Implementation of Severe Accident Countermeasures

シビアアクシデントとは…燃料が溶けるなど、炉心が大きく損傷するような過酷事故

◆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 ways to mitigate the effects of damage to a reactor core. ◆Accordingly, we have decided to implement measures to prevent large-scale release of radioactive material and damage to the reactor vessel.

◆We have also decided to enhance measures for emergency DC power supply.

◆Construction work for these measures is expected to take about two to three years.

Additional Severe Accident Countermeasures

Severe Accident Countermeasures

The following measures are being taken to prevent damage to the containment vessel resulting from excessive pressure, and to prevent deterioration of containment vessel seal material resulting from excessive heat.

Severe Accident Countermeasures

②Installation of water supply line in containment vessel pedestal This is to cool molten reactor core that has fallen into the containment vessel pedestal (under the containment vessel), thereby preventing damage to the containment vessel.

③Reinforcement of alternative containment vessel spray functions This is to cool (condense) steam generated by molten reactor core or other such material, thereby preventing damage to the containment vessel. ④Assurance of cooling function for containment vessel top head flange This is to cool the containment vessel top head flange, thereby preventing damage to the vessel itself. (Prevents leakage of hydrogen, etc. from flange.) ⑤Deploy alternative heat exchange equipment for long-term cooling This is to provide long-term cooling circulation for the containment vessel without using the existing seawater heat exchanger, thereby preventing damage to the vessel itself. (Enables it to be used for preventing reactor core damage.)

Measures to Prevent Large-Scale Discharge of Radioactive Material

⑥Upgrade storage battery capacity This is to extend the period during which critical instruments and other such equipment can be supplied with power. ⑦ Deploy separate dedicated power sources for critical instruments and other such equipment This is to enable measurement of water levels, pressure, and other such factors in the reactor using portable storage batteries and dedicated measuring instruments.

Emergency DC Power Supply Measures

Overview of Measures to Prevent Damage to Containment Vessel

①Installation of filter vent equipment Venting the containment vessel through a filter reduces the amount of radioactive material that is discharged in particle form (cesium, etc.) and prevents long-term soil contamination. The vent further enables reduction of pressure in the containment vessel, and so prevents damage to the containment vessel.

Severe Accident Countermeasures

Severe accident countermeasures taken this time

Spent fuel storage pool

Shared emergency fresh water tank (high ground)

Reactor Condensate tank

Intake pond

Reactor containment vessel

Exhaust stack

Heat exchanger

①Installation of filter vent equipment

②Installation of water supply line in containment vessel pedestal

⑤Deploy alternative heat exchange equipment for long-term cooling

③Reinforcement of alternative containment vessel spray functions

⑥Upgrade storage battery capacity

④Assurance of cooling function for containment vessel top head flange

⑦Deploy separate dedicated power sources for critical instruments and other such equipment

Containment vessel top head flange

①Installation of filter vent equipment

◆Containment vessel vents are necessary to prevent damage to the containment vessel. We are installing filter vents to reduce the amount of radioactive material that is discharged in particle form (cesium, etc.) to prevent soil contamination. ◆This will enable us to reduce discharge of radioactive material in particle form by more than 99.9%.

◆We are reducing pressure in the containment vessel to prevent damage from excessive pressure.

Reactor

Containment vessel

Exhaust stack

Filter vent equipment

Filter

Water

Measures to Prevent Large-Scale Discharge of Radioactive Material

Measures to Prevent Damage to Containment Vessel

Approx. 5 m

Approx. 11 m

Shared emergency fresh water tank (high ground)

Condensate tank

Concrete

Containment vessel

Reactor

Molten reactor core

→

Pump

→

Water injection piping at containment vessel pedestal

→

Place where newly installed

②Installation of water supply line in containment vessel pedestal

◆After any reactor core damage, if a hot molten reactor core has fallen onto the pedestal under the containment vessel, it will be cooled by water injection. This will limit erosion of the concrete floor and the amount of non-condensed gas that occurs as a result of reaction between the molten reactor core and concrete. This will in turn limit increases in pressure and temperature of the containment vessel and prevent containment vessel damage.

