedule for completion of installation.
HOP Closure Criteria for Action A.5.3 – Provisions made for identification and consideration of
any relevant elements of HF involved in development and deployment of modelling tool.
Prior to 2012, manual off-site collection and analysis of remote radiological data wasnecessary. In practical terms, it took about two hours for the station to mobilise its off-site
survey teams to start the collection and transfer of data to the on-site and off-site stakeholders.
This was a cumbersome process requiring several individuals (six at one station) travelling to
the various monitoring locations to take gamma readings. Weather, time of day and off-site
conditions could all impact the ability to successfully carry out these activities. This practicealso increased the potential for worker exposure during an event and data was not available
real time to agencies such as the Province of Ontario, and the Office of the Fire Marshal andEmergency Management, which makes protective action decisions for the public.
In order to address Action Item A.5.3, licensees implemented enhancements to the remotemonitoring systems at the stations. The improved monitoring system collects data via
permanently installed automated gamma monitors along the site boundary as well as locations
within the primary zone (up to 10 km) to monitor any potential releases. The data is collected
remotely and sent wirelessly to a centralised system which interfaces with the current station
information local area network (LAN) systems.
Primary data transmission is via the cellular network, with backup satellite capability. Datastorage and external data access is provided through a remote off-site third-party data storage
network with appropriate cloud security, backup power, and storage facilities.
The remote automated gamma monitoring system provides real-time data (24/7) which isessential to quickly identify the existence of radiological hazards during a major event. These
data play a critical role in supporting the decision-making process related to employee andpublic safety. Use of the system enables real-time modelling of plume progression which isshared with the emergency response organisations called into play during a nuclear event
including local, provincial, federal and regulatory authorities.
Implementation of the automated gamma monitoring system will reduce personnel
exposure, reduce the likelihood of human error, and improve the availability and accessibilityof data for use by stakeholders.
Installation of the remote automated gamma monitoring systems at the utilities has
improved emergency response capabilities, one of the recommendations from the CNSC’s
Fukushima Task Force. This system will offer added protection to licensee staff and the publicin the event of an emergency. Human factors were considered in the design of the remote
automated gamma monitoring system and the effectiveness of the system has been validated
through various site drills and exercises.
During a field walk down of the remote automated gamma monitoring stations at one of thenuclear power plant facilities, it was noted that the units measuring gamma fields weredifferent on some of the stations. This inconsistency had the potential to trigger unnecessary
protective actions. There was also the potential to assume radiological conditions were not as
bad and therefore necessary protective action decisions would not be made. Fortunately, when
the discrepancy was identified, the operator took the necessary steps to ensure that all units
measured the gamma fields in the same stations. It was also confirmed that the software forthe system also used consistent units of measurement. Validation thus plays an important rolein ensuring the adequacy of any new measure taken to enhance emergency response capability.

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PHASE 2 SUMMARY

Figure 2. Remote Automated Gamma Monitoring Station

Source: Canadian Nuclear Safety Commission.

Czech Republic
In response to the Phase 2 request for information, the CEZ Company (represented by the
Accident Management Department of Czech nuclear power plants) provided five lessons learnt
summary sheets. CEZ is an industry group which operates both Czech nuclear power plants.
The following is a list of the topics submitted:
1. Provision of Mobile Diesel Generators (MDG).
2. Enhancement of communication equipment.
3. New backup (diverse) and alternate (mobile) emergency response centre.
4. Improved procedures for diverse and mobile (DAM) equipment and emergency operatingprocedures (EOPs).
5. New Extensive Damage Mitigation Guidelines (EDMG).

Procedures for diverse and mobile equipment:
One of the measures implemented at Czech nuclear power plants after the Fukushima Nuclear
Power Plant accident was the installation of DAM equipment. DAM equipment is intended toensure basic safety functions, especially for long-term blackout events, also called extended lossof AC power (ELAP) events, complete loss of ultimate heat sink (LUHS) events, combination of
ELAP and LUHS, as well as multi-unit events. The new DAM equipment dramatically improved
the ability of the plants to respond to all events leading to ELAP and LUHS caused by external
hazards or other initiators.
Using the new DAM equipment required development of new specific procedures to extend
the applicability of emergency procedures considering all states resulting from design-basis
accidents as well as design extension conditions. The new DAM procedures are:
1. DAM-1: Primary system injection.
2. DAM-3: Injection of feedwater into steam generator.
3. DAM-5: Initial assessment of nuclear power plant status and dislocation of mobile
equipment.
4. DAM-6: Emergency makeup of demineralised water tanks.
5. DAM-7: Loss of key parameters measurement.
6. DAM-8: Boron makeup into the reactor coolant system.

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7. DAM-10: Hydroaccumulators isolation.
8. DAM-11: Spent fuel pool makeup.
9. DAM-12: Containment depressurisation.
10. DAM-13: Switch from mobile equipment to design equipment.
11. DAM-14: Low pressure primary system injection.
The corresponding links to specific DAM procedures were subsequently incorporated into theoriginal emergency operating procedures (EOPs/ECA-0.0, Blackout), Shutdown procedures(SD/SD-0, Shutdown blackout) and Severe Accident Management Guidelines (SAMG) to provide acomprehensive and interconnected structure of the emergency management documentation.
Upgrading documentation to cover the events in the scope of design extension conditions lead tosignificant safety improvements in the area of accident management programme implementation
at Czech nuclear power plants.
An analysis of the recovery of power supply to required electrical loads using MDGs (seeFigure 4) was performed by UJV (Czech Nuclear Power Engineering Company) using aprobabilistic safety assessment (PSA) model (UJV REZ, 2018). Two variants were considered in
the analysis: (1) power supply recovery performed for one unit only and (2) power supply
recovery performed sequentially for all four units (with available time being ten hours in total,
see Figure 3). Four external hazards were considered in the analysis: (1) earthquake, (2) highwinds, (3) extreme snowfall, and (4) extremely low temperatures. The expected time windowsof specific manipulations were examined (i.e. measured during a regular drill) and discussedwith plant personnel. Task allocation, way of communication (i.e. methods and protocols), andsequence of required actions were discussed with the relevant local operators. The following
personnel were required to take part in the scenario:•

control room operators (three per unit);•

shift electrician (one per nuclear power plant);•

inspection electrician (one per nuclear power plant);•

operational electrician (four per nuclear power plant);•

fire brigade;•

DELTA team (special emergency team dedicated to local actions).

