2

Background

This chapter provides background information on the following topics: a review of the surplus plutonium inventory in the United States and the volumes that are relevant to the dilute and dispose plan; the Plutonium Management and Disposition Agreement (PMDA) between the United States and the Russian Federation and its current status; the Waste Isolation Pilot Plant (WIPP) and how it operates and recent changes to the accounting of waste container volumes; and risk assessment. This background is needed to understand the dilute and dispose plans as well as the committee’s analysis of them. Readers who are familiar with these topics may choose to skip this background chapter.

2.1 SURPLUS PLUTONIUM IN THE UNITED STATES

Plutonium is a fissile chemical element with an atomic number of 94 used in nuclear weapons and in mixed oxide (MOX) fuel in a nuclear reactor; its unique characteristics and properties are described in Box 2-1.¹ The United States has declared more than 60 metric tons (MT²) of weapons-useable plutonium material as surplus, meaning it has no programmatic use and does not fall into one of the categories of national security reserves (DOE, 2015a, p. S-1). The plutonium material within the surplus inventory is in many forms ranging from plutonium pits and oxides to plutonium within the Department of Energy (DOE)-managed used fuel (see Figure 2-1).

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¹ Although plutonium is used in MOX fuel for use in nuclear power plants in a few countries, there are no nuclear power plants in the United States that use plutonium fuel.

² One metric ton is 1,000 kilograms or 1.102 U.S. tons; 1 U.S. ton is equal to 2,000 pounds (lbs).

2.1.1 Surplus Plutonium Inventory and Its Current Status

The committee developed Figure 2-1, which has been modified from DOE’s original diagram (DOE, 2015a, fig. S-7), to clearly identify the various disposition plans and the amounts of surplus plutonium associated with each. Thirty-four metric tons of the total are associated with U.S. commitments under the PMDA (discussed later in this chapter) and have been proposed by DOE-NNSA for dilution and disposal. This amount was the main focus of the Statement of Task (see Box 1-1) and was the initial focus of the committee. However, additional amounts of surplus plutonium, beyond the amount identified in the PMDA, are associated with DOE’s dilution and disposal plans and were also within the committee’s tasking (see Box 1-1, Task 2.c). The committee determined that up to 48.2 MT of surplus plutonium either is under consideration or is already slated for (a record of decision [ROD] has been issued for) emplacement as diluted surplus plutonium transuranic (DSP-TRU) waste in WIPP.

The United States has officially declared a total of 61.5 MT of weapons-grade plutonium as surplus. In 2016, DOE’s ROD for 6.0 MT of surplus non-pit plutonium material to be diluted (or downblended) and disposed of at WIPP consisting of 5.1 MT of material already declared surplus and an additional 0.9 MT of possible future surplus plutonium material included in the analysis but not in the official declaration (DOE, 2016a; see also Box 2-2, below).³ For purposes of this report, which is focused on the

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³ As used by different offices within DOE, the terms “downblend” and “dilute” are synonymous and describe the process for mixing surplus plutonium with an adulterant to ensure that plutonium “is not recoverable without extensive reprocessing.”

proposed amount of surplus plutonium material considered for WIPP, the committee chose to include the 0.9 MT in the inventory total. Therefore, in the committee’s analysis there is up to 62.4 MT of U.S. surplus plutonium material for which disposition paths are or need to be identified through National Environmental Policy Act (NEPA) analysis and RODs.⁴

Of the 62.4 MT total, 11 MT is not currently under consideration for disposal at WIPP (see Figure 2-1, gray boxes). The 11 MT consists of 7 MT in DOE-managed used (i.e., irradiated) fuel that is in a proliferation-resistant form with no further action yet identified and 4 MT without a disposition pathway (originally reserved for but no longer needed by the Zero Power Physics Reactor). Another 3.2 MT has already been disposed of in WIPP as transuranic (TRU⁵) waste (see Figure 2-1, yellow box).⁶ The remaining 48.2 MT consists of 6 MT (managed by DOE’s Office of Environmental Management [DOE-EM]) and 42.2 MT (managed by DOE’s National Nuclear Security Administration [DOE-NNSA]). A ROD for the 6 MT—to dilute and dispose as DSP-TRU in WIPP—was issued in 2016 (DOE, 2016a; see Box 2-2). The 42.2 MT is made up of 34 MT (previously associated with the MOX plan), 7.1 MT of pit plutonium, and 1.1 MT to be disposed of at either WIPP or processed at the Defense Waste Processing Facility at the Savannah River Site (SRS) for eventual disposal in a high level waste repository).⁷ The 48.2 MT of surplus plutonium plus the 3.2 MT already emplaced in WIPP totals 51.4 MT, which represents the total amount of surplus plutonium that could eventually be emplaced in WIPP.

A special inventory report, developed by Los Alamos National Laboratory (LANL) for an initial performance assessment (PA; also referred to as an impact assessment) by Sandia National Laboratories uses 42.2 MT for the possible emplacement of DSP-TRU waste by DOE-NNSA. This special inventory report did not include the 6 MT of DOE-EM surplus non-pit plutonium material (LANL, 2017).⁸

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DOE notes in its Surplus Plutonium Disposition System Plan that “[t]he term dilution is the international nomenclature for using an adulterant to provide proliferation resistance and is in no way intended to avoid any applicable regulatory requirements” (SRNS, 2016, p. 8). The committee has chosen to use the terms “dilute” or “dilution” throughout this report, even when referring to DOE-EM’s plans and activities.

⁴ Disposition refers to the consignment of radioactive waste for some specified (interim or final) destination; disposal refers to the emplacement of waste in an appropriate facility without the intention of retrieval.

⁵ Transuranic (TRU) waste is defined in multiple government documents with slight differences in the definitions. In this report, we use the definition from the WIPP Land Withdrawal Act (Waste Isolation Pilot Plant Land Withdrawal Act, Pub. L. No. 102-579, 106 Stat. 4777-4796 (1992) [as amended in 1996 by Pub. L. No. 104-201]): The term “transuranic waste” means waste containing more than 100 nanocuries of alpha-emitting transuranic isotopes per gram of waste, with half-lives greater than 20 years, except for—

1. high-level radioactive waste;
2. waste that the Secretary has determined, with the concurrence of the Administrator, does not need the degree of isolation required by the disposal regulations; or
3. waste that the Nuclear Regulatory Commission has approved for disposal on a case-by-case basis in accordance with part 61 of title 10, Code of Federal Regulations.

