For the safety assessment of Spent Nuclear Fuel (SNF) in disposal conditions, it is crucial to determine the fast release of the potentially critical radionuclides (e.g. ¹²⁹I, ¹³⁷Cs, ⁹⁹Tc, ⁹³Mo, ⁹⁰Sr…) upon contact with water. To underpin the quantification of this fast release, leaching experiments were performed at SCK CEN on a PWR UOX fuel from the Belgian Tihange 1 reactor, with a rod average burnup of 50.5 MWd.kg⁻¹HM, an estimated fission gas release of 14% and an average linear power rate of 321 W.cm⁻¹. Tests were carried out with durations up to one year, with clad and declad spent fuel samples, in a NaCl/NaHCO₃ solution at room temperature for a period of one year, in a set-up designed to prevent the intrusion of airborne oxygen. In the test with the declad segment, the exposed surface area was much larger than in the test with the clad segment. As a result, in the first days of leaching, the release of all radionuclides was larger for the declad segment than for the clad segment, except for Tc. After one year, the cumulated release from the declad and clad segments are similar, except for Tc, as a result of air intrusion leading to a higher oxidation and concomitant dissolution resumption, more pronounced for the clad than for the declad segment. For the declad segment, the Tc and Mo concentrations decrease, suggesting reduction to less soluble species in spite of the air intrusion. The release of ¹²⁹I is similar to the fission gas release, while the release of ¹³⁷Cs is lower, but still accelerated compared to the UO₂ matrix. The release of ⁹⁹Tc, ^95-98Mo (representative of ⁹³Mo) and ⁹⁰Sr is only slightly higher than the matrix dissolution rate. All determined released fractions are in line with the reported values of the literature.

对于处置条件下乏核燃料 (SNF) 的安全评估，确定潜在临界放射性核素（例如¹²⁹ I、¹³⁷ Cs、⁹⁹ Tc、⁹³ Mo、⁹⁰ Sr……）在与水接触时的快速释放至关重要. 为了支持这种快速释放的量化，在 SCK CEN 对来自比利时 Tihange 1 反应堆的 PWR UOX 燃料进行了浸出实验，棒平均燃耗为 50.5 MWd.kg ^-1 HM，估计裂变气体释放量为 14%平均线性功率为 321 W.cm ^-1。在 NaCl/NaHCO _{3 中}对包层和脱层乏燃料样品进行了长达一年的测试溶液在室温下保存一年，在一个旨在防止空气中氧气侵入的设置中。在使用包层段的测试中，暴露的表面积比使用包层段的测试中的大得多。因此，在浸出的最初几天，除 Tc 外，所有放射性核素的释放在包层部分都大于包层部分。一年后，除 Tc 外，包层和包层段的累积释放量相似，因为空气侵入导致更高的氧化和伴随的溶解恢复，包层比包层段更明显。对于 declad 段，Tc 和 Mo 浓度降低，表明尽管有空气侵入，但仍减少为溶解度较低的物质。发布¹²⁹I 类似于裂变气体的释放，而¹³⁷ Cs的释放较低，但与 UO ₂基质相比仍然加速。⁹⁹ Tc、^95-98 Mo（⁹³ Mo的代表）和⁹⁰ Sr的释放仅略高于基质溶解速率。所有确定的释放分数都与文献报道的值一致。