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1
Prospects of Next Generation Safety Analysis
Code and Experience of high performance
computing
2013. 10. 26
Presented for SNA+MC2013 Workshop in Paris, France
Bub Dong Chung1)
1) Korea Atomic Energy Research Institute, Korea
2
Contents
Current safety analysis code in KAERI
Prospects of next generation safety analysis code
Experience of high performance computing (or demands)
LOFT L2-5 LBLOCA Uncertainty quantification by Monte-Carlo
method
Whole core physic analysis using transport code linked with CFD
Concluding remarks
3
Current Safety Analysis Code in KAERI
Design Analysis Codes
Nuclear design codes (from Monte-Carlo to Diffusion scale)
Core TH codes (from RANS to Subchannel scale)
Fuel analysis codes (from FEM to in-house 1D scale)
Safety analysis code
One of key design code for safety system as well as integral system performance
Current Utilization of Safety Analysis Code
Westinghouse Design (PWR) Code (since 1980s)
CEFLASH, WFLASH, WCOBRA/TRAC
AECL (CANDU) Design code (since 1990s)
SOPHT, CATHENA etc
Best Estimate Code utilized by Regulatory Body (since 1980s)
RELAP5/MOD3, TRACE, COBRA-TF, MARS-KS
GEN-IV system TH analysis
MARS-LWR(SFR), GAMMA(VHTR)
4
Current Safety Analysis Code in KAERI
“MOSAIQUE” is a fully automated software to support the uncertainty
and sensitivity analysis of thermal-hydraulic calculations.
Sampling uncertainty parameters
Generating the input files for TH system code with uncertainty parameters
Running a TH code with cluster
Analyzing the results
Client 1 Client 2 Client n
Master
Intra Net
At present, MOSAIQUE supports many system TH codes. Use Client PCs in the Intranet for TH calculations Automatically assigns the TH
calculations to client PCs
Independent parallel calculations in client PCs.
When a client PC completes a TH calculation, it return results to the master PC.
5
Current Safety Analysis Code System in KAERI
CONTAINMENT
CONTAIN2.0
(DLL)
CONTEMPT4
(DLL)
SYSTEM
System Analysis Code
(RELAP5, MARS, MARS-SFR)
CORE 3D Kinetics
(MASTER)
Subchannel analysis code
(MATRA,COBRA-TF)
FUEL Performace
(FRAP, COSMOS)
Uncertainty Analysis Tool
MOSAIQUE
• Master-client Computing
•Parallel computing
6
Prospects of Next Generation Safety Analysis Code
Current Safety Analysis Code System
Validated with huge experimental data base (LWR) during last few decades
Contributing to solve the operating licensing issue for 3D kinetics coupled
problem(CANDU LBLOCA) and 3D TH behavior (UPI PWR)
Utilizing for GEN-IV design analysis with some modifications
Advanced Simulation versus Next Generation Code
By the definition of GIF task force, advanced model is mechanistic modeling
for fundamental phenomena. It is also called “first principle solution”.
Example
Full core simulation with Monte-Carlo method
TH Simulation with DNS (at least LES level)
Fuel, material behavior with Molecular Dynamics (at least microstructure
level)
The depletion calculation with advanced simulation may be possible with
supercomputing power, however transient simulation within next few
decades is doubtful
Focus next generation codes for advanced safety analysis
7
Prospects of Next Generation Safety Analysis Code
Next Generation Safety Analysis
May be categorized according to the objectives of the analysis
In licensing analyses
the objective is to provide a high-confidence measure of the safety
margins and demonstrate the defense-in-depth design. Uncertainties in
the analysis must be quantified to a degree that satisfies a level of
confidence set by the regulator.
