Technical Advances for Geologic Disposal of High Activity Waste

"High activity waste” consists of spent nuclear fuel (SNF)—fuel that has been withdrawn from a nuclear reactor following irradiation—and high-level radioactive waste (HLW), the highly radioactive material resulting from the reprocessing of SNF. The primary inventory of SNF in the United States is from commercial nuclear power plants. There are approximately 70,000 metric tons¹ of commercial SNF assemblies (an example of a commercial nuclear fuel assembly is illustrated in Figure 1)² in the United States. Almost all these assemblies are stored underwater in pools or in dry storage at the reactor sites where the SNF was generated (Pietrzyk 2014).

Figure 1

In addition, the federal government owns approximately 2,500 metric tons of SNF from its defense production, naval nuclear propulsion, research and development, and other activities. The government also has approximately 350,000 cubic meters of HLW from reprocessing for defense purposes, most of which is in large underground tanks in liquid, sludge, or solid forms that will require conversion to an inert solid form prior to disposal.³

Before its termination by the Obama administration in 2009,⁴ the plan was to dispose of the majority of the nation’s high activity waste in a mined geologic repository at Yucca Mountain (Figure 2)—assuming its long-term safety could be established to the satisfaction of the US Nuclear Regulatory Commission (USNRC)—with a second repository to follow upon reaching the capacity of Yucca Mountain.

Figure 2

The purposes of this paper are to highlight some of the accomplishments of the Yucca Mountain project, to outline developments since its termination, and to discuss specific actions for moving forward with the development of a mined geologic repository in the United States.

Technical Advances before Project Termination

Among the advances made by the Yucca Mountain project were a greater fundamental understanding of water flow in unsaturated fractured rock⁵ in arid regions; models to account for runoff, evaporation, and plant transpiration; a better understanding of the effects of capillary forces and other parameters; mapping techniques for locating faults and past volcanic activity; greatly improved understanding of seismic and igneous hazards; improved, state-of-the-art methods for eliciting information from experts; and design alternatives for controlling the temperatures in the repository.

Engineered Barriers

Any repository has two parts: the engineered (or manmade) system and the natural system. The Yucca Mountain project relied heavily on the engineered system to first prevent, then retard entry of waste into the natural system for extended periods. Because an engineered system is designed to a detailed specification and built to exacting standards it is associated with less uncertainty than a natural system, which has inherent heterogeneities that are difficult to fully characterize over many cubic kilometers of geology.

There is increasing evidence that engineered barriers can be designed and constructed to last for very long periods, possibly hundreds of thousands of years or more. Such a delay dramatically reduces the radiotoxicity of the waste via radioactive decay and simplifies the chemistry of the waste that might enter the natural system, thus enhancing the predictability of the long-term performance of a repository.

The key to modeling the degradation of the engineered system is a fundamental understanding of the physical and chemical environment provided by the natural system for the engineered system over very long time periods. The radionuclide source term⁶ may be the most important contributor to the performance of a geologic repository—and its contribution may be the most difficult to quantify.

The Total System Performance Assessment

One of the major achievements of the Yucca Mountain project was the Total System Performance Assessment for the License Application (TSPA-LA) that was included in the Department of Energy’s (DOE) application submitted to the USNRC in 2008. As noted in the US Nuclear Waste Technical Review Board report (NWTRB 2011, p. 49), the “TSPA-LA represented the culmination of the most thorough study of the performance of a geologic repository for high activity waste ever performed by US scientists and engineers.”

The period of performance for TSPA-LA was 1 million years. DOE, its contractors, and the US Geological Survey developed models for all the major components of the repository including the engineered barrier system, the hydrogeologic unsaturated and saturated zones, and the biosphere. The models were abstractions from major studies performed on features, events, and processes (FEPs) associated with the repository, and the figure of merit was a probability-weighted radiological dose to humans. A major effort was made to quantify the contributions to uncertainty by propagating FEP uncertainties throughout the model. The results included the importance ranking of the contributors to the overall dose to humans.

The TSPA-LA had the benefit of the previously prepared performance assessment of the Waste Isolation Pilot Plant (WIPP) in Carlsbad, New Mexico,⁷ and probabilistic risk assessments performed on nuclear power plants and other facilities, but there were scoping requirements not before encountered, of which the 1-million-year period of performance was obviously the most challenging.

