Building technical and social confidence in the safety of geological disposal in Japan

Abstract

Geological disposal has been adopted as the most feasible option for the method of long-term management of high-level radioactive waste (HLW) in every country in the world, regardless of the pros and cons of the nuclear power generation. Building stakeholders’ confidence in safety of geological disposal is indispensable to reach the point where the implementation of geological disposal is accepted by the current generation. The safety case is a key input to build confidence in geological disposal stepwise as the program progresses and regarded to play an important role as a common platform in the communication among stakeholders.

The aim of this paper is to review arguments relevant to building technical and social confidence in the progress of Japanese research and development activities as well as international discussions.

Keywords:

• geological disposal
• confidence building
• safety case
• stakeholder involvement
• high-level radioactive waste
• reversibility and retrievability
• radioactive waste management
• safety assessment

1. Introduction

High-level radioactive waste (HLW) management is a common issue in all countries promoting the development and utilization of nuclear energy. The eventual safe disposal of HLW is a necessity with or without any further construction of nuclear power stations. Since the first discussion in the United States in the 1950s, geological disposal has been adopted as the most feasible option for the method of long-term management of HLW in every country in the world. Even though concepts and programs differ from country to country, it is widely recognized in these countries that decision-making and social acceptance of such geological disposal depends entirely on the level of confidence in its ability to provide adequate protection of humans and the environment at all future times, where “confidence” is the feeling that you are certain that it will happen in the way you want it to. The evaluation and evidence for such long-term safety are compiled and documented in the safety case.

Safety assessment forms a central part of the safety case and its analyses must be conducted over timescales far beyond the normal horizon of social and technical planning. Such assessments must demonstrate convincingly the long-term safety of the geological disposal system prior to its implementation. The aim of this paper is to review arguments relevant to building technical and social confidence in the progress of Japanese research and development (R&D) activities as well as international discussions.

2. Importance of the confidence building in the implementation of geological disposal

International documents reflect the strong international consensus among relevant technical communities that geological disposal is technically feasible and it can be made safe for current and future generations [1–6]. This is supported by the extensive experimental data accumulated for different geological formations and engineered materials (e.g. [7–15]), and by the safety assessment of potential disposal systems (e.g. [16, 17]). There exist unavoidable limitations in the knowledge that scientific investigation can provide about the geological setting, the durability of engineered barriers and future human behavior. These limitations can be reduced but not entirely eliminated by further research. However, since different uncertainties give different potential consequences, careful and extensive analyses of uncertainties can allow most of overall doubts to be resolved. Today, it has begun to be recognized within the waste management community that confidence in the predicted safety by safety assessment could be enhanced by ensuring the robustness of the system concept, the quality of the assessment methodologies, and the adequacy of the development strategy (i.e. such as stepwise and reversible decision-making process), and that decision should be made based on the level of confidence attained at each decision point [18]. In other words, living with unresolvable uncertainties is inevitable in every practices and the issue is whether the level of knowledge is adequate to provide the necessary scientific input to the social decision-making at each stage in the stepwise development process [19, 20].

On the other hand, Japan and other countries, whose disposal program moves into the phase of identifying sites for geological disposal, have encountered a serious difficulty in achieving public support [20]. Some members of the public do not trust not only the ability of experts to understand the future behavior of geological disposal system but also organizations and process involved in HLW management. This segment of the public consequently is opposed to ending active control of the waste, even though its continued management may be a burden on future generations. Building social confidence to overcome such public objections and distrust has become a central part of the waste management process and it has been pointed out that national HLW program should expand their efforts beyond technical project development and implement processes that involve stakeholders [20]. Stakeholders mean any person, group, or organization with a role to play or an interest in the process of deciding about radioactive waste management in the decision-making [4].

