Cr-coated M5_Framatome¹ cladding materials are studied and developed within the CEA-Framatome-EDF French nuclear fuel joint program as Enhanced Accident Tolerant Fuel claddings for Light Water Reactors. The objective of this paper is to bring some insights into the relationship between Equivalent Cladding Reacted (ECR) parameters, oxygen diffusion/partitioning and Post-Quench (PQ) ductility of Cr-coated M5_Framatome fuel claddings oxidized in steam at 1200 °C.

The physical meaning of the ECR parameter, evaluated experimentally from the measured Weight Gain (WG) or calculated using time and temperature correlations such as the Baker-Just (BJ) or Cathcart-Pawel (CP) kinetics correlations, is discussed in the light of the benefit brought by Cr coating to oxidation resistance of cladding. As shown in this article, when applied to the Cr-coated M5_Framatome materials, the “experimental” ECR derived from WG does not have the same physical meaning than for the uncoated cladding materials. As discussed in the paper, this is fundamentally due to the use of the ECR as a surrogate for retained ductility for uncoated claddings, and to the differences between uncoated and Cr-coated cladding in the high temperature (HT) steam oxidation processes and partitioning of the oxygen between the different layers of the oxidized cladding.

It is shown in this article that Cr-coated M5_Framatome cladding brings significant additional time-at-temperature before full embrittlement of the cladding after one-sided oxidation at 1200 °C and quenching, compared to uncoated materials. The oxidation times and associated Baker-Just ECR (BJ-ECR) values, above which the cladding becomes brittle after low temperature quenching, are respectively ten times and three times higher than the ones for the uncoated reference cladding. When analyzing the PQ ductility of the Cr-coated M5_Framatome cladding using a similar methodology as the one used to derive the ECR criterion for uncoated cladding, the 1–2% ductility limit corresponds to a BJ-ECR of about 50% or higher, for a 12-15 μm-thick Cr-coated cladding tested herein.

在CEA-Framatome-EDF法国核燃料联合计划中，作为轻水反应堆的增强型耐事故燃料包壳，研究和开发了镀铬M5 _Framatome ¹包壳材料。本文的目的是对Cr包覆的M5 _Framatome燃料包覆层在1200°C的蒸汽中氧化时的等效包覆反应（ECR）参数，氧扩散/分配和淬火后延性（PQ）延性之间的关系提供一些见解。

ECR参数的物理含义是根据测得的重量增加（WG）进行实验评估或使用时间和温度相关性（例如Baker-Just（BJ）或Cathcart-Pawel（CP）动力学相关性）进行计算得出的，铬涂层带来的好处是覆层的抗氧化性。如本文所示，当应用于镀铬的M5 _Framatome时WG衍生的“实验性” ECR与未涂层的覆层材料在物理意义上并不相同。如本文所述，这主要是由于使用ECR替代了未镀覆层的延展性，以及高温（HT）蒸汽氧化工艺中未镀覆层和Cr镀层之间的差异以及隔板的分配。氧化覆层不同层之间的氧气。

本文显示，与未涂层材料相比，铬涂层M5 _Framatome涂层在1200°C单面氧化和淬火后，在涂层完全脆化之前会带来显着的额外温度。氧化时间和相关的贝克-贾斯特ECR（BJ-ECR）值（在该温度以上，包层在低温淬火后变脆）分别比未涂覆的参考包层高十倍和三倍。当使用与用于得出未涂层熔覆层的ECR标准相似的方法来分析Cr涂层M5 _Framatome熔覆层的PQ延展性时，1-2％的延展性极限对应于约50％或更高的BJ-ECR，适用于本文测试的12-15μm厚的Cr涂层。