3. Similarity validation experiment : SINCRO-V
4.1. Experimental design
4.1.2. Experimental facility design
The prototype reactor for the SINCRO-2D was the PGSFR, and the coolant of the PGSFR is the sodium. For the design of the SINCRO-2D, scaling issue and corresponding system parameters should be determined first. To determine system parameters of the SINCRO-2D, a simulant for the sodium
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and corresponding scale was calculated based on figure 4-1. As discussed in chapter 2 and 3, water is the best simulant for the liquid metal natural circulation. Too much scale reduction could cause another problem like too much simplification of the detailed geometry for manufacturing issue. Water is the best fluid in terms of the economy, proper scale, clearness of the properties, and operating condition. Final length scale difference between the original sodium system, the PGSFR, and our SINCRO-V was 1 : 25. It represents that the SINCRO-V is 25 times smaller than the PGSFR in the aspect of the length scale. According to this scale reduction ratio, several system parameters were automatically determined by the scaling ratio and working fluid. The reference temperature difference, total power, and the Bo’ of the SINCRO-2D, and their ratio to that of the PGSFR were summarized in table 4-1. The radius and height were linearly reduced. The volumetric heat generation rate was maintained, thus, corresponding total power was reduced as cubic of the length ratio. The reference temperature was calculated based on equation (2-10).
SINCRO-2D was designed in two-dimensional shape, a 2-D slab model. Therefore, the original geometry of the PGSFR should be simplified as 2-D. Three-dimensional schematic of the PGSFR was illustrated in figure 4-2. However, essential components should be maintained and reflected into the design. Considering the natural circulation under the RVACS operation, it is the same with that under the normal operation, and includes the core, upper plenum, IHX, narrow gap between the IHX and the redan, lower plenum, and pump and corresponding inlet piping. Therefore, the SINCRO-2D facility should have aforementioned components.
Regard to the slab model, there is another issue for the cross section. Because the PGSFR has three-dimensional shape and could have various cross-sectional geometry depending on the angular position of the cross section. It could be easily recognized by figure 4-2. The IHXs were placed at the side of the figure, while the pump and corresponding piping were placed in the back of the figure. In addition, the top view of the redan is similar to the bow tie. In this regard, the cross section of the two- dimensional facility should be considered. Regard to the natural circulation path of the RVACS, it passes through the IHX and, and cooling would be dominant in that region. Therefore, cross section of the SINCRO-2D was determined as the cross section including the IHX. Position of the pump inlet and piping were neglected, while their effect on the natural circulation flow was considered as the pressure drop through the components.
The cross section containing IHX and the geometry of the SINCRO-2D was in figure 4-3. Left half of the assembly drawing was used for the design of the SINCRO-2D because it was symmetric. The cross section included the IHX. (a) represents the cross section of the PGSFR including IHX. Inside of the yellow line, which represents the redan, there is a hot pool. Under the normal operation, the hot pool is relatively hot than a cold pool because the heated coolant is discharged form the core. Outside of the yellow line, there is the cold pool. The coolant from the hot pool is cooled through the IHX, and
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goes downward to the cold pool. The coolant flow from the cold pool to the core via pump and inlet piping, however it is not shown in (a) of figure 4-3 because it is not located in the IHX plane. The core is tall, however, only active core region, which generates heat, was considered. These components were reflected into the design of the SINCRO-2D. In (b), the redan and corresponding cold pool and hot pool, IHX, active core was modeled. Only for the pump and inlet piping, it was simplified and modeled as inlet orifice before the core. Based on the cross-sectional design, SINCRO- 2D was designed like (c) in figure 4-3.
In addition to the overall geometry of the SINCRO-2D, the pressure drop should be designed. Table 4-2 shows the portion of the pressure drop of the PGSFR under the normal operation. Three components (the core, and inlet piping) were the main components for the total pressure drop. Among these components, the pressure drop of the core had ambiguousness in terms of the pressure drop analysis in the natural circulation due to characteristics of the CFD analysis. In the natural circulation, it was not easy to clearly distinguish between deriving force from the heating and pressure drop of the heating section. Therefore, for the other two components, the IHX and inlet piping, pressure drop analysis was conducted.
According to the similarity law, the pressure drop coefficient (ζ) should be identical. For the pressure drop, we assumed that 1% of the flow rate condition for the natural circulation. However, there was no reference value for the pressure drop under 1% of the flow rate. Therefore, extrapolated pressure drop values were used for the calculation and their process was graphically summarized in figure 4-4. The pressure drop coefficient could be calculated from the pressure drop and the velocity.
Here, the reference velocity for the natural circulation in equation (2-8) was used for the velocity in the pressure drop calculation. Pressure drop coefficient in the SINCRO-V was obtained from the CFD analysis and its domain was shown in figure 4-5. Pressure drop coefficients were calculated based on the reference velocities and pressure drop from the reference, and CFD analysis using equation (4-1).
2 ref
ζ = 2ΔP
ρu (4-1)
These values and results were summarized in table 4-3. In general, the pressure drop is modified by the orifice and the diameter of the flow channel. The values of SINCRO-2D in table 4-3 is the final values after modification of the flow channel area. Diameter of the flow channel of the IHX in the SINCRO-2D was 14 mm, which was 94 % of the linearly reduced value. In case of the inlet orifice, which corresponds to the pump and inlet piping, it had a diameter of the 12 mm. Regard to the error of the pressure drop coefficients, the pressure drop coefficients of the SINCRO-2D showed good accordance with that of the PGSFR, less than 5% of the error.
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Finally, the SINCRO-2D facility was designed like figure 4-6 (a), and thermocouple installed points were summarized in (b). Red points represent the location of the thermocouples for observation of the core region. Considering the natural circulation flow path, it was anticipated that the maximum and the minimum temperature would be observed in the red points. Green thermocouples were installed near the IHX. There is a narrow gap between the IHX and the redan. Through the redan wall, significant of the cooling was anticipated and to observe this cooling phenomena and corresponding temperature distribution near the IHX, these thermocouples were installed. Blue thermocouples were installed in the lower plenum. The lowest thermocouple is to observe the minimum temperature of the pool, which is independent to the natural circulation. The other three blue thermocouple is installed to observe the temperature distribution of the lower plenum (in other words, the cold pool) like a thermal stratification. Through these temperature points, temperature distribution in the reactor pool in the experiment could be recognized and analyzed.