⁶ This material originated from multiple sites and was placed in pipe overpack containers (POCs) prior to disposal. A POC is similar to a criticality control overpack (see Chapter 4).

⁷ Further explanation of the DOE disposition pathway for the 1.1 MT is as follows (DOE, 2015a, p. s-3): “In 2008 and 2009, DOE completed interim action determinations and concluded that 0.6 metric tons (0.66 tons) of surplus non-pit plutonium could be disposed of through H-Canyon/HB-Line and DWPF (DOE, 2008a, 2009); in 2011, DOE amended this determination to add WIPP as a disposal alternative for about 85 kilograms (187 pounds) of these 0.6 metric tons (0.66 tons) (DOE, 2011a). Also in 2011, DOE decided to use H-Canyon/HB-Line to prepare another 0.5 metric tons (0.55 tons) of surplus plutonium for disposal at WIPP (DOE, 2011b); DOE amended this determination in 2013 to also allow preparation in the K-Area Complex (DOE, 2013c). Thus, DOE has determined that a total of 1.1 metric tons (1.2 tons) of surplus plutonium could be dispositioned through H-Canyon/HB-Line and the K-Area Complex to DWPF and WIPP.”

⁸ “The PA models the impact on performance of the WIPP repository by the National Nuclear Security Administration’s (NNSA’s) proposal to dispose of ~42.2 metric tons (MT) of surplus plutonium (Pu) in the WIPP” (LANL, 2017, p. 5).

The committee heard that, as of 2009, approximately 4.8 MT of plutonium material had been emplaced at WIPP but it was difficult to determine how much of this total was part of the declared surplus or the exact amount that had been products of past—but not identical—dilute and dispose processes.⁹ The analysis in Figure 2-1 uses the 3.2-MT value as the amount of surplus plutonium TRU waste already emplaced in WIPP. There is more plutonium disposed of in WIPP as TRU waste but it is not part of the declared surplus plutonium nor is it in the same waste form as diluted surplus plutonium, being the more conventional waste lightly contaminated with transuranic elements including plutonium contamination from defense activities.

Beginning in the mid-1990s, DOE issued a series of environmental impact statements (EISs) and RODs to shape and modify the disposition strategy for U.S. surplus plutonium (see Box 2-2). There is no single document or ROD that defines the United States’ plans to disposition the entirety of its surplus plutonium material inventory. Rather, the disposition pathways depend on the form of the plutonium material, leading to a variety of decisions and different disposition pathways, some of which have changed over the years.

In 2000, DOE issued a ROD selecting two options for dispositioning of 34 MT of surplus plutonium material: the irradiation of MOX¹⁰ fuel using commercial nuclear reactors and the immobilization of the material in combination with high level waste. In 2002, the George W. Bush administration canceled the immobilization program citing budget constraints and made the decision to support only one approach for plutonium disposition, the fabrication and subsequent irradiation of MOX fuel. In 2007, the United States began construction of a facility to manufacture MOX fuel, the Mixed Oxide Fuel Fabrication Facility (“MOX plant”), at the SRS in South Carolina.

In parallel with the decisions being made for the 34 MT of surplus plutonium material, in 2016 DOE-NNSA issued a ROD for the disposition of up to 6 MT of non-pit plutonium material within the U.S. surplus inventory. The ROD states that the surplus non-pit plutonium material “will be prepared and packaged to meet the WIPP waste acceptance criteria for contact-handled TRU waste and other applicable regulatory requirements” and would be disposed of “at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico, a geologic repository for disposal of transuranic (TRU) waste generated by atomic energy defense activities” (DOE, 2016a, p. 19588).

Meanwhile, construction of the MOX plant encountered substantial schedule delays and cost overruns. The Obama administration proposed to stop construction of this facility and instead use a “dilute and dispose process” to disposition 34 MT of surplus plutonium (Goodson, 2018) using the process described in the ROD for the 6 MT of surplus non-pit plutonium material. Congress provided $15 million to DOE-NNSA in fiscal year (FY) 2017 to continue planning and developing a conceptual design for the dilute and dispose process; it also mandated this National Academies of Sciences, Engineering, and Medicine evaluation (U.S. Congress, 2016, p. 114). In May 2018, the Trump administration submitted a report to Congress detailing the Life-Cycle Cost Estimate of the dilute and dispose approach, showing total costs of less than half of those estimated for the MOX option. In October 2018, DOE-NNSA canceled the MOX program (see Box 2-2). The Notice of Intent, which would begin the NEPA process for the disposition of 34 MT through dilution and disposal, has not yet been issued. However, there are indications that a NEPA decision on the 7.1 MT of surplus pit plutonium, processed as DSP-TRU waste for disposal in WIPP, may be issued (DOE-CBFO, 2019a, p. 391, new waste stream: SR-KAC-PuOx-1).

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⁹ Information collected during discussions during the open session of the committee’s April 2019 meeting. See video from the meeting at https://vimeo.com/showcase/6028445/video/338026631 (accessed March 30, 2020).

¹⁰ MOX fuel contains plutonium and slightly enriched uranium, both in oxide form (DOS, 2000).

2.2 PLUTONIUM MANAGEMENT AND DISPOSITION AGREEMENT

The MOX fuel option for surplus plutonium disposition was consistent with U.S. commitments under the PMDA, which was signed by the United States and the Russian Federation in 2000 and amended in 2010. The 2010 agreement commits both countries to the disposition of no less than 34 MT of

weapons-grade¹¹ plutonium by its incorporation into MOX reactor fuel followed by irradiation in nuclear reactors. The United States and the Russian Federation are required under the agreement to begin surplus plutonium disposition by 2018, with implementation to be verified by the International Atomic Energy Agency (DOS, 2000, 2010).

