Characterization of Remote-Handled Transuranic Waste for the Waste Isolation Pilot Plant: Interim Report (2001)

The U.S. Congress, through the Land Withdrawal Act (Public Law 102–579), designated the WIPP to be the nation’s repository for defense-related TRU waste (Congress, 1992). Congress also established the controlling legal criteria for WIPP in the Land Withdrawal Act. This Act stipulates that EPA must establish the disposal regulations for TRU waste at WIPP. EPA promulgated radiation safety standards in 40 CFR Part 191 and Part 194, the latter specifically for WIPP. EPA authorized NMED to regulate radioactive mixed wastes in New Mexico in accordance with EPA’s regulations. This state regulatory authority extends only to TRU mixed wastes destined for WIPP (EPA, 1990). Therefore, NMED regulates the management, storage, and disposal of TRU mixed waste at WIPP, and establishes the general and specific standards for these activities. The main regulatory documents for TRU mixed waste are the New Mexico Hazardous Waste Act as codified in Part 20 of the New Mexico Administrative Code (NMAC).

DOE’s new characterization plan for RH-TRU waste must be in compliance with the above regulatory documents. At the time of the certification of WIPP, DOE interpreted and translated EPA’s and NMED’s regulatory documents into characterization requirements for TRU waste. These requirements were accepted by EPA and NMED and appear now in EPA’s certification and in the RCRA Permit for WIPP. These requirements are described in the following paragraphs.

The Land Withdrawal Act is the only guiding legislation for WIPP. As defined in the Land Withdrawal Act:

• The term “WIPP” means the Waste Isolation Pilot Plant project authorized to demonstrate the safe disposal of radioactive waste materials generated by atomic energy defense activities.

• The term “disposal” means permanent isolation of transuranic waste from the accessible environment with no intent of recovery, whether or not such isolation permits the recovery of such waste.

• 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 of Energy has determined, with the concurrence of the EPA 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 (Congress, 1992).

The Land Withdrawal Act establishes the five main legal requirements for TRU waste in WIPP, some of which apply specifically to RH-TRU waste. These requirements are the following:

• Nature of waste to be disposed in WIPP: the WIPP can only receive transuranic waste (defined above) generated by atomic energy defense activities.

• Total volume of transuranic waste: the WIPP is allowed to contain up to 175,564 m³ of transuranic waste at WIPP.

• Volume of RH-TRU waste: the WIPP is allowed to contain up to 7,080 m³ of RH-TRU waste, which represents about 4 percent of the total volume of TRU waste allowed in WIPP.

• Total activity of RH-TRU waste: RH-TRU waste received at WIPP shall not exceed 23 curies per liter maximum activity level (averaged over the volume of the container). The total curies of the RH-TRU waste received at WIPP shall not exceed 5.1 million curies.¹

• Surface dose rate: no TRU waste received at WIPP may have a surface dose rate exceeding 1,000 rems per hour. No more than 5 percent of 7,080 m³ (354 m³) is allowed to have surface dose rates exceeding 100 rems per hour.

In 1998, EPA certified that WIPP is in compliance with the radioactive waste disposal regulations set forth in 40 CFR 191 and 40 CFR 194 and in compliance with EPA standards set forth by the Land Withdrawal Act of 1992. A characterization program to meet these requirements was developed for TRU waste and is now applied to CH-TRU waste. In EPA’s view, “DOE has established a precedent with CH waste program” (Monroe, 2001). The CH-TRU waste characterization program is therefore perceived as the standard against which the RH-TRU waste characterization application will be evaluated. The characterization requirements, listed in the CH-TRU waste characterization plan, were based on the conclusions drawn from the performance assessment of the repository. DOE presented its performance assessment for WIPP in the CCA submitted to EPA to obtain certification (see Sidebar 2). The characterization objectives for CH-TRU waste are based on waste parameters identified as important to the performance of the repository (Helton et al., 1998). These parameters are the following:

• Amount of free water: In the CCA, DOE stated that the total amount of water or brine present is important because water is the only means to release radionuclides in the environment and because it controls several other factors, such as corrosion and gas generation.² The total limit in the RH-TRU waste inventory of free water must be less than 71 m³. In the CCA, DOE agreed to meet this requirement by demonstrating that a

RH-TRU waste stream or an individual container contains less than 1 percent by volume of residual liquids.³

• Amount of corrodible metals: The CCA includes requirements for a minimum amount of corrodible metals in WIPP. The minimum amount of corrodible metals has been set to ensure a reducing environment inside the repository. A reducing environment maintains radionuclides in a low oxidation state, which usually corresponds to a minimum solubility. Therefore, waste characterization must ensure that the amount of corrodible metals in the waste is above the minimum amount allowed.