Confidence in multiple dimensions of safety must be assured to obtain total confidence in overall geological disposal program. Technical confidence in scientific understanding, which is a prerequisite for and must precede confidence building in non-technical general public, is developed through research and assessment. The relevant information must be compiled and documented in a transparent and traceable manner [21–24]. Also, some social concerns expressed in regard to waste management process may stem from damaged trust or eroded confidence in operating or managing institutions. Thus, building confidence implies that institutions must develop appropriate features in terms of organizations, mission, and behavior. As organizational features, independence, clarity of role, dedicated and sufficient funding, a not-for-profit status, and high levels of skill and competence in relevant areas are required. As mission features, a clear mandate and well-defined goals, a specific management plan, and a well-founded and articulated identity are required. As behavioral features, openness, transparency, honesty, consistency, willingness to be tested, recognition of limits, commitment to a highly devoted and motivated staff, and coherence with organizational goals are required [4].

The safety authorities or regulators are responsible to protect the public health and the environment. Given the highly public nature of the endeavor to find the solution for HLW, the safety authorities or regulators are expected to play an important role beyond the conventional role of simply defining regulatory requirements and guidance for commercial enterprises. Their expected role of providing stakeholders with understandable explanations of the mechanisms of regulatory oversight and decision-making will be more and more important to maintain open and impartial regulatory processes.

Overall, geological disposal of HLW should be taken not only as a technical endeavor but also as a social endeavor. For the social decision-making under the existence of scientific and social uncertainties, a consensus must be reached not only among experts such as technical specialists engaged in the implementing and regulatory organizations and the wider scientific community, but also among various stakeholders with different sense of values. Thus, since communication between various stakeholders is indispensable for this formidable problem solving, important changes must take place in public participation, where dialogue and stakeholder involvement become a central part of the waste management process.

3. Safety case as a tool for confidence building in the safety of geological disposal

In the real world, every act is carried out under the presence of uncertainty since it is impossible to know exactly what will happen in the future and there is no telling what another person is thinking. People, however, do not care all the uncertainties encountered in their lives but care the uncertainties in their prediction only when the consequence has an important value for them.

To assess the influence of geological disposal on humans and the environment, a spatial extent to several kilometers and timescales beyond 10,000 years to a million years usually have to be considered. It has been pointed out that it is impossible to describe fully the future evolution of an open system, such as a repository and its environment. They cannot be completely characterized and may be influenced by natural and human-induced factors outside the system boundaries. A complete description or absolute proof of safety cannot be and is not, however, a requirement of decision-making in repository development. Alternatively, there are requirements to be considered in the decision-making. One requirement is that a description of the possible evolutions of the system has been compiled so as to give adequate confidence in safety. Another requirement is that an efficient strategy has been prepared for the future stages so as to deal with any uncertainties in the description that have the potential to compromise safety. Furthermore, flexibility should be built into the process of repository development, allowing account to be taken of new understanding and technical information, as well as the demands of societal review.

The process of analyzing the performance of a repository and showing, with an appropriate degree of confidence, that it will remain safe over a prolonged period, beyond the time when active control of the facility can be guaranteed, is termed post-closure safety assessment. The OECD/NEA has compiled the state-of-the-art methods on safety assessment of geological disposal [22,24]. They stated that safety assessment methods are available to evaluate adequately the potential long-term impacts of waste disposal systems. In the safety assessment, a wide range of features, events, and processes (FEPs) are potentially relevant over this wide range of space and timescales. Therefore, an assessment of the performance of a repository can only be undertaken by simulation of the potential evolution of the repository system using mathematical or numerical models. The concept of scenario, which is a description of a potential specific evolution of the repository system from a given initial state, is used for the assessment. Scenarios describe the compilation and arrangement of safety relevant FEPs as a fundamental basis for the assessment of post-closure safety which includes assessing the potential consequences on humans and their environment. The uncertainties considered for a geological repository, such as those caused by the randomness or unpredictability of certain events, the natural variability of geological media and the biosphere, the lack of characterization of processes, and the limited possibility to forecast distant-future biospheres and human habits, imply a broad range of the possible evolutions of the system over the very long timescales considered in safety assessment. However, the use of scenarios enables investigation of the impact of distinctly different sets of FEPs (e.g. to represent climate evolution, human intrusion, early canister failure, or seal defects) to see if and how they might impact on repository safety. Through this type of analysis, performance assessment results can usually be condensed into a handful of typical and variant scenarios.

