E-Journal of Advanced Maintenance Vol.15 (2024) 1-18
Japan Society of Maintenology

Study of the Fundamental Concepts for Improving the Safety of
Nuclear Power Plants
Takayuki AOKI1,*
1

Center of Fundamental Research for Nuclear Decommissioning, Tohoku University,
Aramaki-Aza-Aoba 6-6-01-2, Aoba-Ku, Sendai 980-8579, Japan
ABSTRACTThe world nuclear industries and regulatory authorities have experienced many significant accidents, such as
TMI-2, Chernobyl, and the Fukushima Daiichi accident. They strive to incorporate the lessons learned fromthese accidents into technologies, organizational operations, and even the behavior of individuals involved.
They also continuously study the lessons derived from safety activities, including normal operations andmaintenance. And through these reflections and research, they aim to establish a shared, dedicated, and effective"safety culture".
The key concepts, principles, requirements, and measures for nuclear safety established by the many nuclear
organizations in the past, including the IAEA, are evident to be all essential to ensuring nuclear safety. However,the underlying concepts and true intentions behind them may not always be clear or easy to understand. To
understand nuclear safety accurately and accessibly, it is significant to grasp the position and meaning ofimportant aspects of nuclear safety and to comprehend the overall framework or structure and mechanisms that
improve safety. To deeply understand these important matters, the author considers that narrative explanations(or storytelling) and visual aids (or visualizations) are needed, which allow us to go beyond surface-levelcomprehension and explore its essence to achieve a profound understanding of nuclear safety.
This paper reports some instances where such a lack of clarity exists and proposes measures for improvement.
KEYWORDS

ARTICLE INFORMATION

nuclear safety, safety structure, plant system, human system, safety activity,
maintenance, safety improvement mechanism, safety principle, safety
culture, narrative explanation, visualization

Article history:
Received 28 July 2023
Accepted 9 January 2024

1.

Introduction

The International Atomic Energy Agency (hereinafter referred to as IAEA) has established thebasic safety principles [1] in terms of both hardware and software (or humanware) to protect people
and the environment from the effects of ionizing radiation and recommends that operators take safetymeasures based on the principles. It also suggests the meaning and ideal state of culture for safety [2][3], which is very important in the operation of nuclear facilities. Furthermore, in the United States,
the Nuclear Regulatory Commission (hereinafter referred to as NRC) explains how it regulates in thesection of its website, "How we regulate" [4]. There the NRC addresses the Reactor Oversight Process[6] (hereinafter referred to as ROP). This focuses on regulations that make good use of risk andperformance information to monitor nuclear facilities and take necessary actions. The ROP is called“risk-informed and performance-based regulation” [5] and is applied to US nuclear facilities andsafety-related activities to help ensure nuclear safety.
On the other hand, in Japan, the regulatory approach to nuclear power plants previously used has
been fundamentally changed by reflecting the lessons learned from the Fukushima-Daiichi nuclear
power station (hereinafter referred to as 1F) accident. The Japanese Nuclear Regulatory Authority(hereinafter referred to as "NRA") has established a new regulatory framework and associatedstandards, NRA rules No. 5 [8] and No. 6 [9], by referring to the above-mentioned ideas of the IAEA,
NRC, etc. after the 1F accident. The most important points in this change are probably the points
shown in Fig. 1 [7], namely the location of the prime responsibility for nuclear safety and the positionof the regulatory authority in ensuring nuclear safety. And, perhaps most notably, the safety
improvement assessment process [10] [11] has been established on the premise that operators would*

Corresponding author, E-mail: takayuki.aoki.b5@tohoku.ac.jp

ISSN-1883-9894/10 © 2010 – JSM and the authors. All rights reserved.

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T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

continue to rigorously pursue nuclear safety, including exceeding beyond the regulatory requirements,
as long as they operate their facilities.
As mentioned earlier, the global nuclear community has derived valuable lessons from many

Fig. 1 Paradigm shift of the basic principle of nuclear regulation in Japan

accidents that have occurred in the past. These lessons have contributed to developing knowledge
bases and safety measures, which are actively employed. However, although it is evident that thesefundamental concepts, principles, and requirements derived from these lessons are all crucial for
ensuring nuclear safety, the true significance of each idea, their interrelationships, and others are notalways clear. These important matters give rise to questions regarding how nuclear safety is structured,
how the mechanisms for improving nuclear safety work, and how those important ideas can beeffectively utilized to improve nuclear safety. If we can gain clarity on these matters, individuals
assigned to safety-related tasks would have a better understanding of the importance of their roles andcarry out their tasks with confidence. Consequently, it would become much easier to align theawareness and intentions of many individuals involved and mobilize their collective efforts. As aresult, we can expect significant advancements in nuclear safety.
Since few studies have so far attempted to clarify these questions with the awareness of theaforementioned issues, this paper reports important examples of the unclear points mentioned above
and then discusses ways to understand nuclear safety better and more deeply. Note that this paper isbased on my previously published paper [12], with further discussion and some new considerations.

2.