The PMDA Additional Protocol 2010 updated the text in Article III of the 2000 Agreement, outlining the means that are to be used by the United States and the Russian Federation for dispositioning 34 MT of surplus plutonium:¹²

Disposition shall be by irradiation of disposition plutonium as fuel in nuclear reactors; or any other methods that may be agreed by the Parties in writing. (DOS, 2010, p. 2)

Article XIII of the original PMDA specifies how the agreement can be amended and was unaltered in the 2010 Additional Protocol:

This Agreement may only be amended by written agreement of the Parties, except that the Annex on Key Program Elements may be updated as specified in paragraph 5 of that Annex. (DOS, 2000, p. 11)

To the committee’s knowledge, the United States has not notified the Russian Federation in writing about its plans to pursue the dilute and dispose process in place of MOX. However, the Russian Federation government is aware of DOE’s desire to use dilute and dispose to disposition 34 MT of surplus plutonium. Russian Federation President Vladimir Putin raised concerns in an April 2016 meeting with journalists about the United States’ use of the dilute and dispose process for dispositioning surplus plutonium under the PMDA:

[B]ack in the early 2000s, the Americans and we agreed on destroying weapons-grade plutonium. … Each side had 34 tonnes. We signed this agreement and settled on the procedures for the material's destruction, agreed that this would be done on an industrial basis, which required the construction of special facilities. Russia fulfilled its obligations in this regard and built these facilities, but our American partners did not.

Moreover, only recently, they announced that they plan to dispose of their accumulated highly enriched nuclear fuel by using a method other than what we agreed on when we signed the corresponding agreement, but by diluting and storing it in certain containers. This means that they preserve what is known as the breakout potential, in other words it can be retrieved, reprocessed and converted into weapons-grade plutonium again. This is not what we agreed on. Now we will have to think about what to do about this and how to respond to this…. [O]ur partners should understand that … serious issues, especially with regard to nuclear arms, are [where] one should be able to meet one's obligations. (IPFM, 2016)

President Putin subsequently suspended Russian implementation of the PMDA in October 2016 “due to Washington’s unfriendly actions toward Russia” (RadioFreeEurope RadioLiberty, 2016).

The Department of State releases an annual report providing assessments of the adherence of the United States and other nations to arms control, non-proliferation, and disarmament agreement or commitment obligations. The 2019 compliance statement with regard to the PMDA follows:

The United States has not undertaken any activities during or prior to the reporting period that are inconsistent with its obligations under the Plutonium Management and Disposition Agreement (PMDA). This includes U.S. activities during the reporting period to terminate the project to

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¹¹ Defined in the PMDA as “plutonium with an isotopic ratio of plutonium-240 to plutonium-239 of no more than 0.10” (DOS, 2000, p. 2).

¹² The PMDA as amended in 2010 recognized the removal of immobilization as an option for disposition by the United States.

construct a mixed-oxide (MOX) fuel fabrication facility that would have been used to dispose of plutonium under the agreement by turning it into fuel for irradiation in commercial nuclear reactors and to develop plans for a less expensive alternative disposition through dilution and burial of the plutonium. Russia’s assertion that this change in U.S. disposition plans violates the agreement, which was addressed in the 2018 Compliance Report, remains without merit. …

In 2018, the Secretary of Energy exercised the authority under the National Defense Authorization Act for Fiscal Year 2018 and the Consolidated Appropriations Act, 2018 to waive the requirement to use funds for construction and project support activities relating to the MOX facility, including certification that an alternative option for carrying out the disposition program for the same amount of plutonium intended to be disposed of in the MOX facility exists. The Department of Energy took additional steps to terminate the project to construct the MOX facility. The administration will continue to work with Congress to finalize plans for U.S. disposition by the alternative dilute- and-dispose method. Further steps are needed in this respect before engaging Russia to obtain its agreement to this alternative method of disposition as required under the PMDA. (DOS, 2019, pp. 9-10, emphasis added)

In addition to identifying the methods to be used for disposition, the PMDA outlined international verification requirements for the surplus plutonium material. In Article VII (with further details provided in the Annex on Monitoring and Inspections) inspections by the International Atomic Energy Agency (IAEA) are outlined:

Each Party, in cooperation with the other Party, shall begin consultations with the International Atomic Energy Agency (IAEA) at an early date and undertake all other necessary steps to conclude appropriate agreements with the IAEA to allow it to implement verification measures with respect to each Party’s disposition program. (DOS, 2010, p. 4)

The verification and monitoring of the surplus plutonium material apply to pre- and post-dilution stages as well as disposal. The details of how, when, and where the monitoring and verification take place are determined between the IAEA and each Party. The committee received a briefing from the director of the Office of International Nuclear Safeguards at DOE-NNSA on the voluntary agreement between DOE-NNSA and the IAEA concerning monitoring of the 6 MT of surplus plutonium (Veal, 2019). Though the agreement is not legally binding, DOE-NNSA is in the process of working with the IAEA to discuss what role, if any, the IAEA might play in the disposition of the 6 MT. The director noted that they are not currently working with the IAEA on monitoring and verification of the 34 MT.

The System Plan for the DOE-NNSA dilute and dispose program, for the 34 MT, makes one reference to monitoring and verification protocols:

The SPD [Surplus Plutonium Disposition] Program scope includes incremental funding to process a portion of the non-pit plutonium materials associated with the 34 MT nuclear nonproliferation objective and incremental funding to add monitoring equipment required to implement verification protocol using an international agency for the dilute and dispose process of non-pit plutonium. (SRNS, 2018f, p. 12)

The Master Schedule (see also Figure 3-1) indicates that verification protocols for the activities at SRS will be in place in FY 2022 and for WIPP in FY 2023.¹³

In the context of current events, including the United States’ withdrawal from the Intermediate-Range Nuclear Forces Treaty between the United States and the Russian Federation and currently no

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¹³ The Master Schedule document was provided to the committee by DOE. Public testimony, documents, and other materials submitted to the committee are available by request through the National Academies’ Public Access Records Office at paro@nas.edu.

planned action following the conclusion of the New Strategic Arms Reduction Treaty (New START), a renegotiation of the PMDA may not be a reasonable near-term expectation. Furthermore, based on President Putin’s comments about the dilute and dispose option, it could be difficult for the United States to obtain agreement with the Russian Federation for implementing the dilute and dispose process in place of irradiated MOX fuel.

Those same quotes from President Putin juxtaposed with the current stance of the Department of State show that the current status of the PMDA is unclear. To the committee’s knowledge, neither country is moving to resolve the issues of alternative disposition pathways and IAEA monitoring and verification. The uncertainty of the PMDA is a key issue for DOE-NNSA’s dilute and dispose program and will be discussed later in the report (see Chapter 5).

