Choosing the Strength Criterion in Mathematics Modeling the Reactor Graphite Behavior
DOI:
https://doi.org/10.24160/1993-6982-2017-2-20-26Keywords:
graphite block, computer modeling, strength criterion, RBMK, cracksAbstract
During the operation of Type RBMK-1000 nuclear power-generating reactors (high-power pressure-tube reactors), it was decided to extend the lifetime of this type of reactors beyond the initially assigned one. Such an approach is more economically profitable than the commissioning of new power units. To ensure the optimal operating conditions and safe operation of the reactor, it is necessary, apart from carrying out its technical modernization, to substantiate the acceptable strength and shape distortion of graphite blocks after their having been exposed to long-term neutron irradiation by means of computer modeling. The graphite blocks used in high-power pressure-tube (RBMK-type) reactors are elements that in many respects determine the reactor’s lifetime as a whole due to their limited amenability to repair. In view of this circumstance, a task was set forth to develop a computer model of thermo-irradiation behavior of graphite blocks that would take into account the maximum possible number of parameters affecting the thermomechanical characteristics of the graphite block. The anisotropy of graphite was taken into account in the stressed-and-strain state equations. Part of the study is devoted to a detailed analysis of creep effect on the graphite block behavior. The strength calculation was carried out taking into consideration the crack incipience and growth phenomena. A few fracture criteria that are used for the conditions of combined stressed-and-strain state are applied in the article for carrying out a strength calculation of the graphite block as an element of the graphite brickwork, which serves as a moderator and deflector in the RBMK-1000 nuclear reactor. The aim of the investigation is to estimate the influence of different fracture criteria on the results obtained from modeling the thermomechanical behavior of a graphite block subjected to long-term neutron irradiation carried out using the finite element method. A 20-node isoparametric element was used as a single finite element.
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