The discussion on the uncertainties involved in the post-closure safety assessment naturally resulted in the emphasis that the document which claims safety of geological disposal should not only assess compliance with quantitative radiological criteria but also should demonstrate that the design of the overall disposal system including site characteristics is robust (low impact of detrimental phenomena) and that its behavior and evolution is well understood, by showing why the selected scenarios, models, and data are sufficient for the safety assessment, why other scenarios (i.e. volcanic activities, microbiologically influenced corrosion, etc.) can be excluded in the consideration, how natural analogues support the proposed scenarios, and how the residual uncertainties are treated in the following steps, etc. In this way, the scope of the safety assessment has broadened to include the collation of a broad range of evidence and arguments that complement and support the reliability of the results of quantitative analyses. The broader term “post-closure safety case” or simply “safety case” is used to refer to these studies [21].

It has also become obvious that repository development will involve a number of stages punctuated by interdependent decisions on whether and how to move to the next stage. These decisions require a clear and traceable presentation of technical arguments that will help in gaining confidence in the feasibility and safety of a proposed concept. The depth of understanding and technical information available to support decisions will increase in a stepwise manner. The safety case is a key input to support the decision to move to the next stage in repository development. It reflects the state and results of R&D undertaken at a certain stage, and informs decisions concerning future R&D efforts. This aspect of the safety case as a tool to aid decision-making in a stepwise repository development has been formulated in the safety case and safety assessment flowcharts given in the NEA report [24], where safety assessment is placed in the context of safety case which in turn is placed in the context of the stepwise progress of the geological disposal program.

4. Progress of R&D program for the geological disposal in Japan

4.1. Major turning point of Japanese R&D program

Japanese R&D program of geological disposal has been conducted focusing HLW (vitrified waste) generated during the reprocessing of spent fuel from nuclear power plants. The R&D for TRU-waste (low-level radioactive waste generated during reprocessing and MOX fabrication) has been conducted following the concept of geological disposal for HLW.

With respect to HLW, as specified in the 1976 statement of the Japan Atomic Energy Commission (JAEC) [25], geological disposal has been targeted as the most promising option and the technical feasibility of geological disposal was considered to be investigated first. The 1980 report by Advisory Committee on Radioactive Waste Management (ACRWM) of JAEC proposed a plan for R&D [26] consisting of five phases as:

1.	general evaluation and selection of the geological formation feasible for geological disposal based on the examination of the geological formation, natural, and social factors;
2.	selection of test site through the precise examination including borehole drilling of the hopeful geological formation;
3.	establishment of geological disposal system through in situ experiments with using simulated waste form;
4.	in situ experiments using radioactive waste form to establish geological disposal system;
5.	emplacement of the real waste form and starting of the pilot disposal.

The selection of appropriate site was left to Power Reactor and Nuclear Fuel Development Corporation (PNC). This rather optimistic procedure, taking the step of finding a good site or geological formation first and then develop the disposal system comply with its environment, was common to many national programs at that time. In every country, however, this type of siting procedure had never been proceeded smoothly due to the immature rough-and-ready disposal concept and non-transparent program management.

An important policy change occurred when ACRWM indicated the guidelines for revised R&D strategy in 1989 [16]. It was stated a major direction that greater priority should be given to the comprehensive, site generic performance assessment studies and following targets have been set:

1.	detailed analyses of Engineered Barrier Sub-system performance and the near-field geological environment of the repository package;
2.	analyses of the far field and the compliance with requirements of total system performance.

The guidelines also indicated the need for integration of R&D results to discuss the feasibility in generic terms for HLW disposal in Japan, which in turn promotes understanding of geological disposal in both the scientific community and the general public.

4.2. Comprehensive progress reports – H3 and H12

Following the 1989 ACRWM guidelines, PNC conducted R&D for the feasibility of generic geological disposal system based on multi-barrier design, where neither a particular type of rock nor a particular area but wider ranges of rock type and geological formation were considered. The major component of overall barrier performance of the disposal system is borne by the near field, while a geological environment is defined that reinforces and complements the performance of the engineered barrier system (EBS). A very massive EBS is introduced to ensure long-term performance of the disposal system for a wide range of geological environments. Based on these results, PNC published a comprehensive first progress report on R&D in 1992 [28]. The report is known as H3 and supports the following major points.

