Press Release Back Number(2006)

Plants subject to assessment are all Hamaoka reactors, from No. 1 through No. 5.

Equipment / piping systems and buildings / structures subject to assessment will be those defined as S Class in the new seismic durability guidelines, with a focus on safety functions, including the ability to shut off, cool and isolate reactors. Certain B and C Class facilities are also subject to assessment, namely those that have effects on S Class facilities if they are damaged. Table 1 provides an overview of subject facilities, as chosen based on this policy.

Table 1: Overview of facilities subject to assessment (same for Reactors No. 1 - 5)

Chubu Electric will perform its assessment in keeping with the September 20, 2006 document "Basic Stance, Assessment Procedures and Confirmation Standards for Assessing and Confirming Seismic Safety of Existing Power Reactor Facilities, etc. in Light of New Seismic Durability Guidelines" (below, the seismic safety assessment procedures), which was attached to the agency's instructions.

The assessment will first decide on a standard ground motion Ss as based on "the decided ground motion with identified center for each site" and "the decided ground motion without identified center". Next, to assess the seismic safety of facilities, etc., we will check to make sure that in the event of standard ground motion Ss, the foundation ground will provide sufficient support, that buildings / structures, equipment / piping systems and important outdoor structures will remain safe, and that facilities will remain safe against earthquake-caused phenomena.
(Refer to Fig. 1, Overall flow of seismic safety assessment.)

Fig.1: Overall flow of seismic safety assessment

Assessment results will be reported to the agency in this reactor order: No. 3 and 4, No. 5, and No. 1 and 2. The assessment process is planned to follow this schedule.

*The period to decide on the standard ground motion Ss is included in this process. Assessment of "residual risk" will be done separately, so that period is not included here.

• • S Class:
  Pertaining to equipment that contains radioactive materials itself or is directly connected to facilities that contain radioactive materials, and which could leak the radioactive material if it malfunctions; equipment needed to prevent this situation from happening; and equipment needed to mitigate the impact of leaked radioactive material in the event this situation happens, when the impact of any of the above equipment is great. (examples: control rods, reactor cooling equipment, reactor pressure containers, etc.)
• • B Class:
  Pertaining to equipment with a relatively small impact in the above. (examples: waste treatment equipment, main steam turbines, etc.)
• • C Class:
  Equipment other than S Class and B Class, needing only to maintain the same level of safety as ordinary industrial equipment.
• • Decided ground motion with identified center for each site:
  Of earthquakes occurring in the area of the site, decided ground motion when studying characteristics of past earthquakes, active faults and plates and assessing earthquake patterns.
• • Investigated earthquake
  An earthquake predicted to have a major impact on the site, selected to help decide on the "decided ground motion with identified center for each site."
• • Ground motion assessment with response spectrum technique:
  A method of assessing ground motion based on the relationship between earthquake magnitude and distance from its center.
• • Ground motion assessment with fault modeling technique:
  A method of assessing ground motion based on modeling the fault movement that causes the earthquake.
• • Decided ground motion without identified center:
  Ground motion that should be considered in all cases, regardless of results of detailed surveys in the vicinity of the site. This is because even detailed studies that take vicinity conditions sufficiently into account cannot be claimed to be able to assess in advance all earthquakes in the continental crust that could potentially occur in the vicinity of the site.
• • Standard ground motion Ss:
  Ground motion that is extremely rare but possible within the useful life of a facility, as seen in terms of seismology and seismic engineering (including considerations of geology, geological structure and earthquake activity in the vicinity of the site), and of which it is appropriate to anticipate major impact to facilities.
• • Reactor building foundation ground stability assessment:
  An assessment of whether the ground supporting buildings and structures containing equipment essential to seismic design have sufficient capacity to support those buildings and structures in the event of the seismic force of standard ground motion Ss.
• • Seismic safety assessment of important safety-related buildings / structures (equipment / piping systems / important outdoor structures):
  An assessment, based on "seismic safety assessment procedures," of whether important safety-related buildings / structures (equipment / piping systems / important outdoor structures) have sufficient safety function in the event of standard ground motion Ss.
• • Consideration of earthquake-caused phenomena (stability of area slopes):
  An assessment of the risk of the facility's safety functions sustaining major impact in the event of conceivable landslides in area slopes during an earthquake.
• • Consideration of earthquake-caused phenomena (safety during tsunamis):
  An assessment of the risk of the facility's safety functions sustaining major impact in the event of tsunamis, though they may be extremely rare but should be considered possible within the useful life of a facility.