Many lessons were learned from the TSPA-LA about doing probabilistic performance assessments involving very long term performance requirements. Despite its accomplishments, TSPA-LA had some deficiencies over the more mature probabilistic risk assessments for nuclear plants: first, it was compliance driven rather than a realistic evaluation focusing on the more fundamental question, “What is the risk?” A second important deficiency was the use of weighted probabilities to present the results, rather than the more transparent presentation of probability and consequences, an approach used in the quantitative risk assessment field.

Advances since Project Termination

There have been important policy and technical advances in high activity waste management and disposal since the administration’s decision to terminate the Yucca Mountain project.

Policy Advances

On the policy front, in early 2010, at the request of President Barack Obama, Secretary of Energy Steven Chu chartered the Blue Ribbon Commission on America’s Nuclear Future (BRC), a panel of 15 distinguished individuals charged with conducting a comprehensive review of policies for managing the “back end” of the nuclear fuel cycle, including all alternatives for high activity waste storage, processing, and disposal. The commission issued its final report in January 2012 (BRC 2012), with a strategy consisting of eight key elements, four of which were significantly different from the strategy followed since enactment of the Nuclear Waste Policy Act in 1982 and its amendments in 1987:

1. A new, consent-based approach to siting future nuclear waste management facilities.
2. A new organization dedicated solely to implementing the waste management program and empowered with the authority and resources to succeed.
3. Better access by the developer/implementer of the waste management system to the funds nuclear utility ratepayers are providing for the purpose of nuclear waste management.
4. Prompt efforts to develop one or more consolidated storage facilities.

Secretary Chu responded to the commission’s report with a January 2013 report that endorsed the principles underpinning the commission’s strategy and presented the following plan (DOE 2013):

• Site, design, license, construct, and begin operations of a pilot interim storage facility by 2021 with an initial focus on accepting SNF from shut-down reactor sites;
• Begin operations by 2025 of a larger interim storage facility with sufficient capacity both to provide flexibility in the waste management system and to accept enough SNF to reduce government liabilities; and
• Make sufficient siting and site characterization progress to facilitate the availability of a full-scale geologic repository by 2048.

Stops and Starts

In June 2013 a bipartisan group of four senators filed a bill that, if enacted, would implement much of the plan outlined in the DOE report.⁸ Although hearings were held on the bill it has otherwise languished, and no companion bill has emerged in the House of Representatives. Passage of a nuclear waste bill by January 3, 2015—the last day of the 113th Congress—seems extremely unlikely because the topic does not appear to have high legislative priority. DOE, for its part, has been doing nothing visibly to advance nuclear waste policy legislation since issuing its January 2013 report.

The USNRC accepted DOE’s application for a license to construct a repository at Yucca Mountain on September 15, 2008, and immediately began reviewing it (USNRC 2009), but suspended the review in 2010 after the administration’s decision to terminate the project. On August 13, 2013, the US Court of Appeals for the DC Circuit rebuked the USNRC for flouting the law by discontinuing the review and, in effect, ordered the agency to resume consideration of the license application using funds remaining (~$11 million) from prior year appropriations.⁹ USNRC technical staff complied and expect to issue safety evaluation reports in early 2015 (Piccone 2014).¹⁰ The safety evaluation reports will be extremely valuable for any future repository because they will provide an explicit example of how the USNRC technical staff reviews a license application and reaches technical conclusions.

Technical Advances and Research

On the technical front, a relatively small amount¹¹ of generic (i.e., not site-specific) research on high activity waste management and disposal continues under the supervision of the DOE Office of Nuclear Energy. The current emphasis of the research appears to be on (1) direct repository disposal of large, dual-purpose canisters containing commercial SNF (Figure 3), (2) dry storage of high-burnup commercial SNF, and (3) an integrated waste management system—including consent-based siting. Direct disposal of canisters loaded with commercial SNF in a repository without opening them would avoid significant costs, worker exposure, generation of low-level radioactive waste, and a waste of resources as the canisters would not be reusable because of radioactive contamination. Thus it is important that DOE is looking carefully at the practicality of this option. We have no doubt that direct disposal is technically feasible; the question is whether it is practical.

Figure 3

The Office of Nuclear Energy issued a roadmap in 2011 to guide DOE’s waste management R&D program (DOE 2011). The roadmap should be revised to reflect the final BRC report, DOE’s response to that report, and the R&D program’s current emphasis.