1.	A sufficiently stable deep geological environment to ensure the performance of the multi-barrier system can be found in Japan, even though the country is located in a tectonically active zone.
2.	The repository can appropriately be designed and constructed based on presently available engineering technologies.
3.	Long-term safety can be ensured, based on the performance of the multi-barrier system, with particular emphasis on near-field performance provided by a massive EBS, taking into account the complex geology expected in Japan.

It is broadly acknowledged, even in the general public, that the active tectonic setting and complexity of geology are the most critical issues for the technical feasibility of geological disposal in Japan. The results of H3 were, therefore, carefully reviewed by the JAEC to identify the future direction of the HLW disposal program. The review confirmed that the “near-field approach” with a massive EBS, developed as a Japan-specific approach, is appropriate in order to make the safety case. It was, however, also pointed out that this report lacked sufficient information on geological environment and thus the JAEC concluded that further generic R&D activities were needed to increase confidence in the technical basis for disposal and thereby increase flexibility in future siting.

To meet these requirements, R&D work after H3 focused on development of detailed and realistic near-field models and on improving the understanding of key processes and corresponding databases, taking into account a wide range of geological conditions. In the R&D program by the Japan Nuclear Cycle Development Institute (JNC, successor of PNC), three major areas of research were set up following the JAEC Guidelines given by Advisory Committee on Nuclear Fuel Cycle Backend Policy (ACNFC) [29] as:

1.	evaluation of the geological environments for hosting a repository,
2.	engineering technology for a repository and EBS design, and
3.	performance assessment of the disposal system.

The second progress report (referred to as H12), also a generic feasibility study, was submitted to the JAEC in November 1999 [30]. In order to give confidence in the technical feasibility of the repository system, H12 has provided more detailed analyses to demonstrate how the intrinsic safety functions of the repository design, supported by appropriate quality assurance procedures and careful site selection, could provide a robust safety case. It included:

1.	specifying the existence of geological environments that are stable over appropriate timescales and provide favorable conditions for EBS performance and for the radionuclide retardation function of the geosphere,
2.	illustrating an appropriate design for containment and retardation of radionuclides in the EBS for a wide range of geological environments, and
3.	providing results of performance assessment to estimate the long-term reliability of the repository system for a number of different geological settings.

Differently from H3, the process of H12 integration was stepwise and opened to the public to build confidence by ensuring its transparency and eliciting opinions from a wider audience. The H12 was reviewed in a stepwise manner during its documentation. The draft of H12, in Japanese, was prepared based on comments and discussions concerning the preliminary draft, as well as on the results of R&D obtained after the publication of the preliminary draft. The draft consists of a project overview report and three supporting reports that cover the three major fields described above. These documents were submitted to ACNFC and opened to the public to further solicit comments from Japanese experts in various fields. It was also required in the ACNFC Guidelines that, to assure quality, the draft H12 be reviewed by international experts before submission of final reports to the Japanese Government. In compliance with the ACNFC Guidelines, JNC requested the OECD/NEA to carry out an independent, international peer review of the draft H12 Project Overview Report [20]. Taking account of the review comments made by these reviews, JNC finalized the H12 and submitted it to the JAEC.

Judging the technical achievements in H12 and activities for public understanding, government decided for Japanese geological disposal program to move into implementation phase. The “Specified Radioactive Waste Final Disposal Act (referred to as Final Disposal Act)” was promulgated in June 2000, that established the framework for the geological disposal of HLW, such as implementing organizations, financing, and stepwise site selection processes except safety regulation [21]. Based on this act, the implementing organization, the Nuclear Waste Management Organization of Japan (NUMO) was established in October 2000 to conduct the necessary steps for the geological disposal of HLW. The Act also specified that the site selection would proceed in a stepwise manner as follows.

1.	At first, the preliminary investigation areas (PIAs) are chosen on a nationwide basis by literature survey focusing on the long-term stability of geological environment.
2.	Subsequently, areas for detailed investigation (DIAs) are selected among PIAs and surface-based investigations will be conducted to characterize the geological environment as to host a repository.
3.	At the final step, the disposal sites will be defined out of DIAs by confirming the suitability from underground to obtain critical information of the geological environment for making the decision.