2.3 BACKGROUND ON WIPP

WIPP is a salt bed repository located in the southeast corner of New Mexico (see Figures 2-2 and 2-3) and managed by DOE-EM, specifically the Carlsbad Field Office (DOE-CBFO). Appendix C provides a discussion on salt repositories and the characteristics that make them suited for disposal of nuclear waste. WIPP is the only operational deep geologic repository in the United States for disposal of defense TRU wastes; its disposal capacity is limited by law to a certain volume of defense TRU waste (discussed below). The current WIPP repository design consists of 10 panels (see Figure 2-3). Eight of the 10 have been permitted for construction and use under the WIPP Hazardous Waste Facility Permit. Panel 8 is presently being mined and is not yet ready for use, and Panel 9 was abandoned after the WIPP accident.

The current contractor managing the site is Nuclear Waste Partnership LLC. After certification by the Environmental Protection Agency (EPA) in 1998, WIPP received its Resource Conservation and Recovery Act (RCRA) Hazardous Waste Facility Permit from the New Mexico Environment Department (NMED) also in 1998, and began disposal operations in 1999. According to the Permit, WIPP was assumed to reach facility closure in 2034, although there are now plans to extend the disposal operations and emplacement past 2050, which is discussed later in the report.

2.3.1 Disposal Capacity in WIPP

WIPP’s disposal capacity limits are defined by several different laws, agreements, and permits for the purpose of regulating both the physical space as well as the physiochemical and radiological aspects of TRU and hazardous waste disposal. The Waste Isolation Pilot Plant Land Withdrawal Act (LWA) limits TRU waste disposal capacity to no greater than 6,200,000 ft³ (175,564 m³) of defense-related TRU waste, a limit that is overseen by EPA. The ROD for WIPP, issued in 1981, limits the amount of remote-handled TRU (RH-TRU) waste in WIPP to no more than 250,000 ft³ (7,079 m³) of the LWA total (DOE, 1981).¹⁴ DSP-TRU waste is contact-handled (CH) TRU and is not affected by the RH-TRU limit. The Hazardous Waste Permit (overseen by NMED) also regulates waste volumes through the size limitation of the underground waste panels.¹⁵ Until recently, the capacity limits for LWA and RCRA (Hazardous Waste Permit) were measured by the gross internal volume of the outermost disposal containers of the CH-TRU waste containers and were the same number (e.g., the volume of each 55-gallon drum was counted as 0.21 m³).

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¹⁴ CH-TRU waste is defined in the LWA as “transuranic waste with a surface dose rate not greater than 200 millirem per hour.” RH-TRU waste is defined in the Act as “transuranic waste with a surface dose rate of 200 millirem per hour or greater.” LWA section 2.

¹⁵ WIPP is managed as a mixed waste facility and is therefore subject to RCRA. All waste in WIPP is considered mixed TRU waste, meaning that the waste has both a hazardous component and transuranic elements. See “Regulatory Authority” at https://www.env.nm.gov/hazardous-waste/wipp (accessed February 20, 2020).

Shortly after the public release of this committee’s Interim Report, NMED approved a pending permit modification request by DOE-CBFO to change the accounting of TRU waste container volumes for already emplaced and future wastes (DOE-CBFO, 2018b). The permit modification allows for a recalculation of emplaced and future wastes and distinguishes between reporting against the LWA limits (i.e., “statutory” limit) and the RCRA TRU Mixed Waste limits. See Box 2-3.

WIPP operations were suspended from 2014 to 2017 in response to two accidents in the underground area—an engine fire in a truck and an “exothermic reaction involving the mixture of the organic materials (Swheat Scoop® absorbent and/or neutralizer) and nitrate salts” in a waste container in a panel that was being filled (DOE-EM, 2015, p. ES-5).¹⁶ WIPP operations are slowly ramping up, currently supporting 8 to 10 shipments per week, with the goal to return to preincident shipment and emplacement rates. These rates may be obtainable once the new ventilation system is operational, and new zero-emission underground vehicles are in use (DOE-CBFO, 2019b).

There are several factors that are increasing public pressure on the area surrounding Carlsbad, New Mexico. In 2018, the U.S. Geological Survey released a report that assessed the Permian Basin to have the largest continuous oil and gas reserves in the United States, announcing that “assessed undiscovered, technically recoverable continuous mean resources of 46.3 billion barrels of oil and 281 trillion cubic feet of gas in the Wolfcamp shale and Bone Spring Formation of the Delaware Basin in the Permian Basin Province, southeast New Mexico and west Texas” (Gaswirth et al., 2018, p. 1). Oil and gas drilling rates have increased in the area surrounding WIPP since it first became operational. The higher density of drilling sites affects the calculation of probabilities for post-closure human intrusion (via drilling) into the facility and could also raise additional concerns about migration of fluids to WIPP from the drilled formations. Figure 2-4 is a map of the Permian Basin with WIPP’s location overlaid. Holtec International has also proposed an interim storage site for spent nuclear fuel outside of Carlsbad, New Mexico, which has been met with mixed public support throughout the state.

2.3.2 Regulations for WIPP for Pre- and Post-Closure

In 1992, the Secretary of the Interior transferred its control of land at the WIPP site to the Secretary of Energy and granted authority to the Secretary of Energy through the WIPP LWA. The Secretary of Energy closed the area and its immediate surroundings to public use (NRC, 1996, p. 11).

The committee has divided its assessment of the viability of the surplus plutonium disposition concept into issues arising from the addition of such inventory and potentially affecting pre-closure (i.e., operational) and post-closure safety, as regards the respective regulatory frameworks. The key distinction between the pre- and post-closure periods lies in the use of active versus passive safety provisions, and consequently the means and measures of ensuring safety performance (see Box 2-4).

There are many federal and state regulations as well as DOE Orders governing WIPP’s pre- and post-closure periods, which are designed to ensure the health and safety (protection) of the workforce, the public, and the environment from radiological and other hazards.¹⁷ However, a major provision of the LWA requires DOE to demonstrate compliance with federal regulations developed and assessed by EPA. Chief among EPA regulations are 40 CFR Part 191 (EPA, 1994) and 40 CFR Part 194 (EPA, 2014a).¹⁸ Because some waste destined for WIPP also contains hazardous waste constituents (all waste at WIPP is

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¹⁶ From the National Transuranic web page: “Changes in NTP oversight and at WIPP established new requirements pertaining to WIPP WAC compliance and in the WIPP Documented Safety Analysis (DSA) in the summer of 2016,” https://wipp.energy.gov/national-tru-programs.asp (accessed May 20, 2020).

