Kashiwazaki-Kariwa Nuclear Power Plant

The Kashiwazaki-Kariwa Nuclear Power Plant is located on the western coast of Honshu, Japan’s main island, within the boundaries of Niigata Prefecture. The facility is situated on a vast area extending along the coastline of the towns of Kashiwazaki and the neighboring village of Kariwa, from which it derives its name. The plant is positioned along the shore of the Sea of Japan and has a direct infrastructure connection to the sea for cooling water supply. Its geographical location has necessitated a design approach that accounts for both marine-related risks (tsunamis, storm surges) and Japan’s high seismic activity. Consequently, the physical layout of the facility was planned by integrating elevation, coastline features, and protective structures.

The total area of the plant site is approximately 4.2 square kilometers (420 hectares), making it one of the largest nuclear power plants in the world by installed capacity. The facility consists of seven reactor units with a total installed electrical capacity of 8.212 gigawatts. This capacity corresponds to a production potential sufficient to meet the electricity needs of millions of households. The plant is positioned as a strategic element in relation to Japan’s energy supply security, economic stability, and goals for reducing greenhouse gas emissions. Within the context of Japan’s efforts to reduce dependence on fossil fuel imports, the scale of this facility plays a crucial role in the national energy system.

Kashiwazaki-Kariwa is regarded as one of the symbolic facilities of Japan’s nuclear electricity generation infrastructure. This status is not only due to quantitative indicators such as installed capacity and physical size but also because of the facility’s operational history, its experience with earthquakes, and its role in post-Fukushima safety debates. While the plant stands out for its high-capacity generation potential, it is also at the center of discussions concerning safety, regulatory oversight, and local social acceptance. This dual nature has made the facility a critical reference point both in Japanese energy policy and in global nuclear safety debates.

^{Kashiwazaki-Kariwa Nuclear Power Plant (}TEPCO⁾

Construction of the Kashiwazaki-Kariwa Nuclear Power Plant began in the late 1970s and spanned approximately twenty years. Work on the first unit commenced in 1978, followed by the construction of additional units throughout the 1980s. The first unit was commissioned for commercial operation in 1985, with subsequent units gradually brought online during the 1990s. The seventh and final unit was connected to the grid in 1997. Thus, the plant emerged as one of Japan’s most ambitious and long-term nuclear energy projects, completed incrementally between 1978 and 1997.^【1】

The facility incorporates both boiling water reactor (BWR) and advanced boiling water reactor (ABWR) technologies. Some reactor units employ classic BWR designs, while others use the newer ABWR designs. These reactors operate using uranium dioxide (UO₂) fuel elements, each with its own turbine building, control room, and auxiliary systems. Major components such as reactor pressure vessels, containment structures, and suppression pools were constructed according to reinforced design criteria that account for Japan’s high seismic activity. The number of control rods, fuel assembly arrangements, and pressure vessel dimensions are based on detailed engineering calculations specific to each unit.

The overall site layout organizes reactor buildings, turbine buildings, high-voltage switchyards, emergency management centers, freshwater reservoirs, and various support infrastructures within a defined hierarchy. The high-voltage switchyard connects the plant to the external grid and is responsible for transmitting the electricity generated by the reactors to the national network as well as supplying emergency external power during outages. The facility features a multi-layered power supply system including emergency diesel generators, mobile gas turbine generators, and power equipment placed at different elevations. Additionally, fire barriers, logistics routes, control buildings, and maintenance areas are strategically positioned to support both safety and operational continuity.^【2】

The operational history of the Kashiwazaki-Kariwa Nuclear Power Plant reflects the fluctuations in Japan’s attitude toward nuclear energy. Throughout the 1980s and 1990s, the plant operated as a major contributor to the country’s electricity generation, achieving high capacity utilization rates. Its economic appeal, driven by high output power and fuel efficiency, provided significant tax revenues and employment opportunities for local authorities. However, over time, the plant faced prolonged shutdowns due to natural disasters and nuclear safety debates. As a result, its operational timeline has followed an interrupted course compared to its theoretical design lifespan.

The July 2007 Chūetsu Offshore Earthquake marked one of the turning points in the plant’s history. During the quake, four reactors were operating and automatically shut down; incidents including fires and limited radioactive leaks were reported. This event triggered new public and regulatory concerns regarding the plant’s seismic resilience and equipment layout. Following the earthquake, comprehensive inspections and reinforcement measures were carried out before reactors were allowed to restart. Nevertheless, the incident created a significant shift in public perception of the plant and established a reference point for subsequent debates.

The 2011 Great East Japan Earthquake and the subsequent tsunami that caused the Fukushima Daiichi Nuclear Power Plant accident profoundly affected the future of Kashiwazaki-Kariwa, as it did for the entire Japanese nuclear sector. Following the meltdowns and hydrogen explosions at Fukushima, the Kashiwazaki-Kariwa units, like the majority of reactors in Japan, were shut down for an extended period. This period necessitated a fundamental review of nuclear safety regulations, the adoption of new standards, and extensive technical investments by existing plants to comply with these standards. During this time, Kashiwazaki-Kariwa became both a focal point for technical upgrades and a symbolic example in discussions about restarting nuclear operations.

