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

According to the information gathered during committee meetings, DOE’s stated objective is to propose a characterization plan for RH-TRU waste based on the determination of only those waste characteristics that have an impact on the long-term performance of WIPP.¹ The intention is to reduce potential worker exposure to radiation, in compliance with the ALARA (as low as is reasonably achievable) principle, reduce costs, and eliminate self-imposed requirements for waste characterization (DOE-CBFO, 2001d). This plan is different from the existing EPA and NMED-approved characterization plan for CH-TRU waste. DOE acknowledged that the “contact-handled TRU waste characterization program is inefficient and costly. [The] RH-TRU waste characterization program should be performance-driven” (DOE-CBFO, 2001d).

According to the information provided in Documents 1 and 2, the justification for a characterization plan different from that for CH-TRU waste relies on the small inventory of RH-TRU waste compared to that of CH-TRU waste and on the small impact of RH-TRU waste components on the repository performance. The rationale for this new plan is given in two Sandia National Laboratories RH-TRU waste impact analyses, presented in Attachment B of Document 1 and in Appendix 1 of Document 2. The committee received updated information from DOE-CBFO on the RH-TRU waste inventory during its two information-gathering meetings. These data are reported in Tables 1 and 2 in Chapter 2.

The plan proposed by DOE for RH-TRU waste characterization relies primarily on AK to provide adequate characterization information. AK refers to knowledge of waste characteristics derived from information on materials or processes used to generate the waste. This information may include administrative, procurement, and quality control documentation associated with the generating process, or past sampling and analytic data. The major elements of process knowledge usually include information about the process used to generate the waste, material inputs to the process, and the time period during which the waste was generated.² Additional AK is created when old wastes are sampled, treated, or repackaged. Acceptable knowledge is applied on a waste stream basis³ and may be supplemented with sampling and measurement programs or container-by-container measurements.

Based upon EPA’s requirements set forth in 40 CFR 194.22(b), existing process information collected before an approved quality assurance program is in place must be qualified for use as AK. Presumably, this would apply to AK data for any retrievably stored RH-TRU waste. 40 CFR 194.22(b) lists four methods that may be used individually or in combination to qualify such data: (1) peer review, (2) use of corroborative evidence, (3) confirmation by measurements, or (4) qualification of previous quality assurance programs. DOE proposes to use the first three of these options “frequently” to qualify “old” AK data (data collected prior to the approved quality

assurance program plan) for RH-TRU waste characterization whenever a site deems that a 100 percent inspection required for CH-TRU waste characterization to be either too costly or too risky for a particular RH-TRU waste stream (see Document 1, page 5).

Confirmatory activities may be performed on sub-populations samples from the waste stream every time AK meets the characterization requirements and is elected to be the sole method used to characterize a waste stream. These activities will be performed on statistical samples if AK on a waste stream is found to be inconclusive, incomplete, or does not have sufficient information necessary to meet the characterization requirements. If confirmation by representative sampling and measurement is the approach selected, measurements will be performed using standard non-destructive examination techniques, standard radioassay techniques, and standard radiological survey techniques as appropriate for the characterization requirement.

The RH-TRU characterization plan provides some flexibility to the sites for meeting the characterization requirements. The plan allows the sites to manage the waste characterization risk to workers by establishing sub-populations of waste streams that can be characterized using radiography or visual examination to complement AK based on operational considerations (e.g., facility radiation limits). The methodologies for representative selection of containers and of waste stream sub-populations, as well as the frequency for these confirmatory measurements are not specified in the proposed RH-TRU characterization plan. Instead, the plan provides the flexibility to determine how to meet the established characterization requirements using the allowable confirmatory methods described above. No details are provided for how DOE will ensure that sites have appropriately applied the allowable methods. However, the methodology for establishing the representative selection of containers and waste stream sub-populations must be documented and approved by DOE in each site’s quality assurance program plan. In addition, the documents/records associated with the representative container and sub-population selection must be maintained in the site project records and are subject to DOE-CBFO audit.

