This presentation provides an introduction to the basic idea of MCS2SIM method (Minimum Cut Set Usage in Simulators), prerequisites needed to apply this method to nuclear power plant safety studies, examples of MCS2SIM application and conclusions drawn from the pilot test. For more information, go to www.gses.com or email info@gses.com. You can also follow GSE on Twitter @GSESystems and Facebook.com/GSESystems. Thanks for viewing! 

1. MCS2SIM - Method Allowing
Application of PSA Results in
Simulators
info@gses.com

2. Agenda
•
Introduction to the basic idea of MCS2SIM method
(Minimum Cut Set Usage in Simulators)
PSA (MCS)
?
Simulator
•
Prerequisites needed for the application of the MCS2SIM for the
actual safety studies of NPPs
•
Example of MCS2SIM application in R1 simulator
•
Conclusions drawn after the pilot tests using the MCS2SIM
•
R2 simulator: Example of the suitable simulator for the MCS2SIM
application. What is so special about this simulator?
2

3. Basic Idea of the MCS2SIM:
Minimum Cut Set (MCS) Usage in Simulators
•
MCS2SIM method is based on the idea of coupling the
Probabilistic Safety Analysis (PSA) and full-scope simulators
•
The coupling is possible using the PSA results in the form of
Minimal Cut Sets (MCS) and translating these to the equivalent
malfunctions used in the simulators
•
What is the point?
–
PSA is an excellent tool for identifying combinations of failures. However, PSA
can’t provide information about the physical mechanisms of failures and
consequences
–
By knowing combinations of failures, it is straightforward to simulate the physical
failure mechanisms in simulators - Perform DSA (Deterministic Safety Analysis)
–
Simulators in combination with the PSA studies can become powerful tools for
the advanced safety assessment, not just complex tools for the classical
training of operators
3

4. Basic Idea of the MCS2SIM:
Actual System
•
Arbitrary system is assumed
containing two tanks: T1 and T2
•
Water can be pumped from T1 to T2
using pumps P1 or P2
•
Imagine that water flow to T2
cannot be established for some
unknown reason
•
What is wrong? How can the reason
for the failure of the system be
identified?
4

5. Basic Idea of the MCS2SIM:
Application of Fault Tree Analysis Method
•
1st step is to troubleshoot the whole
system to identify what malfunctions
may be causing the failure of the system
•
How to deal with that effectively?
–
•
By using PSA-code like RiskSpectrum or
similar and designing the fault tree model
by defining the top event - No water flow
into tank T2
Let the PSA code calculate the
combinations of malfunctions and figure
out the most probable combinations
5

6. Basic Idea of the MCS2SIM:
Verification and Study in Simulator
•
Assume that a high-fidelity
simulator of this system is available
•
Translate the most probable
combinations of MCS into the
equivalent malfunctions and activate
these in the simulator
•
Run the simulator and review the
physical parameters to verify
consequences and learn details of
the failure mechanism
6

7. Basic Idea of the MCS2SIM:
MCS Usage in Simulators
PSA
Simulator
7

8. MCS2SIM Prerequisites
• High-fidelity fault tree and event tree models for PSA
studies of a specific plant
• High-fidelity, full-scale simulator for a specific plant
• Execution faster than real time
• A team of safety analysts experienced in PSA studies and
operation of simulators
• Effective tools for automated analysis and automated
documentation of the simulation results
8

9. Example of the MCS2SIM Application in
R1 Simulator
• PSA fault tree analysis results of the 323-system
(core spray system failure) were used in the R1-simulator
• MCS-002 was selected, which states that 323-system will fail
if combination of faulty signals from the flow transmitters
323K301 and 323K302 would occur
• In the simulator there is a considerably higher number of
available malfunctions than only “signal is not available.”
Therefore, as a first step, an investigation was conducted into
what kind of malfunction of transmitters is critical
9

10. Example of the MCS2SIM Application in
R1 Simulator
PSA states that 323-system will fail
if combination of the faulty signals from the
flow transmitters 323K301 and 323K302
would occur.
What is going to happen if the equivalent
malfunctions would be activated in the
simulator?
10

11. Application in R1 Simulator:
Results
• If signals coming from the transmitters would be indicating
faulty 0.0 mA current then the consequences would not be
significant
• If the current of the signals would be high or maximum, it
can lead to the total loss of the safety function of the
323-system
• Simulation of consequences in case of a 20% LOCA
in combination with the MCS-002 was performed
11

12. Application in R1 Simulator:
Results
12

13. Application in R1 Simulator:
Results
Simulation results of the 20% LOCA where 323-system is functioning
as intended. The similar behavior would be if transmitters would be
indicating faulty 0.0 kg/s flow.
13

14. Application in R1 Simulator:
Results
Simulation results of the 20% LOCA where transmitters 323K301
and 323K301 are indicating faulty 300.0 kg/s flow as it is predicted
by the PSA.
14

