Bohunice A1 refuelling accident
Czechoslovakia's first power reactor was destroyed by a fuel assembly loaded with its moisture absorber still in place. It was never restarted and its decommissioning is still running.
| Date | 1977-02-22 |
|---|---|
| INES rating | 4 Accident with local consequences
Retrospective. INES was introduced in 1990, so this rating is an attribution made
afterwards rather than an assessment a regulator issued at the time.
|
| Facility | power reactor |
| Unit | Bohunice nuclear power plant A1 |
| Reactor type | Gas-cooled reactor (GCR) |
| Country | Slovakia |
| Deaths at the time | 0 |
|---|---|
| Acute radiation deaths | not established |
No deaths in this event. Two workers had been killed at the same reactor thirteen months earlier, in January 1976, when a fuel assembly was ejected during loading and released carbon dioxide into the reactor hall. That earlier event is not separately rated.
A silica gel packet left in a fuel assembly, blocking coolant flow
What happened
Fuel assemblies were shipped with silica gel packets to keep them dry. During loading, packets were not removed from one assembly, blocking the flow of carbon dioxide coolant. The fuel overheated, the cladding failed, and coolant and heavy water moderator mixed, corroding fuel across the core and contaminating the primary circuit.
Consequences
No off-site release of consequence. The reactor was written off. Decommissioning began in 1979 and is expected to run into the 2030s, more than fifty years.
What changed afterwards
A reactor lost to a packaging step. It ended Czechoslovakia's indigenous gas-cooled heavy water line and pushed the country onto Soviet VVER designs, which is what Slovakia runs today. The site remains one of the longest-running decommissioning projects anywhere.
Other accidents
| Accident | INES | Date |
|---|---|---|
| Chernobyl | 7 | 1986-04-26 |
| Fukushima Daiichi | 7 | 2011-03-11 |
| Kyshtym (Mayak) | 6 | 1957-09-29 |
| Chalk River NRX | 5 | 1952-12-12 |
| Windscale Pile 1 fire | 5 | 1957-10-10 |
| Three Mile Island Unit 2 | 5 | 1979-03-28 |
| SL-1 | 4 | 1961-01-03 |
| Lucens | 4 | 1969-01-21 |
| Saint-Laurent A1 fuel melt | 4 | 1969-10-17 |
| Saint-Laurent A2 fuel melt | 4 | 1980-03-13 |
| Tokaimura criticality accident | 4 | 1999-09-30 |
| Browns Ferry cable fire | 3 | 1975-03-22 |
| Greifswald cable fire | 3 | 1975-12-07 |
| Vandellòs I turbine fire | 3 | 1989-10-19 |
| Tomsk-7 reprocessing explosion | 3 | 1993-04-06 |
| Davis-Besse vessel head corrosion | 3 | 2002-03-06 |
| Paks fuel cleaning accident | 3 | 2003-04-10 |
| Fukushima Daini | 3 | 2011-03-11 |
Sources
- International Atomic Energy Agency INIS, Serious accidents in the A-1 nuclear power plant · retrieved 2026-09-07
How these sources are used, including the corrections applied on top of them and what is deliberately left blank · download the underlying data