An example of a safeguards application to a pyrochemical separation plant is found at the Fuel Conditioning Facility (FCF) located at Idaho National Laboratory (INL). INL, owned by the Department of Energy (DOE) and operated by the Battelle Energy Alliance (BEA), must comply with specific DOE orders regarding nuclear material control and accountability (DOE 2007). This order establishes a program for the control and accountability of nuclear materials at DOE-owned and DOE-leased facilities and DOE — owned nuclear materials at other facilities that are exempt from licensing by the Nuclear Regulatory Commission (NRC). Nuclear material control and accountability must be integrated with the Safeguards and Security Program for two reasons. First, it provides a mechanism for detecting a potential loss of nuclear material for safeguards and security. Second, it provides a periodic check of inventories to ensure that processes and mate­rials are within control limits (Vaden et al. 1996).

The basic FCF mission is to support the Fuel Cycle Research and Development Program (the successor to the Advanced Fuel Cycle Initiative (AFCI)) by treating sodium-bonded metal fuel and producing interim storage products and final waste forms. FCF has two adjacent hot cells known as the “air cell” (that contains a purified air atmosphere) and the

“argon cell” (that contains a purified argon atmosphere). Both hot cells house the remotely operated equipment used to electrochemically treat spent metallic nuclear fuel and are considered one Material Balance Area (MBA). Figure 5.1 shows a block diagram of the basic process steps. Simply stated, the operations performed in FCF consist of: 1) receipt of nuclear material and preparation into a form suitable for electrochemical process­ing; 2) electrochemical processing to remove nuclear material from fission products, bond sodium, etc.; 3) production of a low-enriched product for storage; and 4) preparation of waste forms. The process has been described in greater detail by Ackerman (1991) and Mariani (1993).

Because nuclear materials processed in FCF are contained in many material types and forms, material accountability requires measuring the nuclear material content of all flow streams entering and exiting the MBA and the physical inventory of nuclear material within the MBA. The inven­tory difference (ID) is defined as the difference between the measured inventory and what is expected to be in the inventory based on the previous
inventory and measured flows into and out of the process. The ID is calcu­lated via the following equation (DOE 1995).

ID = (BI + TI) — (EI + TO)

In this equation the summation of the ending inventory (EI) and transfers of nuclear material out of the MBA (TO) are subtracted from the summa­tion of the beginning inventory (BI) and transfers of nuclear material into the MBA (TI). Because measurement errors will occur, the actual amount of material measured will differ somewhat from the expected quantity, most likely resulting in a non-zero ID. The probability of detecting the loss of a given quantity of material (the loss detection capability) depends upon the uncertainty associated with the determination of the ID. In the FCF, mate­rial control and accountability uses twice the standard deviation of the inventory difference for the limit of error, which is propagated from all measurement and sampling uncertainties in an operation. The limit of error means the true ID has a 95% probability of being within two sigma of the measured ID. The true ID is zero if all materials have been measured and accounted for.

Near-real-time accountancy (NRTA) in FCF is accomplished by a com­bination of neutronics calculations, process models, physical measurements, and a computer-based mass tracking (MTG) system. The MTG system tracks the location and masses, by element and isotope, of nuclear material — containing items in near real time. Items may be storage containers, process­ing equipment, and fuel elements and assemblies. The masses are determined using in-cell balances with isotopic and elemental compositions determined by neutronics calculations, by previous measurements, or by computations based on process models. The neutronics calculations and process models are established by measurements applied to a particular process step. Mass values derived from process models are updated when measurement results are available. The MTG system provides a model of discrete accountable items distributed in space and time and constitutes a complete historical record (Adams et al. 1996). Figure 5.2 is a photograph of some of the track­ing stations in FCF that assist in the NRTA.

With this database, material accountancy over the whole facility can be calculated for any specified time interval and space. Material accountancy uses the item weights and compositions and associated uncertainties. The system uses the best available information, which may either include measured or model weights. The Materials Accounting with Sequential Testing (MAWST) computer code is typically used for propagating the errors and establishing the inventory difference and limit of error (Picard and Hafer 1991).

Moving beyond the Fuel Conditioning Facility, safeguarding any process­ing facility requires periodic material balances (Li et al. 2002). This neces­sitates measuring the input streams and output streams. In addition, an accounting of all materials in the physical inventory is also necessary to close the material balance. Two approaches are proposed, a clean out of the physical inventory or measuring the physical inventory. A complete cleanout of the physical inventory is very disruptive to the process and may not be possible in some cases. Measuring the physical inventory is difficult and may result in large uncertainties in the measurement and material balance. As stated in the FCF example, measuring the physical inventory allows for NRTA. Research has just barely begun on non-destructive assay (NDA) of the input stream. In-situ measurements of the physical inventory have not been fully developed. FCF relies heavily on process modeling for its NRTA. In conclusion, a major research and development effort is necessary to measure the input and output streams and the physical inven­tory to establish NRTA for safeguarding a dry processing facility.