atw 2018-04v6

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atw Vol. 63 (2018) | Issue 4 ı April OPERATION AND NEW BUILD 218 | | Fig. 3. Plate heat exchanger model with a two-pass hot side and a single-pass cold side (left) and schematic (right) [2]. If one is looking into thermo dynamic analyses, simple components would be used to represent radiation, conduction, or convection as shown in Figure 2. Thus, heat exchangers can be custom-built to answer the question at hand. Figure 3 shows a simple custom made plate heat exchanger consisting of composite heat transfer components and pipe components. The flow path is represented with a hydraulic diameter and the flow area. The plates are represented with heat transfer area and actual metal thickness. User-specified correlations according to the plate corrugation profiles are defined allowing for full discretisation along the flow path that results in accurate pinch-point calculation and transient response. Another heat exchanger example is shown in Figure 4 where a finned tube air-water heat exchanger can be seen. The air-side is modelled as a straight-through flow path (left to right) whereas the water-side is modelled as an up-down overall counter flow (right to left) configuration according to the design of the header box plates. The fully discretised flow path provides an accurate transient response. The fin-side pressure drop and heat transfer correlations can be specified with Chilton-Colburn J-factor tables. Heat exchangers are crucial for any power plant design. Figure 5 shows the schematic of the Koeberg PWR steam generator and the equivalent model built in the software. For the dryer/separator a complete phase separation is assumed. The recirculation flow rate is calculated from buoyancy-driven flow (red circle) that is dependent on heat transfer coefficient and flow resistance. The model also assumes a homogeneous two-phase flow. The Chen correlation for the shell side was implemented with scripting. Specific material properties can be implemented via Engineering Equation Solver (EES) coupling or scripting if necessary. Table 1 shows the comparison of measured and simulated data of the Koeberg PWR (South Africa) steam generator at 60 % and 100 % power load. The software shows reasonably good agreement to the measured data, especially when looking at the recirculation ratio R circ which is a good indication of the overall calculation accuracy. Another power plant example is the Hamm-Uentrop thorium high temperature reactor (THTR-300, Germany) power plant. One challenge in modelling the THTR is that at certain combinations of flow rate and heat input, the flow could be oscillatory. Several types of oscillation are possible: density wave, pressure wave, and critical heat flux (dryout)-related oscillations. Fundamental fluiddynamic modelling is crucial to detect this, which is provided in the software. Furthermore, this capability is critical to determine the minimum flow through a steam generator because it is typically at low power levels that the steam flow becomes oscillatory. Figure 6 shows the schematic of the THTR-300 and an equivalent model built in the software. The THTR steam generator plant was modelled to verify the steady-state performance of the assembled steam generator model. Figure 7 shows the comparison of measured and simulated data of the THTR-300 at 40 % and 100 % power load. The software shows very good agreement to the measured data. The simulation revealed | | Fig. 4. Model of a finned tube air-water heat exchanger with multiple water-side passes and a single air pass (top) and schematic (bottom) [2]. T pi [C] T po p so [kPa] p si T si x so ṁ s [kg/s] Q boiler [MW] R circ 60 % power Koeberg 294 273 4889 5055 195 1.0 341 670 7.0 Simulation 294 273 4889 4919 195 1.0 341 666 6.4 100 % power Koeberg 312 279 4911 5277 220 1.0 618 1143 3.8 Simulation 312 280 4911 4951 220 1.0 618 1092 3.8 | | Tab. 1. Koeberg PWR steam generator comparison. Operation and New Build Heat Transfer Systems for Novel Nuclear Power Plant Designs ı Sebastian Vlach, Christoph Fischer and Herman van Antwerpen
atw Vol. 63 (2018) | Issue 4 ı April that the helium-side heat transfer correlation needed to have an appropriate Reynolds-number dependence as the error became quite large at lower power or flow levels neglecting this. As aforementioned, heat exchangers are crucial for any power plant design, especially when designing new power plants. In addition to the heat transfer modelling capabilities and with respect to nuclear power generation the software has recently expanded the Generic Nuclear Reactor model to simulate the latest nuclear reactor designs of any geometry. Novel nuclear reactor designs include liquid fuel reactors, liquid-metal-cooled reactors, and high temperature gas-cooled reactors (HTGR). In more detail, there are six reactor types that have gained researches interest all over the world: • Very High Temperature Reactor, • Molten Salt Reactor, • Sodium-Cooled Fast Reactor, • Supercritical-Water-Cooled Reactor, • Gas-Cooled Fast Reactor, and • Lead-Cooled Fast Reactor. The new “generalized fuel zone” in the GNR model that is shown in Figure 8 is capable of handling any fuel geometry and any fluid type. It expands the geometry capability to plate fuel, cylindrical fuel rods, spherical fuel elements, irregular cross-section fuel (like the four-lobe cross-shape produced by the Lightbridge Corporation), as well as prismatic block fuel used in some HTGRs. Appropriate pressure drop and heat transfer correlations can be selected from the built-in library or defined by the user. For neutronic calculations, the generalized fuel zone can provide temperature feedback, as well as heat generation in all solids and in the core coolant. The default neutronics model that is supplied with the software is the point kinetic model which requires the following inputs: • Temperature feedback coefficients, • Heat distribution map, and • Control rod worth vs. position. This point kinetic model is provided in a user-editable C# script, which makes it possible to replace the point kinetic model by linking the simulation model to an external neutronics code. The scripted neutronics model also makes it possible for the user to define one’s own feedback mechanisms based on the design of the specific reactor. | | Fig. 5. Koeberg PWR steam generator schematic (left) [2] and simulation model (right). | | Fig. 6. Hamm-Uentrop THTR schematic (left) [2] and simulation model (right). OPERATION AND NEW BUILD 219 | | Fig. 7. Hamm-Uentrop THTR-300 steam generator comparison experiment (Exp) [3] and simulation (FNX). Operation and New Build Heat Transfer Systems for Novel Nuclear Power Plant Designs ı Sebastian Vlach, Christoph Fischer and Herman van Antwerpen
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atw 2018-04v6

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