Research is needed to better predict the repository emplacement environment for long time periods. Knowledge of the physical and geochemical conditions of this environment is critical for modeling waste degradation and mobilization confidently. Factoring such detail into the choice among geologic media could alter the priorities on which medium to favor. It is not clear, however, how much the DOE research program is considering the effect of the mix of engineered barriers, waste packages, waste forms, and geologic media on the evolution of the emplacement environment.

There also continues to be some research on the impacts of partitioning and transmutation (P&T) and reprocessing on geologic disposal. Studies by entities such as the National Research Council (NRC 1996) and the Swedish Nuclear Fuel and Waste Management Company (SKB 2004) appear to indicate lack of technology or economic incentive to deploy P&T in the near or medium term. Reprocessing would reduce the size needed for a repository but would not eliminate the need for a repository. Furthermore, adoption of reprocessing in the United States does not appear to be economically advantageous for the current fuel cycle and there are significant concerns about proliferation of nuclear materials associated with reprocessing.

Moving Forward

DOE’s January 2013 plan focuses on storage in the near term and delays the opening of a repository until 2048. We know of no careful, objective study comparing the technical, safety, and cost advantages and disadvantages of DOE’s plan compared to other plans. Such a study is needed before proceeding with any plan.

We believe the following three views are shared by the world technical community involved with the management and disposition of high activity waste:

1. Geologic disposal is necessary regardless of the fuel cycle ultimately chosen. No current technology or technology likely to be developed in the near future appears able to preclude the need to develop some geologic disposal capability.
2. Geologic disposal is feasible. Geologic disposal can isolate high activity waste from the human environment for as long as necessary—which could be as long as a thousand millennia or more. Furthermore, many locations and many geologic media—including clay, shale, salt, tuff, and crystalline rock—appear capable of doing the job.
3. Public apprehension about geologic disposal and transportation of high activity waste is high and must be addressed. Interestingly, this apprehension is not necessarily strongest in the communities that would host geologic repositories but in the regions and states in which those communities are located. Both Carlsbad, New Mexico, which hosts the WIPP repository for the disposal of transuranic waste,¹² and Nye County, Nevada, site of the Yucca Mountain repository, want sufficient assurance of the safety of the respective repositories, but otherwise appear to welcome them. The states that house or would house the repositories do not seem to have the same expansive view.

Our position, which is the same as that expressed by the NWTRB, is that the nation should keep a focus on a permanent solution to the disposal of high activity waste for the following reasons (NWTRB 2011, p. 69): “(1) a permanent solution is critical to building public confidence that there is a way of isolating nuclear waste radioactivity from the biosphere to acceptable levels; (2) given the long duration of the hazard of high activity waste, undue delay in a permanent solution could make tenuous a concept of waste management dependent on institutional stability; and (3) experience to date has indicated that deploying a permanent solution to isolating high activity waste could take decades.”

We believe the following specific actions should be taken to keep the nation moving forward in finding a permanent solution to the disposal of high activity waste:

• Do not allow the loss of what has already been learned about geologic disposal; develop a deliberate and systematic process for capturing lessons learned into a formal knowledge base in the manner of a recent special issue on performance assessment (RESS 2014).
• Develop a site selection process that is systematic and based on the fundamental concepts of decision analysis while engaging the public in a meaningful and productive way.
• Develop a site characterization process that is interactive and strongly coupled with probabilistic performance assessments of the site to enable a truly risk-based foundation of knowledge, including uncertainties.
• Develop a transparent roadmap of the phases of a geologic disposal project including decision points, site characterization, design, licensing, construction, operation, and closure.

Importance of Local Engagement

Adopting a consent-based process for selecting a repository or consolidated storage site raises the question, “At what point would communities/states/tribes that would host the prospective facility lose the right to veto the site?” The law applying to the Yucca Mountain project required that dissenting parties reject the site within 90 days of presidential approval of the site. President George W. Bush approved the site on February 15, 2002, and the state of Nevada formally rejected the site on April 8, 2002, but its veto was overridden by Congress on July 9, 2002.¹³

In our view, communities/states/tribes need some form of veto power during designated phases of any repository or consolidated storage project. This implies a much greater degree of transparency, openness, and candor on the part of the implementing organization than DOE afforded the Yucca Mountain project. In particular, in addition to or as part of any TSPAs submitted to the USNRC for compliance purposes, the implementing organization must simultaneously perform TSPAs that (1) extend to the time of peak dose, (2) include sensitivity studies so that the value of various components and parameters of the facility can be evaluated, (3) include FEPs that have a significant chance of occurring after 10,000 years (e.g., criticality), and (4) are realistic rather than conservative. 

