ML19122A309
| ML19122A309 | |
| Person / Time | |
|---|---|
| Issue date: | 02/19/2019 |
| From: | Stephen Bajorek, Beck F, Cheung F, Garrett G, Grant G, Hoxie C, Jin Y, Kirk Tien NRC/RES/DSA/CDB, Pennsylvania State Univ, University Park, PA |
| To: | |
| Tien K | |
| References | |
| Download: ML19122A309 (4) | |
Text
STEADY STATE PREDICTIONS OF REFLOOD CHARACTERISTICS IN A ROD BUNDLE Grant R. Garrett , Yue Jin , Faith R. Beck , Fan-Bill Cheung , Stephen M. Bajorek x , Kirk Tien x , Chris L. Hoxie x Nuclear Engineering Department, 127 Reber Building, University Park, PA 16803, grg5094@psu.edu, yuj118@psu.edu, fxc4@psu.edu Mechanical Engineering Department, 127 Reber Building, University Park, PA 16803, frb115@psu.edu x
Office of Nuclear Regulatory Research, United States Nuclear Regulatory Commission, Washington, D.C. 20555, stephen.bajorek@nrc.gov, chris.hoxie@nrc.gov, kirk.tien@nrc.gov INTRODUCTION Accurate predictions of two-phase flow phenomena ob-served in the Penn State University (PSU)/United States Nu-clear Regulatory Commission (NRC) Rod Bundle Heat Trans-fer (RBHT) facility were made by performing a first order analysis from fundamental thermal hydraulic and heat transfer relations. The calculations were made from a developed script for Engineering Equation Solver (EES). The calculations per-formed are part of an ongoing effort in model development and code validation for reflood phenomenon. In this paper, results from first order calculations are compared to experimental data from the PSU/NRC RBHT facility. The facility is designed to represent a section of a PWR core. Further details regarding the RBHT facility are covered in the following section.
The calculations made by the first order analysis com-pared well with experimental data. Assumptions made during the analysis, and uncertainty in the experiments contribute Fig. 1. Isometric View of RBHT Facility (Hochreiter, 2012) most to the differences between calculated results and experi-mental measurements.
NRC/PSU RBHT FACILITY This section briefly covers the details of the PSU/NRC RBHT facility. Further details can be found in the Rod Bun-dle Heat Transfer Test Facility Description (Hochreiter, 2012).
Figure 1 provides an isometric view of the RBHT facility and figure 2 provides a P& ID of the RBHT facility. The facility, which contains 49 vertical, 3.66 m (12 ft) long test rods (four unheated corner rods and 45 heated rods) with Inconel 600 cladding in a 7x7 geometry, having the rod diameters, rod pitches and spacer grids comparable to those in commercial PWRs, was specifically designed to obtain fundamental flow and heat transfer data during reflood transients. The 45 non-corner rods are electronically heated by a heating coil inside each of the heated rods.
The experiments are performed by introducing power Fig. 2. RBHT Facility P& ID (Hochreiter, 2012) to the heated rods and heating up the test section with no liquid phase water present. The system pressure is controlled EES SCRIPT DEVELOPMENT by a PID controller. When the desired initial conditions are This section reviews the first order approach used to de-met, water, at a controlled temperature and test section inlet velop the Engineering Equation Solver (EES) script used to velocity is pumped through the test section. The experiments make steady state RBHT predictions. The script developed in are performed until the rod bundle completely quenches or a EES is used to predict the steady state quench height in the specified time after a steady state condition is achieved. bundle and the vapor temperature at the exit of the bundle for various RBHT experiments. Physically, liquid phase water will enter the bottom of the test section through the lower plenum. As the coolant rises through the bundle it will remove power from the heated rods and heat up. Once the bulk coolant temperature reaches its saturation value, nucleate boiling will
occur. As the coolant continues to flow through the facility qexcess = qbundle q sl qlv (3) more boiling will occur until nearly all of the liquid in the coolant is vaporized and the vapor is superheated.
To predict the steady state quench location, it was as-sumed that all of the power from the heated rods of the RBHT facility was transferred to the liquid flow until all of the liq-uid phase is vaporized. Since the power profile of the RBHT qexcess T v = T sat + (4) facility is known, the power required to completely vaporize mc pv all of the liquid in the coolant can match with the integrated power of the RBHT facility to a certain height. It is expected that the steady state quench location should be near this lo-cation because when there is little to no liquid in the coolant, Using the EES script developed according to the approach the rods in the facility can no longer be quenched. To make described in this section, predictions were made for the steady this prediction, the power to heat the coolant from its facility state quench front location and the steady state vapor temper-inlet value to its saturation value is calculated and added to a ature at the exit of the test section for multiple experiments.
calculated power required to completely vaporize all the liquid The experimental conditions and comparison of results are in the coolant once it has reached its saturation temperature. described below.
