The dimensional changes of a nuclear fuel in operation are strongly determined by two opposite effects. One of them is due to contraction of the as-fabricated pores, giving place to densification which is evident during the first stages of irradiation. This effect is counteracted by the swelling phenomenon provoked by the fission products that progressively accumulate in the fuel material. A model to evaluate the changes in fuel pellets porosity due to radiation and thermal effects taking into account the point defects flow to and from the pores is presented. A simplification of the model to assess the progress of porosity in isothermal re-sintering tests is also given. Simulations are compared with experimental data measured on UO₂ fuel pellets with a variety of microstructures at different temperatures and radiation conditions, attaining a good agreement.

运行中的核燃料的尺寸变化在很大程度上取决于两个相反的作用。其中一个是由于所制造的孔的收缩，而致密化在辐射的第一阶段是明显的。这种效应被逐渐积聚在燃料材料中的裂变产物引起的膨胀现象所抵消。提出了一个模型，用于评估由于辐射和热效应而导致的燃料颗粒孔隙率变化，并考虑了点缺陷流入和流出孔隙的情况。还给出了模型的简化，以评估等温再烧结测试中的孔隙度。将模拟与在UO _2上测量的实验数据进行比较 在不同温度和辐射条件下具有各种微结构的燃料颗粒，取得了良好的协议。