A hydrogen explosion occurred in an emergency battery container used to transfer fuel elements. The container had five emergency power batteries. Damage was incurred by the explosion.
The H2 concentration in the container increased because the battery charger had been left on charge. In addition, the container was placed in an un-ventilated airlock. Ignition of the H2-air mixture was believed to be caused by the relays and micro switches activated when the airlock door was opened.