In research and development analysis
the objective is to gain better understanding of physical phenomena and
their interactions relevant to materials and equipment for advanced
reactor concepts, expecting the replacement of expensive large
validation experiment
At this moment, the best approach for future safety analysis code may be
dual-path programs in KAERI
An integrated safety analysis with statistical & PSA tool, aiming
uncertainty reduction
Code coupling with next generation analysis codes (i.e. Multi-physics),
aiming more realistic core behavior and accuracy enhancement,
In both areas, high performance computing are needed
8
Experience of high performance computing
LOFT L2-5 LBLOCA Uncertainty quantification by Monte-Carlo
method
Performed by OECD/NEA BEMUSE Program (2007)
Code :
MARS System analysis code (similar to RELAP5)
2 fluid, multi-dimensional system TH
Point kinetics & Simple Fuel model
Whole core physic analysis using transport code linked with CFD
Performed by US-ROK collaborative DOE I-NERI project
Code System
Core Physics: DeCART (3D full core transport) McCARD (MC)
Core TH: Start-CD (RANS CFD)
Fuel : NEPTUNE (FEM)
Coupling technique : Data transfer with TCP/IP protocol
9
World-wide Uncertainty Propagation Method for LOCA
USNRC methods : CSAU method
Response surface construction using sensitivity analysis
Monte-carlo calculation with response surface( > 50,000), Find pdf
GRS, IPSN, K-REM(KEPCO), ASTRUM(W) methods:
identify and combine input uncertainties, using subjective pdfs.
Monte-Carlo calculation with direct calculation
Find 95%/95% tolerance limit value or curve (by limited number of
calculation according to non-parametric statistics; Wilks’ formula)
Number of code calculations can be determined by Wilks’
formula
Number of code runs n
upper statistical tolerance limit (one-sided): 1 - an > b
a is desired probability percentile,
b is confidence level
One sided 95% probability, 95% confidence limit require 59
calculations (non-parametric statistics)
If Wilks’ formula at the second order, 93 sample set is needed
10
LOFT L2.5 EXPERIMENT
400
500
600
700
800
900
1000
1100
1200
0 20 40 60 80 100
time (s)
tem
pe
ratu
re (
K)
EXPMAXMIN2nd MAX2nd MIN
95%/95% Tolerance limit of PCT
11
Full Monte-Carlo Calculation
Motivation to compare with the results from full Monte-Carlo
method
Approach based on Wilks’ formula is an ad-hoc approach with a
limited computing power
Need to find the statistical fluctuation of small sampling (~ 100 runs)
effects for non-parametric statistical method
Full Monte-Carlo approach, more than 10,000 runs are needed
12
Full Monte-Carlo Calculation
UQM2.exe
MakeBatch.exe
Param list
(*.lst)
Input files
(*.i)
Batch files
(*.bat)
AnalysePCT.exe
Calc Matrix
(*.matrix)
MakeInput.exe
CLUSTER PC
(10)
Random
Sampling
Input
Generati
on
Batch
Generati
on
Results
Analysis
This semi-auto process has been now replaced with “MOSAIQUE”, which is a fully
automated software
13
Full Monte-Carlo Calculation
CPU times
3.0 GHZ CPU with Window XP
Estimated computing time for scheduled 10,000 runs
100 days on single core
10 days on 10 nodes PC cluster
When 4,000 calculations were obtained, terminate calculations
intentionally
Selection of results
Failure rate ~ 7%
Calculation failures were not systematic, but random.
