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Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
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3

FINDINGS

Many uncertainties exist with respect to implementation of tank remediation alternatives, including those related to technology, cost, performance, regulatory environment, risk, and waste and environmental characterization. These unknowns make it difficult to identify and evaluate the significant environmental impacts with any confidence. Because of these uncertainties, it would be premature for DOE and the State of Washington to commit to any final waste management decision.

In its recommendations, which appear in a subsequent section, the committee presents a framework for a phased decision strategy leading to selection of the most acceptable alternative or alternatives, as distinct from a phased implementation of a preselected alternative, to resolve these significant uncertainties.

TECHNOLOGY UNCERTAINTIES

With the exception of the No Action and Long-Term Management Alternatives, the technologies for the tank waste remediation alternatives presented in the DEIS have not been demonstrated for the Hanford tank wastes. Therefore, not only is the effectiveness of the alternatives unknown, but whether they are feasible at all for use with the tank wastes is also largely unknown.

The uniqueness, complexity, and enormous scale of the Hanford tank waste problem make the remediation task unprecedented in DOE's experience. The diversity of the reprocessing and other radioactive waste treatment operations carried out at Hanford has produced a broad spectrum of waste types. These types tend to be grouped into tank farms, each having waste that is greatly different from the others. In addition, the excess alkalinity of the wastes, combined with their chemical complexity, has produced a situation that makes characterization of the tank contents difficult. Without adequate characterization it is difficult to decide among remediation alternatives. In any case, for all of those treatment alternatives

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
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that involve removing the wastes from the tanks, a single alternative is unlikely to be suitable for all the different types of waste.

Some of the single-shell tanks contain very refractory solids whose complete removal may be difficult or even impossible without destroying the integrity of the tanks. Most of the single-shell tanks contain sludges that are composed largely of aluminum- or phosphate-containing compounds. Waste removal and transfer operations are likely to alter the physical and chemical natures of these wastes in unknown ways. Dilution of the wastes during sluicing and transfer operations may form colloids and gels, hindering the effectiveness of subsequent process steps. Additional precipitates of unknown physical and chemical composition are likely to form. Removal of the solid cakes could damage the tanks, leading to unacceptable leakage. Conversely, the double-shell tanks contain slurry whose transfer is likely to be relatively easy. However, even in the case of the double-shell tanks the transfer operations may cause changes in any waste whose nature is unknown.

Vitrification of high-level radioactive wastes has been demonstrated for many years on a large scale for well-characterized acid waste feed streams of essentially unvarying composition. However, this is not the case with the Hanford tank wastes for the In-Situ and Ex Situ No Separations Alternatives and is not certain to be the case for the Ex Situ/In Situ Combination, the Ex Situ/In Situ Combination Variation, and the Ex Situ Intermediate Separations Alternatives. In these alternatives, the waste feed to the vitrifier will be alkaline, much larger in quantity than any in previous experience, and of variable composition.

The vitrification operations are certain to be difficult, especially in those alternatives that involve no separations of bulk chemical constituents before vitrification. Radioactive off-gas treatment, particularly in cases involving relatively large amounts of cesium present in the vitrifier, will pose significant technical challenges. Because both cesium and technetium are likely to reach the vitrifier at some point during its operation, it is desirable during operation of the pilot plant to learn how to handle both of these elements in the vitrifier off-gas system.

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
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COST ESTIMATE UNCERTAINTIES

While not necessarily a component of environmental impact assessment, the uncertain and high costs, currently projected at $7 billion to $253 billion in constant dollars, mandate careful review of all of the attributes of the various remediation alternatives. The higher cost estimates for certain alternatives are driven in part by significant uncertainties in waste amount, cost of waste recovery and processing, numbers of waste canisters produced, disposal repository acceptance criteria, and number and timing of repository operations. As an example, estimates of fees at repositories for the ex situ alternatives range from $0.6 billion to $211 billion (DEIS, Vol. One, Sec. 3), a difference of more than 300-fold.

The committee believes that cost uncertainties are even greater than reported in the DEIS. For example, costs of final disposal of high-level waste are used in the DEIS as a major factor in differentiating costs of various alternatives. These costs are estimated on the assumption that the cost of final disposal will be directly proportional to the amount (in volume units) of high-level waste sent to the final repository. This reasoning leads the authors of the DEIS to conclude that extensive separations of the tank waste streams could produce cost savings in the final disposal that counterbalance the cost of the separations.

The assumption that final disposal costs of high-level waste will correlate closely to waste volume is unverified. It is premature to conclude that charges will be based on the volume that is sent to the repository, despite current agreements within DOE. Much of the costs of final disposal stem from fixed costs associated with siting and licensing of the repository and construction of facilities such as shafts and support buildings that are common to all wastes received. The amount of defense waste that will be accepted at the first high-level waste repository is defined in terms of masses of uranium fuel from which the waste was derived. This could mean that the repository will accept a fixed portion of the total Hanford Site inventory of high-level waste, regardless of volume. In that case separation processing that reduces the volume of high-level waste would not change the fraction of the inventory that can be sent to the repository and, therefore, would be unlikely to change the fraction of the fixed costs that will be allocated to defense high-level waste from the Hanford Site.

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

The committee believes that selection of alternatives should not be predicated strongly on repository costs that are highly uncertain at this stage.

