Key Point of President's Regular Press Conference
December 2012 Regular Press Conference: President Mizuno's Message
December 20, 2012
Chubu Electric Power Co.,Inc.
Today, I will be discussing two items:
- Reinforcement of Tsunami Countermeasures at Hamaoka Nuclear Power Station
- Implementation of Severe Accident Countermeasures
Reinforcement of Tsunami Countermeasures at Hamaoka Nuclear Power Station
First, I would like to talk about the reinforcement of tsunami countermeasures at Hamaoka Nuclear Power Station. If you could please look at Reference 1.
Chubu Electric Power has taken data for estimated tsunami height and so on from the second report by the Cabinet Office Committee for Modeling a Nankai Trough Megaquake, which was published in August this year, and used the Cabinet Office’s tsunami fault model to conduct a tsunami simulation.
On the basis of this simulation, we have assessed the impact that a tsunami would have on Hamaoka Nuclear Power Station.
Our objective, as we stated some time ago, was to check the Cabinet Office’s estimates and assess the impact of a tsunami on Hamaoka Nuclear Power Station by December. Since the final results of the assessment are now available, I would like to announce them today.
(Chubu Electric Power's Conceptual Approach to Tsunami Countermeasures)
Before talking about the details of the assessment results, I would like to go over Chubu Electric Power’s strategy for tsunami countermeasures once again.
If you could please look at Reference 1, the press release, section 1, “Chubu Electric Power’s Conceptual Approach to Tsunami Countermeasures.”
[Flooding Prevention Measures 1 and Flooding Prevention Measures 2]
As countermeasures for giant tsunami, Chubu Electric Power has in place sea walls and other such means to protect the power station grounds from flooding by a tsunami, as well as water barriers to protect the seawater intake pumps necessary for cooling reactor equipment in case the site is flooded by overflow from water intake chambers or other facilities connected to the sea by tunnels.
These measures to protect the power station grounds from flooding are referred to as “Flooding Prevention Measures 1.”
Also, we aim to preserve the function of all safety-critical equipment housed within buildings through measures to prevent flooding of buildings.
Even if a giant tsunami overflowing the sea wall and flooding the site should render the seawater intake pumps inoperative, this wall and other such means will as far as possible limit the amount of water entering the site, and an emergency seawater intake system (EWS) housed in watertight buildings will ensure that cooling function is maintained.
Further, the measures to prevent flooding of buildings will protect safety-critical equipment from flooding and allow prompt, reliable cold shutdown of the reactor.
These measures to prevent flooding of buildings and the emergency seawater intake system (EWS) to ensure cooling function are referred to as “Flooding Prevention Measures 2.”
[Reinforcement of emergency countermeasures]
Even if all AC power supply and seawater cooling function are lost, cooling function will be ensured by multiple alternative methods including:
(1) Redundant and diverse means of power supply including gas turbine generators installed on high ground
(2) Redundant and diverse means of water injection for reactor cooling including portable power pumps
(3) Diverse means of heat removal including remote operation of containment vessel venting
The measures are referred to as “Reinforcement of Emergency Countermeasures.”
(Assessment of Current Tsunami Countermeasures in the Light of the Cabinet Office Report)
Now I would like to go into the results of the assessment of tsunami impact on Hamaoka Nuclear Power Station. If you could please look at point 1 (1) on page 1 of the Attachment to Reference 1.
In the simulation, the tsunami’s height at the front of the sea wall is from 14.7 to 20.7 m above sea level. Standing 18 m above sea level, the sea wall will be overflowed on the eastern side of the site, but this wall will limit the amount of water entering the site.
As shown in Figure 1 (2), flooding due to overflow of the sea wall and overflow from the water intake chambers and other such facilities is to an approximate depth of 1 to 3 m (equivalent to 7 to 9 m above sea level) in the vicinity of Units No. 3 and 4, and 1 to 6 m (equivalent to 9 to 14 m above sea level) in the vicinity of Unit No. 5.
If you could please look at 1 (3). The seawater intake pumps needed for cooling the reactor are flooded, but we have determined that the following measures will enable prompt cold shutdown of the reactors even if Hamaoka Nuclear Power Station Units No. 3 to 5 are in operation at the time:
- Measures to enhance pressure resistance and watertightness of building exterior doors, etc. to prevent flooding of buildings.
