Qualla: Mihama Nuclear Power Plant: Japan's First Reactor to Break the 40-Year Rule

Mihama Nuclear Power Plant: Japan's First Reactor to Break the 40-Year Rule: Introduction

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Hirorinmasa, CC BY-SA 3.0. On 23 June 2021, control room operators at the Mihama Nuclear Power Plant watched their instruments climb toward output levels not seen in a decade. Unit 3 was producing power again -- and in doing so, it broke a barrier no Japanese reactor had crossed before. Under regulations imposed after the 2011 Fukushima disaster, nuclear reactors in Japan face a hard forty-year operating limit unless their owners invest billions of yen in safety upgrades and win regulatory approval for a twenty-year extension. Unit 3, a Westinghouse pressurized water reactor that first generated electricity in 1976, had done exactly that. The restart cost Kansai Electric Power Company approximately 165 billion yen -- about $1.51 billion -- and followed a full ten years of shutdown. The reactor sits on 520,000 square meters of land in the town of Mihama, Fukui Prefecture, about 320 kilometers west of Tokyo. Sixty percent of that site is green space. The pastoral setting belies a complex history.

Image: Hirorinmasa | CC BY-SA 3.0

Mihama Nuclear Power Plant: Japan's First Reactor to Break the 40-Year Rule: A Pipe Nobody Checked

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit 663highland, CC BY 2.5. The date that haunts Mihama is 9 August 2004. Workers were preparing for routine inspections of Unit 3 when a pipe in the secondary condensate system ruptured, sending superheated steam into the turbine building. Five workers were killed and six others seriously injured. The pipe...

Image: 663highland | CC BY 2.5

Mihama Nuclear Power Plant: Japan's First Reactor to Break the 40-Year Rule: Faults Beneath the Foundations

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit 藤谷良秀, CC BY-SA 4.0. In March 2012, seismic researchers delivered alarming findings about the Urasoko fault, which runs through the Fukui nuclear corridor. Previous estimates by the Earthquake Research Committee had put the fault at about 25 kilometers long, capable of producing a magnitude 7.2 earth...

Image: 藤谷良秀 | CC BY-SA 4.0

Mihama Nuclear Power Plant: Japan's First Reactor to Break the 40-Year Rule: Two Reactors Retired, One Reborn

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit M'akhr, CC BY-SA 4.0. Post-Fukushima regulations imposed a forty-year limit on reactor operations. Kansai Electric did the math on its two oldest units at Mihama. Unit 1, commissioned in 1970, and Unit 2, online since 1972, were small reactors by modern standards. The cost of fire-retardant cable repl...

Image: M'akhr | CC BY-SA 4.0

Mihama Nuclear Power Plant: Japan's First Reactor to Break the 40-Year Rule: Contested Power

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit (WT-en) Jpatokal at English Wikivoyage, CC BY-SA 3.0. The restart of Unit 3 did not proceed without opposition. Citizens from Fukui, Kyoto, and Shiga prefectures had long fought the operation of reactors in the Fukui corridor. In August 2011, residents near Lake Biwa -- Japan's largest freshwater lake, which provides drinking water ...

Image: (WT-en) Jpatokal at English Wikivoyage | CC BY-SA 3.0

Mihama Nuclear Power Plant: Japan's First Reactor to Break the 40-Year Rule: A Precedent on the Wakasa Coast

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit ENERGY.GOV, Public domain. Mihama sits on the Wakasa Bay coast, part of a concentrated stretch of nuclear infrastructure sometimes called 'Nuclear Alley.' Within a few kilometers stand the Tsuruga Nuclear Power Plant, the now-decommissioned Monju fast-breeder reactor, and other facilities. The region's emb...

Image: ENERGY.GOV | Public domain