Stress analysis of high-level waste canisters: methods, applications, and design data

Abstract

The Pacific Northwest Laboratory (PNL) is conducting research and development studies on technology for immobilization of nuclear wastes. In this report, an overview of stress analysis methods, structural design procedures, and design data is presented for canisters used to package solidified wastes, particularly borosilicate glass. In addition, waste processing, canister materials, fabrication and inspection methods, and performance testing are summarized. Sources of stress in canisters are lifting and handling loads, internal pressure, hightemperature filling operations, transient heating and cooling, differential thermal expansions of canisters and glass, and impact loadings from low-probability accidents. Results of case studies that illustrate applicable methods of stress analyses are presented for these sources of stress. Existing sections of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code are reviewed and found to be applicable to canister fabrication, but the code does not cover many aspects of canister service loadings. Specialized criteria for minimum wall thicknesses to sustain filling stresses are proposed in this report. Results of a test program to measure the creep strength of candidate canister materials are described. Methods to predict residual stresses in the walls of waste canisters are described; predicted residual stress levels agree with measured stress levels. The consequences of these residual stresses are reviewed, and stress-corrosion cracking is identified as the mode of canister failure affected by residual stresses. Canister-closure design is covered in detail, particularly the welding and inspection of the final closure seal-weld. It is shown that the methods of fracture mechanics and fatiguecrack-growth analyses are valuable tools for evaluating the performance of closure welds in the presence of crack-like defects. Canister performance in process trials at PNL shows the ability of canisters to survive high temperatures and loadings during processing. The results of impact tests at PNL show that a suitably designed canister can sustain severe impacts without loss of integrity • iii

Fracturing of simulated high-level waste glass in canisters

“…In this case, fins were Stainless steel fins were found to cause significant fracture damage in 20-cm-dia canisters as a result of the large thermal expansion mismatch between stainless steel and waste glass (Simonen and Slate 1979).…”

Assessment of degradation concerns for spent fuel, high-level wastes, and transuranic wastes in monitored retrievalbe storage

“…Data relating the impact velocity of small glass samples to the weight percent of respirable fragments generated are given in Ross 1975). Other work on impact testing of full-scale canisters has also been completed and provides data that compare well with small-scale test results (Simonen and Slate 1979).…”

“…Elongation of the canister wall (i.e., increase in circumference) is less than 1%, which-is insignificant when compared with the amount of elongation required before failure. Analyses and tests indicate that the residual stress does not reduce the ability of the canister to contain the glass (Simonen and Slate 1979).…”

“…Canister Degradation. Degradation of the canister has been the focus of many studies: Simonen and Slate 1979;Solomon et al 1978;Pavich and Rao 1978;McCoy 1983;Angerman and Rankin 1978;Peters and Slate 1981;Smith and Ross 1975;Wu et al 1978). Under the dry storage conditions of an MRS facility, no significant exterior corrosion of the SS will occur.…”

“…The bottom is a reversed-dished flanged tank head. Extensive structural and thermal analyses on various canister designs have been conducted(Simonen and Slate 1979; 0.1~-------------------------ft/s FIGURE 11. Effect of Impact Velocity on Fraction of Respirable Particles Formed(Smith and Ross 1975)…”