¹⁷ A full list of laws, regulations, and orders can be found in DOE (2015b, table 5-1, Environmental Laws, Regulations, Executive Orders, and Department of Energy Orders).

¹⁸ Part 191 defines standards (EPA, 1994) and Part 194 along with the Part 191 Disposal Regulations describe the specific WIPP site requirements for compliance with 40 CFR Part 191 standards (EPA, 2014a).

managed as mixed waste), certain provisions of RCRA¹⁹ also apply. The LWA, as amended, exempts waste designated by the Secretary of Energy for disposal at the WIPP facility from the treatment standards of RCRA. By virtue of this exclusion, DOE is not required to demonstrate compliance with the Land Disposal Restrictions of 40 CFR Part 268 for TRU mixed waste designated by the Secretary of Energy for disposal at WIPP.

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¹⁹ RCRA, enacted in 1976, is a statute designed to provide “cradle-to-grave” control of hazardous waste by imposing management requirements on generators and transporters of hazardous wastes and on the owners and operators of treatment, storage, and disposal facilities (see https://www.epa.gov/enforcement/resource-conservation-and-recovery-act-rcra-and-federal-facilities, accessed April 22, 2020).

The WIPP LWA required EPA to provide an initial certification of WIPP’s compliance with EPA’s disposal regulations before operations could begin. Thereafter, every 5 years EPA must conduct a recertifcation of WIPP’s compliance with EPA’s radioactive waste disposal standards, and based on updated information submitted by DOE. Much of the application content and review process is effectively governed by the respective requirements of 40 CFR Parts 191 and 194. These two regulations are described in more detail below.

2.3.2.1 Environmental Radiation Protection Standards for Management and Disposal of Spent Nuclear Fuel and Transuranic Radioactive Wastes (40 CFR Part 191)

The principal federal regulations covering radiation protection for the WIPP operational and post-closure phases are found in 40 CFR Part 191, which is divided into three parts as described by the EPA website:²⁰

• Subpart A limits the radiation exposure of members of the public from the management of spent nuclear fuel and radioactive waste prior to its disposal—in other words, during the operational period up to the point when [the WIPP] repository shafts are backfilled and sealed (WIPP facility closure).

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²⁰ See https://www.epa.gov/radiation/environmental-radiation-protection-standards-management-and-disposalspent-nuclear-fuel (accessed May 20, 2020).

• Subpart B sets containment requirements for disposal systems, which limit the amount of radioactivity that may enter the environment for 10,000 years after facility closure. Subpart B also sets individual protection requirements that limit the amount of radiation to which an individual can be exposed from an undisturbed repository. Subpart B also provides assurance requirements that involve additional measures (e.g., monitoring, permanent markers, institutional controls) intended to provide confidence in the long-term containment of radioactive waste.
• Subpart C includes groundwater protection requirements that for 10,000 years after waste disposal, contamination in off-site underground sources of drinking water will not exceed the maximum contaminant level for radionuclides established by EPA under the Safe Drinking Water Act.

The relationship and application of 40 CFR Part 191 to the WIPP operations and post-closure phase are illustrated in Figure 2-5.

The 1996 National Research Council report The Waste Isolation Pilot Plant: A Potential Solution for the Disposal of Transuranic Waste states that EPA’s 40 CFR Part 191 “is unique in that, in addition to regulations based on radiation dose, repository compliance also is based on calculations of release fractions of selected radionuclides” (NRC, 1996, p. 16, emphasis added). This containment requirement addresses the ability of a repository to isolate waste from the environment, without distinguishing releases

that would lead to significant doses from those that would not. The specified release limits scale with the quantity of waste in a repository (i.e., the more disposed waste, the more radiation that may be released); for this reason, they are specified in terms of curies (Ci) that may be released per 10,000 years per 1,000 metric tons of heavy metal (MTHM). For a repository such as WIPP, which is designed for disposal of TRU wastes, EPA has established in 40 CFR Part 191 that 1,000 MTHM is equivalent to 1,000,000 Ci of TRU wastes with greater than 20-year half-lives (note that 1 MT of plutonium-239 contains approximately 63,000 Ci; see Box 2-1).

2.3.2.2 Criteria for the Certification and Recertification of WIPP’s Compliance with the 40 CFR Part 191 Disposal Regulations (40 CFR Part 194)

In addition to the radioactive waste disposal standards in 40 CFR Part 191, EPA issued compliance criteria in 40 CFR Part 194. The criteria are used to guide the initial certification and subsequent recertification of WIPP’s compliance with the final radioactive waste disposal standards of Part 191, and are divided into four subparts as described on the EPA website:²¹

• Subpart A contains useful definitions of terms, references, and reporting requirements for DOE, and describes EPA’s authority to modify, suspend, or revoke certification or recertification.
• Subpart B specifies the content of applications and the procedure for submission.
• Subpart C consists of requirements for demonstrating compliance with EPA’s disposal standards, as well as general requirements regarding quality assurance and the use of computer models to simulate WIPP’s performance, for example.
• Subpart D describes the EPA process for public participation in certification and recertification decisions.

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²¹ See https://www.epa.gov/radiation/epas-role-waste-isolation-pilot-plant-wipp (accessed May 20, 2020).

