Activity

Safety

Nuclear facilities approach their design and operation so as to prevent the occurrence of abnormalities and their expansion, and mitigate the development into an accident. JNFL facilities have adopted the following measures based on this "Defense in depth" philosophy:

1. To prevent occurrence abnormalities

  • Safety designs to prevent criticality, fire, explosion, and leaking
  • Perform to a safety-side through fail-safe systems

2. To prevent expansion abnormalities

  • Monitoring systems to detect abnormalities
  • Automatic stop systems, so called interlock systems, to control abnormalities

3. To mitigate consequence of accidents

  • Physical barriers with thick concrete cell to contain radioactive material and the air pressure control to prevent leaking radioactive materials out
  • Internal air: released after filtering out as much radioactive materials as possible

Example of safety measures based on the defense in depth philosophy at the Rokkasho Reprocessing Plant

Various initiatives were taken for the improvement of safety through the design and construction of our facilities.

The main safety measures at the Rokkasho Reprocessing Plant

True to our firm resolve never to allow an accident such as the one at Fukushima Daiichi Nuclear Power Station to happen again, Japan Nuclear Fuel Limited strives to learn from the accident and put those lessons to use in further enhancing safety.
Here are some of the countermeasures and initiatives that are being implemented in accordance with the new regulatory requirements.

# Click for detailed description

  • 1.Hydrogen explosion countermeasures
  • 2.Measures against leakage of chemicals
  • 3.Internal flooding measures
  • 4.New emergency responce facility
  • 5.Securing access routes
  • 6.Geological survey (on the ground)
  • 7.Geological survey (at sea)
  • 8.Controlling the diffusion of radioactive substances
  • 9.Securing power supply
  • 10.Evaluation of the impact of Tsunami
  • 11.Training assuming various circumstances
  • 12.Fire prevention and protection
  • 13.Securing cooling function
  • 14.Tornado measures
  • 15.Aircraft Crash Probability Assessment
  • 16.Probabilistic Volcanic Hazard Assessment

Hydrogen explosion countermeasures

Even if by chance all the air compressors shut down, air will continue to be sent and hydrogen will be scavenged.

Hydrogen explosion countermeasures

Air compressor with engine

Measures against leakage of chemicals

The amount of any leakage of water or chemicals is reduced.

【Enhancement of Seismic Resistance】

Seismic resistance has been enhanced of any pipes and equipment through which water or chemicals pass.

Enhancement of Seismic Resistance

【Emergency Shut-Off Valves Installed】

Emergency shut-off valves are set to close when earthquakes of a certain intensity or greater are detected, thereby keeping any leakage to a minimum.

Emergency Shut-Off Valves Installed

Measures in place so that water or chemicals do not come into contact with equipment.

【Panels Installed】

Panels Installed

【Waterproofing Enhanced】

Waterproofing Enhanced

Internal flooding measures

Weirs and water-tight doors are installed to protect the equipment, in case water floods inside the facility (breaking of the machinery or piping, sloshing of the spent fuel storage pool* etc.) *When liquid shakes due to external vibrations

Weir

Weir (Image)

Water-tight door

Water-tight door (Image)

Securing access routes

Access routes are roads used to move personnel around as well as transport and construct equipment as part of implemented countermeasures.
Multiple access routes have been prepared within the site. Wheel loaders and bulldozers have been deployed in the event a disaster strikes, leaving debris that makes the routes unpassable.

Access route

Access route

[left] Bulldozer  [right] Wheel loader

[left] Bulldozer [right] Wheel loader

Controlling the diffusion of radioactive substances

Even if by chance large scale damage occurs due to an earthquake etc. water is discharged from multiple directions and the diffusion of radioactive substances from the building is controlled.

Controlling the diffusion of radioactive substances

Water cannon

Water cannon

Water cannon training

Water cannon training

Geological survey (on the ground)

Boring survey, trench survey etc. are carried out in detail at the site environ and in the vicinity of the site, and evaluated, so as to ensure safety with respect to the design-basis earthquake ground motion.

Reflection seismic survey

Artificial seismic waves are generated and waves reflected from under the ground are received, with the help of which the underground structure is investigated.

Boring survey

The ground is excavated in a tubular form and the collected rock samples are analyzed to investigate the underground structure.

Trench survey

Surface of the earth is excavated and the geological situation under the ground is directly verified.


What is Design-basis Earthquake Ground Motion?
Design-basis earthquake ground motion refers to the maximum strength of tremors that are likely to occur in the vicinity of the facility. This is considered as the basis of seismic design. The design-basis earthquake ground motion is established by taking into account inland crustal earthquakes, inter-plate earthquakes, oceanic intra-plate earthquakes, or earthquakes for which the seismic source cannot be identified.

What is Design-basis Earthquake Ground Motion?

Geological survey (at sea)

Marine sonic prospecting or seabed boring survey are conducted and the safety of the facility is verified.

Marine sonic prospecting
Sound waves are generated in sea water by means of a sonic wave generator and the sound waves reflected by the seabed or the sub-bottom geological strata are received with the help of a streamer cable, and these are used to investigate the sub-bottom structure.

Marine sonic prospecting

Seabed Boring Survey

(Rise drilling vessel "Chikyu")

Seabed boring survey off Shimokita off the Pacific Coast
(Rise drilling vessel "Chikyu")

Boring core

ボーリングコア

The underground structure is investigated by observing and analyzing the cylindrical rock samples that are collected.

