During Maintenance

While refilling the hydrogen system after an outage caused by a power failure, the excess flow valve located at the hydrogen tank tripped, but did not go fully shut.

A facility replaced the copper tubing used for hydrogen distribution, with stainless steel tubing. This was done to address a fire protection concern related to the solder on the copper tubing being susceptible to heat, melting, and releasing a flammable gas. The facility maintenance personnel completed the replacement, noted the pressure on the hydrogen bottle, and left the building. When the maintenance person returned on the following day, s/he noticed the pressure on the hydrogen bottle had dropped 500 psi overnight, indicating a leak in the system.

A hydrogen monitor leak detector (HMLD) was out of service because of a failed membrane. The HMLD heater circuit and the ion pump and its associated controller were de-energized and red-tagged to ensure the system remained shut down. The ion pump and controller were later found energized. The ion pump circuit is a low-power (120-V, 1 amp) circuit and the pump operates in the micro-amp range. There was no damage to equipment from this inadvertent energization.

A liquid hydrogen neutron moderator developed a leak between the canister that contains liquid hydrogen and the insulating vacuum jacket.

An unplanned shutdown of the hydrogen supply system occurred, affecting the hydrogen furnaces in the plant. The apparent cause was an inadvertent valve closing, which was contrary to the written procedure.

A facility representative observed pipe-fitters enter a containment tent around a riser with a tool bag that contained a mixture of steel and copper/beryllium tools. The top flange was loosened using a copper/beryllium socket and a steel torque wrench. When questioned, the pipe-fitters correctly stated that this was allowable for initial loosening and tightening of these bolts. A copper/beryllium ratchet was used to accomplish the bolt removal. The bonded riser was shifted to allow access for the IH technician.

A large, hydrogen-cooled generator is driven by steam turbines at a power station. During maintenance shutdowns, the hydrogen cooling loop in the generator is purged with carbon dioxide. After CO2 concentrations are measured with a densitometer to verify the complete removal of hydrogen, the generator is purged with air and the maintenance is performed.

A water treatment plant used an electrolytic process to generate sodium hypochlorite (NaOCl) from sodium chloride (NaCl). The strategy of using liquid sodium hypochlorite for disinfecting water instead of gaseous chlorine (CL2) is popular because the liquid is generally safer and falls under fewer OSHA and EPA standards. The further idea of generating the liquid sodium hypochlorite on an as-needed basis and in limited quantities also has certain obvious safety advantages.

An offgas system mishap involved two explosions occurring within an interval of about 3 ½ hours. The first offgas explosion was reportedly caused by a welding operation on an air line adjacent to a hydrogen sensor line containing off gas. The welding arc initiated a detonation within the offgas piping. The detonation was contained by the piping system but blew out the water seal at the base of the vent stack.The second hydrogen explosion in this incident occurred in the stack base area.

On a given day personnel were removing a blind hub that had been used to temporarily isolate a portion of a gaseous hydrogen system. As a result of a sudden release of 2,800 psig gaseous nitrogen, sand and debris kicked up from the concrete pad and caused minor injury to two technicians.

During the investigation, it was found that: