Nuclear waste package container corrosion in simulated salt repository environments

This paper presents an overview of the program conducted by the DOE Salt Repository Project to develop a waste package for long-term containment of high level commercial and defense nuclear wastes in a geological bedded-salt deposit in Deaf Smith County, Texas. Although this location has recently been dropped from further consideration as a possible site for the first national repository, a discussion of the work on corrosion in not brine environments should be of general interest. The basic requirement that must be met by the waste package container has been established by the U.S. Nuclear Regulatory Commission: radionuclides of the nuclear waste must be contained within the waste packages for 300 to 1000 years after closure of the repository. Low carbon steel was selected early in the program because of its good mechanical properties, ease of fabrication (including weldability), low cost, and anticipated low susceptibility to localized corrosion in brine environments. When employed as a thick-walled container, steel would also provide some shielding of the radiation emanating from the waste form. Specific dimensions of the reference container designs varied with the different types of nuclear waste form (defense waste versus assemblies of commercial spent fuel from pressurized-water or boiling-water reactors). The largest container, designed to contain boiling-water reactor fuel assemblies, measured 15.8 feet in length by 33.3 inch outer diameter, and a cylinder wall thickness of 3.9 inches. The wall thickness required to resist lithostatic pressure is 3 inches, leaving an allowance for corrosion losses of 0.9 inch. A total of about 36,000 packages is estimated to be ultimately needed for the first repository using these waste packages designs