- Measures to assure seawater cooling function by means of pumps inside waterproofed buildings (emergency seawater intake system (EWS))
(Reinforcement of Tsunami Countermeasures)
Next I would like to turn to the reinforcement of tsunami countermeasures.
Adopting an even more rigorous strategy for tsunami countermeasures, Chubu Electric Power will reinforce Flooding Prevention Measures 1 and Flooding Prevention Measures 2 to ensure a higher level of safety even if the maximum-size giant tsunami assumed in the Cabinet Office’s tsunami fault model occurs.
[Reinforcement of Flooding Prevention Measures 1]
If you could please look at point 2 (1) on page 2 of the Attachment to Reference 1.
For maximum protection of the power station site from flooding, the height of the sea wall will be increased from the present 18 m above sea level to 22 m above sea level.
At the same time, the height of the embankment at each end of the sea wall will be raised from 18 to 20 m above sea level to 22 to 24 m above sea level, and the height of the water barrier in the area of the seawater intake pumps will be raised from the present 1.5 to 3 m.
These measures will elimate the possibility that the tsunami assumed in the Cabinet Office’s model would overflow the sea wall.
This means that flooding within the site will be limited to overflow from water intake chambers and other such facilities, and consequently the depth of water entering the vicinity of Units No. 3 to 5 will generally be 1 m or less, and at most 2 m.
The depth of flooding in the area around the seawater intake pumps will be about 1.3 m at most, and a sea wall 3 m in height will definitely reinforce flooding prevention function with regard to the seawater intake pumps.
[Reinforcement of Flooding Prevention Measures 2]
Please look at point 2 (2).
To prepare for increased flooding within the power station grounds by a tsunami overflowing the sea wall and by overflow from water intake chambers and other such facilities, flood protection for building interiors will be upgraded.
When the tsunami in the recent simulation overflowed the sea wall and flooded the power station grounds, the maximum flood level in the vicinity of Unit No. 5 was about 5 m higher than in the vicinity of Units No. 3 and 4. Therefore, the building opening located high up on Unit No. 5 will be equipped with a new automatic closing device that has been under consideration for practical application.
Chubu Electric Power plans to complete the reinforcement of flooding prevention at the same time as the tsunami countermeasures on which work is currently under way (in December next year).
(Assessment of Earthquake Safety)
Now I would like to talk about the assessment of earthquake safety.
Please turn to page 3 of Reference 1, the press release, and look at section 4.
The Cabinet Office Committee for Modeling a Nankai Trough Megaquake issued its second report in August this year. The report examines and evaluates severe earthquake fault models and related matters, and makes corrections to these as required.
In line with any corrections made by the Committee, Chubu Electric Power will evaluate seismic motion at Hamaoka Nuclear Power Station and assess its impact on the facility.
(Dry Storage Facility for Spent Fuel)
Chubu Electric Power announced plans to construct a dry storage facility for spent fuel in December 2008. We will, however, conduct an evaluation of seismic motion at this facility before proceeding with design work.
Chubu Electric Power will engage all its resources in the sure and steady effort for tsunami countermeasures to further enhance the safety of Hamaoka Nuclear Power Station. We are also committed to providing detailed explanations of the substance of those countermeasures to contribute to the peace of mind of local residents and society at large.
Implementation of Severe Accident Countermeasures
Next I would like to address the implementation of countermeasures for severe accidents. If you could please look at Reference 2.
In addition to the tsunami countermeasures described above, and in line with its policy of raising safety standards by continuous improvement of facilities, Chubu Electric Power has now decided to implement severe accident countermeasures.
Since March this year, in light of 「Technical Knowledge about the Fukushima Daiichi Nuclear Power Station Accidents (Summary)」 published by the then Nuclear and Industrial Safety Agency, Chubu Electric Power has been considering measures to prevent large-scale radioactive material release and containment vessel damage in the event of a severe accident accompanied by damage to a reactor core.
Consequently, we have decided to install filter vent equipment and an alternative water injection system.
Construction for these measures is anticipated to take about two to three years.
Chubu Electric Power will engage all its resources in the sure and steady effort to further enhance the safety of Hamaoka Nuclear Power Station. We are also committed to providing detailed explanations of the substance of those efforts in order to contribute to the peace of mind of local residents and society at large.
That concludes my remarks for today.