Structure of Nuclear Safety

2.1. Safety and Activities for Ensuring It at Nuclear Power Plants
The world nuclear community has worked hard to ensure and improve the safety of nuclear
power plants through wisdom, trial, and error. Initially, reliability was improved mainly throughhardware by taking measures for deep protection, ensuring multiplicity/diversity/independence(including positional dispersion) of SSCs, securing safety margins, and taking measures against aging,such as addressing stress corrosion cracking (SCC). Later, after the TMI accident in the U.S., there
was a growing awareness that the safety activities (software and humanware) of the organizations andmembers operating nuclear power plants have a significant impact on safety, and various measures
were implemented. This revised approach led to strong criticism from the industry that the tightened
regulations implemented by the NRC were not efficient and effective, and the aforementioned ROP
was born to achieve improvement.
Recognizing that resources responding regulatory are finite, the ROP has been developed as aunique regulatory framework based on a strategy and policy of focusing resources on safety-critical
nuclear facilities and safety activities by operators to ensure safety and that necessary actions aretaken. This is a breakthrough regulatory framework that has never been seen before. In addition, theexperience of the Chernobyl accident led to hardware countermeasures and accident management
against severe accident events, in addition to the conventional design-based safety countermeasuresand gave birth to the IAEA safety culture concept mentioned above. Furthermore, IAEA took theopportunity of the 1F accident to consider how to assure preparedness for unforeseen events from theperspective of individuals, technology, and organizations (ITO) required to respond and proposed2

T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

measures to achieve that [13] [14]. This recognizes the need to build safety by combining not only the
hardware system but also the human systems required to respond, including human factors andorganizational factors (HOF) (Table 1), which is aggregated in IAEA GSR Part 2, discussed later. In
this way, both hardware and software (or humanware) have become much more sophisticated than
before, based on the bitter experience of accidents in the past, and have been incorporated into many
regulatory standards of the NRC and NRA [15] [16].
Table 1 Examples of human, technology, and organization

2.2. Hardware and Human Systems Supporting Nuclear Safety
When considering the factors that significantly affect the safety of nuclear power plants based on
the discussion in the previous section, the keywords can be listed below.
+ Safety philosophy and safety design of nuclear power plants (Hardware)+ Organization and members of the operator who carry out safety activities (Humanware)+ Strategies, policies, and ideas (Software)+ Safety activities performed by operators+ Technology used in safety activities (Technology)
These keywords are extremely important in examining how the structure of nuclear safety isorganized. The following is a discussion of the structure of nuclear safety.
A nuclear power plant is composed of a huge number of mechanical, electrical, instrumentationand control, and civil/architectural SSCs (Structures, Systems, and Components), which are intricately
related to each other to perform many functions including safety, and capabilities, and then power isgenerated. This hardware system (collectively referred to here as the "plant system") is designed withvarious safety features such as fail-safe, foolproof, interlocking, etc., in addition to defense-in-depth
protection and multiplicity, diversity, and independence, to ensure a certain level of reliability andthus safety as the plant system. However, this alone is not enough. The humanware system(collectively referred to here as the "human system") performs the necessary activities to enable theplant system to fulfill its pre-assigned functions and performance. Safety is ensured only when thehuman system properly performs the necessary activities, i.e., safety activities such as operation andmaintenance, for the plant system to fulfill its pre-defined functions and capabilities as well as
recognition of possible events, e.g., seismic and tsunamis. To achieve this, it is necessary to have agood understanding of the design characteristics and aging degradation of the plant system, as well as
the traits and performance of the human system, and to continuously plan (Plan), implement (Do),evaluate (Check), and correct (Act) the safety activities, considering both. If the PDCA cycle is notproperly implemented, the functions and performance of the plant system cannot be maintained or
improved.
The human system here is such a system that includes not only the front-line people who work toensure, maintain, and improve nuclear safety, but also the on-site organizations and companies towhich these people belong. In addition, since these organizations and companies may be greatly
influenced and changed by society and the world, it is necessary to consider the human system in a
broader scope, and to consider it in such way as the IAEA's ITO mentioned above since humansystems operate using a variety of technologies.

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As mentioned above, nuclear safety can be said to be supported by two systems: the plant systemand the human system, and safety activities PDCA, including operation and maintenance (Fig. 2).

Fig.2 Structure of nuclear safety

2.3. Safety Activities Forming the PDCA Cycle
To effectively and efficiently implement the safety activities of PDCA deployed between theplant system and the human system, it is necessary to have a sufficient understanding of thecharacteristics of both the plant system and the human system and incorporate this understanding
effectively into the safety activities. In other words, to maintain and improve nuclear safety, it isessential to comprehend the characteristics of both systems and incorporate this understanding into thesafety activities. This will lead to enhanced performance in both the plant and human systems,
ultimately ensuring or improving nuclear safety. In this sense, safety activities are a very importantfactor in ensuring or improving nuclear safety.
The plant system is equipped with the capability and functionality to cope with various operating
conditions, including accidents and malfunctions initiated by external events like earthquakes orinternal events like age-related deterioration. However, to maintain and improve this capability andfunctionality, the safety activities conducted by the human system, including maintenance, must be
appropriately carried out.
The human system, on the other hand, does not always perform at the same level at any given
time in safety activities. This is a characteristic that differs from the plant system. The performance ofthe human system varies greatly depending on the organizational structure, the capabilities of its
members, internal and external regulations, work procedures, and so on. The quality of the work
environment and the health of members also have a significant impact on performance. Therefore, it is
crucial to establish and maintain favorable conditions for the human system to ensure sufficient
potential (capability and functionality) to ensure safety and to fulfill its potential. This requires
continuous efforts to improve the various conditions.
Note that in the PDCA cycle, three technologies are used: inspection technology, aging
evaluation technology, and correction technology. In other words, they include a variety oftechnologies and software, ranging from technologies that use special equipment, special tools,
infrastructure, and utilities to software used for analysis and evaluation.
The PDCA cycle for safety activities consists of planning the tasks that need to be performed (P),implementing the plan (D), properly evaluating the results, and developing corrective plans asnecessary (C), and implementing the corrective plan (A). This is thought to follow the practice ofsetting safety goals in advance and repeating the PDCA cycle to achieve those targets since safety
activities are of such a nature that the best method cannot be uniquely determined.
On the other hand, safety activities include both safety activities in normal times and safety
activities in emergencies. The safety activities in normal times discussed so far include not only theactivities for operation and maintenance, but also the activities for fuel management, radiation control,radioactive waste management, and others. The safety activities in contingencies refer to emergency
responses to accidents, abnormal situations, etc.
The emergency response here corresponds to Levels 4 and 5 of the IAEA's 5 Levels of Defense

