Model of cladding failure estimation for a cycling nuclear unit

Nuclear reactor operating modes under multiple cyclic power changes have been promoted recently, and fuel element cladding behavior under the multiple cyclic power changes has been widely known as a key issue in terms of rod design and reliability. A model of nuclear reactor fuel rod cladding failure estimation under multiple cyclic power changes is proposed. The model is built on the basis of the following admissions of the energy version of creep theory: processes of cladding creep and destruction proceed together and affect each other, intensity of creep process is estimated by specific dispersion power W(τ), while intensity of destruction—by specific dispersion energy A(τ) accumulated during time τ. Having calculated the equivalent stress and the rate of equivalent creep strain, the condition of fuel rod cladding failure used on the basis of the energy version of the theory of creep gives us a criterion to decide if a multiple cyclic power change operating mode is permissible for a given variant of power history and coolant conditions.