Conceptual core design of an innovative small PWR utilizing fully ceramic microencapsulated fuel

•A conceptual core design of combining FCM fuel concept with small PWR technology is performed.•Soluble boron free operation is shown feasible by Pu-240 adding, Gd2O3–UO2 rods loading and control rods arrangement.•About six-year cycle length without refueling is achieved in the core.•Fuel temperature is estimated much lower than that of conventional PWR's.

The fully ceramic microencapsulated (FCM) fuel, which has the benefits of retaining fission products, high burnup, and proliferation resistance, is promising to fit in well with small reactors. This paper aims to combine FCM fuel concept with small PWR technology to design a 350 MWt PWR core using FCM fuel, achieving soluble boron free (SBF) operation and at least five-year core life without refueling. In the study, single batch refueling pattern is chosen to avoid frequent refueling. In addition, CASMO-4E/SIMULATE-3 code package is used for nuclear design calculation, and the double heterogeneity of FCM fuel is certified negligible.In FCM fuel design, the packing fraction of TRISO particles is chosen 46%, and with the TRISO particle design, the volume fraction of UO2 kernels in FCM fuel compact is achieved 17.87%. Calculation shows that under the single batch refueling pattern, directly using FCM fuel in conventional PWR design can hardly reach the long core life purpose. In this core design, fuel rod number, FCM fuel compact diameter, and axial active fuel height are all properly enlarged compared to output power level, leading to 13.6 t fuel inventory as well as about six-year core life with 9.3 w/o UO2 enrichment.To achieve SBF operation in the core, Pu-240 is added in some assemblies, and Gd2O3–UO2 rods are loaded in other assemblies, which together hold-down reactivity efficiently, and make the reactivity vary flatly with burnup changes. As many as 10 regulating banks are arranged since the integral worth of each bank is restricted to avoid adverse axial power distribution. With the combination of Pu-240 adding, Gd2O3–UO2 rods loading and control rods arrangement, normal operation and hot shut down can be achieved without soluble boron in the core, and the cold shut down condition needs boric acid injection. It is estimated that the average center temperature of fuel kernel at fuel rod centerline is 845 K, which is much less than that of conventional PWR.