Diesel-driven pump

Motor-driven pump

③ Reinforcement of alternative containment vessel spray functions

◆This is to cool (condense) steam generated by molten reactor core or other such material, thereby preventing damage to the containment vessel. ◆In addition to existing water injection means, we will be able to inject water with motor-driven pumps, diesel-driven pumps and a portable power pump.

原子炉

Containment vessel

Containment vessel spray

[High ground] Shared emergency fresh water tank

Condensate tank

→

→

River water, seawater

Diesel-driven pump

Portable power pump, etc.

Motor-driven pump

→

Connection

Temporary pressure-resistant

hose

Pump

Place where newly

installed

→

Reactor

④Assurance of cooling function for containment vessel top head flange

◆After any reactor core damage, leakage of hydrogen, etc. from the flange will be controlled by injecting cooling water to the nuclear reactor well and cooling the containment vessel top head flange (the junction at the lid). ◆To diversify the water injection means, piping will be connected to ensure the cooling function, and an external connection will be provided that will allow water injection from outside.

Gasket

Nuclear reactor well

原子炉

Cooling water will be injected to the nuclear reactor well, so there will be direct external cooling of the containment vessel top head flange, preventing excessive heat. This will ensure the gasket’s sealing function and control leakage of hydrogen, etc. from the containment vessel.

Condensate tank Pump

[High ground] Shared emergency fresh water tank

External connection

Place where newly installed

Motor-driven pump

River water, seawater

→ Pump

→

→

→

Containment vessel top head flange

Diesel-driven pump

Reactor

Reactor

Following any reactor core damage, the inside of the pressure vessel could become very hot, causing the temperature of the containment vessel top head (lid) to rise, leading the flange gasket (the seal material at the junction) to be damaged from excessive heat and causing leaks of hydrogen, etc.

⑤ Deploy alternative heat exchange equipment for long-term cooling

◆We are providing alternative heat exchange equipment to ensure that the cooling function continues to work, even if both the function to draw seawater, and the function to cool equipment cooling water with drawn seawater, are lost. ◆Adding alternative heat exchange equipment will prevent containment vessel damage by providing long-term circulating cooling of the containment vessel with a residual heat removal pump and heat exchanger, even if there is reactor core damage.

Reactor

Containment vessel

Residual heat removal heat exchange

equipment

Alternative heat exchanger equipment

Residual heat removal

system pump

← ← To sea

Intake pond

→

Underwater pump

Seawater pump Heat exchanger

→

Seawater drawing function Function to cool equipment cooling water

with drawn seawater

⑥ Upgrade storage battery capacity

⑦ Deploy separate dedicated power sources for critical instruments and other such equipment

◆We are upgrading storage battery capacity to strengthen DC power, since there is a possibility of instruments losing their function and valves becoming inoperable if DC power is depleted. ◆Specifically, we are upgrading storage battery capacity to supply at least eight hours of power even if all unnecessary loads on power remain connected, and at least 24 hours if unnecessary loads on power are disconnected.

⑥Upgrade storage battery capacity

Example of a storage battery

◆We are providing batteries for supplying DC power, as well as dedicated portable measuring instruments to provide the necessary instruments to determine the status of the reactor, etc. if DC power is lost.

⑦Deploy separate dedicated power sources for critical instruments and other such equipment

Measuring instruments (pressure gauges,

temperature sensors, etc.)

Control panel

batteries

DC power

DC power

Signal

Portable measuring instruments

◆The Committee for Modeling a Nankai Trough Megaquake of the Cabinet Office made its second report in August 2012, but will be examining and evaluating severe earthquake fault models, etc. and will make corrections if necessary. ◆In line with any corrections made by the Committee, Chubu Electric Power will continue to evaluate seismic motion at Hamaoka Nuclear Power Station and assess its impact on the facility.

Response Hereafter

◆Chubu Electric Power has previously announced plans for building a dry storage facility for spent fuel. This facility, as well, will first undergo an evaluation of seismic motion before design proceeds.

Dry Storage Facility for Spent Fuel

Study of seismic motion