Onagawa — Japan

Onagawa is a 2,174 MW nuclear power station in Miyagi, Japan. It is operated by Tohoku. Based on its capacity (estimated), it can supply roughly 4.9 million homes (estimated). It ranks #25 of 692 Japan power plants by installed capacity. Commissioned in 1984, it is around 42 years old — long-established. As a non-combustion source, it has no direct CO₂ emissions from generation. In context, nuclear supplies about 9.1% of Japan's electricity; the national grid averages 477 gCO₂/kWh (32.7% low-carbon) (2025).

Plant data: WRI Global Power Plant Database (CC BY 4.0), id WRI1000676.

Capacity provenance

The public capacity above is the current source-record value. A 2026 tracker candidate lists 1,650 MW for Onagawa nuclear power plant, but it is not used as the public primary value until scope is verified (unit vs operating vs installed/project total).

Data provenance

Source of the capacity and fuel values:

capacity: Wikidata P2109; fuel: WRI GPPD

In context: how this plant compares

At 2,174 MW, Onagawa is around the median nuclear plant in Japan (2,070 MW). Technically it is described as boiling water reactor. Nuclear plants split uranium to raise steam with no direct CO₂; they run as steady baseload with very high capacity factors and the longest operating lifetimes of any thermal plant.

Capacity comparison computed from the WRI Global Power Plant Database; fuel-type context is general engineering background.

Key facts

Share of Japan nuclear capacity

3.7% of 58,491 MW across 24 plants in this dataset

Age among peers

11 of 17 dated nuclear plants in Japan are older

Calculated from the capacity and generation records in this dataset (WRI Global Power Plant Database (CC BY 4.0)).

Capacity vs largest nuclear plants in Japan

Installed capacity (MW), WRI Global Power Plant Database (CC BY 4.0).

Owner

Operated by Tohoku. All plants by this company →

Local climate & thermal context

This nuclear plant uses heat from nuclear fission to raise steam for a turbine-generator. It sits in a humid subtropical climate (Köppen Cfa) — Northern Hemisphere, latitude 38.4°N — which shapes how much energy it can produce and how its output varies through the year.

Monthly mean temperature

Heating degree-days here run 10% above the median power plant in this dataset — a proxy for how much extra energy heated equipment must replace through its surfaces in winter.

Climate heat-demand index: 54/100 — this site sits in the mid third of the power plants we cover by heating degree-days.

Climate normals: WorldClim 2.1 (1970–2000 monthly normals, 10 arc-min, CC BY 4.0); zone: Köppen-Geiger world climate classification (Kottek et al. 2006, 0.5° grid). Degree-days & heat-demand index computed by PowerAtlas — a modelled heat-demand proxy, not a measured site figure.

Site climate & environmental severity

This site sits in a corrosive environment (estimated ISO 9223 class C4 — High), with humidity / wetness the leading environmental stress.

Indicative estimate via the ISO 9223:2012 informative method (atmospheric corrosivity from temperature, time-of-wetness and airborne salinity), using WorldClim climate normals, the Köppen-Geiger class and coast distance. Indicative, not a measured corrosion rate.

How it compares & nearby plants

The #10 largest nuclear power plant of 24 in Japan by capacity.

Japan has 24 nuclear power plants in this dataset, together about 58,491 MW of capacity.

Nearby power plants

• Ishinomaki · Solar · 14 MW · Miyagi
• Ishinomaki Mill power station · Coal · 98 MW · Miyagi Prefecture
• Kizuna Solar Power Plant · Solar · 3.6 MW · Miyagi
• Sendai Solar Power Plant · Solar · 2 MW · Miyagi
• Sendai Tohoku power station · Gas · 468 MW · Miyagi
• SENDAI REFINERY · Other · 119 MW · Miyagi

Location

Coordinates 38.4, 141.5 from WRI Global Power Plant Database (CC BY 4.0). View on OpenStreetMap.

Frequently asked questions