Nuclear Material Control and Accounting by Process Simulation with Smalltalk

Two aspects of safeguarding special nuclear material (St^M) are controlling its location and accessibility (material control) and knowing the quantity of material at those locations (material accounting). The goal of these two functions is to prevent the loss of SMM and to be able to prove it. Material control generally relies on procedures to regulate the flow of material and the personnel in a processing facility. Material accounting audits these control procedures by periodically inventorying the material and comparing the measured inventory with the facility records. Differences between measured inventory and book inventory are resolved by identifying errors in bookkeeping or errors in measurement, or by determining that material has been diverted. Resolving differences is time consuming and expensive. In modem SNM processing facilities, control procedures are verified as they are performed by automated computer accounting systems. This real time verification localizes discrepancies to individual material transfers and therefore greatly reduces the time and expense of resolving inventory differences. However, the software for automated material control and accounting (MC&A) systems is complex, expensive and, thus far, specific to individual facilities. Also, because of their complexity, MC&A systems are difficult to modify to reflect changes in facility operation. Much of the complexity in MC&A software is due to the representation of data and data processing methods in the computer. Data which describe the facility is stored in array type data structures. The data processing methods, or code, are independent of the data structures, and are usually written to function as an accountant. While this is logical, the data structures and code bear little resemblance to the facility. Details about the facility, such as material transfer conditions or analytical capability, are buried into the code. The cede also contains the description of the data structure^ and, inplicitly, their connection to the facility.