Development and Application of Axially Variable Strength Control Rods for the Power Maneuvering of Pressurized Water Reactors

In this research, lower shifted worth control rods (LSWCRs) are suggested to mitigate problems related to variation of axial power distribution during the power maneuvering of pressurized water reactors. These rods are classified into two types. The first type is "multipurpose control rod," and the other type is "regulating control rod." Two multipurpose control rod banks (LSWCR1, LSWCR2) and three regulating control rod banks (LSWCR5, LSWCR4, LSWCR3) are suggested and developed. The moving characteristics of LSWCRs, related to variation of reactivity and the axial offset (AO), are analyzed, and the operation strategy for LSWCRs is established. Then, an application of LSWCRs for the power maneuvering is performed using the developed strategy, and the reference daily load pattern is 100-50-100%, 2-6-2-14h pattern that is appropriate for operation of the electric grid in Korea. From the results, it is shown that the combinative use of multipurpose control rods (LSWCR1, LSWCR2) makes it possible to control the AO within the target band during the power maneuvering. Also, the results show that the power maneuvering without reactivity compensation by change of boron concentration is accomplished, and consequently the minimization of boron concentration change is possible.