(NURETH-16)-Chicago, Illinois Scaling Analysis for DVI Line Break Accident of APR1400 based on ATLAS Experiment 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16)-Chicago, Illinois Erol Bicer-KINGS 31/08/2015 Kepco International Nuclear Graduate School - KINGS

Kepco International Nuclear Graduate School - KINGS Table of Contents 1. INTRODUCTION 2. ATLAS FACILITY 3. MODELLING 4. ANALYSIS 5. RESULTS 6. CONCLUSION Kepco International Nuclear Graduate School - KINGS 31/08/2015

ATLAS is a scaled-down integral test facility of APR 1400. 1. INTRODUCTION ATLAS is a scaled-down integral test facility of APR 1400. ATLAS : Advanced Thermal-Hydraulic Test Loop for Accident Simulation APR1400 : Advanced Power Reactor 1400 KAERI : Korea Atomic Energy Research Institute DVI : Direct Vessel Injection - A special safety injection feature A DVI line guillotine break with the failure of single EDG The first-ever integral effects test database for various DVI line break: 1st Domestic Standard Problem (DSP-01). [1] A comparative study between model and prototype to address the scalability explicitly by using MARS-KS system code. Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS 2. ATLAS FACILITY Scaling Law: Three-level scaling methodology developed by Ishii and Kataoka [2] Parameters Scaling law ATLAS Design Length 𝐥 𝟎𝐑 1/2 Diameter 𝐝 𝟎𝐑 1/12 Area 𝐝 𝐨𝐑 𝟐 1/144 Volume 𝐥 𝟎𝐑 𝐝 𝐨𝐑 𝟐 1/288 Core DT ∆𝐓 𝟎𝐑 1 Velocity 𝐥 𝟎𝐑 𝟏/𝟐 1/√𝟐 Time Heat Flux 𝐥 𝟎𝐑 −𝟏/𝟐 √𝟐 Core Power 𝐥 𝟎𝐑 𝟏/𝟐 𝐝 𝐨𝐑 𝟐 1/203.6 Pressure Drop Flow Rate Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS 3. MODELLING MARS-KS : Multi-Dimensional Analysis of Reactor Safety Initial and boundary conditions at the experiment were applied to the APR1400 model after proper scaling was taken from ATLAS DSP-01. The power given to ATLAS was 8.0 % of the nominal power. Three SIT and one SIP were modeled at the APR1400 model, Both the SIT and Surge Line were described by using pipe components, The initial pressure and temperature of the SIT: 4.2 MPa and 325 K and SIT starts at a pressure of 4.03 MPa, The SIP injection is actuated by low pressurizer pressure, [10.72 MPa] and a delay of 40.0 sec was assumed. Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS 3. Modelling [con’t] To allow the transition from high to low flow, a valve component was used to simulate the fluid device. A quick-opening valve to model the break at the DVI line was closed to Loop 2a. CCFL model: Bankoff Correlation: 𝑯 𝒈 𝟏 𝟐 +𝒎 𝑯 𝒇 𝟏 𝟐 =𝒄 [3] 𝑐:𝐺𝑎𝑠 𝐼𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡=1.0 𝑚:𝑆𝑙𝑜𝑝𝑒=0.4 The Critical Flow: Modified Henry-Fauske model [4] Discharge Coefficient = 0.75 Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS 4. ANALYSIS Steady State Calculation Parameters Parameter Target Value (ATLAS) APR1400 (MARS-KS) Equivalent Value Primary System Core power (MW) 1.566 318.83 1.566 equivalent Pressurizer press. (MPa) 15.55 - Core inlet temp. (K) 563.85 562.39 Core outlet temp. (K) 597.35 Cold leg flow rate (kg/s) 2.0 396.58 1.95 equivalent Secondary System Secondary press. (MPa) 7.83 7.829 Feedwater temp. (K) 505.35 505.37 Feedwater flow (kg/s) 0.44 90.634 0.445 equivalent ECCS SIT pressure (MPa) 4.2 SIT temperature (K) 323.15 323.95 SIT level (%) 95.1/94.9/94.2 Core Power : 𝐥 𝟎𝐑 𝟏/𝟐 𝐝 𝐨𝐑 𝟐 Flow Rate : 𝐥 𝟎𝐑 𝟏/𝟐 𝐝 𝐨𝐑 𝟐 Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS 4. Analysis [con’t] Chronology of the Accident Time of ATLAS is scaled to time of APR1400 by multiplying scaling ratio of 1.414. Event ATLAS (time, sec) APR1400 Remarks Break Open 0.0   Low Pressurizer Pressure Trip (LPP) 28.28 27.18 P < 10.72 MPa Pressurizer Heater Trip LPP + 0.0 Turbine Isolation LPP + 0.1 Reactor Scram & RCP Trip LPP + 0.5 Main Feed-Water Isolation LPP + 10.0 Safety Injection Pump Start LPP + 40.0 SIT starts 328.0 285.0 P < 4.03 MPa 282.8 sec : Accident initiated 310.0 sec : Primary pressure decreased to set point of low pressurizer pressure (LPP) trip 310.1 sec : Main steam line isolated 310.5 sec : Scram signal generated 320.0 sec : Secondary feedwater isolated 350.0 sec : SIP triggered (after a delay of 40.0 sec from the LPP signal) 567.8 sec : Three SITs started delivering ECC water 2,000.0 sec : Calculation ended Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS 5. RESULTS Primary Pressure Rapid decrease due to sudden loss of coolant inventory, Plateau formed at a certain level until the Loop Seal Clearing (LSC) occurred, After LSC, calculation revealed very high depressurization rate in pressure, compared to the experiment; High stored heat Thermal inertia number Expected phenomena by scaling analysis actually occurred at the experimental facility. Start SIP SIT Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS 5. Results [con’t] Break Flow Critical flow condition was maintained during the entire calculation time Break flow shows a very clear transition of flow regime at the break Two-phase flow to single- phase vapor flow occurred by the depressurization, followed by loop seal clearing Characteristics of the break flow were captured by the modified critical flow model with a discharge coefficient of 0.75. Break Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS 5. Results [con’t] Collapsed Water Level The natural circulation flow path can not be established due to the accumulation of the condensate The pressure difference between the upper plenum and downcomer increased and pushed out the condensate A stable natural circulation path was established, Calculation captured the loop seal clearing phenomena at the same time as the experiment Kepco International Nuclear Graduate School - KINGS 31/08/2015

