The DOE has established an elaborate system for safely transporting transuranic (TRU) waste to WIPP for permanent disposal or between TRU waste generator sites. The waste is transported in four specially-designed shipping casks approved for use by the U.S. Nuclear Regulatory Commission (NRC).
Three shipping casks - the Transuranic Packaging Transporter Model 2 (TRUPACT-II), HalfPACT and TRUPACT-III - are designed for hauling contact-handled (CH) TRU waste, while the RH72-B is used to transport remote-handled (RH) TRU waste. All four casks meet NRC and U.S. Department of Transportation (DOT) radiation limits for public safety.
Each stainless steel TRUPACT-II is approximately 8 feet in diameter, 10-feet high, and constructed with leak-tight inner and outer containment vessels. The TRUPACT-II can hold up to fourteen 55-gallon waste drums, eight 85-gallon drums, six 100-gallon drums, two standard waste boxes, or one 10-drum overpack. A single CH TRU waste shipment can consist of a maximum of three TRUPACT-IIs or a combination of TRUPACT-IIs and HalfPACTs.
Some shipments consist of CH TRU waste drums that weigh as much as 1,000 pounds each. The total weight of the shipment (including the truck and trailer) can be no more than 80,000 pounds, under DOT requirements. To meet these requirements, DOE designed the HalfPACT, a cask for CH TRU waste that is shorter, and therefore lighter, than the TRUPACT-II. Each HalfPACT can carry up to seven 55-gallon drums, four 85-gallon drums, or three 100-gallon drums. A single WIPP shipment can consist of a maximum of three HalfPACTs or a combination of HalfPACTs and TRUPACT-IIs.
Large CH TRU waste containers known as Standard Large Box 2s (SLB2s) are too big to fit inside either the TRUPACT-II or HalfPACT. In an effort to accommodate large waste containers such as these, DOE designed a third CH TRU waste shipping cask. This minimizes the need for size reduction and repackaging. The TRUPACT-III is a large rectangular cask comprised of inner and outer stainless steel plates and polyurethane foam to protect against potential punctures and fire danger. A single TRUPACT-III is transported on a custom-designed trailer. The maximum allowable weight of a TRUPACT-III cask can be up to 55,116 pounds, making a fully-loaded TRUPACT-III shipment 84,096 pounds. A TRUPACT-III shipment is a non-divisible load, meaning parts of the shipment cannot be removed to lessen the weight.
RH TRU waste typically has a higher dose rate on the surface of the waste container than CH TRU waste, but the dose rate limit on the outside of the shipping cask is the same due to lead shielding. The RH-72B has a 15/8 -inch thick lead liner. Because of the weight of the lead shielding, only one RH-72B is loaded per trailer.
Like the CH TRU waste casks, the steel RH-72B is leak-tight and constructed with inner and outer containment vessels. It is a large cylinder, approximately 12-feet long and about 3.5 feet in diameter. The cylinder fits into circular impact limiters, similar to shock absorbers, designed to protect the cask and its contents in the event of an accident. It also has an outer thermal shield to protect the cask against potential fire damage. Inside, a cylindrical canister holds direct-loaded RH TRU waste or up to three 55-gallon drums of RH TRU waste.
Some RH TRU waste is packaged in lead-shielded containers and handled and emplaced as CH TRU waste. The activity of the RH TRU waste must be low enough to result in a dose rate of less than 200 millirem/hour at the surface of the shielded container. Shielded containers are shipped in CH TRU waste shipping casks. The shielded container has a 1-inch thick lead shielding sandwiched between a double-walled steel shell with a 3-inch thick steel lid and base. It is designed to hold a 30-gallon drum and has approximately the same exterior dimensions as a 55-gallon drum. Three containers can be shipped in a HalfPACT. The containers are tracked as RH TRU waste.
Testing and Certification
All transportation casks used to transport TRU waste to WIPP are NRC-certified Type B casks. Type B casks must meet stringent NRC design, fabrication, operation and maintenance requirements. Designs for the Type B casks must withstand normal transportation conditions, such as exposure to high and low temperatures, varying external pressure, and impact from debris.
In addition, NRC certification requires Type B casks to withstand a series of hypothetical accident scenarios without failing. The NRC regulations (10 Code of Federal Regulations Part 71) allow computer-simulated, scale model or full-scale model testing to demonstrate a transportation cask's suitability for certification. A combination of these methods is commonly used. Extensive full-scale model testing was conducted at Sandia National Laboratories.
The tests performed include:
- Free-Drop Test. The transportation cask is dropped from 30 feet onto a flat, unyielding surface (such as a steel-reinforced concrete pad), striking the surface at the weakest point.
- Puncture Test. Next, the transportation cask is subjected to a 40-inch free drop onto a six-inch diameter steel bar at least eight inches long.
- Burn Test. The transportation cask is drenched with jet fuel and ignited, subjecting it to a temperature of 1,475 degrees Fahrenheit for 30 minutes.
- Immersion Test. Using specialized analyses, a separate transportation cask of the same design is subjected to external pressure equivalent to being immersed under 50 feet of water.
When all the requirements for design and testing are met, NRC issues a Certificate of Compliance for the design of the transportation cask. The certificate specifies procedures for the manufacture, operation and maintenance of the packaging. It also defines the packaging's authorized contents. The certificate is valid for five years. At the end of this period, DOE may apply to renew certification.