According to this specification, NUMO decided to solicit volunteer municipalities for selection of PIAs and made an official announcement on the commencement of open solicitation program in December 2002.

Based on the second progress report for TRU-waste published in 2005 by the collaborated team of the Federation of Electric Power Companies of Japan (FEPC) and JNC, the Final Disposal Act was amended in 2007 to provide a framework for management of TRU-waste requiring geological disposal. In 2008, NUMO was designated as the authorized implementing organization for geological disposal of TRU-waste, in addition to its original mission of HLW disposal.

4.3. Trend of R&D in the implementation phase

Since demonstration of robustness and confidence in scientific understanding of the future evolution of geological disposal system in the post-closure safety case has unique importance and special difficulty [6,18], unlike to simply showing the compliance with quantitative criteria, continued efforts have been devoted to this subject by NUMO, Japan Atomic Energy Agency (JAEA, successor of JNC), and Nuclear Safety Commission of Japan (NSCJ).

In TR-04-03 and TR-04-02, NUMO, as an implementing organization, developed and described the “Repository Concept” which includes not only the design and layout of the disposal system but also the associated evaluation of operational and long-term safety and an assessment of socio-economic aspects. It also clarified that a volunteering approach to siting should be constrained by the use of “Siting Factors” which ensure that only locations which have sufficient geological stability are considered – an important factor in a country like Japan which lies in a tectonically active region [33, 34].

In CoolRep H22, JAEA, as a scientific/technical supporting organization, has started a trial to construct knowledge management system (KMS) which compiles enormously large amount of relevant state-of-the-art evidence, analyses, and arguments for safety case in a structured, transparent, traceable, and interactive manner for various scientific stakeholders [35].

NSCJ discussed the appropriate regulating manner to judge whether sufficient attention is paid for the robustness of long-term safety functions in the disposal facility, by taking into account the associated uncertainty of long-term predictions on potential risk of the radioactive waste to be disposed of. As a means to ensure this robustness, the policy of risk-based safety assessment was shown, and the specific system of safety assessment was consolidated for the sub-surface disposal [36–38]. After that, the concept of risk-based safety assessments was expanded to pit disposal and trench disposal, and compiled into “Basic Guide for Safety Review of Category 2 Radioactive Waste Disposal” [39].

4.4. Review of the confidence-building process in the Japanese program and the consequence of the H12 and other reports as safety cases

After the failure of the approach in early 1980s intended to directly demonstrate the feasibility of geological disposal at a selected site, Japanese HLW disposal program has been undertaken by generic R&D studies, without discussion of siting and institutional frameworks. This approach was to some extent motivated by the need to consider the geological features specific to Japan and the need for answering key technical questions relevant to these features. As compared with the approach taken by Western countries which take a procedure first to select promising site and next to develop a technique to adapt the selected site, the Japanese generic R&D approach in the early stages of the repository program seemed rather tardy by taking a detour. When considered in retrospect, however, this approach was unavoidable for Japan and the experience to integrate wide-ranging fundamental scientific information into a comprehensive report played an important role in technical confidence building and fostering of human resources. Thus, it may be said that H12 successfully provided a scientific foundation for subsequent phases moving smoothly toward implementation. In other words, the strategy taken at that time for confidence building had worked successfully.

On the other hand, ever since the NUMO's open solicitation of PIAs, all the interests in the application expressed by the mayors of several municipalities were withdrawn immediately after they were publicized by the media, forced by strong objection of some part of the public. Moreover, Science Council of Japan (SCJ) has recently expressed, in the answer to JAEC [40], his distrust of geological disposal program and relevant technical community as well as of the technical confidence obtained in H12, due to the fact that there still exist some scientists who do not agree with H12 about the stability of geological environment in Japan.

H12 had been prepared without being conscious of the concept of the safety case. After the time of the report, the concept of safety case has been intensively developed by OECD/NEA and other organizations. Considering the smooth shift from feasibility study phase to implementation phase and the later deadlock situation, it is meaningful to reflect on the shortages of H12 from the viewpoint of the requirements which are essential in a safety case.