Primary Pressure at LSC 5. Results [con’t] Primary Pressure at LSC Primary pressure decreased when the loop seal clearing occurred because there was no further pressure build-up in the system, The depressurization of the primary system started again immediately after the loop seal clearing. Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS 5. Results [con’t] Active Core Level During the pressure build-up at the upper plenum, the water levels at the downcomer and the core were different Pressure at the upper plenum was higher than that of the downcomer so the core had a lower water level than the downcomer The core started to be uncovered When the LSC occurred, the pressure difference decreased The water level in the core increased, whereas the water level in the downcomer decreased. Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS 5. Results [con’t] Peak Cladding Temperatures The core started to be uncovered and the cladding temperature of the uncovered fuel rods increased The loop seal clearing plays a very important role in cooling down the uncovered fuel rods by flooding the core The cladding temperature peaked and decreased again The PCT decreased slightly faster in the APR1400 calculation This is because the scaling distortion in thermal inertia Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS 6. CONCLUSION A scaling analysis for a DVI line guillotine break accident has been carried out. The results indicate that the general thermal hydraulic behavior at ATLAS during the experiment was well reproduced by the APR1400 calculation. The loop seal clearing, one of the most important phenomena in determining the PCT, was well predicted. The slower depressurization had been predicted from the higher thermal inertia of ATLAS. It is expected that more scaling analyses for different experiments should be conducted. Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS REFERENCES [1] Y.S. Kim, et al., “First ATLAS Domestic Standard Problem (DSP-01) for the Code Assessment,” Nuclear Engineering and Technology, 43 (1), pp. 25-44 (2011). [2] M. Ishii and I. Kataoka, Similarity Analysis and Scaling Criteria for LWRs under Single Phase and Two-Phase Natural Circulation, NUREG/CR-3267, ANL-83-32 (1983). [3] S. G. Bankoff, et al., “Countercurrent Flow of Air/Water and Steam/Water through a Horizontal Perforated Plate,” International Journal of Heat and Mass Transfer, 24, pp. 1381-1385 (1981). [4] H.R. Ko and T. Kim, "Analysis of a DVI line break accident of the ATLAS facility," Proceeding of Winter Meeting of American Nuclear Society (2013). [5] R. E. Henry and H. K. Fauske, “The Two-Phase Critical Flow of One-Component Mixtures in Nozzles, Orifices, and Short Tubes,” Transactions of ASME, Journal of Heat Transfer, 93, pp. 179-187 (1971). Kepco International Nuclear Graduate School - KINGS 31/08/2015

Kepco International Nuclear Graduate School - KINGS ACKNOWLEDGMENTS This work was supported by the 2015 Research Fund of the KINGS and performed with the data provided within the program the 1st ATLAS Domestic Standard Problem (DSP-01), which was carried out by the Korea Atomic Energy Research Institute (KAERI) under the National Nuclear R&D Program funded by the Ministry of Education, Science and Technology (MEST) of the Korean government. The authors are as well grateful to KINGS and the 1st ATLAS DSP- 01 program participants: KAERI for experimental data and the Council of the 1st DSP program for providing the opportunity to publish the results. Kepco International Nuclear Graduate School - KINGS 31/08/2015

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