4

Additional Processes Affecting the Alternative Treatment Approaches

Among the challenges for the Federally Funded Research and Development Center (FFRDC) team is that the alternative treatment technologies or approaches for supplemental low-activity waste (SLAW) interface with an existing and planned system beginning with waste in tanks, which is itself characterized by numerous uncertainties, and ending with a number of different disposal configurations and locations. The system in which the treatment technology is embedded impacts the choice of technology, and at the same time the choice of technology determines the characteristics and performance requirements of the system. Consideration of the alternative SLAW approaches in isolation from the systems in which they would operate could lead to poor decisions and is almost certain to miss opportunities to adjust other aspects of the SLAW and the system to achieve a faster, safer, more reliable, and less expensive tank remediation.

Finding 4-1

It is reasonable to bound the FFRDC’s scope by having it begin with a pre-treated feed stream from the Waste Treatment and Immobilization Plant’s pre-treatment plant or the Low-Activity Waste Pretreatment System because it is impractical to re-invent the numerous system-wide studies of the Hanford tank waste situation. However, it is important to recognize that some changes external to the FFRDC’s scope could have important downstream impacts on SLAW that are essential to understand when deciding on the preferred SLAW approach.

Sec. 3134 requires an analysis of “further processing of the low-activity waste to remove long-lived radioactive constituents.” In line with that requirement, this chapter addresses four processes integral to the overall objective to treat and dispose of the SLAW, but not necessarily specific to one treatment technology. The four processes are additional SLAW pre-treatment, off-gas treatment, secondary waste generation rate and treatment, and load leveling and waste blending. While at first glance these processes may seem peripheral, in several cases the best available treatment technology strongly depends on the success of effectively applying one or more of these processes. These processes were addressed in the draft report, but to varying degrees. In this chapter, the committee suggests areas concerning these processes that the FFRDC could address in its final report.

ADDITIONAL SLAW PRE-TREATMENT

The draft report in Appendix A states that additional pre-treatment of SLAW to remove strontium can impact the low-level waste classification of the SLAW. This could be significant, but insufficient information was given as to determine whether one would want to remove strontium from SLAW. In particular, while Tables A-1 and A-2 of the draft report list the number of months during the treatment duration that strontium removal would affect the waste classification for the three primary treatment approaches, Appendix A does not discuss how these changes in waste classification would affect whether the waste could be disposed on-site or off-site and how these changes would affect the costs and risks of the disposal options. While this information was discussed in the FFRDC presentations in July 2018, the committee suggests the FFRDC include it in the final report to help decision-makers.

In comparison, presentation of the pre-treatment options for technetium in Appendix A of the draft report seems to be sufficient to make an informed decision relative to the potential removal efficiency of technetium from the waste stream. However, the cost-benefit analysis of that treatment is not presented in Appendix A. Removal of technetium is more impactful for some treatment technologies than others. The final report would benefit from clearly presenting the cost-benefit analysis for technetium pre-treatment for each of the SLAW treatment options to help decision-makers.

The committee observes that presentation of the pre-treatment options for iodine, RCRA metals, and organic compounds are not covered sufficiently—especially in the form of a cost-benefit analysis—in the draft report, and it suggests the FFRDC’s final report provide this information to help decision-makers.

OFF-GAS TREATMENT

The need for off-gas treatment is mentioned in the draft report in Chapters 1 and 2, Appendix B on “Vitrification,” Appendix C on “Steam Reforming,” and Appendix K on “Feed Vector.” The choice and extent of off-gas treatment depend on the pre-treatment and SLAW treatment options that are selected. Decision-makers would benefit from understanding the off-gas treatment that is needed for additional SLAW pre-treatment and SLAW treatment options. To better inform non-technical decision-makers, the committee suggests the FFRDC more clearly present the concept of “flywheel” recycling of the effluent from off-gas treatment. The cost-benefit analysis of additional radionuclide pre-treatment relative to off-gas treatment is not covered in the draft report and would be useful for decision-making for it to be covered in the final report.

SECONDARY WASTE

During the second and third public meetings, the committee heard presentations from Washington River Protection System contractors and the FFRDC team that discuss the baseline of vitrification of LAW with grouting of secondary waste with both waste forms to be disposed at the Integrated Disposal Facility at Hanford. This is one option that the FFRDC is considering for treatment of SLAW and associated secondary waste. The FFRDC presentations from the July meeting and the draft report (mostly in the appendixes) also consider other options for secondary waste such as grouting and shipping it to Waste Control Specialists. Notably, page 49 of Appendix B on “Vitrification” lists a couple of risks that the FFRDC has identified; these are (1) the integrated flowsheet models do not consider the impact of melter idling on secondary waste volume generation, and (2) the flowsheet for immobilized low-activity waste underestimates the volume of liquid secondary waste that will likely be produced. The committee commends the FFRDC for identifying these risks. The committee suggests that the FFRDC clearly present and summarize the secondary waste production considerations in the main body of its final report and consider this issue as part of the cost-benefit analysis.

LOAD LEVELING AND WASTE BLENDING

Variability of feed rate and feed composition can pose problems for SLAW treatment. Table C-6 on page 61 of the draft report shows data that indicate the high variability of both feed rate and feed composition. Load leveling and waste blending have the potential to have a profound impact on the overall cost of the SLAW treatment. Prior work by others resulted in calculation of the System Plan 8 feed vector (ORP, 2017), which is assumed to be the waste stream entering the SLAW treatment process. But the committee is still unclear about what specific scenario(s) from System Plan 8 was used to determine the feed vector and where the feed vector is defined. Furthermore, it is not clear why there are significant fluctuations in flow rate, radioactivity concentration, and some other constituents over the lifetime of the SLAW treatment facilities. If one could make the flow rate level, then it seems that the average throughput of the SLAW treatment facility would be about one-half that of the peak that would exist in the current System Plan 8.

There is certainly a reason for the proposed feed vector, but without that information there seems to be options that could result in a lower lifecycle cost for SLAW treatment. The FFRDC’s next report offers an opportunity to include all of the feed vector assumptions and justifications for those assumptions that are relevant to the cost and risk of the SLAW treatment and how they affect each alternative.

Recommendation 4-1

The FFRDC report should consider the impact of these four processes—pre-treatment, off-gas treatment, secondary waste generation treatment, and load leveling and waste blending—on the treatment rate, reliability, performance of secondary waste following disposal, and cost of alternative approaches to SLAW treatment.