2.3.2.3 New Mexico Environment Department’s Role

Not all of the TRU waste bound for WIPP contains a hazardous component. However, a decision was made to manage all of the WIPP-bound and emplaced waste as mixed hazardous and radioactive waste and therefore subject to RCRA regulations.²² The State of New Mexico is authorized by EPA to carry out the State’s RCRA and mixed waste programs in lieu of the equivalent federal programs. NMED reviews permit applications for treatment, storage, and disposal facilities for hazardous waste, under Subtitle C of RCRA. In the case of the WIPP facility, it is defined as a “miscellaneous unit,” and as such, NMED grants the WIPP Hazardous Waste Facility Permit (HWFP)²³ for such things as the maximum capacity of individual disposal panels (WIPP, 2018) or the more recent permit modification approval (NMED, 2018) regarding the TRU mixed waste disposal volume reporting (see Boxes 2-3 and 2-5). The HWFP has a 10-year term. The first permit renewal application was submitted to NMED in May 2009, and the NMED Secretary issued a final order granting the renewal of the WIPP HWFP, effective on December 30, 2010. The next permit renewal application is due to NMED in July 2020.²⁴ A draft WIPP Strategic Plan, released for public comment in August 2019, cites the need for new panels, presumably to accommodate future TRU waste and a 10-year reapplication to NMED for the HWFP to operate WIPP (DOE-CBFO, 2019b).

Note that EPA certifies continued compliance with disposal safety regulations every 5 years, and NMED issues a facility permit (to operate WIPP) every 10 years. The assumption of continued sustained operations for the next 20-30 years is subject to compliant operations and periodic regulatory review, both of which pose potential risks for consideration (see Chapter 5).

2.3.2.4 Relevant DOE Orders and Standards

In addition to 40 CFR Part 191, Subpart A reporting requirements applying during the operational phase, the WIPP facility operations are also subject to a number of DOE Orders and Standards for the annual preparation, review, and approval of safety basis documents. For example, DOE Standard, “Preparation of Safety Basis Documents for Transuranic (TRU) Waste Facilities,” compels the development of documented safety analyses and corresponding technical safety requirements (DOE, 2007). See, for example, “Waste Isolation Pilot Plant Documented Safety Analysis, Revision 6a” or “Waste Isolation Pilot Plant Technical Safety Requirements, Revision 6a” (Nuclear Waste Partnership, LLC, 2018a,b), which are usually prepared by the operator/contractor for WIPP, in this case Nuclear Waste Partnership LLC, which are ultimately reviewed and approved by DOE in a safety evaluation report (DOE, 2018a). For another example, see Box 2-6.

The committee considered the possible addition of DSP-TRU waste in the context of its potential effect on the demonstrations of regulatory compliance for the pre-closure and post-closure periods. Such considerations are elaborated in the following two sections. The committee reiterates from Chapter 1 that the evaluation provided below should not be construed as supplanting the regulatory function or influencing the determination of safety by regulatory bodies, but rather is intended to contribute to the objectives noted in the Statement of Task (see Box 1-1).

2.3.3 WIPP Pre-Closure/Disposal Operations Through Emplacement

The following activities are part of the operational phase at WIPP: the receipt at WIPP of the waste transporter (e.g., Transuranic Package Transporter Model 2 [TRUPACT-II] or HalfPACT; see Box 3-4); payload and container handling, and conveyance to and emplacement in the underground.

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²² See https://www.epa.gov/rcra (accessed May 20, 2020).

²³ See https://www.env.nm.gov/hazardous-waste/wipp-permit-page (accessed May 20, 2020).

²⁴ New Mexico Administrative Code, http://164.64.110.134/parts/title20/20.004.0001.pdf (accessed May 20, 2020).

The WIPP waste acceptance criteria (WAC; DOE-CBFO, 2018c) places constraints on the physical, chemical, and radiological properties of TRU waste, as well as the properties of the applicable payload containers and packages, and summarizes the quality assurance requirements relating to waste characterization, certification, and transportation, as determined by WIPP’s safety authorization basis and regulatory requirements. Waste is not approved for shipment to and disposal at WIPP until it has been certified as meeting these criteria. Within the WIPP safety basis documents for operations, the WIPP WAC is credited with reducing both the likelihood and consequences of adverse events.

2.3.4 WIPP Post-Closure Performance

The documents supporting the most recent 2019 WIPP CRA, for both operational and post-closure safety evaluations, were not available to the committee until its deliberations were substantially complete.²⁵ However, DOE provided the committee surrogate information supporting much of the same basis and, in April 2019, provided documents supporting the evaluation of post-closure performance with regard to criticality safety and compliance with containment standards per 40 CFR Part 191 (Saylor and Scaglione, 2018; Scaglione and Saylor, 2018; Zeitler et al., 2018).²⁶ The impact assessment (Zeitler et al., 2018) included the general chemical characteristics of the adulterant, which were included in the special inventory report produced by LANL specifically for this analysis (LANL, 2017).

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²⁵ The preparation and delivery of the anticipated March 2019 Compliance Recertification Application (CRA) by DOE-CBFO to EPA has been affected by the 2014 WIPP accident and subsequent recovery efforts; consequently, portions of the application are deferred (DOE-CBFO, 2017a). Notably the post-closure performance assessment calculations were deferred but are now available.

²⁶ As noted by Zeitler et al. (2018, p. 13), “The analysis is not in support of a planned change request (PCR) or planned change notice (PCN) to be submitted by the DOE to the EPA, and was not performed as a compliance calculation. Instead, the planned use of the analysis is as input into a National Environmental Policy Act (NEPA) analysis.”

As noted in Box 2-3, the post-closure phase begins once the facility is no longer receiving waste and is in its final configuration (i.e., shafts are closed and sealed). In this post-closure context, the safety and performance of the disposal facility are provided primarily by passive means inherent in the characteristics of the site and the decommissioned facility (i.e., shaft seals) and in the characteristics of the waste and waste package collectively to provide for long-term containment and isolation from the accessible environment.

2.3.5 Principal Post-Closure Safety and Performance Criteria

The principal waste disposal regulations regarding the WIPP post-closure period are provided by 40 CFR Part 191, Subparts B and C, with the WIPP Compliance Criteria at 40 CFR Part 194. The post-closure performance criteria for WIPP are set forth in the containment requirements of 40 CFR § 191.13, which sets normalized standards for cumulative radionuclide releases to the accessible environment assessed over 10,000 years. Containment standards with normalized releases are distinct from more common radiation protection standards based on dose limits. Unlike regulation of other geologic repositories now under development elsewhere in the world, WIPP is unique in its use of containment standards with normalized releases (NRC, 1996). The 40 CFR § 191.13 containment requirements applicable to WIPP allow radionuclide releases in proportion to the total radioactivity of the disposed inventory. In other words, the more radioactivity is contained in the repository, the more radioactivity can be released. In contrast, a repository with a dose-based radiation protection standard would limit the total inventory of the repository based on the calculated doses from radioactive species that escape containment.