May be from code deficiencies at low P and flow condition, after the
completion of core quench
Discard the failure cases
3,500 success runs were used for statistical treatments
14
Full Monte-Carlo Calculation
95% Blowdown PCT
1150
1155
1160
1165
1170
1175
1180
1185
1190
1195
1200
0 500 1000 1500 2000 2500 3000 3500
Number of Monte Carlo Histories
Blo
wdow
n P
CT
(K
)
95% Blowdown PCT
Mean PCT
1030
1035
1040
1045
1050
1055
1060
1065
1070
1075
1080
0 500 1000 1500 2000 2500 3000 3500
Number of Monte Carlo Histories
Blo
wdow
n P
CT
(K
)
Mean PCT
95% Reflood PCT
1150
1155
1160
1165
1170
1175
1180
0 500 1000 1500 2000 2500 3000 3500
Number of Monte Carlo Histories
Reflood P
CT
(K
)
95% Reflood PCT
Mean PCT
1010
1015
1020
1025
1030
1035
1040
0 500 1000 1500 2000 2500 3000 3500
Number of Monte Carlo Histories
Reflood
PC
T (
K)
Mean PCT
15
Blowdown PCT Distribution
(3500 runs)
0
50
100
150
200
250
630
670
710
750
790
830
870
910
950
990
1030
1070
1110
1150
1190
1230
1270
1310
1350
1390
Blowdown PCT (K)
Num
ber
of
Fre
quency
Reflood PCT Distribution
(3500 runs)
0
50
100
150
200
250
540
580
620
660
700
740
780
820
860
900
940
980
1020
1060
1100
1140
1180
1220
1260
1300
1340
1380
Reflood PCT (K)
Num
ber
of
Fre
quency
Full Monte-Carlo Calculation (PCT Distributions)
Histogram
Use success 3,500 PCT data
Blowdown PCT
Two peaks
Blowdown CHF bifurcation
Reflood PCT
Two peak
Rewet bifurcation just after
blowdown
Bifucation phenomena is difficult to capture using response surface method and others
16
Comparison with Tolerance Limits based on Wilks’ Formula
1000
1050
1100
1150
1200
1250
1300
1350
1400
1450
0 1 2 3 4 5
W ilks' O rder
Blowdown PCT (K)
95/95 Tolerance Lim it95% U pper Value
M ean Value
1000
1050
1100
1150
1200
1250
1300
1350
1400
0 1 2 3 4 5
W ilks' O rder
Reflood PCT (K)
95/95 Tolerance Lim it
95% U pper Value
M ean Value
Tolerance limit value is higher than the 95% limit value by 95%
confidence level, it means there is a risk of 5% under-prediction
Statistical variance can reduce significantly with increasing Wilks’
order, but still too high to quantify the safety margin (license margin)
17
Lessons
Results
The uncertainty method using non-parametric statistics , i.e. Wilks’ formula, is an ad-hoc approach with a limited computing power
It may be useful for auditing evaluation of existing design
However, full Monte-Carlo method is needed to quantify the design safety (license) margin
Need of High Performance Computer
1 week computing time was required for LOFT LBLOCA (50 sec transients) using 10 core machine
For practical BEPU LOCA application to PWR full scale
< 1 day calculation speed may be necessary to get LOCA full spectrum analysis
numbers of core ~ 10core x10(500sec)x10(1day)=1,000 core
For SBLOCA, longer time is needed ( > 3000 sec)
~ 10,000 core is needed
To support risk informed regulation
Huge numbers of scenarios according PSA event tree
18
Experience of US-ROK collaborative DOE I-NERI project
• Whole core physic analysis using transport code linked with CFD
McCARD
DeCART: Deterministic Core Analysis based on Ray Tracing
DeCART
Star-CD NEPTUNE
TCP/IP
protocol
McCARD: Monte-Carlo Code for Advanced Reactor Design and Analysis
19
Experience of US-ROK collaborative DOE I-NERI project
Whole core calculations have been performed successfully for a small
PWR.
The neutronic model included nearly 5 million neutronic zones, while
the CFD RANS model included 73 million cells.
Calculations were performed on the Jazz LINUX Cluster at ANL, using 57
of the available 350 processors.
Results were obtained in several hours, demonstrating the feasibility of
running whole core calculations on currently available parallel computer
systems.
