Publications
Nuclear Fuel Cycle (NFC) Technology and Policy Program
Systematic Study of Moderation Effects on UO2 Fueled Lattices
Z. Xu, M.J. Driscoll, and M.S. Kazimi
MIT-NFC-TR-028 (May 2001)
Abstract
Several factors motivate re-evaluation of future options for light water reactor (LWR) core design: an increased appreciation for the economic benefit of longer core intra-refueling intervals and higher fuel burnup [M-2], and renewed concern for weapon proliferation risks, especially in the export market. Several initiatives are underway tied to specific overall reactor designs, such as the IRIS program [L-1]; or to improve efficiency of fuel utilization in current reactors (e.g., under EPRI auspices). In the present work a more general overview is attempted so that the effect of lattice designs on overall strategic goals from a physics view of point are made evident in a more explicit manner. To do this unit cell calculations are carried out for a wide range of hydrogen-to-heavy-metal (H/HM) ratios, ranging from over-moderated thermal lattice conditions to dilute steam-cooled fast reactor conditions. The results are then analyzed for reactivity-limited burnup capability, beginning-of-life core reactivity control requirements, total plutonium inventory in spent fuel, and plutonium isotopic composition relating to weapon-usability. Based on this review it is shown that either wet or very dry lattices are preferable to those having an epithermal spectrum, and the reasons for, and challenge of, future work on the wet lattice option, which has better anti-proliferation credentials, are presented.
Two state-of-the-art reactor physics codes are employed: CASMO-4 [E-2] and MOCUP (MCNP + ORIGEN) [M-4]. CASMO-4 is a commercial, deterministic transport code for LWR applications. CASMO-4 has excellent technical support and speed, and has therefore been used extensively in our study. Extensive benchmarking has been carried out at MIT to compare CASMO-4 and MOCUP for PWR unit cells [Z-1] and for assemblies [W-1], in general showing quite good agreement. However in the present work we will employ CASMO-4 on considerably dryer lattices than it was designed for. Therefore additional benchmark comparisons were made to validate our scoping analyses using CASMO-4.
