Sensitivity and Optimization Studies on Plutonium Vector Variations for a Plutonium Burning Fast Reactor

Abstract

Sensitivity studies were carried out on a 600MW(e) Pu burning fast reactor, to determine the effects of changing Pu vector and the core design changes needed to adapt to a varying Pu vector. The applicability to Pu burner cores of models developed for breeder reactors was examined. The high flexibility of a fast reactor core for Pu burning was demonstrated by an optimization study to show the feasibility of using a single reactor design with Pu vectors varying from highly enriched (military) Pu to degraded Pu produced by multiple recycling. With fuel limited to MOX (∼45% Pu) and a single sub-assembly geometry for all grades of Pu, effective compensation for changes in Pu vector was achieved by replacing fuel with diluent material. The most suitable diluent had two components-absorber (¹⁰B4C) and a moderator or neutron-transparent material (ZrH was most effective)-this gave an additional degree of freedom for optimizing safety-related core parameters. Where pin power ratings were high, hollow pellets introducing void as diluent were effective. Calculations demonstrated a possibility of flux distortions and anomalous rating distributions; these were a consequence of significant moderation of the flux in combination with the interaction between the core and the above/below core structures in the absence of breeder blankets.

KEYWORDS:

• fast reactors
• reactor physics
• design
• plutonium burning
• plutonium vectors
• diffusion calculations
• diluent
• zirconium hydrides
• boron carbides
• 2D/3D modelling
• flux spectra
• moderation
• feasibility studies