**5. Conclusion**

In this chapter, three models are proposed to describe the properties of irradiated deformed polycrystalline materials.

The first model (see section 2) describes the dose dependence of the yield strength of the irradiated material. It is generalization of the model known earlier (see for instance [5]), as the recombination effects of the radiation – induced vacancy and interstitial barriers and their clusterization are taken into account in it. Within the framework of the model formulated, it is found that the saturation quantity of the yield strength decreases with increasing both the intensity of the mutual barrier recombination and the clusterization intensity. It follows to note that in spite of model's assumption for the mean sizes of the radiation-induced barriers *di* and the shear modulus to be independent the shear modulus increases practically owing to the radiation point defects come on the dislocation and reduce the mean segment length of the dislocation and enhance a degree of the dislocation anchorage. Because of this it can be expected for the obtained dose dependence of the yield strength of the irradiated material to be modified.

The second model describes barrier hardening polycrystalline materials. It is constructed with taking into account interaction of vacancy and interstitial barrier types. In the frame of the proposed model, it can be estimated both contributions to yield strength increment from different type barriers and its total value in dependence on dose.

The third model gives possibility to describe the yield strength dependence of the irradiated materials on experience temperature on a quantitative level. It is based on mechanism of yield strength change as the phase transition between two plastic deformation structure levels characterized by certain values of the athermal stress component. The calculations show radiation promotes the transition of plastic deformation on the higher structure level after that the material undergoes radiation embrittlement. General features found permit to forecast embrittlement temperature intervals of reactor materials in dependence on their mechanical properties.