Regardless of the political situation, the scientific and engineering community must be conscious of the importance of doing its work in a transparent, competent, and understandable manner to provide the public, decision makers, and, yes, politicians with the necessary information to assure them that major project decisions are being made appropriately and that public funds are being managed correctly. Thus, finding a process that minimizes the waste of public funds on major science and engineering projects that end up terminated for political reasons requires extensive interaction of those who have the knowledge about the project and those who have to lead the decision-making process.

Lessons from Yucca Mountain

The Yucca Mountain project was the responsibility of DOE. As a federal project, it was subject to the federal budgeting process and the links of that process to the ever changing political scene as well as the desire to spread the work among many different organizations geographically separated and not always happy to work with each other. Such a project environment rarely results in a tight and dedicated team, which is clearly needed for a project as complex as a first-of-a-kind, multimultibillion-dollar high activity waste transportation, management, and disposal system.

Probably the worst characteristic of the Yucca Mountain project was its inability to effectively transition in a reasonable period from a science project to an engineering project.¹⁴ To be sure, science work had to be an integral part of the project throughout its duration. But our opinion is that the absence of a strong engineering culture and a truly engineering-based project structure greatly handicapped the decision-making process, the efficient movement of the project forward, and the implementation of best practices in engineering for meeting project goals.

It is difficult not to notice the extremely poor success rate of DOE major projects over the past several decades. They are often far past schedule and far over budget, if they work at all. How to organize and manage large, first-of-a-kind projects is not within our scope of expertise, but the need to study how DOE does this and to develop and analyze alternatives to the DOE approach is clear. Thus, we believe that the BRC recommendation to move the disposal program from DOE to a new organization is an excellent one. A compromise would be to separate the commercial waste from the defense waste, moving the commercial waste management to a new organization.¹⁵

Finally, opportunities clearly exist to conduct research and analyses that could greatly facilitate the more efficient deployment of any future geologic disposal program. We are pleased that DOE has had the foresight to continue at least a modest amount of disposal research and development under the aegis of its Office of Nuclear Energy and that Congress has seen fit to fund it. This work and the people performing it will form the nucleus of any new US disposal program.

References

BRC [Blue Ribbon Commission on America’s Nuclear Future]. 2012. Report to the Secretary of Energy. Washington.

DOE [US Department of Energy]. 2011. Used Fuel Disposition Campaign Disposal Research and Development Roadmap, FCR&D-USED-2011-000065 REV 0. Washington.

DOE. 2013. Strategy for the Management and Disposal of Used Nuclear Fuel and High-Level Radioactive Waste. Washington.

GAO [US General Accountability Office]. 2011. Commercial Nuclear Waste Effects of a Termination of the Yucca Mountain Repository Program and Lessons Learned. GAO-11-229. Washington.

NRC [National Research Council]. 1996. Nuclear Wastes: Technologies for Separations and Transmutation. Washington: National Academy Press.

NWTRB [US Nuclear Waste Technical Review Board]. 2003. Report to the US Congress and the Secretary of Energy: January 1, 2002, to December 31, 2002. Arlington, VA.

NWTRB. 2011. Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes: Lessons Learned from Yucca Mountain and Other Programs. Arlington, VA.

Piccone J. 2014. “Restart of the Review of the Yucca Mountain License Application.” Presentation at Nuclear Energy Institute Used Fuel Management Conference, St. Petersburg, Florida, May 6. Available at www.nei.org/Conferences/Conference-Archives/Used-Fuel- Management-Archives.

Pietrzyk M. 2014. “Used Fuel Policy in Uncertain Times.” Presentation at Nuclear Energy Institute Used Fuel Management Conference, St. Petersburg, Florida, May 6. Available at www.nei.org/Conferences/Conference-Archives/Used-Fuel- Management-Archives.

RESS [Reliability Engineering & System Safety]. 2014. Special Issue: Performance Assessment for the Proposed High-Level Radioactive Waste Repository at Yucca Mountain, Nevada. Helton JC, Hansen CW, Swift PN, eds., vol. 122. Oxford: Elsevier.

SKB [Svensk Kärnbränslehantering AB]. 2004. Partitioning and Transmutation: Current Developments. Technical Report TR-04-15. Stockholm.

