Experimental Reactor Core Flow Mixing Characteristics according to - PDF document

Transactions of the Korean Nuclear Society Virtual Spring Meeting July 9-10, 2020 Experimental Reactor Core Flow Mixing Characteristics according to Cold Leg Flow Balance Using a Pipe Core Simulator D.J.Euh a  , K.H.Kim a , W.M.Park a , W.S.Kim a , H.S.Choi a , H.S. Seol a , Y.J.YOUN, T.S.Kwon a a Korea Atomic Energy Research Institute, Daedeok-daero 1045, Yuseong, Daejeon, 34057, Korea * Corresponding author: djeuh@kaeri.,re.kr 1. Introduction system is demineralized water, and tap water mixing with NaSO 4 was utilized for the trace fluid. The mixing behavior of injected cold leg coolant or 2.2 Instrumentation emergency core cooling water inside the reactor vessel is very important in respect of the reactivity variation Fig. 1 shows the schematic of the overall due to the change of boron concentration or coolant instrumentations adopted in the test facility. The temperature. Currently computational flow dynamic instrumentation includes 18 pressure transmitters, 17 analysis technology has been enhanced to adopt the differential pressure transmitters, 11 flow meters, 36 multi-scale and multi-dimensional physical flow thermocouples, 13 conductance sensors, as well as behavior. However, the benchmarking data base is still channel averaged impedance sensors and a wire mesh very limited to validate the analysis tools. sensor. To control the thermal hydraulic parameters, the The mixing characteristics were identified by 21 flow control valves, 8 pumps, 3 heaters, and 4 water measuring the impedance transport for an asymmetric tanks were installed as displayed in Fig. 1. injection of fluid having different impedance. A new The target flow is obtained by controlling the reactor instrumentation to accurately measure the impedance of coolant pump rpm referred by each cold leg flow rate. fluid flowing through the cold leg and hot leg pipes was The temperature is controlled at each cold leg by developed. The mixing factor represents the mixing controlling the heat exchanger’s secondary flow rate by characteristics of the injected cold leg coolant inside referring to the temperature measured by the reactor vessel, which is one of the important input thermocouples downstream of the heat exchanger. parameters for the nuclear reactor safety analysis. The current study has the purpose of experimental DB 1 ½” TF-SCS-01 generation for the flow mixing phenomena by using a PT-SCS-01 FCV-SCS-04 Q-SCS-01 Vent Air Supply 2 ½” C-SCS-01 FCV-PZR-01 Q PT TF FCV-PZR-02 SCS Tank promising facilities representing the prototype plant C Q PT TF TF PT PT TF Q-SCS-02 PZR MV-SCS-04 FCV-SCS-02 H PT-SCS-02 PP-SCS-01 LT (DRAIN) TF-PZR-01 PT-SCS-03 TF-SCS-02 PT-PZR-01 design. QV-LD-01 HT-SCS-01 TF-SCS-03 LT-PZR-01 PT-LD-01 H C TF PT QV RCP RCP TF-LD-01 H-PZR-01 1B 2A C-LD-01 Q Q Q-CL2A-01 Q-CL1B-01 PT-CL2A-01 PT PT-CL1B-01 PT TF-CL2A-01 Letdown TF-CL1B-01 C-CL1A-01 TF MV-LD-01 TF (Drain) C-CL1B-01 2. Methods and Results FCV-PZR-03 C FCV-LD-01 C CL-1B CL-2A DP DVI-03 DP C-PZR-01 DVI-02 C TF-SG1-02 FCV-SG1-02 DP-HCL1B-01 DP-HCL2A-01 FCV-SG2-01 TF-SG2-01 C-DC-01 C TF WM WM IM 0 0 IM TF 180 0 Reactor TF SG1 TF PT Q C HL-1 HL-2 C Q PT TF SG2 TF 2.1 Test Facilities [1][2] TF-SG2-03 Vessel TF-SG1-03 Q-HL1-01 Q-HL2-01 TF TF C C-DC-02 PT-HL1-01 PT-HL2-01 TF-SG1-01 FCV-SG1-01 DVI-01 FCV-SG2-02 TF-SG2-02 TF-HL1-01 90 0 DVI-04 TF-HL2-01 DP C-HL1-01 A C DP C-HL2-01 L FCV-SG2-03 1 IM-HL1-01 L - WM 2 - IM-HL2-01 Top Vent DP-HCL1A-01 C B DP-HCL2B-01 IM FCV-SG1-03 C C The reactor vessel and inner structures of the test Air (½ ” ) Top Vent TF TF Q-CL2B-01 PT PT Q-CL1A-01 PT-CL2B-01 facility are linearly reduced copies of the conventional PT-CL1A-01 TF-CL2B-01 RCP RCP Q Q TF-CL1A-01 C-CL2B-01 1A 2B C-CL1A-01 IM-CL1A-01 Salt PWR prototype. By preserving the major flow path Air Supply Demi Water Vent Tank FCV-CVCS-01 FCV-CVCS-04 FCV-CVCS-03 FCV-CVCS-02 Water geometry and placing a flow condition having a Tank Q-CVCS-01 C-CVCS-02 C C PT-CVCS-01 TF PT Q H HT-CVCS-01 sufficient high Reynolds number, the Euler number of Demiwater TF-CVCS-01 Drain C-CVCS-01 PP-CVCS-01 FCV-CVCS-05 Drain MV-CVCS-01 the prototype reactor has been preserved in the test facility. Fig. 1. Schematics of the overall piping and instrumentation The current study developed a pipe core model representing the fuel assembly. The pipe inner diameter For the impedance measurement at the cold leg and was determined by same flow area as the fuel assembly. hot legs, a channel average impedance measuring Since the pipe model does not have crossflow, most of system has been developed based on the previous the mixing occurs before the flow enters core region, studies. [3] A set of impedance sensors was installed at which can yield conservative mixing results. the injected cold leg and two hot legs. To achieve a The configuration of the loop near the reactor vessel local conductance at the core inlet, the wire mesh are same as the prototype plant. One cold leg, CL1A, measuring system was adopted with a corporation with among the four cold legs was utilized for the electrolyte HZDR of Germany. [4] injection. A pressurized tank containing electrolyte is connected to CL1A via flexible pipe. To simulate the 2.3 Boundary Conditions impedance difference, the working fluid in the main

