A brief history of boxed waste assay systems (primarily those developed at Los Alamos National Laboratory) is presented. The characteristics and design process involved with current generation systems--as practiced by BII--are also discussed in some detail. Finally, a specific boxed waste assay system and acceptance test results are presented. This system was developed by BII and installed at the Waste Receiving and Packaging (WRAP) facility in Hanford, Washington in early 1997. The WRAP system combines imaging passive/active neutron (IPAN) techniques with gamma- ray energy analysis (GEA) to assay crates up to 2.5 m X 2.5 m X 6.5 m in size. (Systems that incorporate both these methodologies are usually denoted IPAN/GEA types.) Two separate gamma-ray measurements are accomplished utilizing 16 arrayed NaI detectors and a moveable HPGe detector, while ³He detectors acquire both active and passive neutron data. These neutron measurements use BII's proprietary imaging methodology. Acceptance testing of the system was conducted at Hanford in January 1998. The system's operating performance was evaluated based on accuracy and sensitivity requirements for three different matrix types. Test results indicate an average 13% active mode accuracy for 10 nCi/g loadings of Pu waste and 5% passive mode accuracy for 10 g loadings of Pu waste. Sensitivity testing demonstrated an active mode lower limit of detection of less than 5 nCi/g of ²³⁹Pu for the medium matrix and less than 20 pCi/g of fission and activation products at 3(sigma) above background.

The WAND (Waste Assay for Nonradioactive Disposal) system scans thought-to-be-clean, low-density waste (mostly paper and plastics) to verify the absence of radioactive contaminants at very low-levels. Much of the low-density waste generated in radiologically controlled areas, formally considered `suspect' radioactive, is now disposed more cheaply at the Los Alamos County Landfill as opposed to the LANL Radioactive Waste Landfill.

Over the past five years, portable High Purity Germanium (HPGe) gamma spectroscopy systems have been used with non- destructive assay techniques to characterize waste items at Los Alamos National Laboratory (LAND). The systems currently are used to characterize approximately 30 percent of Land waste annually, and have been used to segregate low-level wastes from transuranic (TRU) wastes at the generator facilities. As a result of the tremendous cost savings realized from the low-level/TRU waste segregation activities, a pilot program was initiated to recharacterize wastes currently stored and managed at the Solid Waste Operational facility. In the pilot program, 84 cubic meters of plutonium contaminated wastes were characterized, with 10 percent of the waste, by volume, found to be low-level waste. A follow-on effort was commenced to identify wastes in the LAND waste database that may be improperly classified as TRU. The items determined to be `suspect' TRU account for over 90 percent of the TRU waste volume in storage at the Solid Waste Operations facility. In a second recharacterization phase, over 68 cubic meters of TRU waste were recharacterized. Over 62 cubic meters of the recharacterized waste was found to be low-level waste.

The Radioactive Waste Management Complex located within the Idaho National Engineering and Environmental Laboratory (INEEL) contains facilities and equipment to manage and characterize transuranic (TRU) radioactive waste currently stored at the INEEL. This waste was generated primarily at the Department of Energy Rocky Flats Plant. A facility referred to as the Stored Waste Examination Pilot Plant provides space for the systems that characterize and certify the various TRU waste forms for shipping and disposal.

Regulatory agencies governing the disposal of nuclear waste require that the waste be appropriately characterized prior to disposition. The most important aspect of the characterization process, establishing radionuclide content, is often achieved by nondestructive assay (NDA). For NDA systems to be approved for use in these applications, measurement uncertainty must be established.

The Hanford site is home to 177 large, underground nuclear waste storage tanks. Numerous safety and environmental concerns around these tanks and their contents. One such concern is the propensity for the waste in these tanks to generate and retain flammable gases. The surface level of the waste in these tanks is routinely monitored to assess whether the tanks are leaking. For some of the tanks, the waste surface level measurements synchronously fluctuated with atmospheric pressure changes. The current best explanation for these synchronous fluctuations is that the waste contains gas-phase material that changes volume in response to the atmospheric pressure changes. This paper describes: (1) The exploratory data analysis that led to the discovery of the phenomena; (2) A physical mode based on the ideal gas law that explains the phenomena. Additionally, the model allows one to obtain estimates of the retained gas volume in the tank waste; (3) A statistical procedure for detecting retained gas based on the physical model and tank surface level measurements; and (4) A Kalman filter model for analyzing the dynamics of retained gas. It's also shown how the filter can be used to detect abrupt changes in the system.

