An in-tank explosion occurred in a gaseous waste decay tank while the plant was in cold shutdown. The gaseous hydrogen present in the tank formed a flammable mixture and ignited due to air contamination of the inert nitrogen system used to control the hydrogen-oxygen concentrations in the tank. This resulted in a release of about 8.8 curies of noble gases and minor tank damage.Generally, the gas in pressurized water reactor waste gas systems is hydrogen rich and the oxygen concentration must be controlled to prevent flammable gas mixtures.

Piping breakage at atomic power plant- Steam piping (inside diameter: 15 cm; thickness: 1.1 cm) of a heat exchanger for removing residual heat from a reactor was broken during the test of a high pressure core injection system for cooling water provided for an emergency core cooling system at a boiling-water light water reactor with an output of 0.54 million kW, thus resulting in leakage of radioactivity-containing gases. The part of the piping that was located on the 2nd floor of the building as broken but there were no workers there.

At about 3:15 p.m. on Dec. 3 2003, personnel in the Expended Core Facility at the Naval Reactors Facility heard a loud, unexpected noise. Upon investigation, personnel found an irradiated material storage container fell from its normal submerged storage location in the water pool to the pool floor, and that the lid had come off.The lid was found about 10 feet away from the container on the bottom of the water pool. No nuclear fuel was involved.According to a press release, a team of technical experts determined the most likely cause was a hydrogen gas explosion within the container.

A hydrogen explosion had ruptured a pipe in the core spray system at the Brunsbttel BWR in Germany. Although the control room instrumentation had at the time indicated a leak of radioactive steam, the nature of the event had not been fully recognized: operators had isolated the leak and continued operation. Investigations suggested that the hydrogen (formed by radiolysis of the water) accumulated in a part of the pipe between catalytic recombiners.

A technical failure in the High-Pressure turbine blades caused high vibrations in lubricating oil pipes. Some pipes broke off and the oil leak caught fire from hot surfaces. Also the generator's hydrogen leaked out and exploded. The fire caused the loss of control air and electrical power of several safety-related components: for instance, two turbo-blowers and main heat exchanges were inoperable The fire also affected a main circulation water pipe expansion joint causing outpouring of sea water which caused the flood of the lower levels of the turbine and reactor buildings

The event occurred during the decommissioning of a nuclear power plant. It involved a tank containing 100 kg of residual sodium from the decommissioned experimental nuclear reactor which was using liquid sodium as coolant. The reactor had been shut for many years. A heavy alcohol compound was used to to create a stable salt (sodium is very reactive in presence of oxygen or water). This method had previously proved successful.

An hydrogen explosion occurred within the off-gas system, causing the stop of the sump pump; subsequently both trains of the standby gas treatment system were declared inoperable. The sump is part of the off-gas system and the secondary containment. The hydrogen explosion was contained within the system, but the sump pump sustained some damage.

Rockville, Maryland, on June 9th, the control panel door for the 32 hydrogen dryer blew off due to a small hydrogen explosion. No one was injured in the event, which occurred in the non-nuclear side of the plant in the main turbine building. An investigation into the cause for the hydrogen leak is continuing. Plant operations was not impacted by the explosion, and the licensee intends to replace both hydrogen dryer units.Source: U.S.

Hydrogen ignition during welding on a VSC-24 spent fuel cask Pursuant to 10 CFR 72.210 - fuel in an independent spent fuel storage installation at its Point Beach Nuclear Power Plant. The inspection of activities conducted under that general license, found that the weight of the multi-assembly sealed basket (MSB) shield lid was not appropriately translated from the safety analysis report into several procedures and there was an inadequate procedure for placing the MSB transfer cask into the spent fuel pool.

Two hydrogen explosions occurred at a boiling water reactor (BWR). The first explosion occurred at 9:30 a.m. and was mostly confined to the off-gas system. Damage was relatively minor.The second explosion occurred at 13:00 outside the off-gas system in the two-level room at the base of the plant stack. This explosion damaged considerable the stack however, the overall structural capability of the stack was not impaired. One man was injured.The review of the event concluded that the action taken to restore off-gas system drain line loop seals in the stack base space had not been successful.