omission or duplication and whether individual calculation codes are fully verified1-2) andmodels and data adequately validated1-3) for the purposes of the assessment.

Although performance assessment (PA) is a well-developed methodology, additional researchand development efforts are still ongoing in this field. For example, in the 1990s, theOECD/NEA published several consensus reports by international experts in this field statingthat methods for long-term safety assessment of geological disposal systems had reached analmost satisfactory level (e.g. OECD/NEA, 1991; OECD/NEA, 1997a). In this report,Japan’s geological disposal system is examined specifically in the light of this series ofactivities.

1.3 Objectives and scope of the H12 safety assessment

As described in Section 1.1, the main goal of the current stage of R&D is to establish theconcept of geological disposal in Japan in a generic context prior to site selection anddecisions on other key factors such as safety criteria. Accordingly, a range of geologicalenvironments, repository and EBS designs and safety measures are considered in the H12safety assessment.

The objectives of the H12 safety assessment are:

• To establish a reliable safety assessment methodology that is applicable to a variety ofJapanese geological environments and a range of repository designs;

• To assess the feasibility of safe geological disposal in Japan;• To provide a technical basis for site selection and development of safety criteria.

1.4 Structure of Supporting Report 3

This report consists of nine chapters. Chapter II summarizes the AEC Guidelines and safetyassessment procedures. In particular, the approach to treating a variety of alternative disposalsystems is discussed, together with consideration of the various types of assessmentuncertainties. In Chapter III, the geological disposal system defined in Supporting Reports 1and 2 is revisited briefly to make the content of the current report self-contained. Chapters IVto VII summarize key stages of the safety assessment, namely scenario development (ChapterIV), analysis of the Reference Case (Chapter V), sensitivity analysis for the EBS, geosphereand biosphere (Chapter VI), and total system performance analysis (Chapter VII). In ChapterVIII, the level of confidence associated with the assessment is reviewed from a number ofperspectives. Finally, Chapter IX presents a summary and the conclusions of this report.

1-2) Verification: ensuring that calculations associated with a particular model provide the correct results for the

assumptions made (IAEA, 1993).1-3) Validation: demonstrating, through comparison with observations, that a model adequately represents the

system to be evaluated (IAEA, 1993).