The investigation into the root cause of an explosion which destroyed a 2m-long section of auxiliary cooling system piping close to the Brunsbüttel pressure vessel in December has concluded that friction generated by operation of a valve ignited radiolysis gas built up near the valve.
The gas volume accumulated in the auxiliary system at the time of the explosion was greater than had been predicted because the original calculations of expected radiolysis gas production did not take into account hydrogen production resulting from a valve leak. Last year, such a valve leak occurred, investigators have concluded. The leak permitted relatively cool water from the water purification system to flow into the auxiliary piping system and give rise to a large amount of hydrogen gas.
