WIPP RH-TRU Waste Study - Summary

This study was prepared by the Department in fulfillment of a congressional mandate specified in Public Law 102-579, referred to as the Waste Isolation Pilot Plant Land Withdrawal Act. In addition, the Department considers the preparation of the study to be a prudent element in the compliance certification process for the Waste Isolation Pilot Plant (WIPP). The study includes an analysis of the impact of remote-handled Transuranic waste on the performance assessment of the WIPP and a comparison of remote-handled Transuranic waste with contact-handled Transuranic waste on issues of gas generation, flammability, explosiveness, solubility, and brine and geochemical interactions.

SUPPLEMENTARY INFORMATION:

Background

The "Department of Energy National Security and Military Applications of Nuclear Energy Authorization Act of 1980" (Public Law 96-164) authorized the Department of Energy (DOE) to develop a research and development facility to demonstrate the safe disposal of radioactive waste generated by national defense activities. The WIPP is required to meet the statutory requirements of Public Law 96-164.

TRU waste is waste that contains alpha particle-emitting radionuclides with an atomic number greater than that of uranium (92), half-lives greater than 20 years, and concentrations greater than 100 nanocuries per gram of waste. TRU waste is classified according to the radiation dose rate at a package surface. Contact-handled (CH) TRU waste has a radiation dose rate at a package surface of 200 millirem per hour or less; this waste can be safely handled directly by personnel. Remote-handled (RH) TRU waste has a radiation dose rate at a package surface of 200 millirem or greater per hour but not more than 1,000 rem per hour; this waste must be handled remotely (i.e., with machinery designed to shield the handler from radiation). Alpha radiation is the primary factor in the radiation health hazard associated with TRU waste. Alpha radiation is not energetic enough to penetrate human skin but poses a health hazard if it is taken into the body (e.g., inhaled or ingested). In addition to alpha radiation, TRU waste also emits gamma and/or beta radiation, which can penetrate the human body and requires shielding during transport and handling. RH-TRU waste has gamma and/or beta radiation emitting radionuclides in greater quantities than exist in CH-TRU waste.

Before 1970, material that is now classified as contact-handled TRU waste was not segregated from low-level waste and was buried along with low-level waste. At the time of burial, the DOE did not intend to retrieve that waste. Since the Atomic Energy Commission (one of the DOE's predecessor agencies) adopted a policy requiring retrievable storage of certain waste containing Transuranic radionuclides in 1970, DOE TRU waste has been stored in containers so that it could be easily retrieved when future decisions were made regarding the management or disposition of this waste. About 55 percent of the Department's current TRU waste inventory contains hazardous substances regulated under the Resource Conservation and Recovery Act. The fraction of TRU waste streams that contains hazardous substances is expected to decrease in the future due to DOE pollution prevention activities.

In 1992, Congress passed Public Law 102-579, the "Waste Isolation Pilot Plant Land Withdrawal Act" (LWA) which withdrew the land on which the WIPP is situated from public use and transferred jurisdiction over the site from the Secretary of Interior to the Secretary of Energy.

Although the DOE is now conducting experiments in laboratories, at the time the LWA was passed, DOE planned on performing experiments with TRU waste in excavated rooms in the WIPP underground. The LWA limited experiments in the underground to those with small quantities of CH-TRU waste during the planned test phase. The repository tests were abandoned in October 1993. Tests are currently planned at INEL using actual TRU wastes to evaluate waste performance under potential repository conditions.

The LWA prohibits RH-TRU waste at the facility until a decision is made to use WIPP as a permanent repository. However, section 6(c)(2)(B) of the LWA requires a study to evaluate the effects of RH-TRU waste on performance assessment of the WIPP. The LWA also requires the study to compare the two waste types in the areas of gas generation, flammability, explosiveness, solubility, and brine and geochemical interactions. In addition, the LWA requires the study to be completed within three years of the date of enactment (October 30, 1992), be conducted in consultation with states affected by WIPP and the Administrator of the EPA. Views were also solicited from other interested parties. Review comments from the affected states, the Administrator and other interested parties on the RH-TRU waste study Implementation Plan and on a draft report of the RH-TRU waste study helped improve the quality of the final report.

Scope of Study

The Remote-Handled Transuranic Waste Study has been conducted in accordance with section 6(c)(2)(B) of the LWA. The study evaluates the impact of RH-TRU waste on the performance assessment of the WIPP baseline configuration. In addition, the study also compares the characteristics of CH-TRU and RH-TRU waste as expected to be received at WIPP as well as the potential affects of the wastes on gas generation, flammability, explosiveness, solubility and, brine and geochemical interactions after emplacement in the WIPP underground. The Remote- Handled Transuranic Waste Study does not include an analysis of RH-TRU waste characteristics on the transportation and operational aspects of the WIPP program.

Study Summary

The Remote-Handled Transuranic Waste Study has three main sections: the Transuranic waste disposal strategy; comparison of contact-handled and remote-handled Transuranic wastes; and analysis of the impact of remote-handled waste on performance assessment.