In its projection of costs, DOE does not appear to have been responsive to deficiencies noted in its own report System Requirements Review, Hanford Tank Waste Remediation SystemFinal Report (U.S. Department of Energy, 1995). In that report it is suggested that cost estimates for the Tank Waste Remediation System are too uncertain to permit accurate assessment of alternative approaches to meeting performance requirements. Current cost estimates are characterized as “very optimistic” for the many first-of-a-kind systems under consideration (U.S. Department of Energy, 1995, p. v). Privatization of the tank cleanup program further diminishes DOE's ability to predict costs. Because of the many uncertainties about the tank wastes, contracts may have to be repeatedly modified to reflect new information.

There is a potential for enormous cost increases as the program develops. An example of this potential is found in the sensitivity analysis for the Ex Situ Intermediate Separations Alternative. Uncertainties in waste loading parameters are projected to result in a range of $30 billion to $43 billion in total cost, with a repository fee component ranging from $6 billion to $16 billion (DEIS, Table B.8.2.1). The total estimated cost range for each alternative is derived from the input parameters based on best available information, conceptual cost estimates, and engineering judgment. In addition, this range is sensitive to major changes caused by new information on characterization of the wastes, conceptual designs, and assumptions concerning regulatory, land use, and environmental factors (DEIS, pp. B-181). None of the alternatives, even those with high projected costs, include costs for final tank closure, which as discussed below are deferred to a later date and another NEPA review.

PERFORMANCE UNCERTAINTIES

The DOE TWRS System Requirements Review came to several conclusions on uncertainties in the performance of the technologies required for tank remediation. The report noted that the “TWRS

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
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conceptual architecture relies on numerous first-of-a-kind processes ” (U.S. Department of Energy, 1995, p. 2-25). Among the uncertainties and unknowns cited were (1) retrieval of wastes with long-reach mechanical arms that have yet to be developed, (2) pretreatment of wastes by an enhanced sludge-washing process that has yet to be proven in the laboratory, (3) use of sluicing to attain greater than 99 percent waste removal, more complete waste removal than has been required in the past, and (4) immobilization of high-level waste by forming glass in an unproven way in a facility much larger than any existing one.1

In addition, the System Requirements Review found that the “conceptual architecture is vulnerable to single-point failure of any of the assumed processes” (U.S. Department of Energy, 1995, p. xvi). The proposed architecture was found to be likely to take longer and cost more than currently projected to remediate wastes at the Hanford Site. The Review proposed that:

. . .Risks should be mitigated by performing laboratory-and bench-scale tests that validate assumptions and substantiate performance expectations for the preferred and competitive architectures. [italics added ].

A preliminary baseline (technical, cost and schedule) needs to be established with quantified top-level performance requirements that incorporate resolution of key policy issues. This baseline needs to include schedules for the testing and validationof the assumed solutions, as well as solutions that may be substantially

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The DOE System Requirements Review concluded (U.S. Department of Energy, 1995, p. vii):

Uncertainties are still too great and the variations in the Hanford Site wastes are so significant that there is no assurance a unique, generally applicable process may be found. In order to reduce these uncertainties, the following steps must be taken on a priority basis:

  • The wastes must be characterized expeditiously;

  • Viable, competitive alternatives for dealing with various types of wastes must be defined;

  • These competitive alternatives must be tested following the proven engineering practices that begins at the laboratory scale and progresses to bench and pilot scales; and

  • Rigorous trade-off studies using technically defensible criteria at each stage along this path are needed to produce defensible selections of processes for TWRS.”

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
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better. [italics added ] (U.S. Department of Energy, 1995, p. xvi).

Resolving uncertainty about the effectiveness of processes in removing waste from the tanks, particularly the single-shell tanks, is especially important. The DEIS relies heavily on the combination of sluicing and long-reach arm technology for waste retrieval. Based on its experience with the former at both the Hanford and the Savannah River Sites, however, DOE judged both technologies to be insufficiently developed and tested to the point where they could be recommended confidently for use on the Hanford tanks (U.S. Department of Energy, 1995).

Judgments on performance of the strategies can only be speculative since there is little actual experience with the various suggested technologies. The decision by DOE and the Washington State Department of Ecology to adopt a phased approach for removing and treating the tank wastes is clearly a prudent approach in a situation such as that at the Hanford Site, where there are many uncertainties. A phased decision strategy, as recommended by the committee, allows for process improvements to be made based on experience and provides a credible basis for estimating the performance of future operations.

Recognizing such uncertainties, the preferred alternative in the DEIS involves pilot projects for the processes needed to carry out that alternative at full scale. However, because of uncertainty about the performance of the preferred alternative, it is appropriate to carry some backup alternatives into the pilot phase as well. On this point, the DOE TWRS System Requirements Review concluded:

Key testing programs to obtain performance data do not follow proven engineering practice; they are focused on preferred processes with negligible attention being given to alternatives that might be needed if performance assumptions are not met. (U.S. Department of Energy, 1995, p. iv)

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
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REGULATORY UNCERTAINTIES

Regulatory requirements that will be applied to the tanks and their contents are a significant area of uncertainty. Currently, the Tri-Party Agreement states that the tank wastes are hazardous wastes regulated by the Washington State Department of Ecology under various authorities, including the Resource Conservation and Recovery Act (RCRA). The Tri-Party Agreement references a host of other laws as well, including the State of Washington's Model Toxics Control Act, NEPA, and the Clean Air Act. The role of the U.S. Nuclear Regulatory Commission (USNRC) in this arena may also need to be clarified.

