Timeline of Events: Fukushima Daiichi Nuclear Power Station Accident

Enhancements in Infrastructure, Operational Readiness, and Cultural Shifts for Extreme Events

Infrastructure Improvements

Tsunami Protection Measures:

The failure of the seawall during the tsunami revealed serious weaknesses in the plant's flood protection systems. In response, TEPCO has prioritized the construction of higher seawalls and more robust flood barriers to protect against future tsunamis. Furthermore, critical equipment has been relocated above tsunami levels, ensuring that essential systems remain functional even during more powerful tsunamis than initially anticipated.

Emergency Power Systems:

The loss of power caused by the tsunami highlighted the need for more reliable backup systems. As a result, modern stations now feature multiple redundant, mobile, and portable power sources, including diesel generators and battery banks. In addition, power supply vehicles are stationed on high ground to remain unaffected by tsunamis, ensuring continuous operation. The ability to inject coolant into the reactors using AC power sources, such as gas turbine generator trucks, for extended periods has been greatly enhanced, ensuring that cooling can be maintained even in challenging situations.

Hydrogen Explosion and Dispersion of Radioactive Substance Prevention:

Hydrogen buildup in the reactors and reactor buildings led to explosions during the Fukushima Daiichi Nuclear Power Station Accident. To mitigate this risk, TEPCO has implemented advanced systems. These systems include recombiners designed for controlling hydrogen concentration and filter vents for preventing dispersion of radioactive substances. Together, these measures inhibit excessive hydrogen accumulation, hydrogen explosion and the spread of radioactive substances.

Operational Readiness Enhancements

Strengthened Crisis Communication:

TEPCO has overhauled its crisis communication protocols to ensure more effective coordination during emergencies. Enhanced communication channels facilitate information sharing with local communities, the government, and other stakeholders. This enhances transparency and ensures rapid dissemination of critical information, helping to manage the crisis more efficiently and maintain public confidence.

Enhanced Equipment Deployment:

Critical emergency equipment, including alternative heat exchanger trucks, power supply vehicles, and fire trucks, is now stationed on high ground to remain functional even in the event of a tsunami. The ability to deploy this equipment quickly has also been streamlined, enabling faster responses in emergencies. This preparedness ensures that resources can be mobilized without delay, even when the plant’s regular operations are disrupted.

Operational Preparedness for Multi-Plant Accidents:

TEPCO has improved its ability to respond to multiple simultaneous accidents by reinforcing infrastructure and increasing the stock of emergency equipment. Drills have been expanded to simulate a wide range of disaster scenarios, including total power loss and simultaneous failures at multiple plants. These exercises ensure that the organization is prepared for a variety of extreme events, making the response more coordinated and effective.

Cultural and Operational Shifts

The Fukushima Daiichi Nuclear Power Station Accident underscored the need for significant cultural and operational shifts within the nuclear industry. In response, we have made a strong commitment to safety and transparency, driving continuous improvements across our operations. Some of the key changes include:

Empowerment and Collaboration:

A major cultural shift has taken place within organizations, focusing on empowering workers at all levels. This shift encourages stronger collaboration among operators, regulators, and safety organizations. By fostering a more inclusive culture, the industry has enhanced safety awareness and decision-making processes, which are critical during crises.

Crisis Communication and Trust Building:

Improvements in crisis communication protocols have been implemented, including the introduction of real-time updates and transparent information sharing. These measures are designed to build trust with both the public and local communities, ensuring that nuclear operations are understood, and that trust is maintained, even during emergencies.

Operational Resilience:

As part of the defense-in-depth strategy, a comprehensive approach has been adopted to ensure robust operational preparedness at every stage of an emergency. This includes better preparedness for simultaneous multi-plant disasters, the reinforcement of safety systems, and the provision of advanced equipment for post-accident scenarios. This equipment includes radiation measurement tools and advanced communication systems, which ensure that TEPCO can effectively respond to and manage accidents when they occur.

New Regulatory Requirements:

In July 2013, new regulatory requirements were introduced to significantly enhance safety across the nuclear industry. These requirements strengthened existing guidelines for natural phenomena such as earthquakes, tsunamis, volcanoes, and forest fires. Measures that were previously voluntary, like severe accident countermeasures and terrorism countermeasures, were also made mandatory.
To address potential threats, TEPCO has been developing procedures and mobile equipment to maintain safety during scenarios like power or water injection failures caused by intentional impacts, such as aircraft collisions. Regular drills are conducted to ensure readiness, and the government has implemented defense and diplomatic measures to address risks like missile strikes and military attacks.
Security measures have also been reinforced. TEPCO joint training exercises with police and the Japan Coast Guard are conducted regularly, alongside ongoing efforts to prevent unauthorized intrusions. Additionally, external experts, such as former police and fire officials, have been recruited to improve response capabilities.
Other system improvements include strengthened fire prevention measures, improved equipment reliability, and new guidelines to address internal flooding. Together, these advancements represent a comprehensive approach to ensuring greater safety and resilience in the nuclear sector.

For more details on the new regulatory requirements, please refer to the Nuclear Regulation Authority's website: NRA Regulatory Requirements

Defense-in-Depth: A Multi-Layered Approach to Safety

• Stage 1: Prevent Trouble From Occurring:

  The first layer of defense focuses on preventing accidents, such as reinforcing tsunami defenses and sealing buildings to prevent flooding. For instance, flood barriers and watertight buildings are now standard, designed to withstand more powerful tsunamis than initially anticipated.

• Stage 2: Prevent the Situation From Developing Into an Accident:

  If a problem arises, the second layer aims to prevent it from escalating into a full-scale accident. Redundant systems such as additional power sources, manual reactor cooling systems, and increased battery capacity are deployed to maintain safety even under extreme conditions.

• Stage 3: Prevent Core Damage After an Accident:

  The third layer of defense ensures that if an accident occurs, the core is protected. This includes mechanisms to inject coolant into the reactor, lower pressure within the vessel, and remove heat through mobile heat exchangers and other systems designed to withstand adverse conditions.

• Stage 4: Impact Mitigation After an Accident:

  The final layer aims to mitigate the impact if core damage occurs. This includes systems to cool primary containment vessels, reduce radioactive substances leakage through venting systems with filters, and minimize secondary disasters such as hydrogen explosions.