Characterization of Remote-Handled Transuranic Waste for the Waste Isolation Pilot Plant: Final Report (2002)

This appendix is based on information gathered by the committee in the time frame allowed by this study. It should not be considered a comprehensive review of all techniques being considered to characterize remote-handled transuranic (RH-TRU) waste.

Non-destructive characterization of RH-TRU waste is challenging because of the high surface dose rate of waste canisters (up to 1,000 rem per hour) resulting from the high background gamma and neutron radiation generated by fission and activation products in the waste. To reduce the risk of worker exposure during characterization of RH-TRU waste, non-destructive examination and assay techniques are needed to avoid performing destructive analysis such as visual examination and radiochemical assays. According to the information gathered from DOE’s Transuranic and Mixed Waste Focus Area: “Non-destructive examination and assay techniques to characterize remote-handled wastes must still be developed and demonstrated” (DOE-ID, 2001).

Non-destructive assay (NDA) identifies radioactive components, and non-destructive examination (NDE) determines the physical makeup of the waste. These non-destructive technologies must be capable of accurately identifying the physical and radiological properties of wastes in lead-lined containers as well as correcting for precision or bias problems caused by matrix effects (such as heterogeneity problems and interferences with heavy metals in waste) and by the high radiation background. In particular, the neutron emitting RH-TRU solid debris waste at Oak Ridge National Laboratory is the most challenging to characterize.

The following is a brief overview of the major non-destructive characterization techniques currently under development by various Department of Energy (DOE) generator sites, contractors, and private companies. Further development of these techniques and demonstration on actual RH-TRU waste is pending the outcome of the characterization plan for RH-TRU waste. The major NDA/NDE techniques considered for RH-TRU waste are the following:

This NDE technique is often referred to as X-ray radiography or real-time radiography (RTR). X-rays provide a direct measure of material density and as such can be used to establish the physical form of the waste and identify certain prohibited items. In addition, operators can be trained to look for indicators of prohibited items such as electrical components that could contain polychlorinated biphenyls. This technique consists of an X-ray source combined with a TV camera attached to an X-ray detector.

Roney and White (2001) studied the characterization of RH-TRU and lead-lined drums using X-ray imaging techniques. (Roney and White, 2001). Although no real RH-TRU waste was used in their work, they demonstrated the applicability of radiography to surface dose rates up to 100 rem per hour. TMFA states that: “current real time radiography (RTR) techniques cannot analyze the content of the lead-lined drums. Similarly, RH waste inserts and casks are too thick for conventional RTR analysis and interrogation may be further complicated by high radiation levels and contributed ‘white noise’ from inside the drum” (DOE-TMFA, 2002a).

To the best of the committee’s knowledge, radiography has not been demonstrated on real or surrogated waste with surface dose rates close to 1,000 rem per hour.

Gamma-ray spectroscopy uses the gamma emission and transmission properties of radionuclides contained in the waste to obtain qualitative and quantitative information of radionuclide content. Gamma-ray tomography is a variation of gamma spectroscopy and is used to determine the spatial and quantitative information of radionuclide distribution in waste containers. Matrix interferences are corrected by scanning for known gamma-ray sources. For further information on related technologies, see, for example, Meeks and Chapman (1997).

The GSAK approach is used to determine the quantities and types of radionuclides in waste drums. This technique is based on measurement of the radionuclide distribution in the waste followed by normalizing this distribution to the activity of a gamma-emitter such as cesium-137 or cobalt-60, which can be measured outside the waste drum. Based on the measured surface dose rates for cesium-137 or cobalt-60, the amount of these two radionuclides inside the drum can be estimated. This in turn allows the activity of the other radionuclides in the waste drum to be estimated using their ratio to cesium-137 or cobalt-60. The radionuclide distribution may be determined through gamma spectroscopy methods or other nuclear counting methods for alpha- and beta-emitters. Because alpha- and beta-emitters are often difficult to measure in waste, measurements are sometimes used in conjunction with detailed computer modeling to develop a radionuclide distribution that includes these hard-to-measure radionuclides. This technique requires an accurate knowledge of the waste to be characterized before measurements are integrated with computer modeling.

