MCS2SIM - Method Allowing Application of PSA Results in Simulators

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Agenda

• Introduction to the basic idea of MCS2SIM method(Minimum Cut Set Usage in Simulators)

• 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?

PSA (MCS) Simulator?

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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

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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?

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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

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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

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Basic Idea of the MCS2SIM: MCS Usage in Simulators

Simulator

PSA

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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

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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

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Example of the MCS2SIM Application in R1 Simulator

PSA states that 323-system will failif combination of the faulty signals from the flow transmitters 323K301 and 323K302would occur.

What is going to happen if the equivalentmalfunctions would be activated in thesimulator?

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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

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Application in R1 Simulator: Results

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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.

Application in R1 Simulator: Results

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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.

Application in R1 Simulator: Results

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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.

LOCA

Core SprayVisualization of the Void

distribution inside the RPV.RPV-model is simulated using GSE’s RELAP5-HD Core

Application in R1 Simulator: Results

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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

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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

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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.

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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

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R2 Simulator: HDS Structure (High Definition Servers)

SimExec 1: Client

Simulator (BOP):- Topmeret,- Hand written Code,- Other models r5s2_inputs.txt

r5s2_outputs.txt

SimExec 2: Calculation Servers

relap5s2 (100 Hz)(RELAP5-HD Calculation Server 2)

s3rs (10 Hz)(S3R Calculation Server)

s3r_inputs.txt

s3r_outputs.txt

r5s1_inputs.txt

r5s1_outputs.txtrelap5s1 (100 Hz)

(RELAP5-HD Calculation Server 1)

pmaap5s1 (10 Hz)(PSA-HD based on the MAAP5.01

Calculation Server)

jts1_inputs.txt

jts1_outputs.txtjtops1 (20 Hz)

(JTopmeret Calculation Server)

MST

mps1_inputs.txt

mps1_outputs.txt

ExecNameifc.iniRelapifcn (20Hz)

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R2 Simulator: RPV Nodalization (RELAP5-HD)

3 Sectors, Reactor Head

6 Sectors, Downcomer

4 Sectors, Core

4 Sectors, Lower Plenum

6 Sectors, Upper Plenum

1D Bypass

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R2 Simulator: Core Mapping (RELAP5-HD/SIMULATE3-R)

4 Radial Sectors 6 TH Axial Nodes

24 Heat Structures

24 S3R Axial Planes

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R2 Simulator: Pressurizer and SG Nodalization (RELAP5-HD)

SG Primary Side

Pressurizer

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R2 Simulator: SG Nodalization (RELAP5-HD, Secondary Side)

2 Sectors2 Steam Separators

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R2 Simulator: PSA-HD Nodalization (RCS, SG:s and Containment)

Boundaries to BOP

Standard RCS Nodalization

Containment Nodalization

(9 nodes)

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R2 Simulator: PSA-HD Nodalization (Heat Structures)

Heat Structures representing the

walls

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R2 Simulator: PSA-HD Nodalization (Heat-Up Model)

Heat-up model:13 Axial Nodes5 Radial Rings

For more information:Go to: www.GSES.com

Call: 800.638.7912

Email: antanas.romas@gses.se

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