Model Based Structural Evaluation and Design of Overpack Container for Bag-Buster Processing of TRU Waste Drums

This paper describes a materials and computational model based analysis utilized to design an engineered “overpack” container capable of maintaining structural integrity for confinement of transuranic wastes undergoing the cryo-vacuum stress based “Bag-Buster” process and satisfying DOT 7A waste package requirements. The engineered overpack is a key component of the “Ultra-BagBuster” process/system being commercially developed by UltraTech International for potential DOE applications to non-intrusively breach inner confinement layers (poly bags/packaging) within transuranic (TRU) waste drums. This system provides a lower cost/risk approach to mitigate hydrogen gas concentration buildup limitations on transport of high alpha activity organic transuranic wastes. Four evolving overpack design configurations and two materials (low carbon steel and 300 series stainless) were considered and evaluated using non-linear finite element model analyses of structural response. Properties comparisons show that 300-series stainless is required to provide assurance of ductility and structural integrity at both room and cryogenic temperatures. The overpack design were analyzed for five accidental drop impact orientations onto an unyielding surface (dropped flat on bottom, bottom corner, side, top corner, and top). The first three design configurations failed the bottom and top corner drop orientations (flat bottom, top, and side plates breached or underwent material failure). The fourth design utilized a protruding rim-ring (skirt) below the overpack’s bottom plate and above the overpack’s lid plate to absorb much of the impact energy and maintained structural integrity under all accidental drop loads at both room and cryogenic temperature conditions. Selected drop testing of the final design will be required to confirm design performance.

Gamma Scan Confirmation of Lead Pour in a Type B Cask

Packaging Technology, Inc., a subsidiary of the French nuclear consortium Areva, has been tasked with manufacturing six RH-72B (72B) casks for the Department of Energy’s Carlsbad Operations Office. The 72B transportation cask will be used to transport remote-handled (RH) transuranic wastes to the Waste Isolation Pilot Plant (WIPP) located in New Mexico. Certification of each 72B cask includes a gamma scan of the cask lead shielded wall to verify that no significant voids form within the lead subsequent to the lead pour. Voids in the lead would be revealed as spikes in the gamma scan measurements. The radioactive isotope Iridium-192 was used as the source for the gamma scan measurements. To determine the maximum and minimum expected values for the cask gamma scan, a test fixture was required to be developed with flat plate shields that matched the maximum and minimum thicknesses of the steel-lead-steel cask wall. Design of the test fixture was a non-trivial exercise due to the influence of backscatter radiation, which if unshielded resulted in unreasonably high test fixture radiation doses. To properly shield the backscatter radiation, a collimator is required around the source. The measured dose rates using the test fixture is highly sensitive to the diameter of the collimator penetration, as a collimator penetration diameter that is too narrow results in artificially low dose rate measurements when compared to the cask measurements. To assist in the design of the collimator, the Monte Carlo N-Particle (MCNP) gamma transport code was employed. Using MCNP computer simulations, it was determined that a collimator diameter of 6 inches was sufficient to properly mimic the cask configuration.

Independent Technical Oversight of WIPP: An Operating Repository

The Waste Isolation Pilot Plant (WIPP), a geological repository for the disposal of transuranic wastes from the United States defense programs, began disposing of waste in March 1999. The experience of the Environmental Evaluation Group (EEG) indicates that a technical oversight group that focuses on objective technical evaluations can add credibility to a nuclear repository project. The group can also have an effect on a variety of design, regulatory, and operational details of the project.

Cleaning Up the Legacy: Opening and Operating the Waste Isolation Pilot Plant

In 1957, the National Academy of Sciences concluded that the most promising disposal option for radioactive wastes was burial in deep geologic repositories situated in salt formations. In 1981, after decades of study, the United States initiated construction of the Waste Isolation Pilot Plant (WIPP) at a desert site 41.6 km (26 miles) southeast of Carlsbad, New Mexico. This paper provides an overview of the history and the regulatory and public process to permit a repository for disposal of transuranic wastes. In addition, the process to ensure its long-term operation in a safe and environmentally sound manner will also be discussed.