UJV developed the following timeline to illustrate the sequence of the expected failures andrequired actions:Figure 3. Sequence of expected failures and required actions in SBO scenario

Notes: Alternative alternating current system (AAC), diesel generator system (DGS), external events (EE), loss of off-site power (LOOP), mobile
diesel generator (mDG).
Source: ÚJV Řež, a.s.

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PHASE 2 SUMMARY

The failure probability of power supply recovery using the MDG was calculated for “normal”
conditions as well as for cases caused by external events. Based on this analysis, tworecommendations were formulated:

Staffing
In the case of a multi-unit event, the inspection electrician can be expected to have someproblems performing the required actions in time, since there is only one inspection electrician
per nuclear power plant. UJV recommended an increase in the number of inspection electriciansor to share some of the responsibilities of this position with shift electricians, of which there
are four per nuclear power plant.

Procedures
It was found that some of the required actions (e.g. transport of a heavy spool with cables fromthe ground floor to the second floor) may require an increased number of personnel. It would
be beneficial to state such information directly in DAM procedures to avoid any delays during
emergencies.

Figure 4. Mobile Diesel Generator 4 x 352 kW (one per unit)

Source: ÚJV Řež, a.s.

Japan
The FEPC facilitates the development of collective utility policies and strategies related to theelectricity business in Japan. In response to the Phase 2 request for information, the FEPC
provided a detailed response describing actions taken or to be taken for each of the 10 HOF
topical areas identified in Table 2. The following is a summary of the information FEPC provided.
The complete response is available in Appendix B.
Prior to the Fukushima Daiichi accident, nuclear power plants were lacking emergency
response preparedness for a severe accident due to external events that exceed design-basis
events. As a result, it was made clear from the accident that the chain of command was
confused, materials and equipment ran short, and quick and firm information sharing andcommunication were insufficient. Based on these lessons learnt, licensees have been making
efforts to strengthen emergency response and to enhance the response capability.
The Fukushima Daiichi accident has made it clear that a phased approach may be necessary
for an effective accident response. Specifically, as shown in Figure 5, resources can be used most28

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PHASE 2 SUMMARY

effectively if the time since the occurrence of the accident is separated into three phases andaccident response is implemented appropriately in each phase.
•

Phase 1 starts immediately after an accident. Operators and ERO shift personnel that are
stationed at the plant are expected to engage permanent facilities and mobile equipment
to respond to the accident. This is a basic requirement for safety facilities.

•

Phase 2 starts when additional personnel called on after the accident have gathered at
the plant and an additional accident response, such as the use of mobile equipment
located on station premises, can be initiated.

•

Phase 3 starts at least seven days from the day of the accident. In this phase, support
from off-site personnel, equipment and materials can be expected.

Based on this phased approach, safety improvement measures are being discussed not only
for hardware issues but also for personnel/organisational issues such as ERO staffing and manuals.

Figure 5. Conceptual diagram of a phased approach in accident response

Few hours later

External support

7 days later

Accident occurs

Additional support by called on personnel
Shift personnel respond using permanent facilities and mobile equipment
Phase1【Response time: short】

Operators and shift personnel
stationed at the plant respondPhase2【Response time: medium】

Station personnel are called andprovide additional response

Phase3【Response time: long】【time】

Response after receiving support
personnel, equipment, materials
from external sources

The three basic safety functions for power generating nuclear reactor facilities are “stop”,“cool” and “contain”.
Severe accident response measures have been developed to prevent the core fromsignificant damage due to any cause, even if the facilities to deal with design-basis accidents
have lost the ability to eliminate the risk posed by unforeseen events. These facilities have been
made independent from the design-basis accident response facilities as much as possible.
Examples of measures are as follows:•••

Water injection and heat removal functions (enhance 3rd layer of defence in depth, See
Figure 6):–

Enhance high pressure injection function: high pressure alternate cooling system.

–

Enhance depressurisation: backup actuation mechanisms for SRVs.

–

Additional water source: reservoir.

Protection of containment vessel and prevention of uncontrolled release of radioactive
materials (enhance 4th layer of defence in depth):–

Protection of containment by preventing over-pressure/temperature: top head flangecooling, increased durability of seal in severe accident environment.

–

Mitigation of radioactive material release: filtered vent.

–

Prevention of hydrogen explosion: passive autocatalytic recombiner.

Power supply functions:––

Measures for quick power supply:–

Gas-turbine generators and power supply cars on higher ground.

–

Emergency switchgears and installed electrical cable.

Reliability enhancement of DC power:–

Additional DC power on the top floor of the reactor building.

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PHASE 2 SUMMARY

Figure 6. Safety measures to enhance third layer of defence in depth for ABWR
HP injection

Enhanced power supply of
existing injection

LP injection

Depressurization

SLC pumpRHR pump
CRD pumpMUWC pumpFire engine

HPAC
Reactor heat removal
K

L

Back-up battery
and cylinder

PCV

SRVs

R/B

1次格納容器

2次格納容器

M
N
R

P

S

C
T
U

D

D

A

C
A

B

J

B

H

Additional water source

E

F

G

Self-operated 3-way valves

Alternate heat exchange vehicle

Reservoir

Nitrogen cylinders

SRV back-up actuation mechanisms

Notes: Control rod drive (CRD), high pressure (HP), high pressure alternate cooling (pump) (HPAC), residual hear removal (RHR), standby
liquid control (SLC), safety relief valve (SRV), protection of containment vessel and prevention of uncontrolled release (enhance fourthlayer of defence in depth).

Other examples of countermeasures based on the Fukushima Daiichi Nuclear Power Plant
accident are as follows:•

Operation of emergency organisation: An incident command system (ICS) 1 was introduced
to clarify the chain of command.

•

The development of the guidelines and procedures: EROG and EHP were developed to
improve ERO’s capability to respond to a severe accident like the Fukushima Daiichi
accident.

•

Activities relevant to improvements in personnel capability and assignment:

•

1.

30

–

Training for radiation management personnel: At the Fukushima Daiichi Nuclear
Power Plant, since the number of skilled radiation management workers was verysmall compared to the total number of staff working at the plant, support from othersites was necessary.

–

Training and Certifications: Having few workers licensed to use large vehicles inhibited
emergency work such as removing the debris generated by the tsunami and thehydrogen explosions. The relevant recovery work was delayed and transportation
between J-village and Fukushima Daiichi was restricted at the beginning of therecovery work.

–

Assignment of personnel: Since restoration work after the accident was expected to
be a long-term effort, a system of shifts was necessary. However, to make thisshifting regime function, it was necessary to assign work appropriately according to
the personnel’s abilities.