DOE’s proposed method to meet EPA’s certification requirements, addressing also the requirements in the Land Withdrawal Act, is to use AK to meet all or part of the characterization requirements of the approved quality assurance program plan. Where AK is deemed to be the sole source of characterization information, it will be subject to verification and validation using the requirements set forth in 40 CFR 194.22(b). To meet the requirements of 40 CFR 194.22(b), which provide for added assurance that the AK information is adequate, AK characterization results will be qualified, confirmed, or verified using any one or a combination of the four allowed methods from 40 CFR 194.22(b) mentioned above.

DOE is planning to meet the data quality objectives⁴ for RH-TRU waste using the following methods:

• Measure surface dose rate of RH-TRU waste containers to exclude those with surface dose rates exceeding 1,000 rems per hour.

• Track the RH-TRU waste total activity inventory by the quantification of total activity for a unit (waste stream or individual container) within a factor of five of the true value with a confidence level of 95 percent.

• Account for metals by counting containers as they are emplaced in the WIPP repository.⁵

• Account for CPR by automatically assigning a value of 50 percent of CPR in the net weight of an emplaced RH-TRU debris container.

• Constrain the total inventory of free water by limiting individual units or containers of RH-TRU waste to less than one percent by volume of residual liquid. The total inventory of free water is tracked using AK, visual examination during repackaging, or radiography to verify that the water content is less than one percent by volume.

Document 1 provides examples of what DOE would consider “adequate AK” in the determination of EPA’s required parameters. For instance, if process knowledge shows that a waste stream is composed exclusively of pyrochemical salts, this precludes any significant residual liquids and assures that there is less than one percent by volume of residual liquids (Document 1, Attachment A, page 13).

The characterization objectives to comply with the RCRA Permit requirements reflect the waste parameters (described in Chapter 3) that must be known to store or dispose of the waste at the WIPP facility. In Appendix A of Document 2, DOE includes an analysis by Sandia National Laboratories that estimates the inventory impact assessment for the WIPP’s RCRA Permit. A 300-year model of the WIPP facility was used to demonstrate that the air pathway is the only viable pathway for hazardous constituent release even under bounding conditions on the contents of RH-TRU mixed waste.

The simulation results show that there is no migration of contaminated brine across the land withdrawal boundary. According to DOE, an insignificant amount of contaminated brine leaves the waste area and no contaminated gas migrates beyond the immediate boundaries of the repository. Thus, the calculation results show that in the 300-year period, there is insufficient brine to saturate the waste and form a mobile leachate. Without a mobile leachate, RCRA-regulated metals, or other soluble RCRA-regulated substances cannot be transported to the accessible environment in the long term.

A volatile organic compound emissions model was used to demonstrate that the generation of volatile organic compounds from RH-TRU waste could be calculated without requiring headspace gas sampling and analysis. Moreover, according to DOE’s analysis, cellulosics, plastic, rubber, ferrous metal, and free liquid in RH-TRU waste will not have a significant impact on repository performance, even at quantities much greater than expected. Therefore, DOE does not deem it necessary to determine, to a high degree of certainty, the presence and quantity of the above waste components. On the basis of this analysis, DOE proposes that waste characterization information needed for the safe management of RH-TRU waste may be obtained primarily by using AK and be complemented by radiography or visual examination. Under the proposed approach, AK

would also be used to determine the physical form of the waste and the absence of prohibited items. DOE states that the “AK characterization method proposed for RH-TRU waste complies with 40 CFR Parts 260 through 264 requirements, is consistent with formally issued joint NRC [Nuclear Regulatory Commission]/EPA guidance, and reduces worker exposure to radioactivity in compliance with 10 CFR Part 835” (Document 2, Item 2, page 2–12).

The proposed RH-TRU waste characterization plan to achieve NMED requirements is as follows:

• Determine the physical form of the waste at the Summary Category Group level.

• Determine the absence of the following prohibited items:

  1. Liquids;

  2. Pyrophoric materials;

  3. Incompatible waste;

  4. Explosives and compressed gases; and

  5. Polychlorinated biphenyls with concentrations greater-than-or-equal-to 50 ppm.

• Determine the listed and characteristic hazardous constituents in the waste.

• Determine if a waste is listed as specified in 20.4.1.200 NMAC (incorporating 40 CFR 261.31 and 33); assign the appropriate EPA hazardous waste number(s); and list EPA’s hazardous waste number(s).