20
Lessons
Need of HPC
Transient Application of Coupled System
Core : 3D Transport – CFD RANS(+ Subchannel) – Fuel (1D/3D)
System : Conventional System Code (RELAP5, MARS, etc)
Considering a typical core have 50,000 fuel rods and 50,000
subchannels. May need >10,000 core
Expected improvement area of safety analysis
AOO : More accurate DNB margin calculation based on full core
pin-power and subchannel behavior
RIA : More detailed pin-wise power coupled with TH and fuel
behavior, direct evaluation of fuel failure rate
SLB : More detailed thermal mixing and re-critical evaluation
Radiological Consequences : Accurate source term with pin-
wise evaluation
Uncertainty quantification of high fidelity model for engineering
purpose
Brute force MC method may be not possible
Combination of perturbation and MC method
21
Concluding remarks
At this moment
dual-path programs for future safety analysis code system are
considering in KAERI
Integrated safety analysis with uncertainty quantification tools
Demonstrate the defense-in-depth design and reduce uncertainty
Utilizing HPC
Enable full spectrum analysis of DBA with UQ
Support risk informed regulation
– Safety margin quantification for licensing analysis require
huge number of calculations
Code coupling with next generation analysis tools (i.e. Multi-
physics)
More realistic full core behavior and accuracy enhancement based
on high fidelity models which is now available
3D transport neutronics code (few million nodes)
RANS scale TH or subchannel code (few million nodes)
3D FEM or in-house 1D fuel performance code (few million nodes)
Conventional system TH code ( few hundred nodes)
22
APPENDIX
Examples of Calculation Result
23
Application for CANDU (PHWR) LBLOCA
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0
1G
2G
3G
4G
5G
Reacto
r P
ow
er
(W)
Time (sec)
SCAN/RELAP FDM
TPOWER
INTACT
BROKEN
SCAN/RELAP NEM
TPOWER
INTACT
BROKEN
RFSP/CATHENA FDM
TPOWER
INTACT
BROKEN
Safety issue during licensing for Wolsong #1 reoperation
Power peak during LBLOCA due to positive moderator coefficient
Coupled analysis with 3D kinetics is utilizing for auditing calculation
24
Kori Unit 1 UPI LBLOCA Audit Calculation
Safety issue during licensing for Kori #1
Life extension
Multidimensional behaviour during
LBLOCA reflood phase
Full 3D analysis show the non-
conservatism of 1D calculation
BE+Uncertainty still below safety limit
25
Application for Detailed Core TH Behavior
25 Finger Control Element Assemble Drop Accident
• CUPID-MASTER(3D Kinetics) Coupled Calculation
노심출구 온도분포
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99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124
125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154
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185 186 187 1 2 3 4 5 188 189 190
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195 196 15 16 17 18 19 20 21 22 23 24 25 197 198
199 26 27 28 29 30 31 32 33 34 35 36 37 38 200
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205 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 206
207 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 208
209 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 210
211 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 212
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229 230 231 173 174 175 176 177 232 233 234
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Steady State After 25 Finger CEA Drop
Distribution
core exit
temperature
Distribution
of Exit Core
Void Fraction
MASTER mesh, 962x26
CUPID mesh, 241x16
26
Software
Project Thermal Hydraulics Neutronics
System Macro Meso
(DNS)
Commercial
CFD Diffusion Transport
Monte
Carlo
MARS
(SPACE)
MATRA
CUPID
(Developi
ng)
- TBD
(Start-CD) MASTER DeCART
McCARD
(SNU)
Software
Project
Fuel
Performance
Structural
Mechanics Chemistry
Uncertainty
Quantification
Multi-physics
Multi-mesh
Integrator
COSMOS
(developing)
TBD
(NEPTUNE) - MOSAIQUE -
Possible Software for the Multi-Scale Multi-Physics Analysis
27
Establish Base tech and coupling tech.
AMS with personal Supercomp cluster
Application NPP Utilize New Design
Long term prospect (KAERI)
Integrated Analysis Platform
• Coupling Tech.
• Nuclear & Mat. DB
• Core Physics
• Core TH
• Fuel Performance
• Water-chemistry
Realization of Advance M&S
• Structure Coupling
• Material Science
• Base DB Extension
• Parallel Compute
• Utilize personal GPU supercomp.
Application of VR
• Uncertainty Quant
• App. for Design
• App. for SA
• Utilize world-class supercomp.
Short term Mid-term Long term
These pictures were taken from the presentation material of EU-NURESIM, US-CASL Project