For a description of the manner in which the containment requirements are evaluated, see below.

2.3.5.1 Compliance Application and Certification

DOE-CBFO demonstrates compliance with the containment requirements according to the Compliance Criteria in 40 CFR Part 194 by means of PA calculations performed by Sandia National Laboratories. WIPP PA calculations estimate the probability of potential radionuclide releases from the repository to the accessible environment for a regulatory period of 10,000 years after facility closure, presently assumed as 2033 (Brunnel, 2019, p. 9). In the context of the 10,000-year regulatory containment requirement, note that the half-life of plutonium-239, a major component of the DSP-TRU waste inventory, is 24,110 years. See Box 2-1.

Via the WIPP Land Withdrawal Act, Congress required EPA to certify that WIPP complies with the waste disposal regulations of 40 CFR Part 191, Subparts B and C, as well as the WIPP Compliance Criteria of 40 CFR Part 194. Congress also required EPA to recertify the facility every 5 years following the initial receipt of transuranic waste until the end of its operational activities.

EPA describes the recertification as “a process that evaluates changes at WIPP to determine whether the facility continues to meet all the requirements of EPA’s disposal regulations. The recertification process helps ensure WIPP’s continued compliance based on the most accurate, up-to-date information available” (EPA, 2019). The recertification process verifies that changes in the WIPP facility configuration based on the waste emplaced in the preceding 5-year period and the projected inventory comply with EPA’s disposal standards for radioactive waste.

As a baseline, EPA initially certified WIPP on May 13, 1998, and WIPP first received TRU waste on March 26, 1999. DOE subsequently submitted applications for recertification in March 2004, 2009, 2014, and 2019. EPA has officially recertified the WIPP facility, confirming that it continues to comply with the agency's radioactive waste disposal regulations as described above. In each case, EPA and others have raised technical concerns over various model and parameter issues used in the PA.²⁷ Throughout and

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²⁷ Note that each iteration adds further complexity to the baseline code.

between recertifications, DOE-CBFO has worked to address those concerns, and its resolutions are reflected in the subsequent recertification applications; additionally, DOE-CBFO addresses technical concerns without waiting for the next recertification.²⁸

2.3.5.2 Performance Assessment Inventories: The ATWIR and the PAIR

DOE-CBFO compiles an Annual Transuranic Waste Inventory Report (ATWIR) to document the forward-looking inventory estimate of TRU waste reported by the TRU waste generator sites as of December 31 of the prior year. TRU waste generator sites are asked to report the most comprehensive TRU inventory estimate available, including decontamination and decommissioning waste and all other defense-related TRU waste information projected through the presumed WIPP closure date and additional estimates beyond then, if available. The 2018 ATWIR “will provide the basis for the Performance Assessment Inventory Report for development of the 2019 Compliance Recertification Application (CRA) deferred performance assessment (PA)” and “focuses on all TRU waste stored or projected to be generated through CY 2033 at the TRU waste generator sites in order to reflect the WIPP facility closure date for the CRA-2019 deferred PA” (DOE-CBFO, 2018a, p. 9).

ATWIR waste streams are designated as either WIPP-bound (appear to meet the requirements for emplacement in WIPP) or Potential (have one or more criteria-related issues to be resolved) and include estimates for TRU waste volume, radioactivity, waste material parameters, packaging materials, complexing agents, oxyanions, and radionuclides. Emplaced waste is derived from the Waste Data System, the official database of record for waste already emplaced in WIPP and merged with the ATWIR inventory to create a Comprehensive Inventory Database.

An example of a waste stream moving from Potential to WIPP-bound that is important to the committee’s analysis is the waste stream from the 6 MT of non-pit plutonium material. The 2016 ROD for the 6 MT allowed that plutonium waste stream to move from Potential to WIPP-bound. The timing was such that the DSP-TRU waste associated with the 6 MT of non-pit plutonium was not included in EPA’s 2014 compliance recertification. This amount has been included, for the first time officially assessing the impact of some of the DSP-TRU waste in WIPP, in the 2019 CRA. Subsequent recertification applications can be expected to include additional fractions of the total DSP-TRU inventory, for example, in response to relevant RODs that may be issued.

The ATWIR information is used for strategic planning and supports DOE input into, for example, WIPP documented safety analysis, and in appropriate years provides the basis for the Performance Assessment Inventory Report (PAIR) for development of the Compliance Recertification Application (LANL, 2012).

The PAIR compiles the inventory of Emplaced waste with the inventory identified as WIPP-bound, and is used principally as the inventory basis (waste container volume and waste characteristics) for the corresponding PA. If the total inventory volumes in the PAIR compilation are less than the legislated capacity (i.e., 175,564 m³ total TRU waste) then the inventory values are artificially increased (scaled) in

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²⁸ Information on subsequent compliance recertification applications by DOE-CBFO and compliance decisions by EPA (2019) may be found for the following:

• 2014-2017 Compliance Recertification (https://www.epa.gov/radiation/certification-and-recertification-wipp#2014, accessed March 23, 2020).
• 2009-2010 Compliance Recertification (https://www.epa.gov/radiation/certification-and-recertification-wipp#2009-2010, accessed March 23, 2020).
• 2004-2006 Compliance Recertification (https://www.epa.gov/radiation/certification-and-recertification-wipp#2004-2006, accessed March 23, 2020).
• 1998 Compliance Certification (https://www.epa.gov/radiation/wipp-1998-compliance-certification-documents, accessed March 23, 2020).

order to simulate a “full” repository, as the PA explicitly assumes that WIPP is filled to its legislated capacity at time of closure, as required in 40 CFR § 194.24.²⁹

2.3.5.3 Post-Closure Performance Assessment Analyses

In addition to using the PA calculations for the CRAs, PAs may also be used for sensitivity studies in support of, for example, DOE-NNSA’s efforts to comply with NEPA-driven environmental assessments or environmental impact statements on proposed actions. This was the case with the 2016 ROD for DOE-EM’s 6 MT, which reportedly relied on a WIPP PA analysis in support of the DOE Final Surplus Plutonium Disposition Supplemental Environmental Impact Statement (DOE, 2015a).