• Determine if a waste exhibits the toxicity characteristic as specified in 20.4.1.200 NMAC (incorporating 40 CFR 261.24); assign the appropriate EPA hazardous waste number(s); and list EPA’s hazardous waste number(s).

In Document 2, DOE writes: “prohibited items that are not addressed by the hazardous waste number determination are determined through the use of AK, radiography and/or visual examination […]. If sufficient information to determine the absence of prohibited items is not available through the use of one or more of these three waste characterization techniques, the waste is not acceptable for disposal at the WIPP facility. The remaining prohibited items in the RCRA Permit overlap with the prohibited items for transporting the waste in one of the RH-TRU waste shipping casks approved by the U.S. Nuclear Regulatory Commission […]. Therefore, the combination of information available from the proposed characterization techniques and the information used to ensure legal waste transportation to WIPP ensures that the absence of prohibited items is known to a sufficient degree of confidence” (Document 2, Item 2, page 2–7).

On the basis of the analysis presented in Appendix A of Document 2, DOE determined that the proposed RH-TRU characterization plan does not require the determination of material parameter category weights, toxicity characteristic codes, and headspace gas analysis. The determination of these three parameters is required in the CH-TRU waste characterization plan.

In summary, DOE proposes to use AK as much as possible to accumulate the information on RH-TRU waste required by NMED and EPA and to perform only the confirmatory measurements required to complete AK. Details on these confirmatory measurement requirements are not specified in Documents 1 and 2. This plan is quite different from the CH-TRU waste characterization plan currently in use, as explained below.

The CH-TRU waste characterization plan approved by EPA and NMED is described in Appendix A. Briefly, it consists of a 100 percent of confirmatory activities on CH-TRU waste containers by AK, radioassay, headspace gas sampling, radiography, or visual examination. Both EPA and NMED must grant approval of each generator site’s waste characterization process and approval for each waste stream. For homogeneous wastes,⁶ this includes taking core samples of a fraction of waste containers prior to their shipment to WIPP. For debris wastes, a 100 percent confirmation program (with headspace gas and radiography determinations for RCRA compliance, and NDA and radiography determinations for EPA’s compliance) was imposed.

The most significant difference between the CH- and the RH-TRU waste characterization plans is that the latter does not require confirmatory testing, sampling, or analysis on 100 percent of containers and allows for representative selection of containers for radiography and visual examination. According to DOE, and as noted previously, the quality assurance provisions of 40 CFR 194.22(b) allow DOE to qualify AK by (1) peer review, (2) corroboration with new data, (3) confirmation by measurements, or (4) qualification of previous quality assurance programs. Currently, only confirmatory measurements are being considered and their frequency of use is not specified. Like the current CH-TRU program, each specific TRU waste generator site will develop a site-specific RH-TRU waste characterization plan that will undergo audit by DOE and inspection by EPA and NMED before shipment of RH-TRU waste from that site.

From the operational experience acquired with CH-TRU waste, it is possible to obtain some indication of the effectiveness of the AK method as a characterization method. The WIPP permit requires generator sites to prepare an AK Information Accuracy Report. Two measures are specified:

1. Percentage of waste containers that require reassignment to a new Waste Matrix Code.⁷

2. Percentage of waste containers that require designation of different hazardous waste numbers.

AK information accuracy is determined as the result of AK Information Confirmation. Generators are to use radiography or visual examination, headspace gas sampling and analysis, and/or solids sampling and analysis to confirm AK information accuracy. Effectiveness of the CH-TRU acceptable knowledge process is demonstrated by the AK Information Accuracy Reports from the various generator or storage sites (DOE-CBFO, 2001e). During the second information-gathering meeting, DOE showed results of the effectiveness of AK for CH-TRU characterization. Results showed a high accuracy in AK information: above 95 percent for the determination of waste matrix codes at the major CH-TRU waste generator sites and above 93 percent for the determination of hazardous waste numbers, with one exception. At INEEL, an accuracy

of 80 percent was achieved in the hazardous waste numbers determination because this site did not assign new codes on a container basis.