The excess reactivity management in small pressurized water reactor utilizing fully ceramic microencapsulated fuel

In this paper, a neutronics study has been performed to apply burnable poison (BP) for an excess reactivity management in a 200 MWt small PWR adopted soluble boron free (SBF) concept. In this core design, fuel enrichment is set as 19.9 w/o to get long enough cycle length due to the low packing faction of FCM fuels. As a result, the excess reactivity control of the core would be huge at the beginning of core life. In order to suppress excess reactivity efficiently, burnable poison such as Pu-238, Integral Fuel Burnable Absorber (IFBA) and Wet Annular Burnable Absorber (WABA) were evaluated for a cycle in terms of the major core performance parameters such as the suppressing excess reactivity, shutdown margin, and core cycle length. MCNP4C and ORIGEN were used as a tool to perform the results. It has been demonstrated that the burnup reactivity swing over a long cycle period can be reduced from 50,000 pcm to about 20,000 pcm due to utilizing different type burnable poison. It is shown that combinations of burnable poison with control rods make it possible to reduce excess reactivity and get enough shutdown margin during the core life for soluble boron free operation.