Radiant energy – Radiation controlling means – Shielded receptacles for radioactive sources
Reexamination Certificate
2000-11-07
2002-12-03
Berman, Jack (Department: 2881)
Radiant energy
Radiation controlling means
Shielded receptacles for radioactive sources
C250S515100, C250S517100
Reexamination Certificate
active
06489623
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a shipping container for shipping radioactive materials such as low enriched uranium powder, pellets and scrap material and particularly relates to a shipping container for radioactive materials having improved protection for the radioactive materials, as well as affording shipping economy.
Over the years, various types of shipping containers have been designed specifically for shipping radioactive materials, for example, low enrichment uranium oxide powder, pellets or radioactive scrap. One form of prior shipping containers essentially comprised 55-gallon drum-type vessels with inner steel compartments for two 5-gallon pails of radioactive material. Experience with these containers, and over time, have brought to the fore certain problems associated with their use. For example, such shipping containers were typically fabricated from standard 18-gauge carbon steel and the product pails were standard 24-gauge carbon steel. Not only were the containers and pails susceptible to rust and corrosion, but were also susceptible to denting and deformation due to routine industrial handling. Further, those early designs were not sized for optimal loading into currently commercial sea vans. This not only reduced the amount of floor space that could be efficiently used in sea vans but it also required additional bracing and supports to keep the containers from shifting during transport.
Additionally, new regulations, both in the United States and abroad, relating to the shipment of radioactive materials have required a higher degree of structural integrity, resistance to fire and watertightness for the containers than previously applied to older container designs. From the regulatory perspective, neither the inner container drum nor the radioactive material product pails should lose their integrity. That is, the sealed inner containment drum inside the outer drum should not allow contents to leak out or allow water to leak in. Similarly, the product pails should not allow the radioactive material contents to spill. A high degree of resistance to fire is also an important requirement. As a result of the restrictions on structural integrity, fire resistance and watertightness, the radioactive material-carrying capacity per drum of older-style containers has been significantly downgraded.
More particularly, in certain instances, older containers have been found to have significant amounts of rust, including rust on the internal surfaces, which are not capable of inspection without destroying the container. Further, the insulating material has proven to be difficult to fabricate and install, especially in a manner to ensure that the insulation is homogeneous without voids or holes in the region between the inner vessel and outer drum. Further, many of the fixturing devices such as bolts and other securing devices of the older-style containers have been fabricated from typical industrial-grade materials rather than nuclear-grade materials, as consistent with current regulatory requirements. The size and geometry of the older-style containers also is not optimal for loading into standardized sea vans. Such older-style containers achieve a utilization space of only about 38%, while the factor for the present invention is 57%.
The overall regulatory objective of safety for this type of container is principally to ensure avoidance of any possibility of a criticality accident during transportation of special nuclear materials. Both the foreign and domestic regulatory requirements specify that shipping containers for special nuclear materials must undergo a number of tests, such as drop, burn and water intrusion tests, the results of which must be taken into consideration in the safety analysis submitted in support of licensing.
A recent effort by the assignee hereof has resulted in a container for high-density shipment of uranium oxide powder and pellets. Such newer container design employs stainless steel materials for fabrication with silicon rubber gaskets and heavy-duty locking rings for positive leak-tight seals. Fire retardant foam and ceramic fiberboard panel are also employed in such newer-style container to protect the contents against the effect of accident and fire. Moreover, the size and geometry is cubical rather than cylindrical and its inner containers are nine in number, arranged in a 3×3 array. This newer container is the subject of U.S. patent application Ser. No. 09/315,729, titled “Uranium Oxide Shipping Container,” filed May 21, 1999.
BRIEF SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention, there is provided a container for shipping radioactive material comprised of an outer container and an inner containment vessel for receiving and containing product pails. Particularly, the outer container comprises a generally cylindrical container open at its upper end. Bolt brackets are arranged about the inner periphery of the container for receiving bolts to bolt a top onto the container. The bolt brackets are arranged, preferably in 90° sectors spaced about the circumference of the container with a pair of brackets straddling the container's weld seam to reinforce the container when the top is installed. In addition to bolting the top to the container, a retaining ring clamps the top to the container, with a bolt securing end lugs of the retainer ring to one another. The bolt and lugs in the retaining ring are located as close to the outside wall of the outer drum as possible to avoid breakage of containment should the container be dropped or impacted.
The inner containment vessel is generally cylindrical and has a radially outwardly directed flange at its open upper end supported by a plurality of circumferentially spaced gussets to provide strength to the lid-sealing region of the vessel. A lid is bolted to the flange with a heat-resistant gasket therebetween to effect a water seal. The vessel also includes a plurality of spiders or rods which project outwardly, preferably radially, to maintain the vessel centered within the outer container. Between the inner vessel and the outer container is a heat retardant polyurethane foam. The foam limits the maximum temperature the inner containment vessel and its gasket are subjected to, for example, during a fire. The foam also protects the inner containment drum from impact forces resulting from drop and impact tests. Panels formed of neutron-absorbing poisons may also be optionally applied about the exterior surface of the inner vessel.
Upper and lower dunnages are provided at opposite ends of the outer container. The dunnages comprise foam and ceramic fiberboard panels for fire resistance. The upper dunnage includes foam disposed between a pair of circular ceramic fiberboard panels with each having a stainless steel overlay. A reduced combined stainless steel and ceramic fiberboard panel underlies the upper dunnage for reception within the lid of the inner vessel to maintain stability. The lower dunnage is likewise a combination of foam and ceramic fiberboard panels.
The inner containment vessel is permanently fixed within the outer container. For shipping, product pails are placed inside the inner containment vessel. When the lid is bolted to the inner vessel, the upper dunnage is disposed between the lid and the top of the outer container. The upper dunnage is also provided with circumferential slots to enable the upper dunnage to be lowered into the container and pass the bolt connections for disposition on top of the inner vessel container.
Further, to improve resistance to fire, a plurality of plastic-filled vent holes are provided about the outer container and the upper and lower dunnages. The plastic plugs prevent water intrusion during normal conditions but will melt away in a fire to vent the container thereby preventing buildup of gases within the container in the event sufficient heat is supplied to ignite and burn the foam. Consequently, the vent plugs enhance the structural integrity of the shipping container in t
Paulson Lon E.
Peters William Carter
Smith David Grey
Strine Roger Evan
Berman Jack
Fernandez Kalimah
Global Nuclear Fuel - Americas, LLC
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