The Battelle Columbus Laboratories have demonstrated this technique with actual RH-TRU waste (Biedscheid et al., 2002). The Idaho Engineering and Environmental Laboratory is also planning to use this technique for its RH-TRU waste originated in Argonne National Laboratory-East (Bhatt and Clements, 2001). For further information about this technique and its demonstrations see Hartwell et al. (1997, 2000), Jensen (2001), and Klann and Grimm (2000).

Passive and active neutron measurements are widely used in waste management and safeguard operations for fissile mass measurements (usually plutonium-239,

plutonium-241, or uranium-235) and for determination of alpha contents for disposal sites. This technique is based on the spontaneous fission rate determination of fissile material present in the container in (passive neutron measurement mode) and on the induced fission rate by neutron interrogation (active neutron measurement mode). The technique is sensitive to extraneous neutrons coming from secondary alpha decays and from cosmic background. This technique was used to characterize 10 actual RH-TRU waste containers and over 200 containers of surrogate RH-TRU waste at Los Alamos National Laboratory (Estep et al., 1989; Estep, 2001, 2002). For further information on this technique and its variations see DOE (1998), Ensslin et al. (2000), Royce and Lucero (2001), and Schultz et. al. (1995).

The multi-detector analysis system (MDAS) technique is used to obtain a direct isotopic measurement with no prior knowledge of the waste. MDAS interrogates the (unshielded) waste with neutrons, and then collects energy coincidence measurements through multiple detectors for both gamma and neutron data over a small period of time. Coincident neutrons provide information on the quantity of fissile material present, and coincident gamma rays provide information on specific isotopes from fission products. This technique is designed to reduce background measurement interferences so that a direct isotopic measurement is provided. Uncertainties associated with current passive/active neutron measurement techniques are reduced by measuring the coincidence energies fast neutrons. A demonstration of this technique on RH-TRU waste was scheduled for 2001 but did not take place due to problems with the external neutron source. For further information on this technique, see DOE-TMFA (2002b), DOE-ID (2001) and Shelton-Davis (2001).

Bhatt, R. and T.Clements, Jr. 2001. Proposed radiological characterization approach for fuel-based remote-handled waste stored at the Idaho National Engineering and Environmental Laboratory. Paper presented at the Non-Destructive Assay Interface Working Group Meeting. July 20. Indian Wells, Calif.

Biedscheid, J., S.Stahl, M.Devarakonda, K.Peters, and J.Eide. 2002. Adequacy of a Small Quantity Site RH-TRU Waste Program in Meeting Proposed WIPP Characterization Objectives. In Proceedings of the WM’02 Conference. February 24– 28. Tucson, Ariz.

DOE. 1998. Non-destructive Waste Assay Using Combined Thermal Epithermal Neutron Interrogation. Innovative Technology Summary Report. Mixed Waste Focus Area DOE/EM-0465. U.S. Department of Energy. Washington, D.C. Available at: <http://apps.em.doe.gov/ost/pubs/itsrs/itsr1568.pdf>.

DOE-ID. 2001. Transuranic and Mixed Waste Focus Area Multi-Year Program Plan FY2001. DOE/ID-10659. U.S. Department of Energy, Idaho Operations Office. Washington, D.C. Available at: <http://tmfa.inel.gov/Documents/MYPP01.pdf>.

DOE-TMFA. 2002a. STCG Need and Technical Response. Need Title: Techniques to Analyze Shielded and Remote-Handled Drums. MW01-CB-01–02. Available at: <http://tmfa.inel.gov/Needs/needcomp.asp?wp=MW01&id=178>.