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T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

in Depth. The concept of emergency response has made significant progress in recent years with theintroduction of the concepts of Resilience Engineering [17][18] and Safety II [19]. In Resilience
Engineering, there are four abilities in this context, anticipating, monitoring, responding, and learning.
These four abilities are understood as a special case in the safety activities PDCA as discussed below.
Although the emergency response is seemingly different from other safety activities conductedduring normal times, this response can also be explained using the plant system, human system, andPDCA for safety activities including maintenance described so far. In other words, the emergency
response is one of the activities that the human system performs on the plant system, and its activities
correspond to the four abilities of Resilience Engineering: monitoring, predicting, responding, andlearning, the first three of which correspond to the Do, Check, and Act of safety activities,
respectively. In the case of Resilience Engineering, there is no "Plan" phase because the responsemust be made in a very short time, so there is no time to develop plans for monitoring or corrective
actions. Instead, many response plans for a wide variety of emergencies are developed in advance andcompiled into a database and knowledge base, and accident response personnel who learn these plans
through training can respond promptly at any time. This is thought to enable accident response
personnel to respond to accidents without monitoring and corrective action planning. On the other
hand, activities corresponding to Learning in Resilience Engineering are seemingly omitted fromsafety activities in normal times, but this is considered to be covered in the C (Check) phase of the
PDCA for safety activities. (Fig. 3)
Comparing the concept of safety activities in normal times with one in emergencies, there aresimilarities and differences and analyzing the details of these differences may provide new insights.
The author has already conducted several studies on this subject [20]. However, since this paper
mainly focuses on safety activities in normal times, it is not discussed any further in this paper.

Fig. 3 Comparison of PDCA between maintenance and emergency response

3.

Mechanisms for Maintaining and Improving Safety

3.1. Specific Ways to Improve Safety
There are two ways of improving safety: one is to improve safety by improving the plant system(safety improvement measures for the plant system), and the other is to improve safety by improving

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T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

the human system (safety improvement measures for the human system).
(1) Ways to improve the safety of the plant system
The following ways can be considered to improve the reliability of plant system (hardware) andlink this to the improvement of safety:+ Of the many components that compose a system with a safety function, improve the reliabilityof individual components, especially those of high safety importance.
+ Assuming internal and external events impact on the system with safety functions, conductvarious case studies with parameters that are considered to have relatively high sensitivity toidentify system configurations with high reliability and robustness against these events, andextract improvement for the most appropriate one among them.
Thus, in many cases, methods to improve the safety of mechanical systems can be studied using
objective methods such as mathematical methods, and the ideas are well organized. Therefore, nofurther discussion of this issue is made here.
(2) Ways to improve safety by improving the performance of the human system
For example, in the case of nondestructive testing of equipment, it is well known that theperformance of inspection (inspection accuracy, inspection time, etc.) is determined by the
combination of inspection procedure, inspector’s capability, and inspection equipment. To generalize
this, the performance of an organization, if it is a safety activity in the field, is considered to be
determined by the combination of the following three factors: efficient and effective procedure andexecution, the capabilities of fieldwork team members, and materials and equipment/tools used. If it isa technical study, it is still determined by the combination of three factors: efficient and effective
methodology, the capabilities of engineering team members, and technology and software used. In
these cases, the capabilities of team members are considered to include their physical and mental
conditions, since these conditions also have a significant impact on them (Fig. 4).
If the three factors mentioned above, i.e., methodology, members involved, and tools used, are
improved respectively as shown below, these items could improve the performance of safety activities
by the human system and consequently improve plant safety.
(a) Establishing an appropriate quality management system (QMS) through changes in theorganizational structure and members, company rules and regulations, and work practices,and by performing benchmarking activities.
(b) Addressing an enhancement of the capabilities of team members performing safety activities
through training and experience, carefully studying the inherent traits of humans, both
positive and negative1, and adopting systems and methods to take advantage of the positiveand prevent the negative from surfacing or emerging.
(c) Adopting efficient and effective ways by using appropriate materials, equipment, tools, etc.
for fieldwork, or software, IT infrastructure, etc. for analysis and evaluation.

