Chubu Electric Power Co.,Inc. | Amassing our full strength [In pursuit of greater safety] (text) - About Hamaoka Nuclear Power Station

About Hamaoka Nuclear Power Station Amassing our full strength [In pursuit of greater safety]

Amassing our full strength [In pursuit of greater safety]

Chapter 1 About Chubu Electric Power Co., Inc.

This is an introduction to Chubu Electric Power Co., Inc., operator of the Hamaoka Nuclear Power Station.

The area supplied with electric power by Chubu Electric Power is located in the central part of the main Japanese island facing the Pacific Ocean.

The area includes five prefectures: Aichi, Shizuoka, Mie, Gifu, and Nagano.

The Chubu Electric Power Headquarters is located in the city of Nagoya, a major urban area in the region.

Chubu Electric Power's service area is about 39,000 km2, equal to about 10.5% of the Japanese territory.

The population of the area is approximately 16 million, or 12.5% of Japan's total population of 120 million.

Various industries are concentrated in this area, including automobile manufacturing, machine tool, electronic parts, aircraft, robotics, and new materials industries.

The real GDP is as much as 75 trillion yen.

Electric energy sold by Chubu Electric Power in the area totals 126.6TW-h, supporting one of Japan's largest manufacturing districts.

Chapter 2 About Hamaoka Nuclear Power Station

We will talk about the Hamaoka Nuclear Power Station, which supplies energy to the Chubu area.

This is Chubu Electric Power's Hamaoka Nuclear Power Station.

The station is located in Omaezaki city, Shizuoka prefecture, close to Mt. Fuji and located along the Pacific coast.

The Hamaoka Nuclear Power Station commenced operation of its Unit 1 in 1976, and its other reactors were built individually after that.

In 2005, Unit 5 commenced operation, further increasing total output to approx.5000 MW.

Units 1 and 2 both commenced operation in the 1970s and are now undergoing decommissioning following the decision in January 2009 to halt operation.

The total output of the remaining Units, 3, 4, and 5, is 3,617 MW.

Chubu Electric Power is working to achieve a well-balanced "optimum mix of power sources" that includes LNG, coal, oil, nuclear, hydroelectric, and other forms of power.
This mix is based on multiple considerations, including the operation characteristics of each power generation method, environmental impact, and economic efficiency.

As part of this diverse mix, the Hamaoka Nuclear Power Station accounts for about 15% of the company's total power output.

At the request of the Japanese government, all Units at the Hamaoka Nuclear Power Station halted operation as of May 2011.

Chapter 3 Measures taken at Hamaoka Nuclear Power Station for further safety

The Hamaoka Nuclear Power Station has always embraced the most up-to-date knowledge in its effort to enhance safety.

A series of safety measures has been added since the accident at TEPCO's Fukushima Daiichi Nuclear Power Station, including tsunami countermeasures and severe accidents countermeasures.
In September 2013, we decided to adopt additional measures based on the New Regulatory Requirements at Unit 3 and Unit 4, while we continue to explore necessary measures for Unit 5.

"No More Fukushima Daiichi Accidents"
With this resolve, the Hamaoka Nuclear Power Station is making all-out efforts
toward safety.

The fundamental principles of nuclear safety are "shutdown", "cooling" and "containment".

With nuclear generation, fuel continues to generate heat even after the plant operation is "shut down".
This is why it is important to keep "cooling" fuel by way of injecting water into the reactor and "contain" radioactive materials.

Looking back on the accident at Fukushima Daiichi...
The nuclear reactors sensed massive seismic ground motions and automatically shut down.

The collapse of transmission pylons and other damage disrupted the supply of off-site power. Yet, the power station's emergency generators successfully operated to supply power to pumps and other equipment, thereby maintaining the "cooling" function.

However, around 40 minutes after the earthquake, tsunami waves higher than the site of the power station arrived, flooding the site and the insides of buildings.

It made key facilities unusable, including seawater intake pumps for cooling and emergency generators. When batteries ran out, the power station lost its "cooling function ".

Consequently this led to a severe accident in which the inability to remove the heat generated by nuclear fuel caused the fuel to melt. This was followed by damage to the containment vessels, hydrogen explosions, and a massive discharge of radioactive materials.