^{Control room (}TEPCO⁾

Following the Fukushima Daiichi accident, stricter regulations introduced in Japan mandated the creation of additional safety layers against tsunamis and power outages. Analyses at Kashiwazaki-Kariwa indicated that the maximum possible tsunami wave could reach up to 6.8 meters. In response, a seawall 15 meters high was constructed along the coastline. In front of the lower-elevation Units 1–4, steel-reinforced concrete barriers were installed, while higher-elevation Units 5–7 were protected by additional embankments supported by earthworks. Thus, both primary and secondary defense lines were established to prevent a potential tsunami from directly reaching the plant buildings.

A multi-layered power supply system has also been configured to address potential power outage scenarios. Mobile gas turbine generators placed at higher elevations are positioned to provide electricity for reactor and cooling systems during emergencies. In addition, diesel generators, portable generator units, and alternative switchgear connections form a redundant infrastructure. To ensure continuous cooling water supply, a freshwater reservoir with a capacity of approximately 20,000 cubic meters was constructed, designed to serve as a backup source for cooling both reactor cores and spent fuel pools. Furthermore, fire pumps and water spray systems have been arranged to deliver external water directly to reactor buildings when needed.

The hydrogen explosions at Fukushima brought to the forefront the issues of hydrogen accumulation and radiation release management within reactor buildings. In response, Kashiwazaki-Kariwa installed catalytic systems in reactor buildings to prevent hydrogen concentrations from reaching dangerous levels. Additionally, filtered venting systems capable of releasing pressurized gases have been designed to reduce the concentration of radioactive particles released into the atmosphere. Waterproof doors, reinforced drainage systems, and sealed access points have been implemented across various sections of the facility to mitigate flood and water ingress risks. These technical measures are regarded as on-site implementations of the “defense in depth” approach.^【3】

In the process of restarting Kashiwazaki-Kariwa, issues of safety culture, authentication procedures, and physical protection measures have become as central as technical upgrades. In the second half of the 2010s, assessments concluded that Units 6 and 7 met the new safety standards and satisfied the technical conditions for restart. However, safety violations uncovered in 2020 and 2021 significantly altered the course of the process. It was discovered that an unauthorized individual had gained access to the plant’s central control room using an employee’s access card and that intrusion detection systems had remained offline for extended periods. These findings prompted a strong response from the regulatory authority. The incidents led to the recognition that the plant must be evaluated not only on technical safety standards but also on its organizational and operational safety culture.

The Nuclear Regulation Authority (NRA) of Japan imposed a regulatory order halting all fuel-related activities at Kashiwazaki-Kariwa due to these safety gaps. Under this order, the import of new uranium fuel, fuel loading into reactors, and restart preparations were suspended. The authority demanded additional corrective measures concerning the physical protection of nuclear materials, the reliability of access control systems, and the effectiveness of unauthorized entry detection mechanisms. During this period, the plant operator publicly announced that it had implemented various technical and administrative improvements, including staff training and updated procedures. The regulatory body has continued to monitor the implementation of these measures on-site.^【4】

In subsequent developments, the NRA announced that it had lifted the corrective order that had fully blocked fuel activities, citing improvements in the safety management system. Thus, the most significant regulatory barrier to the transport of new fuel and fuel loading into the reactors has been removed. However, the actual timing and sequence of the plant’s restart now depend not only on technical and regulatory conditions but also on approval processes by local authorities and the regional population. In this sense, Kashiwazaki-Kariwa has emerged as one of the most visible test cases for the balance between Japan’s nuclear energy future, public perceptions of safety, and societal support.

The Kashiwazaki-Kariwa Nuclear Power Plant is not merely an electricity generation facility for the region but also a major economic actor. The plant directly employs thousands of people and generates indirect employment and income effects through maintenance, construction, and service sectors. Local budgets are significantly influenced by nuclear fuel taxes, property and income taxes linked to the facility, and various subsidies and grants from the national government. It is noted that revenue derived from the plant constitutes a substantial portion of the budgets of Kashiwazaki and Kariwa municipalities, with a considerable share of total income in some years directly or indirectly tied to the facility. This situation complicates political and social debates regarding the plant’s future.

The prolonged shutdown of the plant has also affected economic and demographic trends in the region. Reports indicate store closures in local commercial areas, contraction in the service sector, and outmigration of the young population. It is stated that Kashiwazaki’s population has declined noticeably between 2010 and 2020, the average age has risen, and similar trends are evident in the village of Kariwa. This scenario has strengthened arguments for restarting the reactors based on employment and economic revitalization. Conversely, it is observed that not all segments of the local population share the same stance; public opinion polls continue to show cautious or opposing views due to concerns over nuclear safety and potential accident risks.

From the perspective of Japan’s overall energy policy, the future of Kashiwazaki-Kariwa is directly linked to the question of how nuclear energy should be positioned within the national energy mix. Efforts to reduce fossil fuel imports, lower greenhouse gas emissions, and achieve the 2050 carbon neutrality target have brought nuclear energy back into focus. In this context, restarting large-capacity and modernized nuclear plants has become part of the broader effort to balance energy supply security with climate policy goals. Kashiwazaki-Kariwa, with its technical capacity, transformation process, and safety agenda, stands out as one of the most concrete examples in these debates and remains at the center of ongoing political, technical, and societal evaluations of nuclear energy’s future in Japan.