15. Application in R1 Simulator:
Results
Simulation results of the 20% LOCA where transmitters 323K301 and
323K301 are indicating faulty 300.0 kg/s flow as it is predicted by
the PSA.
Core Spray
Visualization of the Void
distribution inside the RPV.
RPV-model is simulated
using GSE’s RELAP5-HD
Core
LOCA
15

16. Other Examples of the
MCS2SIM Application
• Tests were conducted in R1 (BWR) and R3 (PWR) simulators
– R1: Verification of event tree PSA results in simulator, considering
station blackout and combination of MCS predicted by the PSA
– R3: Verification of fault tree PSA results in simulator, considering
top event that FUNK-W will not be available and combination of MCS
predicted by the PSA
– R3: Verification of event tree PSA results in simulator considering loss of
400 kV grid due to the failure of the external grid and combination of
MCS predicted by the PSA
•
The results of the tests were conclusive and triggered a number of
additional questions leading to a better understanding of the failure
mechanisms, possible improvements, and increased quality and
confidence in both the PSA results and simulator behaviour
16

17. Conclusions
• Conversion of MCS to malfunctions used in simulators
is possible
• Simulations based on MCS are providing information about
the physics of the failure mechanisms and severity of
the consequences
• It is possible to identify weaknesses and errors both in PSA
studies and simulators
• This method is valuable for the identification of complex
failure cases and for the training of operators to handle
such cases
17

18. Conclusions
•
The simulator is an excellent environment for identifying if the
combinations of failures would be detectable during the plant
operation
•
This method requires gathering a team of specialist with different
areas of expertise - A PSA specialist and a simulator engineer are
needed
•
Some technical improvements are needed in order to make this
method effective and easily applicable by the safety analysts
who are not are experienced simulator engineers
•
Quality and requirements for the simulation of the critical systems
should be increased to the level of usage of the engineering codes
like RELAP5, SIMULATE3, MAAP5, MELCOR, etc.
18

19. R2 Simulator: Example of the Simulator
Suitable for the MCS2SIM Application
•
R2 simulator was upgraded by GSE using the latest
HDS technology facilitating the usage of the engineering codes:
– Simulation of the 3D thermal hydraulics in RCS and SG:s using two
RELAP5-HD models
– Simulation of 3D neutron dynamics using SIMULATE3-R code,
Studsvik Scandpower
– Simulation of containment, RCS and SG:s, by switching to the PSA-HD
code after the severe accident conditions are reached. PSA-HD is
based on the MAAP5.01 (Modular Accident Analysis Program)
•
All the engineering codes were integrated into the SimExec
environment, allowing coupling and synchronization of these
engineering codes and BOP models
19

20. R2 Simulator: HDS Structure
(High Definition Servers)
SimExec 2: Calculation Servers
SimExec 1: Client
r5s1_inputs.txt
Simulator (BOP):
- Topmeret,
- Hand written Code,
- Other models
r5s1_outputs.txt
r5s2_inputs.txt
r5s2_outputs.txt
ExecNameifc.ini
Relapifcn (20Hz)
s3r_inputs.txt
relap5s1 (100 Hz)
(RELAP5-HD Calculation Server 1)
relap5s2 (100 Hz)
(RELAP5-HD Calculation Server 2)
s3rs (10 Hz)
s3r_outputs.txt
(S3R Calculation Server)
mps1_inputs.txt
pmaap5s1 (10 Hz)
mps1_outputs.txt
MST
jts1_inputs.txt
jts1_outputs.txt
(PSA-HD based on the MAAP5.01
Calculation Server)
jtops1 (20 Hz)
(JTopmeret Calculation Server)
20

21. R2 Simulator: RPV Nodalization
(RELAP5-HD)
3
Sectors, Reac
tor Head
6
Sectors, Uppe
r Plenum
1D Bypass
6
Sectors, Dow
ncomer
4
Sectors, Core
4 Sectors,
Lower Plenum
21

22. R2 Simulator: Core Mapping
(RELAP5-HD/SIMULATE3-R)
4 Radial Sectors
6 TH Axial Nodes
24 Heat Structures
24 S3R Axial Planes
22

23. R2 Simulator: Pressurizer and SG Nodalization
(RELAP5-HD)
Pressurizer
SG Primary
Side
23

24. R2 Simulator: SG Nodalization
(RELAP5-HD, Secondary Side)
2 Steam
Separators
2 Sectors
24

25. R2 Simulator: PSA-HD Nodalization
(RCS, SG:s and Containment)
Boundaries to
BOP
Standard RCS
Nodalization
Containment
Nodalization
(9 nodes)
25

26. R2 Simulator: PSA-HD Nodalization
(Heat Structures)
Heat Structures
representing the
walls
26

27. R2 Simulator: PSA-HD Nodalization
(Heat-Up Model)
Heat-up model:
13 Axial Nodes
5 Radial Rings
27

28. For more information:
Go to:
www.GSES.com
Follow us on:
Call:
800.638.7912
Twitter @GSESystems
Email:
antanas.romas@gses.se
Facebook.com/GSESystems
simulation@gses.com