When evaluated as a safety case, H12 lacked in the “purpose and context” section to include discussions on the technical and ethical basis for the selection of geological disposal as a long-term solution for HLW management. Without recognizing the social necessity for HLW to be disposed of in deep underground, hearing the explanation of the safety of the geological disposal may naturally let people feel distrust of the motivation of proponent, which, in turn, may even lead to distrust of technical confidence. Also, post-closure long-term safety has been more or less exclusively discussed without much discussing the safety in the operational period. Since NUMO is soliciting volunteer municipalities, safety in near-future operating phase is important and meaningful for the current generation, as well as the safety in the far future. Moreover, although the containment performance of the multi-barrier geological system was assessed in a quantitative manner by using the groundwater scenario, the isolation performance against natural events and processes and intrusion by future generations may be more important to be explained for the general public since the main concerns of the people in Japan, which is located in a tectonically active zone, are disruptive events such as earthquake and fault activity, volcanic activity, uplift, subsidence, denudation, and climatic and sea-level changes, as well as their effects on the geological environment. Last but not least, in 10 years after H12, there have been no compiled safety cases prepared to include many important updated scientific knowledge and technical information obtained by the R&D activities, carried out at many organizations including activities at Horonobe, Mizunami underground facilities. This might have caused a break for the continuous information provision to stakeholders which is a fundamentally important element to increase the technical confidence in geological disposal.

On the other hand, the importance and difficulty of getting social confidence has been recognized, not only limited in Japan but also in Western countries. National Academy of Sciences of USA has pointed out that difficulties in achieving public support have been seriously underestimated in the past, and opportunities to increase public involvement and to gain public trust have been missed. It has also pointed out that, since complex factors drive the high levels of public concern and lack of confidence in HLW management programs apparent in most countries, demonstrating reversibility of actions in general, and retrievability of wastes in particular, are highly desirable because of public reluctance to accept irreversible actions. Retrievability provides public reassurance that one is able to deal with surprises [20].

5. Challenges to enhanced dialogue and stakeholder involvement

Since long-term radioactive waste management inevitably involves the construction of disposal facilities in a limited number of areas, social agreement among national and local publics must be pursued through the discussion on the strategic choices and confidence in the safety of the long-term management of HLW. As seen in successful or unsuccessful experiences in many Western countries, people begin to show an interest or concern in geological disposal when mass media convey news reporting the conflict between the implementing organization and local/regional residents. In such a stage, all the stakeholders including policy-makers, safety authorities, scientific experts or consultants, implementers, potential host communities, elected local or regional representatives, and waste generators will be involved and necessarily have to communicate each other in order to solve “Not In My Backyard” (NIMBY) problem. Before such stage, as in the current situation in Japan, participating stakeholders are considerably limited. To involve public for confidence building at the national level, a design or framework for social learning should be facilitated. Setting an occasion for interactive communication between various stakeholders and specialists may be considered more effective and valuable to attract public interest than traditional public information if participants succeed in sharing the same incentive.

Because technical confidence in the safety must be established through R&D by experts before the implementation in the society, the largest “information asymmetry” [41, 42] lies between relevant experts and non-expert stakeholders when site investigations are initiated, or when actions are taken to locate a facility in a specific area. In this situation, technical confidence in the long-term safety of the disposal system in deep underground environment depends solely on the prediction based upon the scientific understanding of the extremely gradual evolutions of the geological and technological components of the system. As a result, experts cannot communicate with non-experts with the “seeing is believing” strategy such as direct demonstration and analogies or heuristics by everyday experience. Moreover, in everyday social business transactions, information asymmetry is known to give numerous cases of illegal practices such as manipulation of information or moral hazard.

From a viewpoint of general public with limited information, therefore, they cannot share the expert's confidence nor incentive and they do not trust organizations and process involved in HLW management. Moreover, as pointed out in the report by SCJ, the problem is difficult to set entirely apart from the practices that produce such waste. As a result, disfavor against technocratic or “top-down” approaches to implementing waste management solutions leads to the strong public rejection [4].