Equation 1 is implemented into the EES script and used to determine the power, q sl required to raise the temperature of RESULTS AND ANALYSIS the coolant from its temperature, T inlet at the test section inlet to its saturation temperature, T sat . Equation 2 is implemented This section provides a comparison of the experimental into the same EES used to determine the power, qlv required results and predictions made using a first order approach via to completely vaporize the liquid in the coolant after it has a developed EES script. Two experiments are used in the reached its bulk saturation temperature. In equations 1 and 2, comparison of results, EXP 8095 and EXP 8100. Table I m is the mass flow rate of the coolant, c-p is the specific heat, provides the test conditions for EXP 8095 and EXP 8100.
and hlv is the latent heat of vaporization. Equations 1 and 2 implemented and solved in EES, with fluid properties taken TABLE I. RBHT Experiments 8095 and 8100 Conditions from the STEAM_IAPWS database. Parameter EXP 8095 EXP 8100 Pressure, kPa (psia) 275 (40) 275 (40) 7.62 (0-15) q sl = mc-p (T sat T inlet ) (1) 7.62 (0-15) 5.08 (15-30)
Inlet Coolant 5.08 (15-30)
Velocities, cm/s 2.54(30-45) 2.54(30-45) 1.32 (45-550)
(time after reflood, s) 1.32 (45-1812) 1.22 (550-1920)
Peak Power, kW/ft 0.4 0.4 qlv = mhlv (2) Initial Peak Bundle Temperature, K (F) 1033 (1400) 1033 (1400)
Test Section Inlet Subcooling, K (F) 24 (43) 24 (43)
To predict the steady state vapor temperature at the exit of the RBHT test section, an energy balance approach, similar Figures 3 and 4 provide a comparison of the predicted to that used in the prediction of the steady state quench front and experimentally measured steady state quench front height location was used. Since the total bundle power, qbundle is for EXPs 8095 and 8100 respectively. Also included in these known and the power to completely vaporize the coolant is figures are experimental quench locations preceding the steady calculated in the prediction of the steady state quench front state quench front to show its progression through time as it location, the excess power, qexcess in the bundle that remains approaches its steady state height.
after all liquid in the coolant has vaporized can be determined Figures 3 and 4 show that the steady state predictions of by subtracting these two values. For the prediction of the the quench front location agrees well with the experimental steady state vapor temperature at the exit of the bundle, it is data for both EXP 8095 and EXP 8100. Experimentally, the assumed that all of the excess power remaining in the bundle quench front will oscillate slightly due to oscillating bound-after vaporizing all of the liquid in the coolant is transferred ary conditions. For example, experimentally the pressure is to the vapor. Equations 3 and 4 provide the equations for the not perfectly controlled, and pressure oscillations will occur excess power in the bundle after completely vaporizing all that will cause flashing and condensing. This will result in the liquid and the vapor temperature, T v at the exit of the test oscillations in the quench front. Similarly, oscillations in the section respectively. In equation 4, c pv is the specific heat of test section inlet velocity occur that will subsequently result the vapor, found in the STEAM_IAPWS database. in quench front location oscillations.
t = 250 s t = 750 s t = 1250 s t = 1650 s t = 1795 s 150 150 150 150 150 Rod Bundle Axial Elevation (in) 100 100 100 100 100 50 50 50 50 50 0 0 0 0 0 500 1000 500 1000 500 1000 500 1000 500 1000 Temperature (K) Temperature (K) Temperature (K) Temperature (K) Temperature (K)
Fig. 3. EXP 8095 Quench Front Location t = 250 s t = 750 s t = 1250 s t = 1750 s t = 1900 s 150 150 150 150 150 Rod Bundle Axial Elevation (in) 100 100 100 100 100 50 50 50 50 50 0 0 0 0 0 500 1000 500 1000 500 1000 500 1000 500 1000 Temperature (K) Temperature (K) Temperature (K) Temperature (K) Temperature (K)
Fig. 4. EXP 8100 Quench Front Location Figure 5 provides a comparison of the predicted and exper- The discrepancy in predicted vs experimentally measured imentally measured steady state vapor temperatures at the exit vapor temperature at the exit of the test section is larger for of the test section for EXPs 8095 and 8100. Figure 5 shows EXP 8095 than for EXP 8100. For EXP 8095, the steady state that the prediction of the vapor temperature at the exit of the quench front is at a location closer to the steam temperature bundle agrees well, but on average is slightly higher than the measurement probes. This causes more liquid droplets to be in experimental data. For the predictions, it is assumed that the the flow at the measurement probe locations, and droplets will test section is perfectly insulated. Although insulation is used impinge on the steam temperature probes at a higher average in the RBHT facility, some fraction of energy is still conducted frequency than for EXP 8100. Droplet impingement on the through the insulation and not transferred to the coolant. The steam temperature probe can be seen in figure 5 by observing vapor temperature at the exit of the bundle is sensitive to any the large drops in temperature that approach the saturation power that is conducted through the insulation. Also, experi- temperature of the fluid. High enough droplet impingement on mentally liquid that condenses in the upper plenum has been the temperature probes prohibit them from reaching a steady shown to enter the test section at the exit of the test section state temperature themselves and registering an accurate read-and act as a heat sink to the vapor. Also, liquid droplets can ing for the steam temperature. This can be seen in figure 5 for contact the vapor temperature probes and cause large, nearly the experimentally measured vapor temperature for EXP 8095 instantaneous drops in the measured vapor temperature. Since by examining regions that are between droplet impingements.