Fig. 4 Abilities required for engineering staff and field worker
1

Positive human traits lie in their adaptability and flexibility, enabling them to proactively respond to changing
circumstances. They have also the traits of trying to expand and implement what is working well to a higher
level whenever possible. On the contrary, while machines repeat exactly as programmed to implement at any
given time, humans are not good at maintaining concentration and tension for long periods to perform tasks
accurately and tend to lose sight of their goals and objectives as time passes. They are also not good at uniting
the will of many people toward a single goal or objective. And if the physical and mental environment
surrounding them is not favorable, their performance declines drastically.

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3.2. Efficient and Effective Ways to Improve Safety
As mentioned earlier, humans are inherently lazy, make mistakes and errors, or are easily
influenced by their physical condition or environment, resulting in poor work performance andsometimes failure over time. While these negative traits may not be eliminated completely, it isnecessary to keep thinking about minimizing them, and to come up with specific ways to achieve suchminimization and implement them. What exactly should be done to achieve this? The answers to thisquestion are listed here in the following five points. These are considered to be efficient and effective
ways to quickly and steadily improve safety and bring it to a higher level. These five are discussed indetail in the next section.
(1) Concentrating Resources on Higher Importance Matters
Efficient and effective safety improvement requires minimizing what needs to be done. So, it isvery important to identify SSCs and associated activities in advance that have a potentially significant
impact on safety and to focus resources on them because the organization always has limited
resources (people, material, money, time, information, etc.).
(2) Setting of Specific Goals
It is essential that the goals of the organization for safety activities are clearly set. Because people
have a trait that once the goals are set, they will work hard to achieve them. It is, therefore, necessary
to introduce a system to promote this by making good use of this human trait.
(3) Organizational Management and Roles Assignment
Efficient and effective safety improvement also requires an appropriate organizational
management and roles assignment. The top management of an organization is required to show thepolicy and general goals regarding safety. Based on these, the leaders are required to translate thegeneral goals into specific objectives and to challenge the difficulties and problems in achieving thegoals, so that the organization can achieve them quickly and steadily. The managers are required tocoordinate the smooth and reliable promotion of the daily activities to achieve specific goals asplanned, to maximize the driving force to achieve the objectives, and to pursue the elimination of
unnecessary and wasteful costs as much as possible.
(4) Leadership and Management
Leadership and management play crucial roles in ensuring the efficient and effective
implementation of work. This is because, without effective leadership, initiatives that challenge thestatus quo and aim for continuous improvement and achievement of goals may not be initiated.
Similarly, inadequate management can lead to inefficiencies in the workflow.
(5) Good Working Environment
To enhance the performance of the existing human system as a whole, it is extremely importantto create an environment in which individual members are valued, encouraged, assured, and rewarded
for strong positive results as they demonstrate their capabilities. This is because the capabilities of themembers vary greatly depending on the environment, which generates excellent results.

4.

Discussion
In this section, each of the five items listed in the previous section is discussed in detail below.

4.1. Concentrating Resources on Higher Importance Matters (Graded Approach)A large-scale complex system such as a nuclear power plant consists of a huge number of SSCs.
Therefore, if you uniformly allocate resources to each of SSCs, the total resources required becomehuge. If you have only limited resources, which is usually the case, you can allocate only insufficient
resources to each of them. This is not an effective and efficient way of dealing with this issue.
(1) Identification of the SSCs and associated activities that have a significant impact on safety,
concentration of resources on them, and elimination of wastages
One of the most efficient and effective ways to improve safety effectively and efficiently is to7

T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

identify the SSCs and associated activities in advance that have a potentially significant impact onsafety, then to focus resources (people, material, money, time, information, etc.) on them. This means
achieving the safety objective with the minimum necessary resources. To realize this, the following
steps need to be taken:(i) First of all, it is necessary to identify the SSCs to be maintained by considering the degree of
impact of each SSC on plant safety, i.e., the level of safety importance, aiming to minimize
the scope of maintenance that is considered necessary to achieve the goals for plant safety.
Safety importance can be determined in several ways including PRA (Probabilistic Risk
Assessment).
(ii) For the selected SSCs, the inspection plan (P) and corrective action plan (C), which are theplans for the planning phase, are usually made rationally by applying the PMO (Preventive
Maintenance Optimization) method using the PM basis standards. This ensures that resources
are not wasted on unnecessary tasks or inappropriate timing of implementation. (Table 2)(iii) Then, the inspection implementation plan (D) and corrective action implementation plan (A),which are the plans for the implementation phase, are usually made based on the schedule offieldwork, the allocation plan of maintenance workers, the procurement plan ofmaterials/equipment/tools to be used, and various management plans. Here, appropriate
maintenance work teams should be allocated to the selected SSCs according to their level ofsafety importance and should follow proper procedures to eliminate unnecessary waste ofwork and time, so as not to waste resources. (Table 2)
Table 2 Efficient and effective way at each step of maintenance cycle PDCA

What must be given attention here is not the first step (i) above of selecting the important SSCs
depending on their level of safety importance as discussed above, but rather the steps (ii) and (iii) of
assigning maintenance resources to the SSCs and using the resources to perform maintenancefieldwork. This is because even if the scope of SSCs is minimized in the step (i) above, if there is a lotof wastage in the steps (ii) and (iii), the resultant resources cannot be reduced. Since the step (iii)
requires many workers, equipment, and materials, and involves complex and lengthy work processes,
small wastes may pile up and lead to large wastes. Thus, for example, if a component with high safety
importance breaks down, necessary and sufficient action should be taken. However, if it is not of highsafety importance, the restoration of the failure should be carried out, and no investigation of the
failure cause or countermeasures to similar ones should be carried out (Table 3). This is because if theallocation of resources to less important objects is not thoroughly reduced and unnecessary andwasteful costs are not eliminated, the necessary resources for important SSCs and safety activities