The exact physical and chemical nature of 55 million gallons of radioactive toxic waste held in 177 underground waste tanks at the Hanford Site is not known with sufficient detail to support the safety, retrieval, and immobilization missions presented to Hanford. The purpose of this study is to estimate probability distributions for the inventory of each of 72 analytes in each of 177 tanks. This will enable uncertainty intervals to be calculated for inventories and should facilitate the safety, retrieval, and immobilization missions.

The Lasentec M600F FBRM particle size and population monitor (Lasentec, Redmond, WA) was selected for deployment on radioactive slurry transfer systems at Oak Ridge National Laboratory and Hanford after extensive testing with `physical simulants.' These tests indicated that the monitor is able to measure the change in particle size distribution of concentrated (up to 35 vol.%) slurries at flow rates greater than 2 m/sec. As well, the monitor provided relatively stable mean particle size values when air bubbles were introduced to the slurry pipe test loop and when the color of the slurry was altered. Slurry samples taken during each test were analyzed with a laboratory particle size monitor. For kaolin slurry samples (length-cubed weighted mean of around 55 micrometers ), the Lasentec M600F FBRM in-line monitor measured length-cubed weighted mean particle sizes within 25% of those measured by a laboratory Lasentec M500LF monitor. This difference is thought primarily to be the result of sample handling issues. Regardless, this accuracy is acceptable for radioactive slurry transfer applications. Once deployed, the in-line Lasentec monitor is expected to yield significant cost savings at Hanford and Oak Ridge through the possible reduction in risk of pipeline blockage. In addition, fewer samples of radioactive slurries will need to be measured in the laboratory, further reducing costs and increasing safety.

The active-passive ²⁵²Cf shuffler instrument, installed and certified several years ago in Los Alamos National Laboratory's plutonium facility, has now been calibrated for different matrices to measure Waste Isolation Pilot Plant- destined transuranic-waste. Little or no data currently exists for these types of measurements in plant environments where sudden large changes in the neutron background radiation can significantly distort the results. Measurements and analyses of twenty-two 55-gallon drums, consisting of mixtures of varying quantities of uranium and plutonium in mostly noncombustible matrices, have been recently completed at the plutonium facility. The calibration and measurement techniques, including the method used to separate out the plutonium component, will be presented and discussed. Calculations used to adjust for differences in uranium enrichment from that of the calibration standards will be shown. Methods used to determine various sources of both random and systematic error will be indicated. Particular attention will be directed to those problems identified as arising from the plant environment. The results of studies to quantify the aforementioned distortion effects in the data will be presented. Various solution scenarios will be outlined, along with those adopted here.

The Radioactive Waste Management Complex, located within the Idaho National Engineering and Environmental Laboratory (INEEL), contains facilities and equipment to manage and characterize transuranic radioactive waste generated primarily at the Department of Energy Rocky Flats Laboratory and currently stored at the INEEL. The facility, referred to as the Stored Waste Examination Pilot Plant, provides space for the systems that characterize and certify the various waste forms for shipping and disposal at the Waste Isolation Pilot Plant in New Mexico. This paper describes the processes and instrumentation used in the nondestructive examination of the TRU waste 55-gal drums.

The cleanup of high level defense nuclear waste at the Hanford site presents several progressive challenges. Among these is the removal and disposal of various components from buried active waste tanks to allow new equipment insertion or hazards mitigation. A unique automated retrieval system at the tank provides for retrieval, high pressure washing, inventory measurement, and containment for disposal. Key to the inventory measurement is a three detector HPGe high performance gamma spectroscopy system capable of recovering data at up to ninety per cent saturation (200,000 counts per second). Data recovery is based on a unique embedded electronic pulser and specialized software to report the inventory. Each of the detectors have different shielding specified through Monte Carlo simulation with the MCNP program. This shielding provides performance over a dynamic range of eight orders of magnitude. System description, calibration issues and operational experiences are discussed.

