Reinforcement of Tsunami Countermeasures at the Hamaoka Nuclear Power Station
December 20, 2012
Chubu Electric Power Co.,Inc.
Chubu Electric Power Co., Inc., has used the tsunami fault model from the Cabinet Office to conduct a tsunami simulation in light of data related to estimates of tsunami height and other such matters provided in connection with the second report by the Committee for Modeling a Nankai Trough Megaquake of the Cabinet Office, published in August 2012. This simulation was further used to assess the impact that a tsunami would have on Hamaoka Nuclear Power Station.
As a result, it was confirmed that prompt cold shutdown of the nuclear reactor will be possible given the tsunami countermeasures that are presently underway.
In addition, Chubu Electric Power is committed to even more thoroughgoing pursuit of our approach to tsunami countermeasures announced in July 2011, consisting of Flooding Prevention Measures (1), Flooding Prevention Measures (2), and Strengthening of Emergency Countermeasures. This initiative addresses tsunami under the Cabinet Office tsunami fault model, which are the largest type of giant tsunami (hereafter "tsunami on the Cabinet Office model"), and we will continue to put overlapping countermeasures in place to further heighten safety.
We are therefore announcing the results of the recently conducted assessment of the Current Status of Tsunami Countermeasures together with the reinforcement of tsunami countermeasures that we will be undertaking.
1. Chubu Electric Power's Conceptual Approach to Tsunami Countermeasures (Reported on July 22,2011)
Chubu Electric Power is addressing the issue of giant tsunami by "prevention of flooding within power station sites due to tsunami by sea walls and other such means, and also by using sea walls to protect seawater intake pumps (placed outdoors), which are necessary for cooling reactor equipment, from flooding that occurs on the grounds due to overflow from intake chambers and other facilities that are connected to the sea by tunnels" (Flooding Prevention Measures (1)). We also employ "flooding prevention measures inside buildings to prevent flooding of indoor equipment that is critical to safety" (Flooding Prevention Measures (2)). Our aim in doing so is to maintain the function of all equipment that is critical to safety.
We are further taking steps to provide against the eventuality of flooding within the grounds even if a giant tsunami overruns the sea wall or other such measures so that the seawater intake pumps placed outside buildings lose their function. This is being accomplished by doing everything possible to increase the effect of sea walls and other such means to limit the amount of flooding within the grounds. The idea is to promptly and safely bring about the cold shutdown of the reactor by "assuring cooling function by the installation of emergency seawater intake system (EWS) inside waterproof buildings to function in place of seawater intake pumps, and by preventing the flooding of equipment inside buildings that is critical to safety by means of measures to prevent flooding inside buildings" (Flooding Prevention Measures (2)).
Even in the event of a total loss of all AC power supply and seawater cooling function as occurred at Fukushima Daiichi Nuclear Power Station, cooling functions will be assured by these means: "(1) Providing for redundant and diverse power supply, to include the installation of gas turbine generators on high ground; (2) providing for redundant and diverse means of water intake for reactor cooling using portable power pumps and other such means; and (3) providing for multiple alternative methods to diversify the means of heat removal, such as by enabling remote operation of containment vessel venting" (Strengthening of Emergency Countermeasures).
2. Assessment of the Current Status of Tsunami Countermeasures in Light of Published Results from the Cabinet Office
Chubu Electric Power has used the tsunami fault model from the Cabinet Office to conduct a tsunami simulation in light of data related to estimates of tsunami height and other such matters provided in connection with the second report by the Committee for Modeling a Nankai Trough Megaquake of the Cabinet Office, published in August 2012. The impact that a tsunami would have on Hamaoka Nuclear Power Station was assessed using the simulation.
The water level reached by the tsunami in this simulation was from 14.7 to 20.7 m higher than Tokyo Bay mean sea level (T.P.) at the front of the sea wall. This would overflow the sea wall of T.P.+18 m on the east side of the power station grounds, however the sea wall's function would limit the amount of flooding within the grounds.
Flooding in the area of Units No. 3 and 4 due to overflow of the sea wall and overflow from the water intake chambers and other such facilities is to an approximate depth of from 1 to 3 m (equivalent to T.P.+7 to 9 m), and in the area of Unit No. 5, from 1 to 6 m (equivalent to T.P.+9 to 14 m). The seawater intake pumps required for cooling of reactor equipment will be flooded.
However, there are these countermeasures:
- Measures to prevent flooding inside buildings by strengthening the pressure resistance and waterproofing of doors in outside walls of buildings, etc.
- Measures to assure seawater cooling function by means of pumps inside waterproofed buildings (emergency seawater intake system (EWS))
Consequently, it was confirmed that speedy cold shutdown of the reactors would be possible even if Hamaoka Nuclear Power Station Units No. 3 to 5 are in operation at the time.
Details are as given in the attachment.
3. Reinforcement of Tsunami Countermeasures
Chubu Electric Power has adopted an even more rigorous conceptual approach to tsunami countermeasures in relation to the tsunami on the Cabinet Office model. We will reinforce our Flooding Prevention Measures (1) and Flooding Prevention Measures (2), thereby further increasing safety with regard to tsunami. Specifically, this involves:
(1) Reinforcement of Flooding Prevention Measures (1)
In order to heighten the effect of preventing flooding within the power station grounds to the greatest possible extent, the height of the sea wall will be increased from the present T.P.+18 m to T.P.+22 m. The height of the east-west embankments will also be raised from T.P.+18 to 20 m to T.P.+22 to 24 m. The sea wall in the area of the seawater intake pumps will be raised from its present 1.5 m to 3 m in height.
As a result of these measures, the overflow over the sea wall from a tsunami on the Cabinet Office model will be eliminated. Flooding within the grounds will be limited to overflow from intake chambers and other such facilities, and flooding in the vicinity of Units No. 3 to 5 will generally be to a depth of no more than 1 m or less, or at most 2 m or less. 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.
(2) Reinforcement of Flooding Prevention Measures (2)
Preparations will be made against the eventuality of increased flooding within the power station grounds by a tsunami that overflows the sea wall and by overflow from intake chambers and other such facilities. The measures to prevent flooding inside buildings will therefore be further secured.
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.
These actions to reinforce flooding prevention measures will be pursued with the aim of completion in December 2013, the target for construction work to address the Current Status of Tsunami Countermeasures.
Details are as given in the attachment.
4. Status of Other Matters Under Consideration
[Assessment of Earthquake Safety]
The Committee for Modeling a Nankai Trough Megaquake established by the Cabinet Office issued its second report in August 2012. The report deals with inspection and evaluation of severe earthquake fault models and related matters, with the intention of making corrections as required.
In light of the status of this committee's considerations, Chubu Electric Power will engage in evaluation of seismic motion at Hamaoka Nuclear Power Station and assessment of its impact on the power station.
[Dry Storage Facility for Spent Fuel]
Chubu Electric Power has announced plans to construct a dry storage facility for spent fuel. However, we intend to proceed with design after conducting an evaluation of seismic motion at this facility.
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.