Patnaik S, Lopes D A, Besmann T M, Spencer B W, Knight T W
Department of Mechanical Engineering, University of South Carolina, 300 Main St., Columbia, South Carolina 29205, USA.
Westinghouse Electric, Bränslegatan 1, 721 36 Västerås, Sweden.
Rev Sci Instrum. 2020 Mar 1;91(3):035101. doi: 10.1063/1.5119361.
Temperature gradients in ceramic light water reactor (LWR) uranium dioxide (UO) nuclear fuel pellets generate thermal stresses that cause fractures in the fuel, which begins early in the life of fresh fuel. The combination of heating due to fission and forced convective cooling on the exterior of LWR fuel rods generates a temperature profile that is difficult to replicate outside the reactor environment. In this study, a state-of-the-art experimental setup using electrical heating to study certain aspects of temperature driven fracture was built, and surrogate fuel materials such as ceria (CeO) were used to validate the system. Cracking experiments were conducted on these surrogates by inducing reactivity-initiated-accident like temperature gradients in the pellets via induction and direct resistance heating. Induction heating was done using copper coils and molybdenum susceptors, which heated the surrogates to a threshold temperature that is sufficiently high for the fuel material to conduct current. Thereafter, direct resistance heating was achieved by passing current through the specimen using a DC power supply to introduce volumetric heating to replicate LWR operating conditions. The pellets were held against nickel electrodes and mounted on a boron nitride test-stand. All the tests were carried out in a stainless-steel vacuum chamber. Simultaneous real-time dual imaging of the surrogate pellet surface was implemented using an optical and infrared camera system that was mounted along axial and perpendicular directions to the pellet surface, respectively. A beam-splitter was used to split the incoming radiation from the sample into two halves. While one of the beams was transmitted from the splitter through a bandpass filter to obtain optical images, the other beam was reflected from the splitter to the thermal camera to capture full-field temperature gradients of the as-fabricated pellet surface during cracking. Some initial tests were conducted with a 2-color pyrometer that was later substituted with a forward-looking infrared thermal camera to capture the temperature profiles. A LabVIEW data acquisition system was set up for collecting useful data during experiments.
陶瓷轻水反应堆（LWR）二氧化铀（UO）核燃料芯块中的温度梯度会产生热应力，导致燃料破裂，这种情况在新燃料的早期寿命阶段就会开始。轻水反应堆燃料棒外部因裂变产生的加热与强制对流冷却相结合，产生了一种在反应堆环境之外难以复制的温度分布。在本研究中，构建了一种使用电加热来研究温度驱动断裂某些方面的先进实验装置，并使用二氧化铈（CeO）等替代燃料材料来验证该系统。通过感应和直接电阻加热在芯块中诱导出类似反应性引发事故的温度梯度，对这些替代材料进行了开裂实验。感应加热使用铜线圈和钼基座，将替代材料加热到一个阈值温度，该温度足够高以使燃料材料能够传导电流。此后，通过使用直流电源使电流通过试样来实现直接电阻加热，以引入体积加热来模拟轻水反应堆的运行条件。芯块与镍电极接触并安装在氮化硼试验台上。所有测试均在不锈钢真空室内进行。使用分别沿轴向和垂直于芯块表面方向安装的光学和红外相机系统，对替代芯块表面进行同步实时双成像。使用分光镜将来自样品的入射辐射分成两半。其中一束光从分光镜透过带通滤波器以获取光学图像，另一束光从分光镜反射到热成像相机，以在开裂过程中捕捉制成的芯块表面的全场温度梯度。一些初始测试使用双色高温计进行，该高温计后来被前瞻性红外热成像相机取代以捕捉温度分布。设置了一个LabVIEW数据采集系统，用于在实验过程中收集有用数据。
