Effect of Irradiation and Thermo-Induced Processes On Reactor in Vessel Elements During Long-Term Operation

Abstract

A method for determining the effect of inhomogeneous temperature distribution, irradiation damage, irradiation swelling, irradiation creep of the material on the long-term strength of reactor in vessel internals and their deformation has been developed. The deformed state of the WWER type nuclear reactor baffle was determined. Constitutive equations taking into account the hidden damage of the material are proposed. According to the results of computer simulations, the strain fields of the section of the baffle during its operation for 60 years were analyzed, the place of possible occurrence of a macroscopic defect was determined.

Numerical Modeling of Hidden Damage Accumulation Due to Radiation Exposure and Hydrogen Embrittlement

“…Function S [25,26] depends upon accumulated dose D a , time t, temperature and experimentally determined parameters.…”

“…For the description of irradiation creep in considered conditions we use the constant b cr = 1.21410 -12 MPa -1 /h [26].…”

“…We obtain: (25) In the moment of the finishing the hidden damage accumulation . Set t=t * , = * we have: (26) From Eq. ( 26), we obtain the value of the constant G. To use this approach, it is necessary to know the values included in (26).…”

“…Set t=t * , = * we have: (26) From Eq. ( 26), we obtain the value of the constant G. To use this approach, it is necessary to know the values included in (26). Analyzing results presented in [2] and [9], we will assume =460 MPa (the maximum stress value in the reactor baffle), t * =31 h, * =2.4%.…”

“…In this software the numerical simulation under a two-dimensional stress state is performed using the FEM and differential time integration methods. The main components of the method with the features of its application to elements of nuclear reactors are described in [25,26]. In this paper, additionally developed software modules were used for the implementation of the evolution equation and for determining the sets of finite elements that are situated near the surface of the structural element in order to assign them additional properties of accumulation the hidden damage levels due to hydrogen embrittlement.…”