2.3.6 Post-Closure Criticality Safety Analysis

As described in more detail later in the report, the surplus plutonium waste form is targeted for packaging in the CCC, which itself is nested within a CCO; see Figure 3-4), which as the name suggests, is designed to safely maintain subcriticality, particularly during the transport and disposal operation phases at WIPP (Washington TRU Solutions, 2008). This safety basis should remain as long as the CCC retains its physical configuration (i.e., the inner can does not sustain damage). Once all the waste is emplaced underground at the end of disposal operations, the post-closure phase begins. The disposal room will eventually close, as the salt creeps around the waste as intended, and this will ultimately damage the waste containers. This needs to be factored in when assessing whether the plutonium mass might someday be reconfigured in a way that could lead to an accidental criticality (see Figure 2-6).

For the post-closure PA at WIPP, the analysis of features, events, and processes (FEP), including those regarding nuclear criticality, is governed by 40 CFR Parts 191 and 194, which allow an FEP to be screened out from incorporation in the PA on either a low-consequence or low-probability rationale. A low-probability rationale includes either a qualitative rationale that the FEP is not credible, or a quantitative demonstration that the probability is less than 10^–4 in 10,000 years. In prior years, with waste streams anticipated at the time having generally more dispersed fissile material, the issue of potential criticality was routinely screened out as mechanisms to concentrate fissile radioisotopes dispersed throughout the waste were considered absent (e.g., Rechard et al., 2000). Later in the report, the committee explores and reviews the post-closure criticality analysis which includes the diluted surplus plutonium waste streams (see Chapter 5).

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²⁹ PA scaling has assumed a distribution of 168,485 m³ CH-TRU and 7,079 m³ RH-TRU. Under the volume accounting for the TMW volume, it is likely that the CH TMW volume will be greater than the CH LWA volume of 168,485 m³.

2.4 OVERVIEW OF RISK ASSESSMENT

This section briefly describes the different types of risk considered by the dilute and dispose plan and within this report. Specific risks are explored by the committee in greater detail in key sections of the report, for example, in the committee analysis related to scale-up of operations and transportation.

There is no single definition of “risk,” considering the multiple disciplines it spans including public health, environmental science, design and engineering, business, law, and many others. For example, the Society for Risk Analysis found more than two dozen definitions for risk in the literature (Lowrance, 1972; Greenberg et al., 2012; Haimes, 2016). While there is no single definition, for purposes of this dilute and dispose report, which is heavily focused on human health, costs, schedule, and diversion or theft of material, we define risk as a measure of the probability and severity of consequences (Lowrance, 1972; Greenberg et al., 2012; Haimes, 2016).

2.4.1 Human Health, Safety, and Ecological Risks

The field of risk assessment emerged from concerns about human health and safety that had become major public policy issues in the 1970s. Three well-known applications of the risk concept were to chemical carcinogens, nuclear power plants, and hazardous waste management. These early applications focused on human health and safety with researchers defining three risk assessment and three risk management questions. By no means do these six questions represent a universally accepted consensus. Others have as few as four and up to a dozen questions and subquestions (Greenberg et al., 2012; Haimes, 2016).

Risk assessment:

1. What can go wrong? (hazard event);
2. What are the chances that something with serious consequences will go wrong? (likelihood); and
3. What are the consequences if something does go wrong? (consequence).

Risk management:

1. How can consequences be prevented or reduced? (prevention);
2. How can recovery be enhanced, if the event occurs? (resilience); and
3. How can officials, expert staff, and the public organize and be informed to reduce risk and concern and increase trust and confidence? (organization).

PA is a version of human health-and-safety-oriented risk analysis used by designers who are called upon to demonstrate that a facility or structure is able to withstand stresses and contain material over a required lifespan. DOE’s PAs at WIPP represent among the most important and challenging applications insofar as DOE must demonstrate the effectiveness of geological and engineered barriers to prevent movement of hazards from a contained environment to an open one that could expose people and the environment over a 10,000-year period. To address these requirements, analysts have used deterministic simulations to drive the process and added probability tools to simulate epistemic (knowledge-related) and aleatory (time-related) uncertainty (Helton, 1994; Helton et al., 1999; Society for Risk Analysis, 1999).

The PA’s parallel in traditional risk assessment is a “level 3 probabilistic risk assessment,” which is a multistage analytical process that begins with identifying hazard events and ends with an estimate of human health and safety risks in the environment. For example, when DOE-NNSA was considering the MOX fuel option, it used a level 3 PRA to compare the human health consequences of design-basis and beyond-design-basis accidents with normal nuclear fuel and a combination of MOX and normal uranium fuel (DOE, 2015c, Appendix J).

2.4.2 Economic Risks and Opportunities

Economic risk and opportunity analysis focuses primarily on costs. Human health and safety risks are or should be part of cost considerations but are not explicitly calculated (Epstein and Rejc Buhovac, 2005; World Bank, 2013; Stebbins-Wheelock and Turgeon, 2018). The essence of an economic risk and opportunity analysis is to sort through many options to find those with the lowest level of economic risk and highest level of economic opportunity, and then narrow down the list to an affordable and manageable set of priorities so one can most effectively invest to reduce economic risks and increase economic benefits. A common business example in the early 21st century is that many manufacturers are reluctant to invest in major new facilities because of the health, ecological, regulatory, and community challenges involved. Instead of building entirely new facilities, many are increasing capacity by adding on to existing sites and at the same time upgrading the technology of existing facilities so that they represent the latest, cleanest, most efficient, most reliable, and safest technology. Those steps are made to reduce both human health and economic risks (Greenberg, 2018; Kunreuther and Isseem, 2018).

Traditional risk analysis, PA, and risk and opportunity analysis share and face many major challenges with traditional analyses. Two of the many major challenges are discussed here. First, each requires likelihood estimates (hence Bayesian Monte Carlo simulation is a component of applications of the dilute and dispose option). Second, the complexity of these applications poses a challenge to those charged with explaining these risks to a diverse set of audiences.

As discussed above, the dilute and dispose project has international implications for the surplus plutonium management as well as political, legal, and social challenges for the states and local governments that are origination and destination points for the plutonium (such as New Mexico, where the DSP-TRU waste will be disposed, and South Carolina, where it will be processed). These challenges along with risks to human health, safety, and diversion and theft of material are discussed in the chapters that follow.