Qualla: Monju: The Reactor Named for Wisdom That Never Learned Its Lesson

Monju: The Reactor Named for Wisdom That Never Learned Its Lesson: Introduction

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Nife, CC BY-SA 3.0. One hour. In the twenty years between its first test run and June 2011, Japan's prototype fast-breeder reactor Monju generated electricity for exactly one hour. The reactor consumed over one trillion yen -- approximately $9.8 billion -- during that time, not counting the 375 billion yen budgeted for a decommissioning process expected to stretch until 2047. Named after Manjusri, the bodhisattva of transcendent wisdom in Buddhist tradition, Monju became something closer to a parable about institutional failure. Construction began in 1986 near the Tsuruga Nuclear Power Plant on the coast of Fukui Prefecture. The reactor achieved criticality in April 1994. It was a sodium-cooled, MOX-fueled, loop-type machine designed to produce 280 megawatts of electricity from 714 megawatts of thermal energy, with a breeding ratio of 1.2 -- meaning it would produce more fissile material than it consumed. The dream was a reactor that created its own fuel. The reality was a facility that spent most of its life shut down.

Read more: Monju on Qualla

Image: Nife | CC BY-SA 3.0

Monju: The Reactor Named for Wisdom That Never Learned Its Lesson: Three Tons of Solidified Sodium

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit IAEA Imagebank, CC BY-SA 2.0. On the evening of 8 December 1995, an alarm sounded inside Monju. Intense vibration had snapped a thermowell inside a pipe carrying liquid sodium coolant, possibly at a defective weld point. Several hundred kilograms of sodium poured onto the floor below. Liquid sodium reacts vio...

Read more: Monju on Qualla