Characterization of containers of transuranic waste is accomplished by passive and active neutron interrogation. In the passive approach, neutrons from spontaneous fission of ²⁴⁰Pu are detected by coincidence counting. An inherent limitation of this measurement is the presence of alpha particles from ²³⁹Pu, and from other radionuclides, which induce neutron emission by way of the ((alpha) ,n) reaction. Since detection of neutrons does not necessarily imply the presence of ²⁴⁰Pu, the content of plutonium is not uniquely determined. In the active mode, neutron pulses induce fission events, producing neutrons. Gated counting permits some discrimination between the pulse and the fission neutrons. Several different artificial intelligence techniques for representing uncertainty have been investigated to determine which ones might yield additional insight in a manner similar to the judgment of experts. Three experts were asked to evaluate two sets of data, a training set and a test set, and to provide an estimate of their confidence in the results. A neural-genetic optimizer was employed to evolve a neural network to mimic each expert's characterization. The conclusions of this study are useful in refinement of the logic for both Bayesian and fuzzy techniques.

The need for a continuous air monitor capable of quick and accurate measurements of airborne radioactivity in close proximity to the work environment during waste management, site restoration, and D&D operations led to the Los Alamos National Laboratory development of an environmental continuous air monitor (ECAM). Monitoring the hostile work environment of waste recovery, for example, presents unique challenges for detector design for detectors previously used for the clean room conditions of the typical plutonium laboratory. The environmental and atmospheric conditions (dust, high wind, etc.) influence aerosol particle penetration into the ECAM sampling head as well as the build-up of deposits on the ECAM filter.

Neutron-sensitive scintillating glass fiber sensors provide several advantages over ³He and BF₃ gas-tubes for plutonium detection and surveillance. Large active areas provide significant improvements in sensitivity versus cost. In addition, the glass sensors offer a wide dynamic counting range, fast response time, and low microphonic susceptibility relative to conventional sensors. We report the results of detection limits for neutron glass panels used for portal, freight and vehicle monitoring.

A radiation detector has been assembled that monitors human intrusion in rooms containing kilogram quantities of special nuclear material (SNM). The detector is fabricated from scintillating glass fibers that contain ⁶Li as the neutron absorber. The detector is designed to consume a minimum of power and to be placed in a standing position, thereby presenting a minimum profile and allowing placement in existing facilities. A small footprint is achieved by using intrinsically-thin fiber optics and by undermoderating the system. The detector operates by alarming on a rapid change in the thermal neutron count rate, which corresponds to albedo neutrons that are thermalized or absorbed in the hydrogen and carbon of human body tissues when someone enters the existing neutron flux found in SNM storage rooms.

Coincidence counting of time-correlated spontaneous fission neutrons from even-atomic-numbered Pu isotopes has been a well documented methodology for determining quantitatively the amount of Pu present in a waste container. This paper will show the results of subsequent measurements, the Pu gram equivalents, and coincidences of the presumed muon- initiated events versus the amount of Pb present.

At the Plutonium Facility at Los Alamos National Laboratory, a series of non-destructive assays were performed on five transuranic waste drums containing non-actinide scrap metal that was potentially contaminated with weapons grade plutonium and trace quantities of curium. Typically, waste drums containing metal matrices are assayed for plutonium content using passive neutron coincidence counting techniques. The presence of trace quantities of ²⁴⁴Cm prevents this type of analysis because of the strong coincidence signal created by spontaneous fission of ²⁴⁴Cm. To discrimination between the plutonium and curium materials in the matrix, an active neutron measurement technique was used. A californium shuffler designed for measurement of uranium bearing materials was calibrated for plutonium in the active mode. The waste drums were then assayed for plutonium content in the shuffler using the active-mode calibration, which is relatively insensitive to the ²⁴⁴Cm contamination. The curium contamination levels were estimated from the difference between the active-mode measurement in the shuffler and a passive assay in a neutron coincidence counter. Far field gamma-ray measurements were made to identify additional radioactive contaminants and to corroborate the plutonium measurement results obtained from the active-mode assay. This report describes in detail the measurement process used for characterization of these waste drums. The measurement results and the estimated uncertainty will be presented.

A unique gamma detection system has been developed that provides significant background suppression at low gamma-ray energies (< 400 keV). This suppression is accomplished with a segmented intrinsic germanium Duode detector developed by Princeton Gamma Tech. While active Compton suppression shields and passive shields are well known for their background suppression capabilities, the Duode design provides additional suppression capabilities not previously available for low intensity, low energy measurements.