Transactions of the Korean Nuclear Society Virtual Spring Meeting July 9-10, 2020 The uniform and non-uniform cold leg flow conditions were considered. The uniform flow cases mean that all the cold leg flow rates entering the reactor vessel are same. A uniform downcomer flow distribution is expected for the same cold leg flow conditions. The other cases are non-uniform conditions, which have lower flow at one of cold leg and lager at the other three cold legs. The flow ratio is summarized at Table 1. The 10 test cases data for uniform and non-uniform flow conditions respectively, are ensemble averaged in this study. Table 1. Flow Rate Ratio of Each RV Boundary Leg Test Flow Ratio ( each leg flow rate / total reactor flow rate) Condition Fig. 2. Contour of the core mixing factor under balanced flow Flow Rate CL1A CL1B CL2A CL2B HL1 HL2 condition Uniform 0.25 0.25 0.25 0.25 0.5 0.5 Non- 0.175 0.275 0.275 0.275 0.45 0.55 Uniform Since the current test focuses on the flow characteristics, the test were performed at 0.3 MPa and 60 o C. The flow rate corresponds to 1/38.5 Re number of prototype condition. 2.4 Results In this paper, the key characteristics of the core mixing behavior were highlighted. Fig. 2 shows the core inlet mixing factor distribution for the uniform cold leg flow condition, which shows a concentration peak at almost 225 o . However, the tracer injected cold leg, CL1A, is actually connected to the reactor vessel at Fig. 3. Contour of the core mixing factor under unbalanced 240 o .which is slightly lower position then the flow condition concentration peak location. It is evidence that the injected tracer is moved clock-wise toward the hot leg 1 3. Conclusions position inside the downcomer. The movement can be explained by the transition for the momentum balance The present study performed experiments for for the even flow distribution. The pressure near the hot identifying the flow mixing characteristics of the leg nozzle is expected to be lower than the other at core injected tracer of one cold leg at each fuel assembly outlet due to the flow merging at the exit nozzle. It can inlet. The facility was designed by the 1/5 linear scale induce a momentum to move the injected cold leg flow law and all the geometric and thermal hydraulic to the hot leg angle. parameters were set based on the scale. The fuel Fig. 3 shows the core inlet mixing factor distribution assembly has been simplified by using the pipe model. for the unbalanced cold leg flow condition. The results The local mixing characteristics were identified at each shows the movement more drastically. Since the cold fuel assembly by using wire mesh measuring system. leg 1A flow is lower than the other cold leg flows, the The current study focused on the mixing injected tracer from the cold leg 1A gets forces laterally characteristics under uniform and non-uniform cold leg toward loop 1 side. Therefore the peak point of the flow conditions. The drastic non equilibrium mixing concentration can be analyzed more shifted clock-wise pattern were quantified in this study. than the results of the balanced flow conditions. The High quality experimental data were produced by current dynamics is highly multi-dimensional flow using the advanced impedance measuring systems, behaviour, which is very valuable data for the validation which is very unique based on the previous studies. The of the current multi-D flow dynamic analysis code. current experimental DB will be valuable for the evaluation of nuclear reactor performance. The

Transactions of the Korean Nuclear Society Virtual Spring Meeting July 9-10, 2020 experimental DB can also be utilized for the CFD validation for the multi-dimensional flow behaviour. REFERENCES [1] D.J.Euh et al, Methodology for the Reactor Flow Mixing Test - Part B, THRSD-ACOPV-DD-17-01, Rev. 00, (2017) [2] D.J.Euh et al, Mixing Factor Test Report, KAERI, KAERI/TR-7712/2019 (2019) [3] D. J. Euh, Ph. D Thesis, A Study on the Measurement Method and Mechanistic Prediction Model for the Interfacial Area Concentration, Seoul Univ., (2002) [4] Prasser H. M. et al. Coolant Mixing in a Pressurized Water Reactor: Deboration Transient, Steam-Line Breaks, and Emergency Core Cooling Injection, Nuclear Technology, 143, pp.37-56, (2002)