Fukushima Daiichi was not fully prepared for the arrival of the tsunami nor the subsequent accident. To prevent a similar accident, the Hamaoka Nuclear Power Station takes into account the massive Nankai Trough Megaquake anticipated by the Cabinet Office in implementing measures to withstand a megaquake, block a tsunami and ensure the cooling function to prevent from escalating into severe accidents.

Furthermore, in the case of a severe accident, the power station has adopted measures to reduce the discharge of radioactive materials.

Withstanding a megaquake

As the Hamaoka Nuclear Power Station is located within the hypocentral region of the anticipated Tokai Earthquake, the Hamaoka Nuclear Power Station has been built with a conservative seismic design since the very start of its construction.

The reactor buildings, which house nuclear fuel, are built directly on solid bedrock, some 20 meters below the surface of the ground.
The design comprises a large, thick foundation and numerous thick walls arranged systematically to bring the center of gravity lower, like a pyramid. This approach provides a stable structure that is resilient to seismic motions.

The Tokai, Tonankai, and Nankai earthquakes are predicted to result in a triple megaquake. Considering this possibility, in 2005 approx. 1,000 gals on bedrock was set as the basis for design.

To ensure resilience against a quake of this magnitude, the power station has added reinforcing supports to pipes inside the buildings, and remodeled exhaust stacks for improved seismic safety.

Considering that the Nankai Trough Megaquake is expected to be even greater than the triple megaquake, in September 2013 additional measures were planned for Unit 3 and Unit 4.

The seismic motion to be considered in anti-quake measures was increased to 1,200 gals, which is greater than the maximum anticipated seismic ground motion up to around 1,000 gals based on the model developed by the Cabinet Office.

Suruga Bay Earthquake in August 2009 registered greater motions at Unit 5 than the other reactor units. In response, the hypothetical amplified ground motion to be considered for anti-quake measures was raised once again to 2,000 gals, higher than the seismic ground motion of up to 1,900 gals which was simulated by reflecting the amplification observed.

Based on the results of seismic observation within the station site, we examined the need to reinforce facilities that are important in a seismic design. The seismic motion of 1,200 gals was used for facilities near observation points that showed no significant amplification, while the seismic motion of 2,000 gals was used for facilities near observation points that reported significant amplification.

Based on the findings, we are further reinforcing supports to pipes at Unit 3 and Unit 4, and applying reinforcement to slopes within the station site. Reinforcing the ground work is also being carried out at the tsunami protection wall around Unit 5.

It has been confirmed that main facilities such as the reactor buildings and containment vessels have sufficient quake resistance and do not require reinforcement.

Blocking a tsunami

In order to prevent a tsunami from flooding the site, we are constructing a tsunami protection wall measuring 22 meters above sea level, stretching around 1.6 kilometers along the front side of the station ground on the ocean side.

The wall is implanted into solid bedrock, which lies some 30 meters underground at the deepest point, to ensure resilience against tsunamis and earthquakes.

In order to prevent a tsunami from entering the station site from the sides, "cement-mixed soil embankments" measuring 22 to 24 meters above sea level are also being installed on the eastern and western ends of the site.

The power station is also building walls surrounding its water intake pond, which is linked to the sea via a tunnel, to prevent seawater from entering the site.

These measures are designed to prevent flooding within the station site even in the event of the largest scale of tsunami anticipated under the Cabinet Office model.

Preparedness even for a tsunami higher than the tsunami protection wall

The pressure resilience and waterproof performance of exterior doors are reinforced by replacing reactor buildings' waterproof doors with watertight doors and combining them with new tsunami protection doors for dual protection. Watertight doors are also being installed at rooms that contain important facilities.

The power station also implements a range of flood prevention measures including the installation of automatic closing gates at the openings of the buildings' exterior walls to ensure that the buildings and equipment rooms do not become flooded.

Now, let us explain the power station's response to loss of the "cooling function", which occurred at Fukushima Daiichi.

There are multiple alternative means prepared for electric power supplies, water injection and heat sink, factors that are essential to the "cooling function ".
The core factor of this function is the availability of "electric power supplies".

The Hamaoka Nuclear Power Station already has multiple-level preparedness, which includes using power from three separate systems of transmission lines, and having flood-prevention measures in place to protect "emergency generators" in the reactor buildings. Yet, the power station is prepared against even the loss of all of these power supplies.