Environmental rules are often written in general terms that leave a substantial amount of discretion to regulatory agencies. Industrial companies commonly engage in informal negotiation with regulators over detailed implementation of the rules. In addition, waivers of specific rules are frequently available when it can be shown that the underlying aim of the requirement can be achieved in a different way, or when the cost of compliance is excessive. Such flexibility is most important and most frequently used with unusual materials and processes that are unlike those that were envisaged when the rules were written. Regulation of the Hanford tanks under Environmental Protection Agency (EPA) rules written for ordinary chemical wastes is such a case. Furthermore, environmental regulations change over time. It is difficult to know what rules will apply to treatment and disposal processes some decades in the future, and it is important for those involved with the Hanford Site cleanup to ensure that the processes under development and any relevant regulatory changes are on convergent paths. The committee notes that the Hanford Tri-Party Agreement has been amended through negotiation four times since it was entered into in 1989; a fifth amendment is currently being negotiated.

There are several important areas in which the DEIS contains restrictive interpretations of rules that are ambiguous, takes insufficient account of regulators' flexibility in dealing with unusual situations like the Hanford tanks, or neglects the likelihood that environmental rules will change over time. For example, the DEIS concludes that many alternatives that leave waste in the tanks would violate the land disposal restrictions under RCRA (DEIS, pp. 3-47 and 3-92). This conclusion is premature.

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

Under the land disposal restrictions, EPA defines treatment standards for particular waste streams from particular industries. These standards are based on existing technologies and practices whose costs are not prohibitive. The EPA standard for high-level waste treatment as expressed for specified technologies (40 CFR Part 268.42) appears to assume that the waste is from commercial reactors because it requires vitrification in a plant regulated by the USNRC. A treatment standard for single-shell tank high-level waste that required dewatering and tank stabilization with gravel or other stabilizers would appear to be consistent with the EPA philosophy in setting land disposal restrictions for other industries. The DEIS should not prejudge this regulatory decision.

The DEIS states that waste recovered in the ex situ/in situ option would require USNRC licensing for disposal in a geologic repository. However, implementing this option would also result in the creation of residues from the high-level and low-activity waste vitrifiers and residues in the form of the “heel” left behind in the tanks following waste removal. The committee believes these residues would be novel enough that the regulatory regime would be unique and require a special determination.

In other areas, the DEIS relies on favorable interpretations of regulations. Several of these were noted in the DOE TWRS System Requirements Review(U.S. Department of Energy, 1995).2 What constitutes “incidental waste” [waste originating from nuclear fuel

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“. . .To avoid wasteful expenditures of money and resources on the design of an unacceptable system, policy-level decisions are needed urgently to validate several assumptions including the following:

  • The low-level waste fraction separated from the waste in single-shell tanks, miscellaneous underground storage tanks and catch tanks, and placed in near surface vaults will be accepted by the U.S. Nuclear Regulatory Commission as incidental waste not subject to their regulatory jurisdiction;

  • Any residual material left in the tanks after practical retrieval operations will be suitable for in situ tank closure, i.e., how clean is clean;

  • The transuranic waste can be blended with high-level waste for disposal in the geologic repository if it is determined that separation of some, or all, of the in-tank transuranic waste for disposal at the Waste Isolation Pilot Plant is more costly or presents significant safety or environmental hazards;

  • The projected volumes of immobilized high-level waste in the selected size canisters will, in fact, be accepted for the geologic repository, and that the expected and bounding fees for permanent disposal of waste will be established expeditiously; and

  • Multiple, nonconforming glass compositions, significantly different than Defense Waste Processing Facility and West Valley Project borosilicate glass, are to be pursued despite risks that regulators might not accept one or more of these glasses.” (U.S. Department of Energy, 1995, pp. xii-xiii)

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

processing that is not defined as high-level waste (DEIS, p. G-11)] may prove critical to decisions on both waste treatment and tank closure. The exact requirements of the regulations that will apply to the Hanford Site waste treatment and disposal activities are as yet unknown. Furthermore, DOE and the public have significant opportunities to influence the regulations through negotiation with regulators in an arena that includes public participation. It seems likely that what makes environmental, technical, and economic sense will have more influence on future rules than predictions based on the wording of the current rules, even though DOE needs to be mindful of the current regulatory environment.

The DEIS needs to expressly recognize the dynamic nature of decision making with respect to the tank wastes by providing review and revision approximately every 5 years as allowed by 10 CFR Part 1021. Given the large scale of the Hanford Site environmental remediation, it is prudent to review periodically total costs, total risks, and cumulative and indirect environmental impacts for the entire Hanford Site environmental remediation, and for the TWRS program specifically, in a public process.

UNCERTAINTIES IN TANK AND ENVIRONMENTAL CHARACTERIZATION

An important component of a long-term commitment to remediating the single-shell tanks at the Hanford Site is an adequate understanding of the nature of the present contents in the tanks and the extent to which the soil and ground water beneath the tank farms have been contaminated. Characterization should continue until such an understanding has been obtained.

