Instant release fraction and matrix release of high burn-up UO2 spent nuclear fuel: Effect of high burn-up structure and leaching solution composition
Instant release fraction and matrix release of high burn-up UO2 spent nuclear fuel: Effect of high burn-up structure and leaching solution composition
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高燃耗UO2乏核燃料的瞬时释放分数和基质释放：高燃耗结构和浸出液成分的影响
DOI：
10.1016/j.jnucmat.2012.04.036
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发表时间：
2012
影响因子：
3.1
通讯作者：
A. Martínez
中科院分区：
文献类型：
--
作者：
D. Serrano‐Purroy;F. Clarens;E. González;J. Glatz;D. Wegen;J. Pablo;I. Casas;J. Giménez;A. Martínez
关于乏核燃料（SNF）改造的性能评估（PA）练习的两个弱点是所谓的即时释放分数（IRF）的贡献和高燃耗结构（HBS）的影响。本手稿重点关注 HBS 在基质中的影响（长期）以及在平均燃耗 (BU) 为 60GWd/tU 的商业反应堆中辐照的压水反应堆 (PWR) SNF 的即时释放。为了研究 HBS 的贡献，准备了来自不同径向位置的两个样本。一份来自 SNF 的中心，标记为 CORE，一份来自外围，富含 HBS 并标记为 OUT。使用两种合成浸出溶液进行了静态浸出实验：碳酸氢盐（BIC）和膨润土花岗岩地下水（BGW），并且在所有情况下都在氧化条件下进行。 IRF 值是根据确定的水相库存分数 (FIAP) 计算得出的。在所有研究案例中，一些放射性核素 (RN)：Rb、Sr 和 Cs，显示出比铀更高的释放率，特别是在实验开始时，并被视为 IRF。人们发现像 Mo 和 Tc 这样的氧化还原敏感性 RN 的溶解速度比铀稍快，可能需要进一步研究来确认它们是否也可以被视为 IRF 的一部分。大多数剩余的研究RN，主要是锕系元素和镧系元素，已被发现与铀基质同成分溶解。最后，Zr、Ru 和 Rh 的释放速率低于基质。已确定 CORE 样品的基质释放量高于 OUT 样品，表明 HBS 的形成可能对 SNF 的氧化腐蚀具有保护作用。相反，两种研究的浸出溶液（BIC 和 BGW）之间没有观察到显着差异。已经确定了两种不同的 IRF 贡献。一个对应于在外部开放晶界中隔离的库存部分，直接可供水使用，并且在实验的第一天非常重要；第二个对应于较难接近的，最有可能位于内部晶界，在相同的给定溶解时间下比第一个低一个数量级，但发生时间更长。与基质释放结果不同，OUT 样品中的 Cs IRF 释放量高于 CORE 样品。这种效应可归因于辐照期间铯热迁移到燃料的外围。在 Rb 的情况下，CORE 和 OUT 之间没有观察到明显的差异，表明相反的热迁移和基体效应之间达到平衡。最后，Sr CORE/OUT 释放比显示出与基质释放相似的行为，从而证明辐照期间没有显着的热迁移。
Two weak points in Performance Assessment (PA) exercises regarding the alteration of Spent Nuclear Fuel (SNF) are the contribution of the so-called Instant Release Fraction (IRF) and the effect of High Burn-Up Structure (HBS). This manuscript focuses on the effect of HBS in matrix (long term) and instant release of a Pressurised Water Reactor (PWR) SNF irradiated in a commercial reactor with a mean Burn-Up (BU) of 60GWd/tU. In order to study the HBS contribution, two samples from different radial positions have been prepared. One from the centre of the SNF, labelled CORE, and one from the periphery, enriched with HBS and labelled OUT. Static leaching experiments have been carried out with two synthetic leaching solutions: bicarbonate (BIC) and Bentonitic Granitic Groundwater (BGW), and in all cases under oxidising conditions. IRF values have been calculated from the determined Fraction of Inventory in Aqueous Phase (FIAP). In all studied cases, some radionuclides (RN): Rb, Sr and Cs, have shown higher release rates than uranium, especially at the beginning of the experiment, and have been considered as IRF. Redox sensitive RN like Mo and Tc have been found to dissolve slightly faster than uranium and further studies might be needed to confirm if they can also be considered part of the IRF. Most of the remaining studied RN, mainly actinides and lanthanides, have been found to dissolve congruently with the uranium matrix. Finally, Zr, Ru and Rh presented lower release rates than the matrix. Higher matrix release has been determined for CORE than for OUT samples showing that the formation of HBS might have a protective effect against the oxidative corrosion of the SNF. On the contrary, no significant differences have been observed between the two studied leaching solutions (BIC and BGW). Two different IRF contributions have been determined. One corresponding to the fraction of inventory segregated in the external open grain boundaries, directly available to water and very significant during the first days of the experiment; and a second one corresponding to a less accessible, most probably located at the internal grain boundaries, one order of magnitude lower than the first one at equal given dissolution times but of much longer period of incidence. Unlike matrix release results, higher Cs IRF release was found for OUT than for CORE sample. This effect can be attributed to thermal migration of Cs to the periphery of the fuel during irradiation. In the case of Rb no clear differences were observed between CORE and OUT showing equilibrium between the opposing thermal migration and matrix effects. Finally, Sr CORE/OUT release ratio showed similar behaviour to matrix release, thus proving no significant thermal migration during irradiation.