A newly-installed gas turbine generator, on high ground 40 meters above sea level, drives large-capacity pumps to inject water into the reactors.

Also, seawater intake pumps for cooling have been installed inside a building with a waterproof structure. They are run with electricity received from the gas turbine generator to remove heat from the reactors.

If even the gas turbine generator becomes unavailable, power is drawn from batteries to operate the pumps for water injection with pressure from residual heat and steam after reactor shutdown.

The pumps are also to be driven with electricity from generators installed on the rooftops of the buildings, as well as transportable and mobile power supplies, to provide additional means of water injection.

Even if we exhaust the means of power supplies, mobile water injection pumps are available to draw water from an underground water tank, to be installed on high ground 30 meters above sea level, as well as other water storage tanks and the Niino River that runs on the west side of the station site, and feed it to the pipes connected to the reactors for water injection.

The power station is equipped with these multiple layers of alternative means to ensure the "cooling function" and prevent events from escalating into severe accidents.

We would like to explain what the power station will do should a "severe accident including the melting of nuclear fuel" happen, even after the mentioned measures.

Measures for preventing damage to the containment vessels include reinforcing the facilities for cooling steam inside the containment vessels, and introducing facilities for cooling heated fuel that has melted and dropped inside the containment vessels.

Filter vents are being installed to prevent the large-scale discharge of airborne radioactive materials.

When releasing gas into the outside atmosphere to depressurize the containment vessel, the exhaust is fed through a filter that absorbs radioactive materials to cut the amount of released airborne radioactive particles, including cesium, to one-1,000th.

The power station is also installing hydrogen concentration meters and introducing ways to release hydrogen from the reactor buildings in order to prevent a hydrogen explosion.

To reduce the spread of airborne radioactive material, if the reactor buildings release hydrogen, the buildings will be sprayed by "water cannons" to drop the radioactive material to the ground.
These measures ensure the reduction of discharge and spread of the radioactive materials.

Other measures include the reinforcement of radiation shielding measures to enhance the livability of the emergency response center, which serves as the command center in the event of a severe accident.

In July 2013, the government introduced the New Regulatory Requirements.

The requirements reflect lessons learned in the Fukushima Daiichi accident and insights from overseas. They include stricter requirements concerning earthquakes and tsunamis, and new and tighter requirements against tornadoes, fires and indoor flooding.
Requirements on preventing and mitigating the effects of a severe accident have also been introduced.

The Hamaoka Nuclear Power Station is combining the measures already explained with new measures against tornadoes, fires, flooding and other conditions.

We believe implementing these measures will establish the comprehensive facility preparedness required to meet the New Regulatory Requirements for Unit 3 and Unit 4.

However, no matter how many facility measures we implement against earthquakes and tsunamis, at the end of the day, everything comes down to the "human ability to respond".

This is why the Hamaoka Nuclear Power Station has repeatedly carried out "emergency drills", anticipating the loss of the cooling function and a severe accident, as seen in the case of Fukushima Daiichi.

The Emergency Response Headquarters are set up both at the head office and at the power station to collaborate under the command of the company president to gather information and address emergencies.

These images show simulation training in progress at the Main Control Room, which can be described as the brain of the power station.
The training is based on a scenario that a massive tsunami has flooded the power station site, triggering a loss of the entire AC power supply.
The scenario is not provided to participating operators, so that they can develop the ability to perform plant operation reliably and calmly even in the event of an emergency.

In addition, "individual trainings" for verifying response procedures and their effectiveness are repeatedly carried out, including "training to connect power supplies", "training to perform water injection with a pump", and "training to manually open a vent valve" in darkness.

Training for accurately and swiftly identifying the effect of an emergency to the surrounding environment is also carried out, in an effort to maintain and improve the response capacity of plant personnel.

The power station also actively participates in emergency drills organized by the central and local governments.
Local collaboration is being reinforced through the distribution of plant information to local communities and the measurement of radiation levels for evacuees.

We continue to make all-out efforts to steadily enhance the safety of the Hamaoka Nuclear Power Station, thereby bringing a sense of safety and security to local communities and the rest of the nation.