Enhancing internal communication: It is necessary to communicate and share
information with interested parties, even under difficult situations, such as loss of power.
This enhancement aims to make sure necessary information is shared, even in case of

An equivalent standardised emergency organisation management system exists in the United States(fire department, police, military, etc.) with regard to on-site command applied to disaster/crime sites.

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PHASE 2 SUMMARY

AC/DC loss. For that purpose, a radio communication facility, satellite phone andtransceiver were installed.
•

Enhancement of external communication (see Figure 7):–

Enhancement of liaison function with external organisations.

–

Upgrade of communication tools: video conference system, simultaneous fax system,
and mobile communication tools (dedicated line or satellite circuit).

–

Risk communicators to ensure better external communication.

Figure 7. Example of improvement of external communication

Notes: Off-site centre (OFC), personal computer (PC), personal handy phone system (PHS).

FranceIn response to the NEA WGHOF Phase 2 information request, the IRSN provided a lesson learnt
submission describing insights gained from exercises evaluating the minimum staffing of theoperation team (a summary of that response is provided in Appendix B, France). The following
is background to that lesson learnt.

Regulatory requests
In Europe, the scope of the “stress tests” carried out as part of the Fukushima lessons was
harmonised by European regulators through the ENSREG association (see. Phase 1 France report).
The French request for a “stress test”, called ECS (Evaluation complémentaire de sûreté),
was issued within a few weeks by the Prime Minister to the French nuclear safety authority(ASN) and then to the nuclear operators. The regulator (ASN) set three key objectives:•to avoid significant releases into the environment and long-lasting contamination;•

to ensure robustness against more severe hazards than the design-basis events(commonly referred to as design extension), prevent fuel melt, mitigate severe accident;
and to cope with long-lasting and multi-unit accidents induced by extreme hazards;•

to perform emergency management duties in extreme contexts.

The focus of the ECS was on severe hazards (earthquake, flooding) and the ASN request wasmore specifically also on scenarios of loss of electricity (LoE) and cooling (LoC). The request dealt
with measures to prevent a core melt and mitigate severe accidents (with support ofsubcontractors). Several requirements were prescribed by the ASN (see Appendix A, France for
additional details).

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PHASE 2 SUMMARY

Actions taken by the French nuclear power plant licensee, Electricité de France
The licensee defined the concept of “hardened safety core”. The strategy is to protect andstrengthen critical structures, systems and components to prevent and mitigate severe accidents
initiated by beyond-design-basis accidents (BDBA) induced by natural hazards. The operational
objective is to prevent core melt despite loss of cooling and/or electricity. The goal is to cover all
reactor states, spent fuel pools, multiple simultaneous reactor accidents, and large volumes ofcontaminated water. It led to the extension of the scope of severe accident management(e.g. residual heat reduction without venting and with water injected). The main control room wasprovided with more robust and redundant instrumentation (e.g. water temperature and level,
radiation in containment building and outside, time to boiling point, hydrogen, earthquake, coremelt), powered by new batteries and backup diesel generators. The operator built new emergency
control rooms within new buildings resistant to extreme situations and established redundant
and robust telecommunication systems. New organisational means were set up with 300 people
on duty in four locations in France, ready to implement mobile equipment (e.g. to supply water,electricity, air, fuel) within 24 hours. The minimum staffing for the operation team was also
revised.
At the public level, the national nuclear emergency plan was updated. The local emergency
plans are expected to be updated and the radius to consider inhabitants’ exposure andinvolvement was raised from 10 to 20 km. Additional detail concerning the ASN regulatory
requests and the actions taken by Electricité de France can be found in Appendix A, France.

Implementation of minimum staffing in operations team
The Fukushima accident showed the need to guarantee the autonomy of nuclear power plantstaff, especially after extreme natural hazards when the plant can be isolated (e.g. Blayais in1999).
The post-Fukushima regulatory request (ECS35-I) was to ensure that all actions required arefeasible even in extreme contexts and can be performed by qualified staff.
The nuclear operator developed a method focusing on operations (main control room [MCR]and field actors) interfacing with national crisis teams, using simulator calculations to define thetiming and deadlines to perform critical actions to prevent loss of control. The goal was toestablish the general time and staffing levels needed with sufficient margin to control thesituation. The nuclear operator conducted several exercises in 2014, 2015, 2016 on one or two MCR
simulators on loss of coolant (LoC) and loss of electricity (LoE) scenarios that were controlled by
the operations team. The nuclear operator assumed that the operations team might have toperform them all without the support of local emergency teams for 24 hours. It led to the additionof one supervisor for the two operators in the MCR by 2020; the chief and deputy of the operation
teams are in charge of key decisions, safety control, and external interfaces.
To reduce the operations staff workload, some operator actions should be prioritised bymodifying dedicated procedures but the diversity of situations due to unexpected scenarios limits
this possibility. This potentially leaves a significant workload for the operations team in real time.
The operations team workload has been adapted by changing roles and responsibilities asproposed by the operator. However, the exercises (mentioned above) highlighted the challenge ofaccumulating functions onto the lead members of the operations team (chief, deputy andsupervisor).
The exercises also showed the multitude of influence factors on human actions in the field(e.g. darkness) and the difficulty to translate them into quantitative analyses of time andstaffing margins. In this domain, the implementation of post-Fukushima actions revealed that
there is a lack of fundamental scientific and evidence-based data on the quantitative impact ofinfluence factors on human actions. Conducting risk analyses in the case of extreme events may
further show that design measures could be necessary to protect paths and workplaces toensure that necessary actions can be performed.

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PHASE 2 SUMMARY

Korea
In response to the Phase 2 request for information, the Korea Hydro and Nuclear Power Co. Ltd.
(KHNP) provided 15 lessons learnt summary sheets. The nuclear power plant operator, KHNP, isthe only licensee in Korea. The following is a listing of the different topics submitted:
1. Conducting stress tests in Korea’s nuclear power plants.
2. Securing additional equipment in preparation for prolonged emergency.
3. Reinforcing radiation emergency exercises.
4. Devising a means for securing necessary information in case of a prolonged loss ofelectrical power.
5. Amending the radiological emergency plan to include such events as the simultaneous
declaring of an emergency at multiple units.
6. Improving the seismic capacity of the seismic alarm in the main control room.
7. Reinforcing education and training on severe accidents.
8. Revising the Severe Accident Management Guidelines (SAMG) to enhance effectiveness.
9. Developing low-power shutdown SAMG.
10. Improving the emergency response facilities.
11. Assessing the adequacy of operating manpower.
12. Developing accident coping strategies.
13. Strengthening the accident management programme.
14. Ensuring Multi-barrier Accident Coping Strategy (MACST) equipment availability.
15. Setting up a MACST team.

