Uncertainty of the Level 2 PSA for NPP Paks Gabor LAJTHA , Attila - - PowerPoint PPT Presentation

▶
uncertainty of the level 2 psa for npp paks
SMART_READER_LITE
LIVE PREVIEW

Uncertainty of the Level 2 PSA for NPP Paks Gabor LAJTHA , Attila - - PowerPoint PPT Presentation

May 07, 2023 32 likes •203 views

Uncertainty of the Level 2 PSA for NPP Paks Gabor LAJTHA , Attila BAREITH, El d HOLL, Zoltn KARSA, Pter SIKLSSY, Zsolt TCHY VEIKI INSTITUTE FOR ELECTRIC POWER RESEARCH Institute for Electric Power Research Co Budapest

slide-1
SLIDE 1

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Uncertainty of the Level 2 PSA for NPP Paks

Gabor LAJTHA, Attila BAREITH, Előd HOLLÓ, Zoltán KARSA, Péter SIKLÓSSY, Zsolt TÉCHY VEIKI INSTITUTE FOR ELECTRIC POWER RESEARCH

slide-2
SLIDE 2

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 2

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Outline

  • Introduction
  • Uncertainties propagated from level 1 to level 2 PSA
  • Uncertainties considered in CET
  • Melt progression arrested (ECC restoration)
  • Hydrogen burn, early containment failure
  • Late containment failure
  • Propagation of uncertainties to containment failure

states

  • Summary
slide-3
SLIDE 3

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 3

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Introduction

  • Level 1 PSA for internal initiators and internal hazards

– Nominal power and shutdown state

  • Over 500 core damage sequences considered
  • Level 2 PSA is based on Level 1

– 17 PDS, 13 release categories

  • Uncertainty analysis

(aleatoric and epistemic uncertainties)

slide-4
SLIDE 4

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 4

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Level 1 – Level 2 Interface: Uncertainty Analysis

  • Aleatory uncertainties were propagated numerically from level 1 PSA

results to PDS frequencies

  • Basic event level uncertainty parameters were taken from level 1 model
  • Additional estimations were made for component failures and human

actions not included in level 1 analysis

  • Quantification was performed on PDS level minimal cut sets
  • Special purpose computer programme was developed due to complexity
  • f model and limitations of PSA software applied
  • Monte Carlo simulation was applied for quantification
slide-5
SLIDE 5

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 5

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Level 1 – Level 2 Interface: Uncertainty Analysis cont’d

1e-9 1e-8 1e-7 1e-6 1e-5 1e-4 PDS_05C PDS_05J0 PDS_05JA PDS_00B PDS_00E PDS_02A PDS_12B PDS_05F PDS_03B PDS_02B PDS_08B PDS_13C PDS_05B PDS_11B PDS_09F PDS_13F PDS_17F 95%, 5% 75%, Median, 25%

slide-6
SLIDE 6

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 6

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Level 1 – Level 2 Interface: Sensitivity Analysis

  • Focus on operator action for primary depressurisation upon severe

accident signal – New EOP action not considered previously in level 1 PSA – Interest in examining changes in profile of dominant plant damage states as a function of this action

  • Importance and sensitivity measures were calculated for the given

human failure event – Re-generation of PDS level cut sets with modified assumptions on failure probability – Calculation of most common measures of change

  • Results show that no significant changes can be expected upon

moderate changes in human error probability except for one high pressure PDS

slide-7
SLIDE 7

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 7

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Uncertainties in the Containment Event Tree

  • Severe accident simulations (MAAP4/VVER code) for each PDS by

sampling important process parameters as random variables – 40 MAAP parameters – 10 parameters for hydrogen ignition and containment fragility – Latin hypercube sampling – 200 simulations for each PDS/branch in CET

  • Generation of uncertainty distributions for CET headings

– Use of results from multiple severe accident analyses – Considerations of human failure probabilities, structural and equipment failures

  • Propagation of uncertainties from plant damage states to containment

states and release/consequence categories

slide-8
SLIDE 8

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 8

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Containment Event Tree

slide-9
SLIDE 9

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 9

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Example 1 :Melt progression arrested and spray system recovery

  • Uncertainty analysis

– Variability in available time (i.e. time window) for ECCS and spray system recovery actions was considered using the results of MAAP4/VVER calculations – Probability of recovery was calculated from the time window values of the sampled MAAP analyses. – Variability in the context of recovery actions (performance influencing factors other than time) was not assumed in quantitative uncertainty analysis.