In the section on the Transuranic waste disposal strategy, elements of the WIPP baseline configuration considered to be important for the study are described. These elements include: room configuration, waste packaging, RH-TRU waste emplacement and shield plugs, and the physical and radiological characteristics of the TRU inventory.

The comparison section of the study includes two areas of evaluation. These include a comparison of CH-TRU and RH-TRU waste characteristics as expected to be received at the WIPP and a comparison of CH-TRU and RH-TRU waste after emplacement in and closure of the WIPP underground. In the latter area of evaluation, the study specifically addresses the issues required by the LWA: gas generation, flammability, explosiveness, solubility, and brine and geochemical interactions.

In the last section of the study, the impact of RH-TRU waste on performance assessment is evaluated. Four radionuclide release scenarios are identified for evaluation: releases by gas generation, groundwater transport, human intrusion and heat generation.

Study Findings

A summary of the important findings of the Remote-Handled Transuranic Waste Study include the following:

• The contribution of RH-TRU waste to the total radioactivity in TRU waste will be insignificant after about 200 years following emplacement in the WIPP. RH-TRU waste has a greater abundance of those radionuclides that characteristically have more penetrating radiation and more specific radioactivity, but these radionuclides also have rapid decay rates and short half-lives reducing their contribution to the radioactive component of TRU waste to a short period of time (200 years). By contrast, the majority of the radionuclides in CH-TRU waste have less specific radioactivity, but decay at a much slower rates.

• RH-TRU waste contributes only a small portion to the total TRU waste inventory because the "Agreement for Consultation and Cooperation with DOE and the State of New Mexico on WIPP" (1981) restricts the quantity to only 5 percent by volume. In addition, RH-TRU waste is composed of the same materials as CH-TRU waste because they are derived from similar processes. Therefore, the impact of RH-TRU waste on performance assessment is insignificant.

• No significant accumulations of gas pressure, or flammable or explosive gases are anticipated in "as-received" waste at the WIPP for the following reasons:

  • WIPP Waste Acceptance Criteria requires containers to be vented to allow pressure to be relieved from the containers during transportation;

  • The WIPP Waste Acceptance Criteria sets strict limits on the amounts of liquids and flammable gasses allowed in WIPP waste, and

  • WIPP Waste Acceptance Criteria prohibits any explosive materials from being in the waste.

• The presence of brine in the WIPP underground can impact the total amount of gas generated by influencing the mechanisms that cause waste decomposition. The degree to which gas generation occurs depends on the amount of brine present in the WIPP underground and the point in time in the decomposition process brine encounters the waste.

• The decomposable materials in RH-TRU waste can contribute up to about 31 percent of all potential gases that may be generated in the WIPP underground.

• RH-TRU waste contains about 13 percent of the portion of TRU waste materials that can potentially generate flammable gases.

• The additional curies of radioactivity introduced into the repository by RH-TRU waste will not impact the overall TRU waste inventory solubility. The reason for this is that the gamma emitters in RH-TRU waste will decay to levels approximating those in CH-TRU waste before the waste containers degrade and allow interactions with brine (about 200 years following WIPP closure).

• The effects of heat and radiation from RH-TRU waste on the WIPP underground are expected to be minimal. Because the Waste Acceptance Criteria restrict the radiation doses and heat allowed, only a small portion of the WIPP underground will be irradiated and any thermal gradients produced will be insignificant.

• Long travel times, as predicted by modeling studies, are required for brine to reach a regulatory boundary. Therefore, it is highly unlikely that gamma-emitting radionuclides from RH-TRU waste would be part of a release to the accessible environment due to groundwater migration since the rapid decay rates of these radionuclides result in much smaller quantities after a relatively short period of time (200 years).

• Gamma-emitting radionuclides in RH-TRU waste can have little or no contribution to releases caused by human intrusion activities because their rapid decay rates result in much smaller quantities after a relatively short period of time (200 years).

• Studies to evaluate the effects of heat on repository performance have shown that at expected levels of waste package heat output, insufficient heat will be available to influence WIPP performance.

Two major conclusions can be drawn from the findings of the Remote-Handled Transuranic Waste Study: (1) RH-TRU waste has no significant impact or influence on the outcome of performance assessment and (2) RH-TRU waste is similar to CH-TRU waste in terms of its characteristics as expected to be received at WIPP and in its behavior in the WIPP underground.

Issued in Carlsbad, New Mexico, this 11 day of October, 1995, for the United States Department of Energy.

ADDRESSES: To obtain a copy of the Remote-Handled Transuranic Waste Study (Document Number DOE/CAO 95-1095) telephone the WIPP Information Center at 1-800-336-9477. In addition, copies of the Remote-Handled Transuranic Waste Study are available for inspection at WIPP reading rooms.

FOR FURTHER INFORMATION CONTACT: Written questions and comments should be directed to: George Basabilvazo, Carlsbad Field Office, U.S. Department of Energy, P.O. Box 2078, Carlsbad, New Mexico 88220.

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