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Design and Economic Evaluation of an Advanced Tight-Lattice Core for the IRIS Integral Primary System Reactor

J. G. B. Saccheri, N. E. Todreas, M. J. Driscoll

Nuclear Technology / Volume 158 / Number 3 / June 2007 / Pages 315-347

Technical Paper / Fission Reactors /

An 8-yr core design for an epithermal, water-cooled reactor has been developed based upon assessments of nuclear reactor physics, thermal hydraulics, and economics. An integral-vessel configuration is adopted, and self-supporting wire-wrap fuel is employed for the tight lattice of the epithermal core. A streaming path is incorporated in each assembly to ensure a negative void coefficient. A whole-core simulation of the tight core with the stochastic, continuous-energy, transport code MCNP shows a negative void coefficient for the whole cycle during normal operating conditions. Analysis of in-core, flow-induced vibrations indicates that the design has a greater margin to fluid-elastic instability than a standard pressurized water reactor, allowing for higher coolant mass flux and improved safety. Enhanced flow mixing and thermal margins are also achieved, and the VIPRETM code for subchannel thermal-hydraulic analysis has been used to calculate the critical heat flux (CHF) by means of a wire-wrap CHF correlation specifically introduced in the source code. The combination of increased fuel enrichment (~14 wt% 235U, still below the proliferation-resistant limit of 20 wt% 235U), relatively low core-average discharge burnup (70 MWd/kg HM), and very long core life (8 yr) lead to high lifetime-levelized fuel cycle unit cost [in mills/kWh(electric)]. However, both operation and maintenance (O&M) and capital-related expenditures strongly benefit from the higher electric output per unit volume, which yields quite small lifetime-levelized capital and O&M unit costs for the overall plant. Financing requirements are included, and an estimate is provided for the lifetime-levelized total unit cost of the epithermal core, which is ~16% lower than that of a more open-lattice thermal spectrum core, fitting into the same core envelope and with a 4-yr lifetime.

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