  • Sensitivity analysis

– Studying sensitivity of overall results to likelihood of recovery (by numerical analysis) – Basemat melthrough is largely affected but not shown in release categories

slide-10
SLIDE 10

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 10

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Example 1: Melt progression arrested and spray system recovery cont’d

PDS_05C Relocation time of core (200 calculated sequence)

5 8 1 11 32 91 36 12 2 2 20 40 60 80 100 1 2 3 4 5 6 7 8 9 10 time groups Number in groups

22905 25696 28487 31279 34070 36861 39652 42443 45235 48026 50817 s

2 17 , 3 cov T T ery re non

e C e B A P

− − −

⋅ + ⋅ + =

PDS_05C Core melt starting time (200 calculated sequence)

13 95 5 2 54 22 9 20 40 60 80 100 1 2 3 4 5 6 7 8 9 10 time groups Number in groups

22063 23753 25443 27133 28823 30513 32203 33893 35583 37272 38962 s

Estimate * type of failures (recoverable or not) * time for recovery

  • 0.1
  • 0.2
  • 0.3
  • 0.4
  • 0.5
  • 0.6
  • 0.7
  • 0.8
  • 0.9
  • 1
  • 0.005
  • 0.01
  • 0.015
  • 0.02
  • 0.025
  • Average •1.25E-02
  • Median
  • 1.30E-02
  • 5%
  • 5.76E-03
  • 95%
  • 1.83E-02

Uncertainty in ECCS Recovery

slide-11
SLIDE 11

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 11

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

  • A complicated process appears in a simplified manner in the CET. For the

quantification of burn probabilities and in order to evaluate consequences the DET concept is introduced.

  • Hydrogen mole fraction

– different hydrogen quantities are produced in each sample (MAAP4/VVER code calculation)

  • Ignition – probability of ignition depends on the existence
  • f

igniting sources (spontaneous ignition, recombiner) and also on the hydrogen concentration

  • Combustion mechanism – three combustion mechanisms

are distinguished (burn, accelerated flames and DDT) for the determination of containment pressure load the H2AICC is used with Modified Adiabatic Isochoric Complete Combustion (AICC) model

  • Containment failure - Joint treatment of containment loads

and fragility curves

Example 2: Hydrogen burn, early containment failure

slide-12
SLIDE 12

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 12

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

  • PDS_05 C (no ECC recovery)
  • Uncertainty calculation
  • Hydrogen Production in Vessel Phase
  • 100
  • 200
  • 300
  • 400
  • 500
  • 600
  • 20
  • 40
  • 60
  • 80
  • 100
  • 120
  • 140
  • 160
  • 180
  • 200
  • No of Calculation (ordered according to H2 in vessel )
  • Hydrogen Mass (kg)
  • H2 total in vessel production
  • H2 production until lower grid failure

Hydrogen production - MAAP4/VVER Hydrogen concentration - MAAP4/VVER Containment load - H2AICC Ignition probability - 4 variables (LHS)

Example 2: Hydrogen burn, early containment failure cont’d

PDS_05C Generated H2 Mass at Vessel Failure (200 calculated sequence)

5 11 39 48 37 22 1 2 3 32 10 20 30 40 50 60 1 2 3 4 5 6 7 8 9 10 H 2 mass groups Number in groups

1 21 1 59 1 97 235 273 31 2 350 388 426 464 502 kg

HYDROGE N LOAD 5 10 15 20 25 30 35 40 Number in groups Num ber in groups 4 13 24 24 34 32 35 21 8 5 P ressure (bar) 1.8 2.2 2.6 3 3.5 3.9 4.3 4.8 5.2 5.5 1 2 3 4 5 6 7 8 9 10

slide-13
SLIDE 13

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 13

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Example 2: Hydrogen burn, early containment failure

(Cont’d)

P D S _ 0 5 C C o n ta in m e n t E a rly F a ilu re , R u p tu re

1 .0 0 E -0 9 1 .0 0 E -0 8 1 .0 0 E -0 7 1 .0 0 E -0 6 1 .0 0 E -0 5 1 .0 0 E -0 4 1 .0 0 E -0 3 1 .0 0 E -0 2 1 .0 0 E -0 1 1 .0 0 E + 0 0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0 N o . Probability

Average 0,078 Median 5,29·10-5 Max. 1 Min.

  • Std. dev.

