Nuclear waste encapsulation

A. R. Boccaccini, S. Atiq and R. W. Grimes, Hot-Pressed Glass Matrix Composites Containing Pyrochlore Phase Particles for Nuclear Waste Encapsulation, Adv. Eng. Mat. 5, 501-508 (2003). 

TBq (14,000 Ci) of reportedly low-level nuclear waste, concrete-encapsulated in at least 47,500 55-gallon 16-gauge steel drums (life-expectancy 30 year in sea water) (Suchanek et al. 1996). These were deposited at three sites 100, 900, and 1,800 m deep. 

The induction periods for the reaction of sodium nitrate—bitumen mixtures (43 57 wt) heated at 195, 234 or 260°C are 44, 2 and 0.5 h, respectively. Further study of sodium nitrate/bitumenised waste systems held at these temperatures showed an initial weak exotherm around 260°C and a larger exotherm (0.96—1.21 kJ/g) accompanied by 50% wt loss around 430°C [1]. Following an actual accident while encapsulating nuclear waste the system has been re-examined. With small nitrate crystal size, the mixing process can potentially give runaway from little above 160°C, by initial surface reaction slowly warming until the salt melts, whereupon exother-micity sharply increases [2]. 

A fire and explosion reulted from encapsulating nuclear waste [15], consisting mostly of sodium nitrate, in asphalt. The full details of the reaction reported are complex, the principles simple [12]. Nitrate/asphalt has previously seen application as rocket fuel and may have been behind Greek Fire [Editor]. A more theoretical study, also looking at the influence of silver compounds has appeared [13]. 

In the past ten years the number of chemistry-related research problems in the nuclear industry has increased dramatically. Many of these are related to surface or interfacial chemistry. Some applications are reviewed in the areas of waste management, activity transport in coolants, fuel fabrication, component development, reactor safety studies, and fuel reprocessing. Three recent studies in surface analysis are discussed in further detail in this paper. The first concerns the initial corrosion mechanisms of borosilicate glass used in high level waste encapsulation. The second deals with the effects of residual chloride contamination on nuclear reactor contaminants. Finally, some surface studies of the high temperature oxidation of Alloys 600 and 800 are outlined such characterizations are part of the effort to develop more protective surface films for nuclear reactor applications. ... 

Many of these approaches have been used in mixed potential models to predict the behavior of copper nuclear waste containers in a compacted clay environment (22), and to predict the corrosion rate of nuclear fuel inside these containers once they have failed and water allowed to contact the nuclear fuel (U02) wasteform (6). The container is lined with a carbon shell liner to give it mechanical integrity. Consequently, when the container floods with water on failure, two corrosion processes are possible, corrosion of the U02 wasteform (conservatively assumed to be unprotected by the Zircalloy cladding within which it is encapsulated) and corrosion of the carbon steel liner. The reaction scheme underlying... 

Nuclear power reactors have the following safety issues nuclear waste, plutonium buildup and radioactivity. Nuclear waste from the reactor fuel consists of uranium that has been formed into a usable metal alloy and provided as small pellets, rods, or plates. The fuel is encapsulated with a metal cladding, such as zircaloy, which adds mechanical strength and also prevents radioactive contamination. 

Donald IW, Metcalfe BL, Greedharee RS (in press, a) A glass-encapsulated ceramic wasteform for the immobilization of chloride-containing ILW Formation of halite crystals by reaction between the glass encapsulant and ceramic host. In Scientific Basis for Nuclear Waste Management XXV, Materials Research Society Proceedings... 

In 1999 the Waste Isolation Pilot Plant (WIPP) in New Mexico began receiving nuclear waste. This facility employs tunnels carved into the salt beds of an ancient ocean. Once a repository room becomes full, the salt will collapse around the waste, encapsulating it forever. 

Engineered barriers generally include a waste form (spent nuclear fuel or glass containing radioactive wastes) encapsulated within a metallic container (e.g., steel and copper), which may be surrounded by a low-permeability, clay-rich buffer and backfiU. Natural barriers include the repository host rock and a volume of rock between the repository and biosphere. The engineered barriers and immediately adjacent host rock are referred to as the near field [1]. 

Swedish Nuclear Fuel and Waste Management Co. 1995. RD D Programme 95 - Treatment and Final Disposal of Nuclear Waste. Programme for Encapsulation, Deep Geological Disposal, and Research Development and Demonstration. The... 

Sulfur polymer cement shows promise as an encapsulation and stabilization agent for use with low level radioactive and mixed wastes. Use of SPC allows accommodation of larger percentages of waste than PCC. As of this writing (1997), SPC-treated waste forms have met requirements of both the Nuclear Regulatory Commission (NRC) and the Environmental Protection Agency (EPA). 

There has been a past perception, particularly in the nuclear community, that the issues of waste isolation lie primarily in the political and socio-economic arena and that no real technical problems remain. I believe that this is correct with respect to the first category of issues, namely, there is no question that we understand how to encapsulate, transport and safely handle radio-... 

Copper as Encapsulation Material for Unreprocessed Nuclear Fuel Waste", KBS TR 90, 1978... 

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