In the 200 Areas of the Hanford Site where the tank farms are located, the waste in the tanks (approximately 177 million Ci) and the cesium and strontium capsules (173.5 million Ci) account for approximately 90 percent of the 391 million Ci of the total inventory (DEIS, p. 1-5). Another 1.4 million Ci is estimated to have been released or leaked to the ground. Approximately 4.9 million Ci has been disposed of in solid waste burial grounds, and 2.6 million Ci is stored in solids or contained in irradiated fuel storage. The DEIS addresses only the

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

management and disposal of tank wastes and part of the inventory of cesium and strontium capsules. Other waste disposal activities in or near the Hanford Site 200 Areas that are not addressed in the DEIS include (1) site waste from the environmental restoration program (to be disposed of in the Environmental Restoration Disposal Facility), (2) commercial low-level waste disposed of at the U.S. Ecology site, and (3) submarine reactor compartments.

Recent monitoring in the vadose zone beneath a single-shell tank revealed 137Cs at the bottom of a 125-foot (38-m) well (Rust Geotech, 1996). This finding does not appear to be consistent with what is otherwise known about cesium mobility in the subsurface environment surrounding the tanks. The source of this radionuclide may be a tank, or it may have come from other past disposals in cribs or directly into the ground. The cesium may have been carried down the well during drilling, entered the hole through faulty casing, or migrated along some other preferred path. In another recent finding the State of Washington Department of Ecology noted contamination by 99Tc of the ground water under a tank farm, citing evidence leading to the conclusion that this radionuclide came from the tanks (Leja, 1996). More discoveries are possible as tank and environmental characterization studies proceed, and it is unclear at this point what implications they may have for the conduct of the remediation program.

The committee understands that a first step in characterizing single-shell tank conditions under the new Hanford Tanks Initiative (U.S. Department of Energy, 1996b) will be to investigate two single-shell tanks: tank AX-104, reported in 1977 to be a leaker and now mostly empty of liquids primarily due to pumping; and tank C-106, which has a high heat generation problem. Removal of material from tank AX-104 is to be done mechanically and will provide data on the effectiveness of this approach. Presumably, hydraulic sluicing of an almost empty but formerly leaking tank would not be desirable or practical and will not be attempted.

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
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HEALTH RISK UNCERTAINTIES

In the DEIS, analyses of health risk effects are divided into two time periods: short-term impacts during remediation and during the post-remediation monitoring and maintenance period, assumed to be a 100-year administrative control period; and potential long-term impacts beginning after the 100-year administrative control period and continuing for 10,000 years into the future. Short-term potential health effects would result from occupational nonradiological accidents, occupational radiological exposure during operations and waste transportation, radiological and chemical accidents, and transportation accidents from deliveries of materials and supplies to the site (DEIS, p. S-22). The primary potential long-term impacts are ground water contamination, health effects associated with consumption of the ground water, and potential health effects resulting from post-remediation intruders and accidents (DEIS, p. S-25).

Presentation of Key Risk Parameters and Health Impact Projections

Several key parameters directly affect the calculation of potential health effects, including the range of variation in source and source term, exposure parameters, risk coefficients and hazards indices, size and temporal distribution of populations at risk (both workers and public), and degree of conservatism in health risk calculation methodologies. Many of these parameters have been selected on an upper-bound rather than expected value basis to provide conservative projections of potential health effects. In some instances, cascading of conservatively-derived parameters has produced conservative estimates that may not reflect meaningful values. Examples of such cascading found in the DEIS include the calculation of probability of risks from radiological and toxicological accidents (DEIS, pp. E-27 through E-28) and the treatment of a sample accident scenario involving a mispositioned jumper (short connecting pipe) (DEIS, pp. E-247 through E-248).

Estimates of potential health effects, both short- and long-term, for each of the remediation alternatives are scattered throughout the DEIS volumes, making comparison difficult. Risks are frequently presented as individual health effect probabilities without reference to time frame or size

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
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of population at risk (DEIS, Table 5.14.1). The expected values of these health effects projections and their uncertainties are either not displayed or are difficult to locate within the DEIS.

Use of Guidance on Collective Dose

The estimates of latent health effects in the DEIS are based on collective dose multiplied by risk coefficients and, for chemicals, exposure multiplied by hazard coefficients. While the National Council on Radiation Protection and Measurements (NCRP; 1995) and the International Commission on Radiological Protection (ICRP; 1991) have provided guidance on the use of such methodology for estimating exposure to radiation, both groups recognize that collective dose can be used to derive an estimate of collective or total health detriment from radiation exposure only under limited conditions.3More explicit guidance is given by NCRP with respect to the use of collective dose to determine societal risk from future exposures to long-lived environmental radioactive contaminants.4

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“. . .However, the legitimate applications of collective dose must include clearly defined boundary conditions for the time, locations and pathways of exposure, as well as characteristics of the exposed populations. The uncertainties must not only be stated, but should be used to determine the extent to which the collective dose can be used as a surrogate for risk.

When the combined uncertainties in the exposed population, e.g., size, those related to characteristics, exposure pathways and individual doses, result in a collective dose with a relative uncertainty of more than an order of magnitude, neither estimates of collective dose nor estimates of collective risk are adequate for making decisions. ” (National Council on Radiation Protection and Measurements, 1995, p. 48)

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“Neither population size and characteristics nor environmental exposure pathways for most radioactive elements are predictable with any degree of confidence for more than a few generations into the future. . . Consequently, there can be no meaningful calculation of collective or individual doses for populations far in the future. For this reason, collective dose projected more than a few generations into the future should not be used as a basis for estimating societal risk or for limitation or practices, although such projections may have some utility for other purposes.

