DEVELOPMENT OF CONTAINMENT-IN-PLACE
Development of the containment-in-place technology requires the installation of effective barriers to migration of contaminated fluids. The committee commends the excellent progress that is being made on this problem at Hanford. After an extensive program of research, the Hanford group recently installed a prototype of the Hanford Surface Barrier in the 200E area that is being subjected to an intensive program of performance monitoring. The Hanford researchers have expanded the concept of surface barriers to the control of contaminant migration and have recently proposed three conceptual designs that are engineered according to the nature of the waste and to comply with regulatory design requirements (U.S. Department of Energy, Richland, 1994). In addition, the Hanford group is also investigating the use of subsurface low-permeability barriers (Treat et al., 1994) that can be installed beneath the single-shell tanks. This work could very well result in significant improvements to existing barrier approaches. In the opinion of the committee, these are essential programs that should be pursued in a timely manner if DOE is to develop cost-effective methods of containment-in-place.
Another reason for the committee's suggestion that the concept of containment-in-place needs further analysis is that, in the near-term, the risk and cost associated with this method of remediation may be substantially less. Detailed analyses of these factors for five different alternative methods of remediating the radioactive wastes in both the single- and double-shell tanks are reported in the Final Environmental Impact Statement (FEIS) (U.S. Department of Energy, 1987). These analyses do not cover exactly the same operations as are envisioned by the requirements of the Triparty Agreement, but the results provide an insight into the magnitude of the problems that must be addressed. We are not aware of any more recent investigations of these issues.
With regard to collective operational radiation dose, the results indicate that the workers at Hanford who will be involved in the extensive tank retrieval and processing of the waste by vitrification will face a risk that is seven times higher than if the wastes were stabilized and isolated in situ (U.S. Department of Energy, 1987, Table i, p. xiii). With regard to nonradiological injuries and illnesses to workers, the results suggest that the alternative of extensive retrieval and processing will lead to a ninefold increase in nonradiological effects as compared to the alternative of in situ stabilization and isolation of tank wastes (U.S. Department of Energy, 1987, Table ii, p. xiii). The projections also indicate that the retrieval and processing alternative will lead to a few probable fatalities among the workers, whereas the containment-in-place alternative does not.
An analysis of risks over 10,000 years was also included in the FEIS (U.S. Department of Energy, 1987, Tables 3.10 to 3.14, pp. 3.59-3.65). This analysis projected some 64 health effects to the public in a worst case scenario, in which people lived and farmed on the site, and all passive institutional barriers to intrusion had failed or been ignored. The same analysis projected no public health effects from the removal option, but
there is no indication that this analysis considered the health effects from the wastes left in the soil by past tank leakage, waste discharge to adjacent cribs, or the leakage that might occur during sluicing to remove the waste. In deciding how best to deal with the single-shell tanks, the relatively likely near-term health and safety effects to cleanup workers from removal of the wastes should be balanced against these more speculative projections of long-term public health effects from containment-in-place.
A comparison of costs for the five alternative methods of remediating the tank wastes was also included in the FEIS (U.S. Department of Energy, 1987, Table iii, p. xiv). The results indicate that the alternative of retrieving and processing wastes costs $15 billion more ($17.5 vs $2.4 billion) than the alternative of in situ stabilization and isolation. The costs of monitoring contaminant migration will be incurred in either remediation scenario.
Finally, each of the tanks contain a variable mix of long-lived radioisotopes (such as technetium-99 and plutonium-239 and -240) and short-lived radioisotopes (cesium-137 and strontium-90). Analyses of the potential use of containment-in-place for a given tank should consider the inventory of radioisotopes and the short-term and long-term risks to the public posed by such an approach.