8T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

may not be allocated, resulting in a decrease in safety.
Table 3 Relationship between component failure and its importance of safety (Example)

This approach discussed above would lead to the concentration of resources on the SSCs withhigh safety importance, to drastically reducing the resources required without any major deteriorationin safety, and finally achieving the objective (Fig. 5).
In general, when implementing specific projects, the resources allocated to activities (such as
personnel, materials, finances, time, and information) are limited, and it is essential to achieve successwithin these constraints. The same applies to safety activities in nuclear power plants. To maintain andimprove the safety of nuclear power plants beyond a certain level, it is necessary to identify
safety-significant components and allocate sufficient resources to them while economizing resources
as much as possible for less critical SSCs. This effective and efficient approach ensures that resources
are appropriately allocated based on importance, allowing for the development and implementation ofadequate safety plans for activities. It results in an overall improvement in the quality of safety
activities throughout the plant. Otherwise, unnecessary resources might be allocated to less important
SSCs, leaving insufficient resources for crucial SSCs. Consequently, the overall plant safety level may
be reduced.

Fig. 5 Creation of effective and efficient maintenance plans

9T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants(2) Visual understanding of identification of SSCs and associated activities having a high level ofimportance
Figure 6 shows the whole plant of a nuclear power plant using one plane; the upper plane
represents the whole plant consisting of SSCs at a certain point in time, and the lower plane represents
the whole plant consisting of SSCs after a certain amount of time has passed. Each segment on theplanes represents a system consisting of components. The vertical axis connecting the two planes
represents the flow of safety activities, including operations and maintenance, performed on thevarious SSCs in the plant.

Fig. 6 How to identify an importance from the viewpoint of nuclear safety and economic efficiency

The upper plane of this figure is, for example, the planning stage of maintenance activities. By
taking a bird's-eye view of the whole NPP in the planning phase, you can understand the perspective
and idea of allocating resources by clarifying which SSCs and associated activities are most importantfor safety and which ones are most important for the economy. That is just the perspective and idea toderive an efficient and effective way described in the previous section. When implementing safety
activities with finite resources, it is essential to apply efficient and effective ways, such as knowing
which SSCs and associated activities are of high safety importance and focusing resources on them.
Otherwise, it may not be possible to allocate sufficient resources to SSCs and associated activities
needed to ensure and improve safety, which may cause a decline in plant safety. It is also essential toevaluate how much resources can be saved for less important SSCs and associated activities andallocate the savings to more important things. The same concept should be applied to economic
activities to maintain and improve plant availability, i.e., shortening planned and unplanned shutdown
periods and eliminating unnecessary and wasteful costs as much as possible by allocating resources
according to their importance.
On the other hand, as the safety activities move along the time axis, errors or problems may
occur in the contents of technical study, or problems such as malfunctions or failures may be found in
the field operation. The events that occur in SSCs are not concentrated at one time but may occur atvarious points in time, but here they are symbolically expressed as the systems, components, or
activities at the point in time when the problem is found. If a problem occurs at a certain point, itmeans that there is some kind of problem in the safety activities before the problem occurs, and it isimportant to deal with the problem effectively and efficiently and not waste resources. For example, it
is important to evaluate appropriately the safety importance of the error or problem that occurs,
allocate resources depending on their level of safety importance, perform post-processing, and reflect
the results on the next plan. Of course, it is also important to identify the errors or problems of highimportance beforehand, before they occur, and to implement management that pays attention to theactivities and tasks that may cause these errors or problems and make changes to eliminate theiroccurrences.
In this way, to enhance the efficiency and effectiveness of safety activities within the plant, it is10