a small change in power causes a much larger change in the These regions are steadily increasing, but are not able to reach temperature of vapor, as compared to liquid phase water, the a steady state temperature before another droplet impinges combination of the effects explained are likely the cause of the on the surface of the measurement probe. Since the average over-prediction of the vapor temperature at the exit of the test frequency of droplet impingement on the vapor measurement section. probes is less for EXP 8100, the temperature probe itself is
able to reach a steady state temperature for certain times. Ad- 8100 and were on average a few degrees lower than the pre-ditionally, liquid droplets in the flow will cool the vapor due dicted values. Experimentally, a fraction of the power from to interfacial heat transfer. The vapor at the exit of the test the bundle is conducted through the insulation and not trans-section will experience more interfacial heat transfer for EXP ferred to the coolant. This fraction of energy is not accounted 8095 than for EXP 8100 because the interfacial heat transfer for in the predictions. Also, unintended liquid entering the area will be larger for EXP 8095 (more droplets). system through the upper plenum acts as a heat sink for the superheated vapor. Additionally, liquid droplets can contact 600 EXP 8095 experimental vapor temperature the vapor temperature measurement probes. These factors EXP 8095 predicted vapor temperature EXP 8100 experimental vapor temperature are not accounted for in the steady state predictions made.
580 EXP 8100 predicted vapor temperature Oscillating experimental boundary conditions contribute to 560 the oscillations seen in the experimental vapor temperature measurements. Overall the prediction of the steady state va-540 por temperature at the exit of the bundle agrees well with the Temperature (K) 520 experimental data.
500 ACKNOWLEDGMENTS 480 460 The work performed at the Pennsylvania State University was supported by the U.S. Nuclear Regulatory Commission 440 under Contract Number: NRC-HQ-60-16-T-0002.
420 REFERENCES 400 0 20 40 60 80 100 Experimental Steady State Time (seconds) Hochreiter, et. al., (2012), RBHT Reflood Heat Transfer Ex-periments Data and Analysis, The Pennsylvania State Uni-Fig. 5. EXP 8095 and EXP 8100 Steady State Vapor Tempera- versity, U. S. Nuclear Regulatory Commission, NUREG/CR-tures at exit of Test Section 6980.
CONCLUSIONS A first order study was used to predict steady state be-havior in the NRC/PSU RBHT facility. The RBHT facility is designed to model a section of a PWR core and was specifi-cally designed to obtain fundamental flow and heat transfer data during reflood transients. An EES script was developed that predicted the steady state quench front location and va-por temperature at the exit of the RBHT test section using an energy balance approach.
For the prediction of the steady state quench front loca-tion, an energy balance was performed to determine the power required to completely vaporize all of the liquid in the flow, assuming all power from the bundle was transferred to the liquid phase. Since the power profile of the RBHT facility is known, the prediction of the steady state quench location can be made by finding the height in the bundle that corresponded to the same total integrated power from the test section inlet as the calculated power to completely vaporize all of the liquid in the coolant. The predicted results from using this approach agreed well with the experimental data. The experimental steady state quench front locations oscillated about the pre-dicted values for both EXP 8095 and EXP 8100. Oscillating experimental values are caused by not perfectly controlled boundary conditions.
To predict the steady state vapor temperature at the exit of the RBHT test section, it was assumed that the excess power in the bundle after vaporizing all of the liquid in the coolant was completely transferred to the vapor in the coolant. The experi-mental steady state vapor temperature at the exit of the bundle oscillated below the predicted values for both EXPs 8095 and