On February 9, 1994, an operator at the Savannah River Site FB-Line vault discovered a bulging lid on a sealed forty-ounce plutonium oxide storage can. By February 18, personnel had discovered six other slightly deformed cans containing stabilized plutonium oxide blended with other stable oxides. Pressure buildup within the cans could cause a rupture that could result in the spread of radioactive contamination. (ORPS Report SR--WSRC-FBLINE-1994-0010)
Investigators found that six of the seven cans were in the same material shipment delivered from the Hanford facility about ten years ago. All of the cans were commercial grade. Inside each can was another can closed with a slip-fitting lid containing thermally stabilized oxide material.
Investigators had not determined what caused the cans to deform. There are a number of reasons for storage canisters to become over-pressurized including gases generated by corrosion of metals such as uranium, zinc, magnesium, or zirconium; radiolysis of organic materials; chemical reactions involving incompatible materials; decomposition of waste caused by anaerobic bacteria; and vapors resulting from volatile materials stored at unsafe high temperatures.
A significant source of hydrogen generation is corrosion of uranium metal. The rate of hydrogen generation is highly dependent on the form of the metal and on the extent to which water remains in contact with the metal during storage. The hydrogen generation rate can easily surpass the venting capability of a container, resulting in over pressurization.
There are several techniques to prevent or treat an over pressurized waste container. Savannah River personnel were developing a plan to safely handle the cans and correct the problem. The techniques available to correct the pressurization problem include the following.
Verify that drum contents will not create a chemical reaction resulting in the buildup of gases.
Evaporate liquids from solid waste before placing the contents within the drum.
Transfer the pressurized drum to a cooler location.
Vent the container if over pressurization occurs.
A search of the Occurrence Reporting and Processing System revealed similar occurrences at other DOE facilities.
On February 3, 1993, an employee at the Sandia National Laboratory was moving a ten gallon acid-waste container when the top ruptured, spraying the employee with an acid mist. Pressure buildup within the container was the result of acids containing hydrogen-peroxide-producing gases. (ORPS Report ALO-KO-SNL-6000-1993-0001)
On August 28, 1992, personnel at Hanford discovered a 55-gallon waste drum bulging at both ends. Investigators determined that the metal drums were air-tight, which may have contributed to a chemical or heat reaction of the contents within the drum causing a gas buildup. (ORPS Report RL--WHC-WHC200EM-1992-0051)
Safety Notice 93-01, "Fire, Explosion, and High-Pressure Hazards Associated with Waste Drums and Containers," provides additional information about similar events.
Safe storage and handling of hazardous materials require good management of process chemistry, waste, safety, and health reviews, together with excellent design, fabrication, inspection, and maintenance of containers.