• Amount of biodegradable cellulosics, plastic, and rubber (CPR): DOE must account for the volume of CPR because of the potential gas generation from the decomposition of these organic materials.

In 1999, NMED granted a RCRA Permit to WIPP to manage and dispose of mixed CH-TRU waste only. This permit currently contains requirements for the characterization of mixed CH-TRU waste. DOE is now proposing a change to the RCRA Permit to allow disposal of mixed RH-TRU waste. NMED recommended that DOE build its proposed RH-TRU waste characterization plan based upon the requirements in the existing permit and to provide justification for any difference between the RH-TRU and the existing CH-TRU characterization plan (Zappe, 2001). Currently, the RCRA Permit requires that the characterization of mixed TRU waste be based on the knowledge of the physical form of waste (homogeneous solids, soil or gravel, debris) and the exclusion of prohibited items, listed as follows:

• Liquid waste,

• Non-radionuclide pyrophorics (addressed by the hazardous waste numbers⁴),

• Hazardous wastes that do not contain TRU waste,

• Incompatible chemicals (addressed by the hazardous waste numbers),

• Polychlorinated biphenyls greater than or equal to a concentration of 50 ppm (addressed by the hazardous waste numbers),

• Explosives (addressed by the hazardous waste numbers) and compressed gases, and

• Ignitable, corrosive, and reactive wastes (addressed by the hazardous waste numbers).

Items such as polychlorinated biphenyls, compressed gas, and other types of hazardous waste were probably not accounted for in the AK accumulated for retrievably stored RH-TRU waste. For this type of waste, AK must be complemented by other methods, as those listed in Chapter 4 from 40 CFR 194.22(b).

The current RCRA Permit also excludes RH-TRU waste, any waste container that does not have volatile organic compound concentrations reported for the headspace, any waste container that has not undergone radiographic or visual

examination, and any waste container that has not been preceded by a certified Waste Stream Profile Form.⁵

The 1998 Committee on WIPP found “inadequate legal or safety bases for some of the National TRU Program requirements and specifications. That is, some waste characterization specifications have no basis in law, the safe conduct of operations to emplace waste in WIPP, or long-term performance requirements” (National Research Council, 2001, page 77). The 1998 Committee recommended that DOE “eliminate self-imposed waste characterization requirements that lack a legal or safety basis” (National Research Council, 2001, page 78). The 1998 Committee understood that those requirements that have no legal or safety bases are also not important to the long-term performance of the repository.

A recent study by DOE showed that some waste characterization procedures are indeed not prescribed by safety or legal requirements (DOE-CAO, 1999a). This review of the CH-TRU waste characterization procedures by DOE-CBFO revealed that “there is no regulatory requirement to conduct homogeneous waste sampling and analysis, however, in an effort to meet the intent of 40 CFR 264.13, WIPP has imposed additional characterization requirements on the waste generators.” DOE also informed the 1998 Committee that “there is no regulatory requirement to conduct headspace gas sampling and analysis, however, in an effort to meet the intent of 40 CFR 264.13, WIPP has imposed additional characterization requirements on the waste generators.”

Finally, the 1998 Committee found that there is no legal requirement for the verification of radiography results by visual examination.⁷ According to the study by DOE-CBFO and according to the 1998 Committee, DOE developed self-imposed waste restrictions in the waste acceptance criteria (DOE-CAO, 1996b, 1999b) and in the requirements for waste generating sites presented in the quality assurance program plan⁸ (DOE, 1998b). Therefore, sampling and analysis of homogeneous waste, headspace gas sampling and analysis, and visual examination procedures to characterize CH-TRU waste are based on terms negotiated in the RCRA Permit rather than driven by performance-based characterization requirements (National Research Council, 2001, Appendix A1).