New emergency responce facility

In the event the main control room cannot be used as an operations base when a problem arises, a new earthquake-resistant emergency response center will be set up to improve operability for responders and expand the selection and quantity of equipment and materials available.

Emergency Response Center (Illustration)

Emergency Response Center (Illustration)

Emergency Response Center

Securing power supply

In order to maintain safety at the facility, electricity needs to be supplied at all times.
Power source is multiplexed so as to ensure that electricity does not get interrupted due to natural disasters etc.


Framework for securing power supply

External power supply lines (2 lines)

External power supply lines (2 lines)

Even if
power
transmission
stops
Emergency Diesel Generator

Emergency Diesel Generator

Even if
this
malfunctions
Power supply vehicle

Power supply vehicle

Evaluation of the impact of Tsunami

An assessment was conducted that took into account the tsunami caused by the 2011 Great East Japan Earthquake and the latest available knowledge. These results confirmed that the reprocessing plant is situated at a sufficiently high elevation to sustain the projected tsunami height.

  • Cabinet Office-projected tsunami height for Rokkasho Village coastal zone 10.7 m (2020)
  • Aomori Prefecture-projected tsunami height for Rokkasho Village coastline 6-12 m
  • Height of tsunami caused by 2011 Great East Japan Earthquake 3.5 m (Obuchi, Rokkasho Village)
Evaluation of the impact of Tsunami

Tornado measures

Maximum tornado intensity is set to a wind speed of 100 m/s and measures implemented to withstand such force.

Protective steel netting and panels are installed to protect cooling towers against flying objects propelled by tornado force.

Cooling tower (before construction)

Cooling tower (before construction)

Facility with protective netting (CG image)

Facility with protective netting (CG image)


Sturdy garages and fastening devices are installed to prevent vehicles from blowing off in the event of a tornado.

Illustration of Measures to Prevent Flying Objects

Illustration of Measures to Prevent Flying Objects

Training assuming various circumstances

JNFL conducts training and exercises anticipating a range of severe scenarios, such as a major earthquake resulting in a station blackout or multiple events occurring simultaneously at facilities, so that personnel are able to respond rapidly and appropriately to resolve such incidents.
These training exercises are repeated in an effort to build up response and technical capabilities.

Response headquarters

Response headquarters

Training in unrolling hoses to transfer cooling water

Training in unrolling hoses to transfer cooling water

Training in stretching out power cables during a power outage scenario

Training in stretching out power cables during a power outage scenario

Training in connecting power cables during a power outage scenario

Training in connecting power cables during a power outage scenario

Training in drawing water from wetlands during midwinter

Training in drawing water from wetlands during midwinter

Training in removing debris to secure access route

Training in removing debris to secure access route

Securing cooling function

Arrangements have been made for various equipment including portable pumps, so that high level radioactive liquid waste etc. can be cooled even if the existing cooling function is lost. Also, water required for cooling can be acquired from a diversity of sources, such as river, pond etc. in addition to the water storage tank within the site environ.

Large transfer pump vehicle

Large transfer pump vehicle

Medium sized transfer pump vehicle

Medium sized transfer pump vehicle

Portable pump

Portable pump

Fire prevention and protection

Deployment of Firefighting Vehicles
Several firefighting vehicles have been deployed to facilitate fire control in the event a fire breaks out.

Large chemical fire engine

Large chemical fire engine

Fire engine that can move around on uneven ground

Fire engine that can move around on uneven ground


Firebreak Constructed
In the event of a fire burning outside the facility premises, a firebreak has been constructed to prevent the fire from spreading into the site and causing damage.

*Firebreak:
A long narrow strip of land with no combustible material that is created to contain the spread and damage from an external fire.

防火帯の設置

Firebreak

Aircraft Crash Probability Assessment

Although the possibility of an aircraft crashing into the reprocessing plant is extremely low, JNFL has adopted appropriate countermeasures to deal with such an event.

【Aircraft Crash Countermeasures】

Countermeasures ensure that an aircraft crash does not compromise safety function.

Robust structures protect facilities

Robust structures protect facilities

Isolation distance assured

Isolation distance assured


Moreover, assessments conducted to determine the probability of an aircraft crashing into the reprocessing plant have verified that the required safety is assured.

Aircraft crash probability
0.000000046 event/year (4.6×10-8 event/year)
Below Japan's criteria necessitating protective design
(10-7 events/year)

Probabilistic Volcanic Hazard Assessment

JNFL protects facilities against failure caused by volcanic ash released during an eruption.

Maximum volcanic ash fall is estimated to be 55 cm. This is based upon the Mount Hakkoda eruption approximately 200,000 years ago.

【New Regulatory Requirement-Based Measures】

Filter cloth has been placed on external air intakes to prevent filters from clogging. Additional filtering devices and other mechanisms are in place so that, even if a filter does clog, it may be cleaned or replaced.

External air intake countermeasures for primary emergency diesel generator

External air intake countermeasures for primary emergency diesel generator

Workers replacing a filter

Workers replacing a filter


Although the possibility of a massive volcanic eruption is sufficiently low, volcanic activity is monitored. If there is a significant change in observational data, JNFL takes into account the advice of volcanologists, makes a comprehensive judgment, and determines what specific action to take.