The most reasonable risk assessment that can be made for such situations is to calculate potential individual doses for a range of scenarios in order to: (1) evaluate protective measures and (2) to try to place some boundaries on estimates of future individual risks. For the few very long-lived radionuclides that are metabolically regulated in the body and more or less uniformly distributed within the biosphere (e.g., 14C and 129I), future average individual doses may be estimated from total quantities in the environment even though there could be no valid estimate of collective dose because of the lack of knowledge regarding future populations and their demographics.” (National Council on Radiation Protection and Measurements, 1995, pp. 57-58)

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

The DEIS derivations of potential long-term health risks from collective dose estimates have gone beyond what the NCRP guidance suggests is appropriate. Adverse health effects have been projected for 10,000 years, rather than the few generations recommended by NCRP, with significant uncertainties concerning sources, pathways of exposure, and characteristics of future populations at risk. The NCRP admonitions concerning the use of collective dose as a risk surrogate should be recognized in the risk projections. Moreover, all estimates of exposures that could lead to future adverse health effects were calculated on an upper-bound basis in the DEIS rather than on the basis of expected values.5 In keeping with the NCRP guidance and to facilitate a more meaningful comparison of alternatives, both the expected value and range of health risk estimates, as well as the upper-bound values, should be provided when possible for each remediation alternative. To provide a public health context for the estimates, statistics on the background cancer rates and occupational risks to workers and the general population should be presented.

Risk Assessment for Comparison of Alternatives

The risk estimates for occupational accidents given in the DEIS appear to be within average experience, taking into account the size of the populations at risk and the period of time for remedial actions. Summaries in the DEIS of potential long-term health effects of each of the remediation alternatives all present post-remediation potential cancer incidences and fatalities from exposures out to 10,000 years. It is not clear whether these estimates are calculated from radiation exposures or combinations of radiation and chemical exposures. Unavoidably, the uncertainties

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For example, in the DEIS (p. S-23):

“…a bounding approach to estimating accident consequences was taken in the EIS. Conservative estimates were made for the type and amount of contaminants that would be released and how they would be transported in the atmosphere to expose both workers and the public. Therefore, the health effects calculated provide an upper bound for the health effects that could occur.”

Also, in the DEIS (p. D-297):

“The summation of cancer risk across pathways or for multiple pathways makes the total cancer risk more conservative. This is because each slope factor for each chemical carcinogen is an upper 95th percentile estimate and such probability distributions are not strictly additive. ”

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

associated with these estimates are high (DEIS, p. 5-150) because assumptions must be made concerning data on sources, transport, dose-response relationships, hypothetical land use, population distributions, and receptor behavior. The risk estimates thus derived should reflect the NCRP guidance noted previously. The uncertainty in the risk values for certain receptors increases as time into the future increases.

It is important to recognize that risk to human health, especially to workers on the site, increases significantly as the degree of remediation and its complexity are increased. Ultimately there are trade-offs between occupational risks, completeness of in situ remediation, export of wastes with concomitant risk during transportation, and uncertainties about risks at an external site.

While the committee recognizes the utility of quantitative risk assessment in the comparison of remedial alternatives, the limitations of analysis must be underscored. Given the complexities of the tank farms, many of the potential uncertainties cannot be measured, quantified, or expressed through statistically derived values. Therefore, the characteristics of risks and their ranges must go beyond a synthesis of statistical estimates. Characterization of risks should be both qualitative and quantitative. Qualitative information should include a range of informed views about the risks and the evidence that supports them, the risk likelihood, and the magnitude of uncertainty (U.S. Environmental Protection Agency, 1996; Commission on Risk Assessment and Risk Management, 1996).

The practice of maximizing risk by upper-bounding of the parameters inevitably leads to biased decision making when comparing alternatives. As noted in a recent report of the National Research Council:

Organizations responsible for characterizing risks should plan to blend analysis with deliberative processes that clarify the concerns of interested and affected parties, help prevent avoidable errors, offer a balanced and nuanced understanding of the state of knowledge, and ensure adequately broad participation for a given risk decision. (National Research Council, 1996a, p. 72)

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

Both expected values and ranges of risk estimates and their uncertainties should also be provided, and limitations on the assessment of long-term societal risks acknowledged. In addition, as noted in the DOE guidance for NEPA:

Analyses generally should be based on realistic exposure conditions. Where conservative assumptions (i.e., those that tend to overstate the risk) are made, describe the degree of conservatism, and characterize the “average” or “possible” exposure conditions if possible. (U.S. Department of Energy, 1993, p. 21)

Intruder Scenario Estimates

The DEIS projects a high probability of significant risk to the waste site intruder over the long-term of 1-in-1, making it a major component of projected long-term risk. It projects 5.5 intrusions into single-shell tanks and 0.58 (or 1) intrusion into double-shell tanks over the 10,000 year period (DEIS, Table D.7.5.1). Significant uncertainties in intruder risk result from the way in which certain factors have been selected to produce a maximum or upper-bound risk estimate. For example, the amount of radioactivity to which the intruder is exposed is based on the tank inventory in the year 2095. No correction is applied for radioactive decay over the remainder of the 10,000-year period, although the anticipated 5.5 intrusions may be expected to be randomly distributed over that time period.