DOE-TMFA. 2002b. TMFA TTP Summary Information. Available at: <http://tmfa.inel.gov/Needs/ttpscope.asp?id=156>.

Ensslin, N., D.R.Mayo, M.C.Browne, L.A.Carrillo, L.A.Foster, W.H.Geist, J.E. Stewart, and K.Veal (Los Alamos National Laboratory). 2000. Evaluation of Several Fast Neutron Coincidence Counter Options for Characterization of Remote-Handled Transuranic Waste. Seventh Non-destructive Assay Waste Characterization Conference. May 22–26. Salt Lake City, Utah.

Estep, R.J., K.L.Coop, T.M.Deane, and J.E.Lujan. 1989. A Passive-Active Neutron Device for Assaying Remote-Handled Transuranic Waste. LA-UR-89–3736. Paper presented at the Topical Meeting on Non-destructive Assay of Radioactive Waste. November 17–22. Cadarache, France.

Estep, R. 2001. LANL Experience Assaying RH-TRU Waste Using a Modified DDT/PAN Counter. Presented at the Non-destructive Assay Interface Working Group Meeting. July 20. Indian Wells, Calif.

Estep, R. 2002. Personal communication with National Research Council staff, May 15.

Hartwell, J.K., W.Y.Yoon, and H.K.Peterson (Idaho National Engineering and Environmental Laboratory) . 1997. A Preliminary Evaluation of Certain NDA Techniques for RH-TRU Characterization. Proceedings of the Fifth NDA/NDE Waste Characterization Conference. Salt Lake City, Utah. Available at: <http://plutoniumerl.actx.edu/thefifth.html>.

Hartwell, J.K., R.T.Klann, and M.E.Mcllwain. 2000. Gamma-Ray Spectrometric Characterization of Overpacked CC104/107 RH-TRU Wastes: Surrogate Tests. Proceedings of the Seventh Non-destructive Assay Waste Characterization Conference. May 22–26. Salt Lake City, Utah.

Jensen, C. (Battelle Columbus Laboratories). 2001. Methodology for Determining Radiological Properties of RH-TRU Waste. Paper Presented at the Non-Destructive Assay Interface Working Group Meeting. July 20. Indian Wells, Calif.

Klann, R.T. and K.N.Grimm. 2000. Acceptable Knowledge for Argonne National Laboratory Remote-Handled Transuranic Waste. Proceedings of the Seventh Non-destructive Assay Waste Characterization Conference. May 22–26. Salt Lake City, Utah.

Meeks, A.M., and J.A.Chapman. 1997. Development of the Remote-Handled Transuranic Waste Radioassay Data Quality Objectives: An Evaluation of RH-TRU Waste Inventories, Characteristics, Radioassay Methods and Capabilities. ORNL/TM-13362. Oak Ridge National Laboratory. Oak Ridge, Tenn.

Roney, T.J., and T.A.White. 2001. Characterization of RH-TRU and Lead-Lined Drums Using X-Ray Imaging Techniques. INEEL/EXT-2001–00625. Idaho National Engineering and Environmental Laboratory. Idaho Falls.

Royce, R., and R.Lucero (BNFL Instruments, Inc.). 2001. Characterization of RH Waste at Melton Valley Using PAN/GEA/ETA Technology. Available at: <http://tmfa.inel.gov/Documents/RHWASTE.pdf>.

Schultz, F.J., G.Vourvopoulos, P.C.Womble, and M.L.Roberts. 1995. A feasibility study for a LINAC-based transuranic waste characterization system. Journal of Radioanalytical and Nuclear Chemistry, 193(2):369–375. Available at: http://www.wku.edu/Dept/Academic/Ogden/Phyast/API/research/hawaii94.pdf>.

Shelton-Davis, C.V. 2001. Multi-Detector Analysis System Fiscal Year 2000 Summary Report. March. INEEL/EXT-01–00367. Idaho National Engineering and Environmental Laboratory. Idaho Falls.