UWFDM-1295 Preliminary Study of Time-Dependent Isotopic Inventory of the In-Zinerator Actinide Management System

Efficient burnup of minor actinides is one of the most promising alternatives for minimizing waste in advanced nuclear fuel cycles. This work examines the concept of employing a Z-pinch driven fusion source in a sub-critical transmutation reactor designed to burn up actinides and generate constant power. Its fuel cycle is designed to allow on-line fission product removal and fuel replenishment. The actinide inventory in the system is an essential input used to calculate the energy multiplications and neutron spectrum, as well as to design its control mechanism. In this paper we develop a method to calculate time-dependent isotopic distributions, fuel feeding rate and fission product removal rate necessary to obtain a constant power level. The calculation is performed by using both MCise, a Monte Carlo isotopic inventory code, and MCNP. An important feature of MCise for this system is the ability to simulate the on-line removal of fission products from the actinide mixture. In addition to reporting the actinide inventory and burn rates, the impact of the actinide inventory on the fission/fusion energy multiplication will be examined. Background A Monte Carlo inventory simulation engine (MCise) has been developed and implemented for modeling activation of materials with complex processes and irradiation histories[1]. This tool is specifically aimed at systems with flows that separate into multiple streams, each one subject to different processes or irradiation environments before rejoining into a common stream. Monte Carlo (MC) techniques based on following the history of individual atoms allows these atoms to (a) follow randomly determined flow paths, (b) enter or leave the system at arbitrary locations and (c) be subjected to radiation or chemical processes at different points in the flow path. Many elements of the methodology for MC inventory analysis have direct analogs to neutral particle MC radiation transport, where neutral particles traveling through space and changing their energy are replaced by isotopes traveling through time and changing their isotopic identity.