MACST (Multi-barrier Accident Coping Strategy)
Since the Fukushima accident occurred, the public in Korea has become increasingly concerned
about the safety of nuclear power plants in conditions of extreme natural hazards such as
earthquakes or tsunamis exceeding the design basis. As described in the Korea response to thePhase 1 information request (see Appendix A, Korea, Section 3), as part of its response to the
Fukushima Daiichi accident, the regulatory body established criteria for accident management.
To address these requirements, KHNP established MACST, through which emergency response
up to 72 hours after the onset of an extreme natural hazard accident is made using on-siteequipment. It has assessed that 72 hours is sufficient to secure an access route for off-site
personnel and equipment. In order to cope with extreme external events, three phases of coping
strategies are developed with MACST equipment. Figure 8 shows the coping strategies, that is
MACST, to cool the reactor core.
•

Phase 1: Initially cope with equipment in the plant, such as tanks, piping, batteries, andpumps, within eight hours of the accident.

•

Phase 2: Cope with equipment on site, such as mobile generators, and mobile pumps,
between 8 and approximately 72 hours after accident initiation.

•

Phase 3: Cope with all available equipment, including equipment delivered from off-site,
after 72 hours from accident initiation.

For the coping strategies, MACST operating guides (MOGs) are prepared. Table 3, Figure 8 and
Figure 9 show the purpose of each MOG and the relation between procedures used in theemergency situations. MACST equipment for Phase 1 are stored inside each unit to use as soon as
possible. Except the pre-staged equipment, other mobile equipment for Phase 2 and Phase 3 arestored in the seismic designed integrated storage building which is constructed for each site.
Besides the MACST equipment for essential safety functions, subsidiary equipment such as
multipurpose communication units, emergency lighting, tractors, and wheel loaders is also stored
in the integrated storage building.

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PHASE 2 SUMMARY

Table 3. List of MACST procedures
MOG No.

Purpose1

Long-term reactor coolant system inventory control

2

Alternative auxiliary feed water supply

3

Alternative low pressure injection

4

Battery load shedding after extended loss of all AC power

5

Site survey and MACST equipment deployment

6

Condensate storage tank makeup

7

Electrical loss of essential instrument

8

Alternative borated water injection

9

Temperature control at low decay heat

10

Safety injection tank isolation

11

Alternative spent fuel pool makeup and cooling

12

Alternative containment building cooling

13

MACST equipment termination (turnover)

14

Reactor coolant system makeup during shutdown

Source: Korea Hydro & Nuclear Power Company.

Figure 8. MACST core cooling strategies

Notes: Steam generator (SG), turbine driven auxiliary feed water pump (TDAFWP), condensate storage tank (CST), main steam
atmosphere dump valve (MSADV, safety injection tank (SIT), diesel generator (DG), reactor coolant system (RCS), refuelling water tank
(RWT), ultimate heat sink (UHS), heat exchanger (HX).
Source Korea Hydro & Nuclear Power Company.

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PHASE 2 SUMMARY

Figure 9. Relation between procedures

Notes: MACST operating guideline (MOG), Severe Accident Management Guideline(SAMG), abnormal operating procedure (AOP), emergency operating procedure(EOP), Extensive Damage Mitigation Guideline (EDMG).
Source Korea Hydro & Nuclear Power Company.

Example of MACST equipment (3.2 MW mobile generator):
The mobile generator has a capacity of 3.2 MW to supply electrical power for the safety-related
A or B bus during an extended loss of AC power (ELAP) accident. It has enough capacity for all
essential equipment including the cooling pumps, motor operated valves, HVAC, etc. The
objective is to cool down the plant to the cold shutdown status after 72 hours since the accident
occurred. However, like the pre-staged 500 kW generator, the pre-staged and pre-wired
electrical lines of a 3.2 MW generator can reduce the time to establish an alternate power source
drastically and remove the uncertainty of transportation. A few (two or three operators) canstart the generator and supply the electrical power instead of 18 workers. Two 3.2 MW mobile
generators are placed at each site. They are pre-staged with pre-installed cables even though
they are still mobile. Unlike the pre-staged 500 kW generator, the 3.2 MW mobile generators arestaged on a remote area more than 100 metres from the unit and they use long pre-installedcables. The remote area has dedicated fuel tanks with a protection dike. The 3.2 MW mobile
generators are commercial grade and non-seismic but the pre-staged foundation, fuel tanks,and dike are seismically designed.

Figure 10. 3.2 MW mobile diesel generator (Korea)

Source Korea Hydro & Nuclear Power Company.

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PHASE 2 SUMMARY

Spain
In response to the Phase 2 request for information, the Spanish Nuclear Energy Committee(Comité de Energía Nuclear, CEN) provided nine lessons learnt summary sheets. The CEN
represents both the owner utilities and the licensees of the Spanish nuclear power plants andoperates under the umbrella of the Spanish Nuclear Industry Forum (Foro de la Industria Nuclear
Española, Foro Nuclear). The responses provided are from Spanish nuclear power plants. The
following is a listing of the topics submitted:
1. Verification and validation in emergency situations.
2. Communication during emergency situations.
3. Magnetic help guides for portable equipment.
4. Visual aids for identifying emergency equipment.
5. Training for emergency equipment transport.
6. Communication system improvements.
7. Stress management guide and posters.
8. Leadership during emergency situations.
9. Command and control during emergencies guide.

SP-01 — Verification and validation in emergency situations
These lessons learnt come from the validation of the filtered containment venting system(FCVS), which was installed in nuclear power plant A after the Fukushima Daiichi Nuclear Power
Plant accident (as mentioned on slides 47 and 49 of CSN’s Phase 1 submission [see Appendix A,
Spain], FCVS were requested of the Spanish nuclear power plants):

36•

Principal lesson learnt: personnel need training to be prepared for these kinds of situations.

•

Validations must be done while taking into account the most adverse scenarios.

•

Even when procedures cannot take into account every possible situation, humanperformance specialists need to go further and raise those situations to evaluate
responses from plant personnel.

•

Difficult personal situations (happening outside the plant) for operators in the field were
simulated to analyse their responses (e.g. uncertainty about relatives because of external
events affecting the area).

•

Management of concurrent relevant mitigation strategies, taking place in the same unit
or even in different units of the nuclear power plant, must be considered (e.g. effects ofventing in one unit on the mitigation strategies of the other).

•Time available and execution time are no longer the “only” factors to be considered invalidations. Other relevant factors include radiation levels, oxygen bottle duration, andhigh temperatures.