0,187 5% percentile 90%percentile 0,31 95% percentile 0,49

PDS_05 C Containment Early Failure Rupture Probability

0.00E+00 1.00E-01 2.00E-01 3.00E-01 4.00E-01 5.00E-01 6.00E-01 7.00E-01 8.00E-01 9.00E-01 1.00E+00 1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 No Probability

Fragility curve: Frag(p) = P(pfail < p) The probability of the load pressure is in the interval (p, p+dp): P(pload = p) = F(p+dp) –F(p) = f(p)dp. The Containment Failure Probability : CFP(pload = p) = f(p)dp⋅Frag(p). CFP = integral dp f(p) Frag(p)

slide-14
SLIDE 14

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 14

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Example 3: Late containment failure Cavity Damage

  • Reactor vessel cavity damage leads to late enhanced leakage
  • Probability of cavity (door) damage determined as a function of two major

factors (by using the results of MAAP calculations)

  • Temperature in the cavity
  • Corium level in the cavity
  • Discrete probability values calculated from

sampled simulations for each PDS

PDS_05C Maximum Level of Corium in the Cavity (200 calculated sequence)

14 1 2 16 45 50 44 20 8 10 20 30 40 50 60 1 2 3 4 5 6 7 8 9 10 Max level groups Number in groups

0.004 0.053 0.103 0.152 0.201 0.250 0.299 0.349 0.399 0.448 0.497 m

PDS_05 C Cavity Door Load and Probability of Failure

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 20 40 60 80 100 120 140 160 180 200 No Probability (-) Corium Level (m) 100 200 300 400 500 600 700 800 Temperature (deg C) Corium Level (m ) Failure Probability Tem perature (deg C)

Mean 0,85 Median 0,99 Minimum 0,015 25% 0,81 75% 1 Variation 0,25

slide-15
SLIDE 15

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 15

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Example 4: Late Containment Failure Overpressurization

  • Without enhanced leakage the containment pressure in late

phase depends mostly on spray system operation

  • Containment pressure at basemat melt-through was calculated

for each sample

  • Failure probability distribution was obtained by comparing

calculated pressure values with that of the sampled fragility (pressure capacity) curves

1e-7 1e-6 1e-5 1e-4 0.001 0.01 0.1 1 SPRAY NO_SPRAY 95%, 5% 75%, Median, 25%

slide-16
SLIDE 16

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 16

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

Results of Uncertainty Propagation

1e-15 1e-14 1e-13 1e-12 1e-11 1e-10 1e-9 1e-8 1e-7 1e-6 1e-5 1e-4

PCD IS I LCLS LCFS ECFS LCL LCF ECF B HPME

95%, 5% 75%, Median, 25% Frequency, 1/year Containment State Average Median 95% 5% 1 Higy Pressure Melt Ejection 5,38·10

  • 8

3,64·10

  • 8

1,47·10

  • 7

1,09·10

  • 8

2 By-pass 1,70·10

  • 6

1,34·10

  • 6

4,04·10

  • 6

4,59·10

  • 7

3 Early Containment Failure 2,05·10

  • 6

1,32·10

  • 6

6,17·10

  • 6

5,22·10

  • 7

4 Early Containment Leakage 0,00 5 Late Containment Failure 8,77·10

  • 7

2,50·10

  • 7

3,65·10

  • 6

1,24·10

  • 9

6 Late Containment Leakage 1,09·10

  • 5

8,83·10

  • 6

2,39·10

  • 5

2,43·10

  • 6

7 Early Containment Failure with Spray 7,54·10

  • 7

3,63·10

  • 7

3,06·10

  • 6

1,12·10

  • 7

8 Early Containment Failure with Spray 0,00 9 Late Containment Failure with Spray 4,88·10

  • 11

7,87·10

  • 12

2,26·10

  • 10

1,35·10

  • 14

10 Late Containment Leakage with Spray 3,32·10

  • 8

2,83·10

  • 8

6,73·10

  • 8

1,33·10

  • 8

11 Intact containment 6,92·10

  • 7

1,13·10

  • 7

2,67·10

  • 6

3,29·10

  • 10

12 Intact containment with Spray 7,47·10

  • 6

6,43·10

  • 6

1,45·10

  • 5

3,23·10

  • 6

13 Partly Damaged Core 6,03·10

  • 6

5,12·10

  • 6

1,23·10

  • 5

2,71·10

  • 6
slide-17
SLIDE 17

Workshop on Evaluation of Uncertainties in Relation to Severe Accidents & Level 2 Probabilistic Safety Analysis Aiix-en-Provence, 7-9 November 2005 17

Institute for Electric Power Research Co Budapest lajtha@aed.veiki.hu

SUMMARY

  • Uncertainty analysis for the level 2 PSA of NPP Paks has been performed

with a combination of multiple severe accident simulations and the use of dedicated probabilistic methods and tools to express uncertainties

  • f accident phenomena and consequently, containment states.
  • The main advantage of this method is that it has proven capable of

determining aleatory uncertainty of a level 2 PSA. Also, the method is robust and easy to use with the elaborated computer program.

  • On the other hand the calculations were very time consuming in spite of

the fast running code, MAAP. The automation of producing input for the codes and of running the MAAP and H2AICC code and finally uncertainty processing was allowed to perform this work in a reasonable time frame.