چكيده لاتين
After the Fukushima Daiichi nuclear accident in 2011, the importance of ensuring the safety of nuclear reactors, especially their fuels, became more prominent than before. One of the factors that contributed to the severity of the Fukushima accident was the destruction of the fuel cladding, which led to the release of radioactive materials. Accordingly, in recent years, extensive research has been conducted on the physical and mechanical properties of new clads, known as Accident Tolerant Fuel (ATF).
In this research, the effect of clad changing on some thermohydraulic and thermomechanical parameters of a typical reactor core (300 MWe) has been investigated. Based on this, using Ansys Fluent software, parameters such as DNBR and fuel, gap, clad and coolant temperatures were calculated, for Zircaloy-4, Steel 347 and Steel 409 clads with thicknesses of 0.07 cm and 0.04 cm, and at the average and maximum power (Hot Rod). The reactor was assumed to be in BOC condition. In the following, with the help of Abaqus software, parameters such as stress, strain and displacement of these clads were calculated for Hot Rod.
The thermohydraulic results showed that there is no significant change in DNBR by changing the type of cladding. It was also observed that the temperature of the fuel is slightly reduced by changing the clad material from Zircaloy-4 to Steel 347 and Steel 409 (thickness of 0.07 cm); but this reduction was not significant. Also, by reducing the thickness of the clad from 0.07 cm to 0.04 cm, the temperature of the fuel and coolant were slightly decreased. The thermomechanical results showed that the Zircaloy-4 clad maintains its strength in both thicknesses and does not fail. However, the Steel 347 and Steel 409 clads with a thickness of 0.07 cm were strongly deviated from the original shape; and were failed by a thickness of 0.04 cm.
Based on this, it can be concluded that Steel 347 and Steel 409 have much lower strength compared to Zircaloy-4, and may be severely damaged. Although these two steels are resistant to heat and corrosion, they are classified as soft steels. It is possible to improve the properties of these two steels by using the cold rolling method, but there is a possibility that they will return to their original characteristics in operational conditions.