•

Validation of the co-ordination between the technical support centre (located in theplant) and the licensee headquarters (outside emergency centre located in Madrid) was
conducted as considered relevant.

•Video recording of some parts of the validation exercises was useful.

•A review of the guidance for verification and validation to include lessons learnt has
been completed.

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PHASE 2 SUMMARY

Figure 11. Validation of the filteredcontainment venting system (1)Figure 12. Validation of the filteredcontainment venting system (2)Source CSN.

Considerations from the regulatory point of view of CSN
Based on the validation exercises performed by all the Spanish nuclear power plants, from CSN’s
regulatory point of view, some common additional lessons have already been learnt (or are
expected to be considered) by the nuclear power plants:•

Integrated validations must be conducted to be fully effective. They should include, atthe same time, different groups of personnel (e.g. licensed operators, auxiliary operators,
maintenance staff, fire brigade, radiological protection personnel), different locations(e.g. control room simulator, local sites at the plant, technical support centre, licensee
emergency outside centre) and the whole sequences of tasks to be conducted in a coordinated way.

•

A common and single HOF validation guide should be available at the nuclear power
plant. It should be developed by experts according to the state of the art, and it must be
used by any of the organisational units of the nuclear power plant (e.g. operation, nuclear
safety and regulatory affairs, PSA, engineering, training, maintenance) validating andlicensing designs that require human actions.

•This common HOF validation guide should be used as a reference when developing thespecific procedures for validating any human action (each validation case might warrant
different methods and acceptance criteria). This is applicable to any human actions,
independently of its origin (e.g. design modifications, procedures changes, modificationsof the FSAR), or its categories (e.g. risk important human actions, local actions).

•

Video recording of the validation exercises (an essential tool used by many professional
teams to assess and improve individual and team actions and performance: e.g. in sports,high risk activities and industries) becomes necessary to improve validations related tohuman actions.

•

The development, in advance, of clear and detailed validation acceptance criteria is a must.

•

It is crucial to consider real operating experiences, and to make use of state-of-the-art
validation methodologies and reports, in order to design high quality validation exercises.

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PHASE 2 SUMMARY

United States
In May 2019, the task group issued an invitation for US nuclear power operating companies tosubmit post-Fukushima actions lessons learnt. Although no US nuclear power operatingcompany submitted lessons learnt in response to this invitation, the NRC provided lessons
learnt submissions on the following topics:•

Development and application of human reliability analysis methods for use of diverseand flexible coping strategies (FLEX) strategies and equipment.

•

FLEX diesel generator experience.

These lessons learnt were gleaned from efforts that the NRC Office of Nuclear Regulatory
Research has undertaken to examine the application of human reliability analysis methods tothe use of FLEX equipment and from the NRC programme for analysis of operating experience.
The lesson learnt from FLEX Diesel Generator Experience is described here as an example of theinsights gained from the US post-Fukushima action implementation experience.

FLEX diesel generator experience
As described in the US Phase 1 submission (see Appendix A, United States), following theaccident at Fukushima, the NRC assembled the Near-Term Task Force (NTTF) to provide
recommendations for agency action (NRC, 2011). NTTF Recommendation 4 was to strengthen
station blackout mitigation capability for design-basis and beyond-design-basis external events.
To address this recommendation, the NRC issued the Mitigation Strategies Order on 12 March2012 and, in 2019, made final the requirements in Title 10 of the Code of Federal Regulations,
Part 155, Mitigation of beyond-design-basis events. In response to these requirements, NRC
licensees use FLEX equipment at nuclear power plants to implement long-term core cooling,
spent fuel cooling, and containment integrity in beyond-design-basis event scenarios.
On 26 September 2019 and again on 1 April 2020, the licensee for the River Bend nuclear
power station conducted periodic testing of their FLEX diesel generators. In both instances,multiple FLEX diesel generators failed to operate. On 11 July 2019, the licensee for Clinton Power
Station (Clinton) discovered that the electrical phase rotation of the “A” FLEX diesel generator
was opposite to that of the load centre for its in-plant loads. If the facility had used the “A” FLEX
diesel generator to power any in-plant equipment, it would have caused phase-dependent loads
to rotate backwards, potentially damaging in-plant safety-related equipment.
On 15 September 2020, the US Nuclear Regulatory Commission issued “Information Notice2020-02, FLEX Diesel Generator Operational Challenges” (NRC, 2020). The information notice
informed addressees of these recent operational challenges involving FLEX diesel generatorsand described the deficiencies in licensee design, testing, and maintenance practices that
contributed to the failures. These deficiencies included failure to provide adequate oversight ofvendor provided maintenance and failure to test under the loading conditions that would
actually be present during a beyond-design-basis external event.

Insights from Phase 2
The WGHOF task group reviewed the characteristics of the lessons learnt to understand thecommonalities and diversity of the submissions. As described in Chapter 3 and shown in
Exhibit 1, respondents to the Phase 2 information request submitted responses using a tenquestion template. These questions included several that could be answered by checking theappropriate box or boxes, as applicable. Specifically, questions 4-7 asked the respondent tocharacterise the applicability of the lesson learnt with respect to on-site or off-site actions(question 4), plant location (question 5), job category (question 6), and HOF topic (question 7).
Examining the responses to these questions, the task group found that the sample of 40 lessons
learnt had the following general characteristics:•

38

The vast majority (38) were applicable to on-site activities, though a substantial minority(14) were also applicable to off-site activities. Only two were characterised by thesubmitters as only applicable to off-site response.

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The lessons learnt were most frequently identified as applicable to the emergency
operations facility (29), though the main control room (21), technical support centre (23),and other control locations (20) were also identified frequently as work locations towhich the lessons learnt applied.

•

Consistent with the results for applicability to plant location, the lessons learnt were
frequently characterised as applicable to the personnel of emergency operations facilities
and/or technical support centres (23) and other emergency response organisation
personnel (30). The lessons learnt were also frequently characterised as applicable to main
control room operators (26) and field operators (21), with fewer being seen as applicable tomaintenance (11), security (8) or health physics/radiation protection/chemistry (6).

•The HOF topics most frequently identified as the subject matter that the lesson learnt
concerned were: mitigation strategies (15), other procedures and guidelines (12),communication (12), emergency response facilities (15), emergency response plans (15),and training (12).