Moreover, the representative waste tank source area used for the analysis (called source area “3EDS” in the DEIS and made up of three adjacent double-shell tank farms, AN, AZ, and AY) has the highest radioactive inventory (in total curies of 137Cs) of the eight aggregated tank source areas used (DEIS, Table A.2.1.8). These tank farms were combined as source areas for the purpose of ground water modeling, based on tank contents (inventory), tank proximity, and ground water flow direction. The inventories from individual tank farms were combined to create the waste inventory for each source area (DEIS, p. A-2). Selection of a double-shell tank source area with the highest combined inventory of 137Cs highlights

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
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the conservatism of the approach used in the DEIS to estimate risks associated with the intruder scenario, especially as it is applied to the single-shell tanks, and reinforces the need to provide both expected values and upper-bound estimates of risk.

Dose-Response Estimates

The uncertainties of long-term risk projections were recognized in previous reports of the National Research Council:

The uncertainty, especially regarding human intrusion into a repository over a 10,000-year time span, is such that “it is not possible to make scientifically supportable predictions of the probability” of such an intrusion (National Research Council, 1995:11 [1995a, p. 11]). (National Research Council, 1996a, p. 107)

In the DEIS, estimates of risk based on upper-bound assumptions do not represent expected values or reflect changing conditions over the 10,000-year period.6 For example, the 1-in-1 risk of latent cancer fatality given to a waste site intruder (DEIS, Table S.7.4) would apply only to the post-drilling resident. The total inventory of the eight aggregated tank sources ranges from 20.8 Ci to 1,030 Ci, with an arithmetic mean of 326 Ci (DEIS, Table D.7.1.1). Adjusting for source term and radioactive decay, the expected values for dose estimates for the intruder scenario must be lower by one or two orders of magnitude or more over time. A more realistic approach is needed, and both expected values and ranges of risk should be provided subject to uncertainties noted above. Similar considerations apply to other groups evaluated for the period following the 100-year administrative control period.

6  

Under the No Action, Long-Term Management, and In Situ Fill and Cap Alternatives, which are stated to convey the greatest risks, the probability of a latent cancer fatality was calculated to be 8.52E-03 for the driller, and 2.96E+00 for the post-drilling resident (DEIS, Table D.7.4.2.). The dose-to-risk conversion factors used for cancer fatality are 4.00E-04 for the well driller and 5.00E-04 for the post-driller resident (DEIS, Section D.7.4). By dividing the estimated probabilities by the pertinent risk coefficients, the calculated doses are 21.3 rem to the driller (received over 40 hours) and 5,920 rem to the post-driller resident (received over 70-year lifetime), or an average of 84.5 rem per year.

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

UNCERTAINTIES ABOUT REMEDIATION OF RESIDUAL CONTAMINATION

Under RCRA a hazardous waste management unit must be “closed” after it is no longer used. Such an end point may be accomplished either by “clean closure,” which requires removal of all detectable contamination and is not a realistic option for the Hanford tanks, or “closure as a landfill,” which requires stabilization and capping to limit waste migration, followed by long-term monitoring. The term “closure ” refers to a legal determination by regulators that an acceptable technical job of remediation has been accomplished. As applied to the Hanford tanks, closure requires remediating the tank wastes, as well as the tanks, ancillary equipment, and contaminated soil and ground water. In common usage, “closure” sometimes refers only to the legal determination and sometimes to the remediation activities as well.

Conceptually, the Washington State Department of Ecology and DOE have divided the technical work of remediating the Hanford tanks into two parts. One part, removal, treatment, and disposal of the wastes in the tanks, is the subject of the DEIS. The second part, remediation of the tanks themselves, waste that cannot be removed from the tanks, waste from deliberate discharges, and environmental contamination that is associated with the tanks, is outside the scope of the DEIS and will be addressed separately in the future.

This division artificially limits the alternatives available. For one, the option of deliberately leaving some waste in tanks is precluded. Furthermore, decisions on waste in the tanks are interrelated with decisions regarding the tanks themselves, associated equipment, and soil and ground water contaminated by past leaks and deliberate discharges.

For example, some of the tank retrieval activities are projected to lead to further leakage of tank contents. The retrieval of single-shell tank waste under each of the ex situ alternatives was assumed to result in the release of approximately 15,000 liters (4,000 gallons) of material from each single-shell tank to the soil surrounding it during retrieval operations (DEIS, p. B-176). No leakage was assumed to occur from the double-shell tanks during retrieval operations. For the single-shell tanks, the total release from the 149 tanks would be 2.3 million liters (600,000 gallons).

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

The single-shell tank radionuclide inventory of 104 million Ci is contained in approximately 140 million liters (36 million gallons) of waste. Discounting any dilution during the waste slurrying process, retrieval of the single-shell tank wastes could result in the release of an additional 1.7 million Ci of radioactivity to the surrounding soil, an amount on the same order of magnitude as the 1.4 million Ci already estimated to have been released or leaked to the soil in the 200 Areas. This leakage is explicitly excluded from the scope of the DEIS (p. 5-12).