T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

crucial to follow the approach below which involves several key steps:
 Identifying significant SSCs (Safe Shutdown Classes) and related activities in advance.
 Adopting appropriate procedures and standards.
 Planning the allocation of resources based on the importance level of activities during theplanning phase.
 Addressing problems that arise or may arise during the implementation phase, considering
their level of importance.
This approach is the same one mentioned in Section 4.1(1) above. This means that it ensures that
resources are appropriately allocated based on importance, allowing for developing and implementing
adequate safety plans for activities. It results in an overall improvement in the quality of safety
activities throughout the plant. This also can be seen in the aforementioned NRC's risk-informed (RI)
and performance-based (PB) regulation in ROP. In the former approach, risk information, including
the results of probabilistic risk assessment (PRA), is used to identify SSCs with significant safety
risks, as well as activities, operations, and measures related to them, and regulations are based on the
results. In this approach, events and problems that occur because of plant operations or safety
activities are identified, significance analyses of them are conducted, and how to deal with them is
discussed and determined, which are safety activities called PI&R (Problem Identification and
Resolution) and SDP (Significance Determination Process).
From the above, it can be understood that the idea behind both RI and PB is to improve safety byfocusing resources on high-importance areas to ensure sufficient resources, to enable careful planningand implementation of safety activities with sufficient resources, and thereby to improve the quality of
the activities.
4.2. Setting of Specific Goals (Unification of Many People's Will)To improve safety effectively and efficiently, you must set the goals of the organization for safety
activities. Because once people set goals, they tend to work hard to achieve them. It is, therefore,
necessary to introduce a system to promote this by making good use of this human trait. That is, toprevent the human traits of losing sight of goals from surfacing after a long time, the idea is to set
specific goals, create a system that forces people to strive to achieve them, and then work to achieve
the goals by running that system. In this case, performance indicators for safety activities need to berelated to the specific goals. The results should be readily accessible quantitatively and should bemonitoring the gap between the goals and actual performance. That will lead to necessary andeffective corrective actions taken. This approach avoids the human traits of having goals but notmonitoring activities on them, resulting in being forgotten and returning to regular activities. Actions
by the human system best ensure safety by continuously implementing them.
The mechanism of human activities to achieve a goal is shown in Fig. 7. This figure uses daily
human activities as an example in general discussion, but if the goal of these activities is to "ensure
nuclear safety”, they become "safety
activities", and if the goal is to "ensure
economic
efficiency",
theybecome"economic
activities”.
Maintenancemanagement activities, which are one type ofsafety activities, also have the objective of"ensuring safety and economy"[21], so eachactivity can be represented as shown in thisfigure. The same is true for other safety
activities (operation management, fuelmanagement, radioactive waste management,
radiation management, etc.).
Humans are not highly capable atholding on to a specific goal for a long timeand making steady efforts and effective
improvements. So, it is extremely importantFig. 7 Safety activities for achieving final goals
to set goals, evaluate the gap between the11

T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

current status and the goals, constantly check the gap so that we can consider how to address the gap
and continue to make steady efforts to reduce and eliminate the gap. It is also important that the goals
are specific or objective and preferably quantified. If they are broad subjective views or different
perceptions of the goals, there is a possibility of disparate thinking in an organization composed ofmany members. This leads to difficulty unifying wills and awareness and combining theorganization’s power to achieve the goal. In the case of nuclear safety, it is essential to set objective
safety goals. Once the goals have been achieved, it is necessary to continuously pursue further
progress because safety may deteriorate if we remain complacent.
Such a concept can also be found in the framework of the NRC ROP and maintenance rule
(10CFR50.69) mentioned above [22]. The ROP says if assessment reveals a situation where theregulatory standards or performance indicators are not met, the operator is required to take corrective
actions, including enforcement (Fig. 8). Similarly, the maintenance rule also requires setting thetargets for SSCs performance and monitoring SSCs performance and then requires maintenancechanges or corrective actions if the targets are not met (Fig. 9). Thus, the NRC has adopted aneffective method that considers human traits to ensure safety effectively and efficiently by setting
objective target values for safety activities, evaluating and confirming the gap between the target
values and the current status, and requesting corrective actions when necessary.

Fig. 8 Framework of USNRC reactor oversight process

4.3. Organizational Management and Roles Assignment (Mechanisms to Improve Safety)
Efficient and effective safety improvement requires an appropriate way of organizational
management and roles assignment. The contents described in the previous section 3.2 (3)"Organizational management and roles assignment", can be considered to represent the mechanism bywhich human organizations maintain and improve the safety of the plant system. To do this, the top
management of an organization sets the ultimate safety policy and goal for the entire organization.
The leaders of the organization are expected to have the leadership skills to convert the policy andgoal into specific, realistic objectives or targets; then point and drive the teams to achieve the goal andtargets. The management monitors and coordinates all related teams to ensure the smooth progress of12

T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

safety activities implemented by manymembers of the teams. The members need tohave the ability to carry out these roles. The
combination of these factors creates thedriving force to improve safety. The above
can be summarized and illustrated in Fig. 10.
Looking at this figure, it looks like a car
heading for its destination. The PDCA
(Plan-Do-Check-Act) cycle of safety
activities is an engine, which is the source ofpower; the management, which coordinates
the smooth progress of the activities, is alubricant. The leadership by leaders of theorganization, which drives the direction ofFig. 9 Framework of USNRC maintenance rulethe driving force obtained from these
activities toward the goal, is a steering wheel; and the goal set by
the top management is the destination to which the car is to go.
Each member of the organization must have the ability, skills, andexperience to carry out these roles. So, it is clear that if the factors
mentioned above are combined to achieve the goal effectively andefficiently, quickly and steadily, and the situation continues for along time. As a result, safety is greatly improved.
While it is indisputable that top management needs to set
goals, it is a difficult and important role for leaders to translate thegoals set by top management into concrete objectives, explainthem persuasively to the members under their command, andcreate the conditions for their implementation. In particular, thegoals set by leaders must be challenging ones that require new
approaches. It is also an important role of the manager to Fig. 10 Mechanism of generating acoordinate the activities toward the goals set by the leader so that driving force to achieve the goals
they can be carried out smoothly, to provide satisfactory
explanations to the members of the organization, and to create the conditions for implementation.
Manager must also assure personnel who are in charge of safety activities under the manager must
recognize their own roles and carry out their assigned tasks as quickly and steadily as possible(Fig.11). The same idea as above can be seen in the IAEA's safety culture document mentioned above(Fig.12).