Figure 13. Applicability of lesson learnt to on-site and off-site activities
on-site38

off-site

16
0

5

10

15

20

25

30

35

40

Figure 14. Applicability of lesson learnt to work location
Main control room

21

Technical support centre

23

Remote shut down facility

4Emergency operations facility

29

Other local control station

20

Other

2
0

5

10

15

20

25

30

35

40

35

40

Figure 15. Applicability of lesson learnt to job categories
MCR operators

26

Emergency Op facility/TSC

23

Field operators

21

Other ERO personnel

30

Maintenance technicians

11

Security8

HP-RP/chemistry

6

Other

5
0

5

10

15

20

25

30

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PHASE 2 SUMMARY

Figure 16. Applicability of lesson learnt to humanand organisational factors topical areas
Mitigation strategies

15

Plant instrumentation/controls

3

Other procedures and guidelines

12

Human-system interfaces

3

Staffing

6

Communications equipment

6

Organisational structures

5

Work planning

3

Communication

12

Technical support

0

Decision-making authorities

5

Emergency response facilities

15

Safety culture

3

Emergency response plans

15

Personnel qualifications

3

Extended longer-term response

8

Training

12

Other

2
0

5

10

15

20

25

30

35

40

The task group notes that given the small sample size of lessons learnt and that respondents
selected the lessons learnt to submit (i.e. the sample is small and non-random) the reader should
not infer that the sample is representative of the population of HOF lessons learnt throughimplementation of post-Fukushima actions.
The task group also looked at how the lessons learnt were identified. The majority werecharacterised by the respondent as being identified during initial analysis/development of theaction (13) or during audits/self-assessments (21). Only a small number were identified throughdrills/exercises (2) or validation (2) and none were characterised as the result of training. The task
group believes that the relatively small number of lessons learnt being attributed to drills/exercise
and training, relative to initial analysis/development and audits/self-assessments, is likely due toboth the initial efforts being effective in identifying implementation issues and also the limited
opportunity to date for subsequent drills/exercises.
In addition to examining the characteristics of the Phase 2 submissions using the check box
responses as described above, the task group examined the content of the narrative responses(i.e. the text description of the lessons learnt). One general observation concerning the Phase 2
submissions is that the responses to the Phase 2 request often describe only the post-Fukushimaaction that was implemented and do not include implementation lessons learnt. Although thisinformation is quite useful, the objective of the Phase 2 request was to elicit lessons learnt during
the implementation phase of actions taken in response to the accident at Fukushima. The
ultimate goal of this WGHOF initiative is to be able to provide insights that can be used by others
implementing similar actions. The rationale for the focus on implementation lessons learnt wasthat the task group assumed that decisions concerning what actions were to be taken had alreadylargely been made and therefore HOF insights regarding how to best implement these actions
would be the information of greatest current and future relevance. However, the task group foundthat most of the submissions provided in response to the Phase 2 request focused on describing
the actions that were taken and included few HOF implementation insights derived fromovercoming initially unforeseen or inadequately addressed HOF challenges.

40

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There may be multiple reasons why the content of the Phase 2 submissions frequently
differed from the intended focus.
•

The information request may have been misunderstood to be a variant of the samequestions that have been a nuclear industry focus for several years since the Fukushima
accident (i.e. what was learnt from the accident and what actions are being taken toaddress those lessons). The information request included a clear statement regarding
the objective of the information request and specific instructions concerning sources oflessons learnt (see Chapter 3 of this report) but these may have been insufficient toovercome the pre-existing focus on lessons learnt from the accident itself.

•Documentation of actions taken in response to the accident focused on the final outcome
and not on the resolution of interim challenges. As a result, the type of insights the task
group sought to gather had not been formally captured by the respondents to the Phase
2 request and therefore could not be readily shared using existing documentation.

•

Licensees may have been apprehensive about the perceptions or regulatory attention
that could result from the identification of challenges experienced implementing thepost-Fukushima actions.

•

Nuclear plant licensees, industry organisations, and regulatory authorities dedicatedsubstantial resources to the development and implementation of post-Fukushimaactions. There may have been few lessons learnt as these efforts were effective in
minimising the incidence of unforeseen challenges during implementation.

•

New capabilities that have been put in place in response to the Fukushima accident havenot been sufficiently tested, either through formal validation methods or by exercisingthem in drills or training, to expose the HOF challenges.

As noted earlier in this report, there are practical and safety limitations on how well suchactions can be validated.
Although it remains unclear whether these or other factors may have contributed to thepredominant focus on the actions taken, rather than the lessons learnt in the process, thepossibility remains that few lessons learnt were reported as there was limited licensee experience
testing these new capabilities in drills or exercises when they received the solicitation for
information. Consistent with this view, through their review of the Phase 1 submissions, the task
group observed that whereas training for extreme external events and severe accidents may be
performed in some cases on an annual basis, requirements and guidance concerning thefrequency of related drills and exercises, where specified, typically had longer periodicities(e.g. three years), commensurate with these being low probability events. Accordingly, theworking group proposes that assessments of the safety enhancement achieved by putting in place
mitigation capabilities for extreme external events and severe accidents should continue to betempered by the extent to which the ability of personnel to implement these capabilities has been
demonstrated under the conditions that they will be required.
Given the content of the Phase 2 submissions, the task group expects the information provided
in response to the Phase 2 request will likely be of more value to those seeking to understand therange of challenges presented by extreme external events and severe accidents, and the diversityof approaches that operating companies have implemented to address those challenges. Suchinformation can nonetheless be of substantial value as it points to issues and options that one
may have not previously considered. Regarding how well these approaches have effectively
addressed HOF considerations, readers are likely to find that additional information would benecessary to understand the extent to which the measures were verified against applicable HOF
standards and how the measures were validated with respect to their ability to support intended
performance outcomes under the range of conditions for which they are intended.
Of the limited HOF implementation experience reported in response to the Phase 2
information request, that experience is related to:
1. Implementation of diesel generator as alternate power supplies (see Appendix B Lessons
Learnt: CZ-04, SP-01, and US-02).
2. Analysis/validation of mitigation strategies (see Appendix B Lessons Learnt: CZ-04,
SP-01, and US-01).

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PHASE 2 SUMMARY

3. Analysis/validation of minimum staffing (see Appendix B Lessons Learnt: FR-01).
4. Remote automated gamma monitoring (see Appendix B Lessons Learnt: CA-05).
Although these examples provide an insufficient basis to infer the areas where humanperformance challenges might be most prevalent in the implementation of post-Fukushimaactions, the importance of alternate power supplies to many mitigation strategies and the broad
applicability of validation practices to ensure that intended outcomes can be achieved suggestthat these may be areas on which to focus future monitoring/assessment efforts.