Thus, for the non-expert stakeholders in the existence of information asymmetry, both lack of the technical confidence in the safety of geological disposal system and lack of the trust in waste management organizations and/or other actors of national programs equally contribute to the uncertainties which may compromise broader sense of safety for the public. Opposition to ending active control of waste, therefore, may be interpreted to be rooted in this social distrust [43]. The concept of geological disposal is to contain HLW in deep underground and permanently isolate from the human environment. However, when people do not fully trust management organizations and other actors, and cannot have enough technical confidence in the ability of geological disposal system to contain and isolate HLW, they would worry about the future unexpected situation and absence of the responsible organization to deal with the surprise.

Therefore, focus of the communication should move away from former technocratic approach, or “DAD (decide, announce and defend)” model, for which the focus is almost exclusively on technical content, to one of “EIC (engage, interact and co-operate)” model, for which both technical content and quality of process, or social content, are equally important to a constructive outcome [4]. Since the goal of the communication is for the society to reach the solution for HLW, it should aim at all participating stakeholders to encourage “informed and comparative judgment”. Also, stakeholders’ concerns should be discussed with precedence, where how to cope with the insufficiency in the technical and social confidence is by far the most important.

In this context, the NSCJ pointed out the importance to create a “safety communication” mechanism that enables stakeholders to participate in a process of enhancing confidence in the long-term safety when building confidence in the safety of geological disposal [44]. Also, for the promotion of safety communication, the NSCJ pointed out that it is important to establish the safety cases, which are meant to gradually increase confidence in the safety of geological disposal, as a common platform for building confidence among stakeholders, and actively utilizing it to minimize the information asymmetry potentially existed among respective stakeholders. Another important aspect in the safety communication is to present clearly the safety case along with how reversibility and retrievability (R&R) are sustained at each stage during the period until the stakeholders understand and accept the closure of a disposal facility. “Reversibility” means the possibility to reverse a certain specific stage or several stages related to planning and implementation, to the previous stage at any phases of the process throughout the course of disposal business. “Retrievability” implies the possibility to physically return back the emplaced waste, and this is the means of ensuring reversibility after the waste has been emplaced in the underground [45, 46]. Geological disposal intends to ensure that HLW remains permanently isolated from the human environment and inaccessible to man. However, there are possibilities that the disposal stage is reversed from the viewpoint of safety, technology, economics, or society, or that the decision is made to retrieve the waste. The responsibility of today's society is to maximize the safety of future generations while imposing minimum future burdens. Thus, to what level and until when R&R are sustained depend on the level of technical and social confidence perceived by the society as a whole. They should be decided not by the technical expert but by the society. In the same way, to what level and until when various means of passive and active oversight, i.e. watchful care, such as institutional controls, monitoring and surveillance, keeping archives, markers, etc. should be or is expected to be effective should be also intensively communicated.

6. Concluding remarks

The management of HLW is a multi-dimensional question that is difficult to set entirely apart from the practices that produce such waste, and impossible to reduce to a few simple issues. While proceeding to geological disposal is a technical endeavor, planning for it and overseeing its implementation include more than just technical aspects. Since the decision is to be made not by the technical experts but by the society, the participation and the communication of relevant stakeholders including policy-makers, safety authorities, scientific experts or consultants, implementers, potential host communities, elected local or regional representatives, and waste generators are indispensable for the success of the scheme.

Among other things, a politician's role is the most critical for the solution of this formidable and complicated problem. Since the stakeholders to be involved are not specifically identified yet in the current stage in Japan, nationwide consensus building on the implementation of disposal program requires extensive social activities which take full advantage of expert's scientific and technical knowledge. In such a scene, active involvement of politicians who have full of a sense of responsibility with foresight and courage is highly expected.

Acronyms

ACNFC	=	Advisory Committee on Nuclear Fuel Cycle Backend Policy
ACRWM	=	Advisory Committee on Radioactive Waste Management
DIA	=	detailed investigation area
EBS	=	engineered barrier system
FEP	=	features, events, and processes
FEPC	=	Federation of Electric Power Companies of Japan
HLW	=	high-level radioactive waste
JAEA	=	Japan Atomic Energy Agency
JAEC	=	Japan Atomic Energy Commission
JNC	=	Japan Nuclear Cycle Development Institute
NUMO	=	Nuclear Waste Management Organization of Japan
PIA	=	preliminary investigation area
PNC	=	Power Reactor and Nuclear Fuel Development Corporation