Performance of Trasuranic-Loaded Fully Ceramic Micro-Encapsulated Fuel in LWRs Interim Report, Including Void Reactivity Evaluation

Abstract

SUMMARYThe current focus of the Deep Burn Project is on once-through burning of transuranics (TRU) in lightwater reactors (LWRs). The fuel form is called Fully-Ceramic Micro-encapsulated (FCM) fuel, a concept that borrows the tri-isotropic (TRISO) fuel particle design from high-temperature reactor technology. In the Deep Burn LWR (DB-LWR) concept, these fuel particles are pressed into compacts using SiC matrix material and loaded into fuel pins for use in conventional LWRs. The TRU loading comes from the spent fuel of a conventional LWR after 5 years of cooling.Unit cell calculations have been performed using the DRAGON-4 code to assess the physics attributes of TRU-only FCM fuel in an LWR lattice. Depletion calculations assuming an infinite lattice condition were performed with calculations of various reactivity coefficients performed at each step. Unit cells containing typical UO 2 and mixed oxide (MOX) fuel were analyzed in the same way to provide a baseline against which to compare the TRU-only FCM fuel.The main objective of this interim report is to report progress in the following areas:x Evaluate reactivity-limited burnup of TRU-only FCM fuel cells in a Pressurized Water Reactor (PWR)x Calculate key reactivity coefficients, including total coolant void coefficient, of the TRU-only FCM fuel at various levels of depletion and evaluate the effects of varying the kernel size and packing fraction (PF) on these coefficientsx Compare these results to reference UO 2 and MOX unit cellsIn addition to the above mentioned goals, a companion report [B. Boer, et. al., FCR&D-2011-000064 or INL/EXT-11-21435] reports on use of the PASTA code to evaluate the integrity of FCM fuel for normal operation states at various levels of depletion and in a simulated LOCA transientIt was shown that due to the limited space available for heavy metal loading within the FCM fuel, the reactivity-limited burnup (in days) at typical LWR power densities may be short compared to ordinary LWR cycle lengths if only FCM fuel is used. Thus, even before evaluating the reactivity feedback performance of the fuel, it is recognized that the idea of using heterogeneous assemblies containing pins of TRU-only FCM alongside pins with low-enriched uranium (LEU) deserves consideration.The reactivity parameters calculated with depletion were the Moderator Temperature Coefficient (MTC), the void coefficient (assuming 10% void), the Doppler coefficient, the soluble boron worth, and the reactivity effect of complete voiding of the coolant. Several different combinations of TRISO particles packing fractions (PF) and kernel diameters were evaluated for the FCM fuel. It was found that the total heavy metal (HM) loading of the FCM fuel is the primary driver for reactivity-limited burnup and for reactivity coefficients, not how it is distributed in various kernel sizes and PF values. The MTC of the TRU-only FCM fuel was negative at beginning of life, but less so than the MTC of UO 2 and MOX reference cases. With burnup, the MTC becomes less negative, and in the c...