As an answer to the reactor accidents in Fukushima, an additional safety concept is currently under development. The aim is a retrofitting of existing and installation in new nuclear power plants. The new concept is a self-propelling supercritical CO₂-operated decay heat removal system based on the Brayton cycle. To be able to prove the functionality of such a system or to investigate next-generation power cycles, existing thermal-hydraulic system codes have to be extended and experimentally validated. In this publication, a novel modelling approach for thermal-hydraulic system codes is presented and validated. For model validation, we take results from our 82 experiments including heat transfer and pressure drop characteristics involving two different compact cross-flow heat exchangers with straight channel dimensions of 2 × 1mm and 3 × 1mm (width × height). On the heat source side, condensing steam flows downwards and on the heat sink side, sCO₂ flows horizontally at pressures of 9.50MPa and 7.75MPa. At 9.50MPa, the experimental results of the 3 × 1mm CHX show a better thermal-hydraulic performance than the 2 × 1mm CHX due to an improvement of the heat transfer rate of up to 6% and an approximately 20% lower pressure drop. The experiments at 7.75MPa show a slight increase in the heat transfer rate compared to 9.50MPa. By modelling just one representative plate and additional agglomeration of subvolumes, the approach enables fast and accurate calculations. Compared to the experimental results, most of the simulated cases show a deviation of less than 8% in terms of the heat transfer rate. The simulated pressure drop is in all cases within 92% of the experimental error band. This approach also enables to simulate large-scale cross-flow CHXs with limited numerical effort (low number of subvolumes). However, the impact of mass flow maldistribution, the choice of modelling options, and the effect of thermodynamic property variations need to be analysed in more detailed further investigations.

作为对福岛核反应堆事故的回应，目前正在开发一种附加的安全概念。目的是改造现有的和安装在新的核电厂中。新概念是自推进超临界CO ₂布雷顿循环的电动衰减式除热系统。为了能够证明这种系统的功能或研究下一代功率循环，必须扩展现有的热力液压系统代码并进行实验验证。在该出版物中，提出并验证了一种用于热工-液压系统代码的新颖建模方法。为了进行模型验证，我们从82个实验中获得了结果，包括传热和压降特性，其中涉及两个不同的紧凑型横流热交换器，其直通道尺寸分别为2×1mm和3×1mm（宽×高）。在热源侧，冷凝蒸汽向下流动，而在散热器侧，sCO ₂在9.50MPa和7.75MPa的压力下水平流动。在3.50 mm压力下，3×1mm CHX的实验结果显示出比2×1mm CHX更好的热工性能，这是由于传热率提高了6％，压降降低了约20％。与9.50MPa相比，7.75MPa的实验表明传热速率略有增加。通过仅对一个代表性板块进行建模并进行附加的子集聚，该方法可以实现快速而准确的计算。与实验结果相比，大多数模拟案例的传热率偏差都小于8％。在所有情况下，模拟的压降均在实验误差带的92％之内。这种方法还能够以有限的数值努力（较小的子体积）来模拟大型错流CHX。但是，质量流分布不均的影响，建模选项的选择以及热力学性质变化的影响需要在更详细的进一步研究中进行分析。