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CONCLUSIONS

Chapter 4. Conclusions

The summaries and questionnaire responses submitted by national nuclear regulatory authorities
in response to the Phase 1 information request, and compiled in Appendix A, provide acompendium of the important steps that have been taken to substantially enhance the ability ofplant operators to mitigate the impact of extreme external events and severe accidents on nuclear
facilities and public health and safety. These steps mainly comprise the provision of new,additional, or improved facilities, equipment, supplies, and strategies that support, but do notsupplant, the roles and responsibilities of plant personnel in responding to such events. Whereas
most post-Fukushima actions have been previously described from various engineering, safety,
and regulatory perspectives, this WGHOF effort has focused on the human and organisational
factors and the implications and challenges associated with these actions.
The Phase 1 submissions confirm that plant personnel continue to have important, often
critical, roles in mitigating extreme external events and managing severe accidents. These roles
cover the gamut from initial accident assessment to event mitigation, off-site, and long-term
event response. Whether the safety enhancements will provide their full intended benefits will
depend on the extent to which plant operators have accounted for, and adequately addressed, thechallenges that these events pose to effective and reliable human and organisational performance.
It is evident from the Phase 1 submissions that many of the actions were implemented withspecific consideration of such challenges (e.g. response strategies were formalised in guidelines
and procedures to aid decision making, connections for portable equipment were colour coded toreduce the cognitive burden of determining appropriate connections; required local actions for
mitigation strategies were limited to areas with protection from external hazards). Unfortunately,
the Phase 2 information request yielded limited information regarding the validation of themeasures that operators put in place. The lessons learnt included in some instances limited initial
validations, suggesting that more insights will come to light as licensees implement their periodic
training and testing activities.
The implementation actions summarised in the Phase 1 responses, and described in greater
detail in the Phase 2 submissions, show that each country typically addressed three major aspectsof response to extreme external events and severe accidents: (1) analysis and decision support(e.g. assessment of plume pathways), (2) mitigation strategies and equipment (e.g. portable
generators, pumps, and procedures/strategies for their use), and (3) command, control, andcommunication capabilities (e.g. improvements to command centres, communications
equipment, and assignment of decision and response functions). Although each aspectcontributes uniquely to response effectiveness, there are often substantive and importantinterdependencies between these aspects of accident response. In sum, an effective response to
extreme external events and severe accidents largely depends on a co-ordinated and integrated
response by a relatively large, and to some extent diverse, group of human actors (e.g. control
room operators, field operators/technical, technical support centre staff, local authorities off-siteorganisations, and regional response centres) who are working under conditions that at minimum
are novel (i.e. rare) and likely include mental and/or environmental stressors.
The mitigation of extreme external events and management of severe accidents at nuclear
facilities can thus be viewed as relatively complex systems of individuals, technologies, andorganisations in which the human element is essential to mission success. Such a “systems”
view has two important implications. First, it helps us to more fully appreciate and consider theeffects that degraded human performance in one sphere or “subsystem” of the response canhave on other elements of the response. Delays or errors in the human actions required forevent mitigation, including decision making, can ripple through the system, resulting indesynchronisation of the various response organisations, further degradation of the plant state,
and loss of available response options. Validation of the ability to reliably perform such required
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CONCLUSIONS

actions is therefore central to ensuring the overall system can successfully respond to such
events.
The second implication of viewing mitigation of extreme external events and management ofsevere accidents as a complex system is that it reminds us that in nearly every complex system,in addition to those subsystem interactions that are present by design to achieve intended
outcomes, there are often unanticipated interactions that can have deleterious consequences.
This is true at least for the case of new, or newly modified systems. “New” or “newly modified”
are descriptors that can reasonably be applied to the many new capabilities that have beendeveloped and put in place for event response post-Fukushima. It follows that in addition tovalidation of elemental human actions required for event response, tests of event response
systems as a whole are important to ensure that the subsystems are capable of functioning
together, and that the human and organisational elements of the response do not reveal thefunctional equivalents (e.g. “sneak circuits”, signal distortion, sequencing errors, inadequate
bandwidth) that often plague the integration of technological systems.
This view of mitigation of extreme external events and management of severe accidents
leads the task group to assert the importance of validating required human actions, but withthe understanding and caveat that such validations can be complex and resource-intensive
undertakings. Additionally, the notion of acceptance criteria for “successful” validation is nota simple matter.
Validation of time-limited required manual actions might appear to be relatively
straightforward to carry out until the context of extreme external events and severe accidents
is considered. From the human performance perspective, these contexts introduce the needto consider testing human performance under psychological and environmental conditions
that might be viewed as unsafe or unethical to reproduce with fidelity in a simulated
validation environment. From a regulatory/licensing perspective, such events are typicallyconsidered to be outside the design basis of the facilities, causing them to be unbounded
conditions. As a consequence, even if it is determined that validation can be performed undermore realistic and extreme conditions, there can be debate as to what degree of psychologicalor environmental stressor (e.g. flood water depth, temperature, debris field) is sufficient tosatisfy validation objectives.
Considering validations of the overall response to extreme external events and severe
accidents, added to the challenges described above is the sheer magnitude of exercises required
to evaluate and demonstrate integrated response capabilities. Engaging multiple on-site andoff-site organisations in simulations of events, which can span days, is an expensive and timeconsuming undertaking in both planning and implementation, and must be conducted on afrequency and in a manner that justifies the safety benefits.
These acknowledged challenges to validating human and organisational responses to extreme
external events and severe accidents should not, however, be taken as basis for dismissing such
validation efforts as of limited value or impractical, but rather call for innovative thinking andcollective action as discussed in Chapter 5.

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RECOMMENDATIONS

Chapter 5. Recommendations

As observed in the NEA report, Five Years After the Fukushima Daiichi Accident (NEA, 2016b), andreiterated in the NEA report, Fukushima Daiichi Nuclear Power Plant Accident, Ten Years On: Progress,
Lessons, and Challenges (NEA, 2021), continuous and innovative progress is fundamental toensuring safety, even where many improvements have been made. Lessons learnt throughoperating experience and research will require continued attention. This is particularly true forcomplex areas such as the human aspects of nuclear safety as reflected in safety culture,training and organisational factors. Constant vigilance and effort are needed at the national andinternational levels.
The WGHOF initiative documented in this report was undertaken to support such innovativeand continuous progress. The effort had two primary objectives: (1) gather the human andorganisational factors (HOF) lessons learnt (positive and negative) that are being gained while
implementing the actions that many regulatory authorities and nuclear facility operators aroundthe world are taking to strengthen their ability to respond to events like that experienced at
Fukushima; and (2) share these implementation lessons learnt broadly (e.g. with nuclear facility
operating companies, technical support organisations, research institutions, and regulatory
authorities) so that they can be used to facilitate and enhance these efforts going forward. To thatend the WGHOF offers the following recommendations:•