It is not at all evident how a preferred tank waste retrieval and treatment remediation alternative can be selected rationally without simultaneously considering what is to be done with the contamination left behind. Some of the decisions to be made concerning disposal of tank waste will limit future decisions on what to do about the tanks themselves and any unremoved wastes. The DEIS provides little information on this subject. For purposes of analysis, it assumes that the tanks will be covered with a multilayer cap, the Hanford Barrier (DEIS, Figure S.6.2), except in the No Action and Long-Term Management Alternatives, which essentially maintain the present tank farm status.

The DEIS confuses these issues in its choice of terminology. The word “closure” is used to describe both the second part of the remediation (the tanks and waste left in the ground) and the final legal determination that both parts of the cleanup have been concluded satisfactorily. DOE and the Washington State Department of Ecology state that they intend to develop a plan for closure, defined in this way, at a later date. No timetable is given, but waste treatment operations that must precede closure are not projected to end before the years 2009 to 2028 for the various alternatives (DEIS, Tables 3.7.1 and B.11.0.1). Indeed, this schedule seems optimistic in view of the new technologies, construction and operations activities, and resources required.

TRANSFER OF RISK TO OFF-SITE POPULATIONS

Risks that may be transferred to off-site populations by transfer of waste from the Hanford Site to repositories, while not a component of this DEIS (p. S-16), are an important part of the risks of the various

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

remediation alternatives and should be considered when the alternatives are compared. For example, in the in situ alternatives, all radioactive wastes remain in the 200 Area tank farms and convey their risks to the public and the environment from those locations. In the Ex Situ/In Situ Combination Alternative, appropriate tanks would be selected so that 90 percent of the contaminants that contribute to long-term risk would be disposed of ex situ while only 50 percent of the waste would be retrieved (DEIS, pp. 3-86 to 3-88). Thus, only 10 percent of the projected long-term risk would remain on site, while most of the risk would be transferred to transportation of the retrieved wastes and to an off-site geologic repository.

For all other ex situ alternatives, tank waste would be separated into low-activity waste and high-level waste fractions. The high-level waste fraction, varying in volume according to the degree of separation applied, would be immobilized by vitrification or some other solidification process and sent to a geologic repository for off-site disposal. All of the long-term risk from high-level waste would be transferred to transportation of the wastes and to the repository site. The radioactivities estimated for wastes left in place are within the 10- to 15-millirem limits prescribed in 40 CFR Part 191 for repository doses.

Basing health and environmental risk estimates solely on on-site source terms results in inconsistencies and gives an inappropriate basis for comparing various remediation alternatives. In other environmental impact statements DOE has prepared comparative analyses of risks for alternatives involving waste disposal on and off site, including transportation risks. Such a comparison need not require elaborate analysis; for example, risks from final repositories could be assumed to equal the risk targets set in the EPA regulations. Such a comparison for 200 Area wastes could provide insight as to levels of acceptable risk. The appropriate portions of this off-site risk should be allocated to each of the pertinent alternatives in the DEIS.

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

FUTURE LAND USE UNCERTAINTIES AND EFFECT ON ALTERNATIVES

Future land use is a critical factor for making decisions concerning tank waste at the Hanford Site. The DEIS defers discussion of future land use of the site. The absence of a comprehensive land use plan and analysis creates the possibility that proposed tank decisions may involve the application of cleanup standards that are not consistent with intended uses of the 200 Areas or other portions of the site. The ability of DOE to make final cleanup decisions anywhere on the site is thus limited. Although difficult to accomplish, development of a plan detailing future land uses and analyzing their implications for cleanup would be extremely useful.

Land use is closely related to risk assessment. EPA guidance on land use of Superfund sites should be cited and considered when developing exposure scenarios (U.S. Environmental Protection Agency, 1995). Future land uses may be restrictive, unrestrictive, or conditioned in specific ways.

The DOE report Charting the Course: The Future Use Report (U.S. Department of Energy, 1996a) describes efforts by the Hanford Future Site Uses Working Group to develop a Hanford Remedial Action Environmental Impact Statement and Comprehensive Land Use Plan. Such a document could meet the need for a broader context for decision making discussed above. This potentially significant effort is not referenced in the DEIS, however. The numerous commitments that have been made in the Tri-Party Agreement to specific timetables for elements of the cleanup have rendered coordination of environmental documentation for the Hanford Site difficult, a problem exemplified by the limited discussion in the DEIS of land use consequences of TWRS cleanup alternatives.

CAPSULES AND MISCELLANEOUS TANKS

There is little substantive discussion in the DEIS of the management and disposal of the cesium and strontium capsules and of the miscellaneous underground storage tanks. To be sure, more than 99

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

percent of the tank wastes is in the single- and double-shell tanks, where the greatest potential for health risks exists. However, the high concentration of radioactivity and the nature of the materials in the capsules warrant a more thorough discussion of their treatment, disposal, and environmental impact. Additionally, the large number and wide distribution of the miscellaneous underground storage tanks make a more complete discussion of their management necessary.

Cesium and Strontium Capsules

Although the DEIS describes the capsules and discusses their treatment and disposal, it is not clear that adequate attention has been given to the changes in chemical and isotopic composition that will occur over time. The capsule remediation alternative is missing important information. The No Action and Onsite Disposal Alternatives would leave a large amount of both 137Cs (half-life of 30 years) and 135Cs (half-life of 2.3 million years) in a near-surface disposal facility. Even though the hazard of the long-lived radionuclide will persist well beyond the 100-year institutional control period assumed in the DEIS, the risk to intruders or the general public from other release mechanisms is unspecified.

