Publication of the Investigation Report on Improper Practices Regarding the Formulation of Design Basis Earthquake Motion in the Compliance Review for the Hamaoka Nuclear Power Plant Under the New Regulatory Standards

*The terms defined in the Investigation Report (Disclosure Version) (hereinafter referred to as “this Report”) are used as appropriate below.

In this Report, Section 4-2 (pages 72–86) provides an overview of the potentially problematic actions (hereinafter referred to as "the Acts in Question") taken by Chubu Electric Power Co., Inc. (hereinafter referred to as "Chubu Electric Power") regarding seismic motion assessment and the formulation of reference seismic motions.

With regard to the acts in question, this Committee has not determined that they were appropriate and free of issues. On the other hand, we do not consider it appropriate to simplify and concisely describe them using terms such as "fabrication," "underestimation (of seismic motion)," or "data manipulation."

The seismic motion assessment and the formulation of reference seismic motions originally planned by Chubu Electric Power are described in Section 4.1 (pages 65–72) (see Section 3 for an overview of the systems and regulations pertaining to the construction of nuclear power plants, which serve as the basis for these). Furthermore, a comparison with these is crucial when evaluating the relevant acts.

Furthermore, Section 4.3 (pages 86–126) details the specific acts in question; Section 4.4 (pages 126–174) describes the circumstances and background under which these acts were carried out; and Section 4.5 (pages 175–187) presents an evaluation of the acts in question. With regard to the acts in question, since the details of seismic motion evaluation methods are not necessarily clearly defined in laws, regulations, or other rules, evaluations are sometimes conducted from perspectives that include academic elements—such as the randomness of calculations based on random numbers or consistency with the seismic motion evaluation methods advocated by the statistical Green's function method.

Therefore, for each evaluation, not only the simple question of whether it is appropriate or inappropriate but also the perspective from which the evaluation is made (the evaluation criteria) is an important factor.

Section 5 (pages 188–221) details the internal and external observations regarding the acts in question, as well as the facts concerning Chubu Electric Power's response to them. With regard to these facts as well, the severity of the acts—which Chubu Electric Power committed without taking advantage of opportunities for correction—will vary depending on the content of the evaluation (based on the evaluation criteria outlined above).

Furthermore, in addition to the above, the inherent difficulty of seismic motion assessment itself and the complexity of that process are also relevant to the analysis of causes in Section 6 (pages 222–234) and the content of the measures to prevent recurrence in Section 7 (pages 235–244).

We would appreciate it if Chubu Electric Power and its stakeholders would review this report, taking the above perspectives into account, should the company disclose it.

Section 1 (pages 11–21) describes the composition and operation of this Committee, as well as an overview of the investigation, while Section 2 (pages 22–38) presents the facts underlying this report, including Chubu Electric Power’s compliance promotion framework and an overview of its nuclear power business.