USNRC [US Nuclear Regulatory Commission]. 2001. Final Environmental Impact Statement of Construction and Operation of an Independent Spent Fuel Storage Installation on the Reservation of the Skull Valley Band of Goshute Indians and the Related Transportation Facility in Tooele County, Utah. NUREG-1714, Vol. 1, p. 2-27. Washington: USNRC Office of Nuclear Material Safety and Safeguards, US Bureau of Indian Affairs, US Bureau of Land Management, US Surface Transportation Board.

USNRC. 2009. NRC’s Decision to Accept DOE’s Repository License Application for Review. Available at www.nrc.gov/waste/hlw-disposal/licensing/acceptance-safety/ doe-handout-feb09.pdf.

FOOTNOTES

This paper is based in part on a 2011 NWTRB report (NWTRB 2011), of which Dr. Garrick was the major contributor and Dr. Di Bella the principal compiler and editor. The views in this paper are those of the authors and not necessarily those of their current or past affiliations.

¹ “Metric tons” here is short for metric tons of initial heavy metal, i.e., metric tons of uranium and higher-atomic-number elements before irradiation in a nuclear reactor.

² About two-thirds of US commercial power reactors are pressurized water reactors (PWRs). A typical PWR nuclear fuel assembly has dimensions of approximately 21 cm × 21 cm × 4 m and contains approximately 0.5 metric ton of fuel. The balance of US commercial power reactors are boiling water reactors.

³ A small fraction of the HLW has been converted to inert solid form already. The total radioactivity of the HLW is less than a few percent of the total radioactivity of the commercial SNF.

⁴ On March 11, 2009, Secretary of Energy Steven Chu stated, “Both the President and I have made clear that Yucca Mountain is not a workable option.…” Statement before the Senate Committee on the Budget, Washington, DC, available at www.energy.gov/sites/prod/files/ciprod/documents/3-11- 09_Final_Testimony_(Chu).pdf. However, “termination” is not strictly correct. Although the Yucca Mountain project has been completely destaffed and defunded, unless and until changes are made to the Nuclear Waste Policy Act, as amended, development of a repository at Yucca Mountain is still the law of the land. The project was terminated for social and political reasons (GAO 2011), not cost or technical ones.

⁵ The unsaturated zone is essentially the rock above the water table.

⁶ “Source term” in this paper refers to the radionuclides that leave the engineered system and enter the natural system.

⁷ US Title 40 CFR Part 191, Subparts B and C, Compliance Recertification Application for the Waste Isolation Pilot Plant (WIPP) Appendix PA-2009 Performance Assessment, US Department of Energy WIPP Carlsbad Field Office, New Mexico, 2009. Available at www.wipp.energy.gov/library/CRA/2009_CRA/CRA/Appendix_ PA/Appendix_PA.htm.

 ⁸ The Nuclear Waste Administration Act of 2013 (S. 1240), sponsored by Sen. Ron Wyden (D-OR) and cosponsored by Sens. Lamar Alexander (R-TN), Dianne Feinstein (D-CA), and Lisa Murkowski (R-AK), was introduced June 27, 2013.

⁹ US Court of Appeals for the District of Columbia Circuit, On Petition for Writ of Mandamus, No. 11-1271, August 13, 2013.

¹⁰ USNRC technical staff issued “technical evaluation reports” in 2011 after the review had been suspended. Although these reports are valuable, they lack any conclusions about whether in the staff’s opinion the repository would meet the safety standards in the regulations. The safety evaluation reports will contain those conclusions.

 ¹¹ Approximately $45–75 million/year, roughly a tenth to a fifth of the average annual expenditures on the Yucca Mountain project for the two decades ending in 2008.

 ¹² Transuranic waste contains more than 100 nanocuries of alpha-emitting transuranic isotopes with half-lives greater than 20 years per gram of waste, except for high activity waste.

 ¹³ See NWTRB (2003, p. 3) for citations and additional discussion.

¹⁴ The transition was finally made soon after Edward (“Ward”) Sproat became director of DOE’s Office of Civilian Radioactive Waste Management, the office responsible for the Yucca Mountain project. He served in that position from May 2006 until January 2009.

¹⁵ Defense HLW and commercial fuel need not be disposed of in the same kind of repository. For example, defense HLW could be disposed of in deep (3–5 km or more) boreholes, and commercial spent fuel in a mined geologic repository.