WIPP Gas-Generation Experiments
An experimental investigation was conducted for gas generation in contact-handled transuranic (CH TRU) wastes subjected for several years to conditions similar to those expected to occur at the Waste Isolation Pilot Plant (WIPP) should the repository eventually become inundated with brine. Various types of actual CH TRU wastes were placed into 12 corrosion-resistant vessels. The vessels were loosely filled with the wastes, which were submerged in synthetic brine having the same chemical composition as that in the WIPP vicinity. The vessels were also inoculated with microbes found in the Salado Formation at WIPP. The vessels were sealed, purged, and the approximately 750 ml headspace in each vessel was pressurized with nitrogen gas to approximately 146 atmospheres to create anoxic conditions at the lithostatic pressure estimated in the repository were it to be inundated. The temperature was maintained at the expected 30°C. The test program objective was to measure the quantities and species of gases generated by metal corrosion, radiolysis, and microbial activity. These data will assist in the specification of the rates at which gases are produced under inundated repository conditions for use in the WIPP Performance Assessment computer models. These experiments were very carefully designed, constructed, instrumented, and performed. Approximately 6 1/2 years of continuous, undisturbed testing were accumulated. Several of the vessels showed significantly elevated levels of generated gases, virtually all of which was hydrogen. Up to 4.2% hydrogen, by volume, was measured. Only small quantities of other gases, principally carbon dioxide, were detected. Gas generation was found to depend strongly on the waste composition. The maximum hydrogen generation occurred in vessels containing carbon steel. Visual examination of carbon-steel coupons confirmed the correspondence between the extent of observable corrosion and hydrogen generation. Average corrosion penetration rates in carbon-steel of up to 2.3 microns per year were deduced. Conversion of carbon to carbon dioxide was calculated to be as high as 4.7 µg mol/yr/g carbon. Carbon monoxide was detected in only two waste compositions, and methane was detected in only one. In all three of these cases, the concentrations of these lesser gases detected were barely above the detection limits. No hydrogen sulfide was ever detected. Initial rates of hydrogen generation measured in the carbon-steel-bearing wastes during the first year of testing did not always correspond to rates measured over the longer term. Compared to the long-term trends, the initial gas-generation rates for some waste types were higher, for some lower, and for others remained constant. Although carbon-steel corrosion was clearly the dominant hydrogen generator, the rates of generation were found to be reduced in test vessels where the same quantity of carbon steel was co-mingled with other waste types. This is a beneficial phenomenon relative to performance of the WIPP repository. Statistical analyses of the results were made to quantify these negative interaction effects. Electron microscopy analyses of the carbon-steel coupons revealed that corrosion products were predominantly iron chlorides and oxides. Iron, chlorine, oxygen, uranium, magnesium, calcium, aluminum, silicon were all present in the corrosion products. No americium nor neptunium, both present in the wastes, were detected in any of the corrosion products. All
- Research Organization:
- Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Sponsoring Organization:
- DOE - NE
- DOE Contract Number:
- DE-AC07-99ID-13727
- OSTI ID:
- 920400
- Report Number(s):
- INL/EXT-07-12631; TRN: US0805311
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALPHA-BEARING WASTES
ALUMINIUM
CARBON
CARBON DIOXIDE
CARBON MONOXIDE
CARBON STEELS
CHEMICAL COMPOSITION
CORROSION
CORROSION PRODUCTS
ELECTRON MICROSCOPY
GASES
HYDROGEN
HYDROGEN GENERATORS
HYDROGEN SULFIDES
IRON CHLORIDES
WASTES
WIPP
CH-TRU
contact-handled transuranic wastes
gas generation