Fig. 11 Relationship among the organization, positions androles of members involved, and work environment13

T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

Based on the above discussion, it can be seen that the main components necessary for improving
safety consist of "goal setting", "leadership", "management", and "PDCA", which are organicallylinked to form a mechanism that generates the driving force for improving safety.

Fig. 12 Illustration of the presentation of safety culture

4.4. Leadership and Management (Functions to Enhance Organizational Performance)
Safety activities at nuclear power plants are diverse. In addition, the number of people involvedin them is enormous. Therefore, it is necessary to work together toward a common goal, smoothly
carry out the work with an advanced division of labor, and quickly and steadily achieve the goal.
However, even if the individual members of the organization are prepared to do so, problems may
arise when they actually perform their daily work. In such cases, it is necessary for the top
management of the organization to clearly state the outlined goals and their intentions, for the leadersof the major departments to translate the goals into concrete objectives and set them, to change theway they have been doing things, and to lead the department to achieve them. In addition, themanager must have appropriate management skills to coordinate the smooth and steady progress ofthe safety activities. Finally, the engineers and workers in each department who have the ability toactually carry out the safety activities need to carry out the activities decided upon.
What is described above is the concept of how to manage an organization to improve safety andhow to clarify the roles and responsibilities of members of the organization, and how to carry out
work efficiently and achieve the goal quickly and steadily by having each person devotehimself/herself to that role. The following are the key points (Fig. 12).
+ Clarification of the direction of policies and goals for ensuring safety by the top managementof the organization+ Leadership by the leaders who set specific goals based on the above and lead the organization
toward those goals+ Management by the managers who unify the will and awareness of the many personnel who
actually carry out safety activities and coordinate with the relevant departments to ensure thatpractices proceed smoothly based on the QMS (Quality Management System)+ Many personnel who are well aware of the importance of safety and who have the will andability to do exactly what has been determined
All of these relate to the members of the organization and their roles, which are very important in
improving safety. Among them, leadership by the leaders to direct the power of many people to thedestination and management by the managers to ensure smooth and reliable activities to improvesafety are very difficult and their success or failure has a great impact on safety.
The aforementioned IAEA's "Fundamental Safety Principles" consists of ten(10) principles

14

T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants
Table 4 IAEA fundamental safety principles(Table 4) and emphasizes the leadership andmanagement to ensure nuclear safety. A focus
is placed on Principle 1 and Principle 3.
Principle 1 states that the prime responsibility
for safety must rest with the person ororganization responsible for facilities andactivities that give rise to radiation risks, i.e., it
requires the operators to assume theresponsibilities. Principle 3 states that effective
leadership and management for safety must be
established and sustained in organizations
concerned with, and facilities and activities
that give rise to, radiation risks, i.e., it requires that an effective leadership and management system
for safety be established and maintained. Especially, it states that it is important for the management
system to recognize the interaction between individuals and technology at all levels, as well as
between individuals and organizations and that operators are required to continuously improve safety
through the systems and organizations that promote safety improvement. These points clearly
emphasize the need for operators to utilize the mechanisms and organizations to promote continuous
safety improvements, as mentioned earlier. Understanding this, when revisiting Fig. 10 and 11, theimportance and role of leadership and management become much clearer, leading to a deeper
understanding of them.
According to the IAEA's GSR Part 2: Leadership and Management for Safety [23], leadership for
safety means: defining and integrating the organization's vision, goals, strategies, plans, andobjectives; leading individual safety personnel to commit themselves to protect people and theenvironment from the adverse effects of ionizing radiation; supporting the IAEA Fundamental Safety
Principles and clarifying what actions are expected of them and fostering a strong safety culture. It isalso important to support the IAEA's Fundamental Safety Principles, clarify what actions are expected,
and foster a strong safety culture. The document also states that management for safety is theestablishment and implementation of an effective management system, which defines therequirements for safety, applies them consistently with other requirements, including those for humanperformance, quality, and security, and ensures that safety is maintained to meet other requirements.
From the above, it can be seen that among "goal setting", "leadership", "management", and"PDCA for safety activities", which generate the driving force for safety improvement, "leadership"and "management" are of special importance in achieving reliable safety improvement. The members
in charge of these two roles are required to have special abilities to carry out their jobs, plus the
personality and popularity necessary to mobilize the power of many members.
If we reconsider the leadership and management based on the way of understanding shown in Fig.
10, which visualizes the safety improvement mechanism, and Fig.11, which visualizes the relationshipbetween the organization, its members' positions and roles, and the environment, their importance andmeaning will become clearer and lead to a deeper understanding.

