Publications
Advanced Nuclear Power Program
A Tight Lattice, Epithermal Core Design for the IRIS Reactor
J.G.N. Saccheri and N.E. Todreas
MIT-ANP-TR-096 (May 2003)
Abstract
A core design for a long-life, epithermal, water-cooled reactor has been developed. Assessments of nuclear reactor physics, thermal-hydraulics and economics have been performed and the results have been presented as a function of key parameters such as discharge burnup, 235U enrichment, H/HM ratio, fuel rod diameter and coolant velocity. Trade-offs amongst such parameters have been analyzed and an optimized core configuration has been chosen.
Self-supporting wire-wrap fuel is adopted for the tight lattice configuration of the epithermal core and a streaming path is incorporated in each assembly to ensure a negative void coefficient. Monte Carlo simulations of the hot bundle have provided the burnup-dependent values of the void coefficient, which is always negative for homogeneous voiding lower than 80%.
Thermal-hydraulics analysis have provided the steady state temperature distributions within the core and the defined margin to critical heat flux (CHF) has been met for both Condition I and Condition II occurrences. The KfK-3 correlation, developed for wire wrapped fuel rods arranged in a triangular configuration, has been implemented in the VIPRE™ code to perform the CHF calculations, while the Cheng and Todreas correlation has been used to calculate the in-core pressure drop. With regard to the maximum allowable linear power at steady state, the loss of coolant accident (LOCA) scenario resulted in a more limiting value than given by the critical heat flux (CHF) occurrence. Chosen values of linear power and rod diameter are consistent with neutronics and core lifetime. Fluid-elastic instability analysis has been performed to define an upper limit to the coolant axial velocity.
Economically, such an epithermal design has been compared to the IRIS open core, which has been selected as a reference core. The high fuel enrichment (14% w/o 235U) and the very long core life (8 ys) of the IRIS tight core caused a higher fuel cycle cost (FCC), while the higher output power per unit volume yielded a smaller unit capital cost (UCC). After including operation and maintenance costs (O&M), the total cost (TC) of the epithermal core option is estimated to be about 20% higher than for a plant using the reference core. Future work will include whole core void coefficient assessment and reflooding analysis of the tight core, which will be based on experimental data. A feasibility assessment for a steam-cooled cycle will be also provided to improve the economics of the core.