Cesium Capsules

The situation with the cesium is more complex than that considered in the DEIS. Table 2 provides the cesium isotope composition as a function of decay time. It is important to note that approximately 5 percent by weight of the capsule contents is long-lived 135Cs and that approximately 40 percent of the capsule is composed of elements other than cesium. The 135Cs activity will exceed that of the 137Cs after approximately 560 years. The times required for the cesium capsule

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

Table 2. Isotopic Composition of Hanford Reservation Cesium Capsules (after A.G. croff, personal communication)

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

contents to reach the low-level waste Class A, B, and C concentrations that are generally acceptable for various types of near-surface disposal, based on 10 CFR Part 61, are given in the lower portion of Table 2. While these limits are not directly applicable to DOE operations, they are indicative of the long times over which the cesium capsules remain a potential risk.

Of particular relevance, the capsules will be intensely radioactive for hundreds of years because of the presence of 137Cs, and they will remain hazardous for millions of years because of the presence of 135Cs, with an activity of approximately 60,000 nCi/g during the first million years. The capsules are Class C low-level waste for approximately 410 years because of the 137Cs alone, and they are estimated to remain in such a classification for a few millions of years because of the 135Cs.

There is no indication in the DEIS that the longer-term (beyond 100 years) hazard from the 137Cs or 135Cs in the capsules was considered in characterizing the impacts of cesium capsule management alternatives. The committee believes it is necessary to include this consideration, especially when characterizing alternatives that involve leaving the capsules on the Hanford Site.

The non-cesium components of the capsules should also be considered in assessing the performance of cesium capsule management alternatives. Of the 40 percent of the capsule contents that is not cesium, approximately half is chlorine (as chloride) initially associated with cesium. The rest is composed of stable barium resulting from the decay of the cesium, and an assortment of incidental chemicals that accompanied the CsCl during its recovery. Some trace radionuclides are also to be expected but are not identified. The amount and composition of incidental species is poorly characterized and can vary from several percent to approximately 15 percent. It is composed of elements such as sodium, potassium, barium (present in the Hanford tanks when the cesium was recovered), iron, and nickel.

An additional complicating feature is that the decay of monovalent cesium results in the production of divalent barium. Because the amount of chlorine combined with the radioactive cesium is only one-half of that needed to balance the divalent barium produced by the decay of cesium, it it is likely that the more noble impurity elements present in the capsules will be reduced by the barium. Any unreacted barium will be present as

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×

metallic barium, which is likely to persist over a long time period. The change in chemical species is also likely to cause volume changes of unknown direction and magnitude that may become important. The identity and impact of these other elements on the long-term integrity of the cesium capsules, which must be taken into account in assessing the impacts of the various alternatives, have not been addressed in the DEIS.

Strontium Capsules

Strontium-90, which is divalent, decays with a 28.5-year half-life to stable 90Zr, which is normally tetravalent. It is not clear what the effect of the resultant deficiency of fluoride ion will be on the stability of the capsules. There will be a significant change in chemical composition as the transmutation from strontium fluoride to zirconium fluoride (and presumably to uncombined zirconium metal) takes place. Additionally, there is the potential for a net increase in the volume of the capsule contents. In the DEIS there is no discussion of the potential effects of these changes on the integrity of the capsules and, thus, the risk associated with capsule disposition. In contrast to the situation with the long-lived 135Cs, the changes are not a long-term issue in the strontium capsules. In approximately 830 years the concentration of 90Sr in the capsules would be less than the low-level waste Class A level of 0.04 Ci/m3.

Miscellaneous Underground Storage Tanks

There is too little discussion of the miscellaneous underground storage tanks in the DEIS for a meaningful analysis of their proposed treatment and management and an evaluation of the adequacy of the alternatives in this application. In the DEIS, it is assumed that the same general approach will be used for these tanks as for the single-shell and double-shell tanks.

Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
×
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Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
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Suggested Citation:"3 Findings." National Research Council. 1996. The Hanford Tanks: Environmental Impacts and Policy Choices. Washington, DC: The National Academies Press. doi: 10.17226/5403.
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The Hanford Site (also known as the Hanford Reservation) occupies approximately 1,450 km2 (560 square miles) along the Columbia River in south-central Washington, north of the city of Richland. The site was established by the federal government in 1943 to produce plutonium for nuclear weapons. Currently, the mission of the site, under the responsibility of the U.S. Department of Energy (DOE), is management of wastes generated by the weapons program and remediation of the environment contaminated by that waste. As part of that mission, DOE and the State of Washington Department of Ecology prepared the Hanford Site Tank Waste Remediation System Draft Environmental Impact Statement (DEIS).

The Hanford Tanks is a general review of the DEIS. Its findings and recommendations are the subject of this report. Selection of a disposition plan for these wastes is a decision of national importance, involving potential environmental and health risks, technical challenges, and costs of tens to hundreds of billions of dollars. The last comprehensive analysis of these issues was completed 10 years ago, and several major changes in plans have occurred since. Therefore, the current reevaluation is timely and prudent. This report endorses the decision to prepare this new environmental impact statement, and in particular the decision to evaluate a wide range of alternatives not restricted to those encouraged by current regulatory policies.

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