4.5. Concentrating Resources on High-importance Issues (Graded Approach)To enhance the performance of safety activities by the human system, it is assumed that each of
the three aforementioned factors, "efficient and effective procedures", "capabilities of crew members",
and " materials/equipment/tools used", should be improved. Then, to enhance the performance of theexisting human system as a whole, it is extremely important to create an environment in which
individual members can demonstrate their capabilities. Because if a good work environment isestablished, both mentally and physically, and if work can be carried out in a comfortable manner, it
becomes possible for each individual who is responsible for safety activities to fully demonstrate hisor her abilities, and as a result, goals can be achieved quickly and steadily. The capabilities of themembers vary greatly depending on the given environment.
For many members to come together, unify their wills, and continue to carry out their roles
appropriately toward a single goal, it is necessary to establish QMS that includes a system for carrying
out works, work processes, company rules, and regulations, etc., and that these are clearly stated15

T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

within the organization and shared by the members. This is a precondition for safety activities, and if
it works, safety is improved. In addition, there is another important precondition that cannot beignored. That is the work environment.
The work environment in this context refers to the physical environment at the worksite and in
the office including human relations. The
total work environment also includes theregulatory environment created by theregulatory body (regulatory policies,
systems,
standards,
administrative
processes, guidance, decisions, procedures,practices, codes of conduct2, etc.)2. It has asignificant impact on the morale andmotivation of the licensees or operatorsand their affiliated people, as well. The
surrounding the members of safety
social environment, including criticism Fig. 13 Environment
management organizationfrom society, also has an impact. (Fig.13)
Different from machines, humans have feelings. A poor physical or mental environment can leadto poor performance. It can also lead to low morale or a decline in morale. On the contrary, however,
if a good work environment is created and it is comfortable and positive to work in, morale rises andmotivation to work increases, thus resulting in much better work performance. Such examples areoften seen and heard in the world.
The above also can apply to safety activities at nuclear power plants. If such a good work
environment is ensured, the motivation and drive of the members increase dramatically, and highperformance can be brought out, which leads to the improvement of nuclear safety. Fig. 14 shows asummary of the above.

Fig. 14 Driving force for safety improvements

5.

Conclusion

The author has long had the following concerns and has been considering how to help many
stakeholders understand nuclear safety more deeply and more easily.
 The key concepts, principles, requirements, and measures for nuclear safety established in the past
2

The NRC has developed a regulatory framework based on scientific rationality and an appropriate
understanding of human traits, and has implemented efficient and effective measures, which is believed to have
led to the safe and stable operating record of nuclear power plants in the United States. Consequently, the NRC
has gained the trust and respect of the global nuclear community. The reason for the success of the NRC's
nuclear regulation is suggested by the content of its code of conduct, the Principles of Good Regulation [24].

16T. Aoki/ Study of the Fundamental Concepts for Improving the Safetyof Nuclear Power Plants

by the many nuclear organizations, including the IAEA, are evident to be all essential to ensuring
nuclear safety. However, the underlying concepts and true intentions behind them may not always
be clear or easy to understand.
 In general, merely executing a task without adequate understanding is often insufficient to perform
it well. However, when individuals engaged in nuclear safety activities possess a thoroughunderstanding of the fundamental concepts, principles, and requirements mentioned above, they
can recognize their roles and implement their tasks with conviction, confidence, and satisfaction.
 By achieving a deep understanding of these crucial aspects of nuclear safety, it is possible to unify
the awareness and intentions of those involved, harness their collective efforts, and strive towards
improving safety. As a result, it is expected that nuclear safety will be improved.
Therefore, the author tried to clarify the matters that are important for improving nuclear safetyor the systems and mechanisms to improve safety. This was done by building on the understanding
obtained through careful analysis of the important aspects of nuclear safety and trying to give anarrative explanation (or storytelling) to this understanding and visualize it as much as possible. As aresult, the important points identified in the previous sections were demonstrated in a narrative andvisual representation, along with the following findings.
 The author focused on the mechanism for improving nuclear safety in nuclear power plants and theconditions required for safety improvement. When considering nuclear safety, the factors that havean impact on it are diverse, broad, and profound. Among these factors, it is essential to pursue andidentify the "core" elements that have a significant influence on nuclear safety, rather than gettingcaught up in the less impactful "branches." Once the essence of these factors is understood, it ispossible to pursue safety improvement without missing the goal significantly.
 Attempting to prepare for every possible crisis comprehensively and flawlessly is impossible forany organization. Overemphasizing such pursuit can lead to a situation similar to the misguided
pursuit of "absolute safety" experienced before the Fukushima Daiichi nuclear accident, ultimately
distancing us from achieving true safety assurance. Instead of getting caught up in the details, it isessential to understand the fundamental principles, approaches, and necessary minimum conditions
that serve as the "core" for ensuring safety. Once these fundamentals are secured, it is crucial tocontinuously strive for safety improvement.
 Maintaining the safety of a large-scale complex system such as a nuclear power plant for a longtime requires an organization that establishes a scope, specific goals, efficient and effective ways
or processes, tests and measures the goals are met, and fully cooperative unity among the many
managers and individuals who make up the organization.
 To prevent negative results from emerging, it is important for the leaders in the organization tounderstand the mechanism by which such results can occur in the current set-up and teamorganization and to show new directions and concrete objectives suitable for the organization.
They must constantly seek to improve safety: assign roles among the members in the organization,
improve work processes and rules, etc. for consistency with the scope and goals, and constantly
develop initiatives to improve safety rather than maintain it.
Based on the above, the author believes that further promotion of efforts, including the narrative
explanation and visualization ways discussed in this paper, will lead to a deeper understanding andacceptance of nuclear safety by all individuals involved. As a result, their awareness and intentions toimprove nuclear safety will be unified, and effective and efficient safety improvements will be
implemented to bring significant outcomes.

Acknowledgement
The author would like to thank Dr. Douglas M. Chapin, formerly of MPR Associates Inc. for his
useful advice and information on nuclear safety.

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[3] IAEA Home Page: "Culture for Safety",17

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