1. (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

2. Kepco International Nuclear Graduate School - KINGS
Table of Contents
1. INTRODUCTION
2. ATLAS FACILITY
3. MODELLING
4. ANALYSIS
5. RESULTS
6. CONCLUSION
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3. 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.
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4. 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
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5. 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.
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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
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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
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4. Analysis [con’t]
Chronology of the Accident
Time of ATLAS is scaled to time of APR by multiplying scaling ratio of
Event
ATLAS
(time, sec)
APR1400
Remarks
Break Open
0.0
Low Pressurizer Pressure Trip (LPP)
28.28
27.18
P < MPa
Pressurizer Heater Trip
LPP + 0.0
Turbine Isolation
LPP + 0.1
Reactor Scram & RCP Trip
LPP + 0.5
Main Feed-Water Isolation
LPP
Safety Injection Pump Start
LPP
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
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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
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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
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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
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12. 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.
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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.
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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
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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.
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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 (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 (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 (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 (1971).
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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.
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18. Thank You for Your Attention!
Any Questions?
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Nodalization
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Planar Arrangements
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