Appendix A to this report is a compendium of summaries from regulatory authorities inseven countries that describes the breadth and diversity of post-Fukushima actions thathave been undertaken, with an emphasis on the human and organisational aspects. The
summaries also point to the applicable requirements and guidelines. Each summary isaccompanied by questionnaire responses that draw the relationship between the specificactions described in the summaries and each of ten topical areas concerning human andorganisational factors. Readers are encouraged to explore the contents of this appendix
and use the information as a resource (e.g. identification of alternative tools, methods, andstrategies) for informing their current and future efforts pertaining to the mitigation of
extreme events and management of severe accidents. Additionally, this report proposes a
systemic human, technology and organisation (HTO) approach to implementing postFukushima actions so that the interactions of humans, technology and organisational
factors are considered in an integrated manner, as it could prove useful in gaining the full
benefit of these efforts.

•

Appendix B to this report is a compendium of 40 lesson learnt submissions describing
specific implementation activities that have been undertaken and the insights gained in
the process. These submissions bring to life the actions and requirements described inAppendix A, including some of the challenges that were encountered and overcome in
the process. Readers are encouraged to explore the contents of Appendix B to gain adeeper understanding of the material presented in Appendix A, consider the human andorganisational factors of response to extreme external events and severe accidents, andassess the applicability of the lessons learnt to their efforts and capabilities for event
mitigation and accident management.

•

As described in Chapter 4, although many technological enhancements have been madeto improve the mitigation of extreme external events and management of severe
accidents at nuclear facilities, responses to these events rely in large measure on humanactors performing under challenging conditions. Validations of required actions at theelemental and integrated level are fundamental to ensure that the intended safety
benefits of post-Fukushima actions for event mitigation and accident management havebeen achieved and will be maintained. Chapter 4 also identified specific challenges to

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RECOMMENDATIONS

conducting such validations. This report encourages initiatives that target thesechallenges with the aim of developing innovative and practical solutions and sharing
these solutions broadly. Efforts are recommended to enhance validation for such actions
at both the elemental and integrated levels.
•

46

Lastly, this effort towards aggregating and disseminating the HOF lessons learnt during
implementation of post-Fukushima actions should be viewed as a modest first step. The
challenge remains of accelerating learning in managing the human and organisational
factors of complex and challenging event mitigation and accident management activities.
This report encourages initiatives, such as the effort documented above, that facilitate
the identification and broad dissemination of insights and best practices for HOF aspectsof mitigating extreme external events and the management of severe accidents.

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REFERENCES

References

CNSC (2011), CNSC Fukushima Task Force Report, INFO-0824, CNSC, Ottawa, http://nuclearsafety.
gc.ca/eng/resources/fukushima/fukushima-canada-action-plan.cfm.
Laarni, J. (2019). “Cognitive Heuristics and biases in process control and maintenance work”,
Proceeding of the 11th International Topical Conference on Nuclear Plant Instrumentation, Control &Human Interface Technologies, American Nuclear Society, Florida.
NEA (2021), Fukushima Daiichi Nuclear Power Plant Accident, Ten Years On: Progress, Lessons andChallenges, OECD Publishing, Paris, www.oecd-nea.org/jcms/pl_56742/fukushima-daiichinuclear-power-plant-accident-ten-years-on.
NEA (2016), Five Years after the Fukushima Daiichi Accident: Nuclear Safety Improvements and Lessons
Learnt, OECD Publishing, Paris, www.oecd-nea.org/jcms/pl_14978/five-years-after-thefukushima-daiichi-accident.
NEA (2015), “Human Performance under Extreme Conditions With Respect to a Resilient
Organisation - Proceedings of a CSNI International Workshop, Brugg, Switzerland,
24-26 February 2014”, NEA/CSNI/R(2015)16, OECD Publishing, Paris, www.oecd-nea.org/jcms/
pl_19668/human-performance-under-extreme-conditions-with-respect-to-a-resilientorganization-proceedings-of-a-csni-international-workshop-brugg-switzerland-24-26february-2014.
NRC (2020), “Flex Diesel Generator Operational Challenges”, Information Notice 2020-02, NRC,
Washington DC, www.nrc.gov/docs/ML2019/ML20196L822.pdf.
NRC (2011), Recommendations for Enhancing Reactor Safety in the 21st Century: The Near-Term Task
Force Review of Insights from the Fukushima Daiichi Accident, NRC, Washington DC,
www.nrc.gov/docs/ML1125/ML112510271.pdf.
NRC (1994a), The Impact of Environmental Conditions on Human Performance, NUREG/CR-5680, NRC,
Washington DC, www.nrc.gov/docs/ML0704/ML070460030.pdf.
NRC (1994b), The Effects of Stress on Nuclear Power Plant Operational Decision Making and Training
Approaches to Reduce Stress Effects, NUREG/CR-6127, NRC, Washington DC, www.nrc.gov/
docs/ML1025/ML102530314.pdf.
UJV Rez. (2018), “Safety analysis of recovery of power supply using MDG”, Z-5064-T, UJV Rez.,
Husinec.

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APPENDIX A

Appendix A: Regulatory Authority Responses to the Phase 1
Information Request - Summaries of Actions Taken andQuestionnaire Responses Regarding Human and Organisational
Factors Addressed by these Actions

This annex is available online: www.oecd-nea.org/7578-annex1

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APPENDIX B

Appendix B: Responses to Phase 2 Information Request –Human and Organisational Factors Lessons Learnt Implementing
Post-Fukushima Actions

This annex is available online: www.oecd-nea.org/7578-annex2

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NEA PUBLICATIONS AND INFORMATION

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Post-Fukushima Action Implementation
at Nuclear Installations

This report compiles and shares some of the lessons learnt from implementing post-Fukushima actions
related to human and organisational factors (HOF), including at nuclear facility operating companies,
technical support organisations, research institutions, and regulatory authorities.
It summarises a two-phase information-gathering exercise, overseen by the NEA Working Group on
Human and Organisational Factors, about the requirements and guidelines that countries and nuclear
licensees have adopted since the accident.
The report discusses the central role of human and organisational performance in mitigating extreme
external events and the management of severe accidents. It addresses the importance of validating theability to perform these actions, and the challenges associated with performing such validations withfidelity to the conditions likely to be present during such events. The report concludes by providing four
key recommendations that seek to promote greater sharing of information and the identification of bestpractices.

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NEA No. 7578