20.08.2015   Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process

BWR and PWR Base Case LOCA Frequencies

The Base Case LOCA frequency models are based on three Excel files entitled “PlantBWelds” (BWR Base Case), “PlantA. aWelds” (PWR RC-HL and Surge Line), and “PlantA. bWelds” (PWR HPI/NMU). These Excel files are part of the plant design information supplied by members of the Expert Elicitation Panel. Adding information on weld type by location and weld failure parameters to respective Excel files provides the basis for calculating LOCA frequencies including uncertainty distributions.

D.6.1 LOCA Frequency Models

For the BWR Base Case, the original “PlantBWelds” includes two spreadsheets, one for the feedwater system and one for the reactor recirculation system. In a first step to create a LOCA frequency model, each spreadsheet was split into two, one for Loop A and one for Loop B of respective system. Next a new column was added to each new spreadsheet to include information on weld type by location. A review of isometric drawings provided the input to the new columns.

The statistical information that is summarized in Section D.5 of this report is included in five separate spreadsheets of the modified Excel file. The posterior weld failure rates are included on Tab “Parameters,” each parameter assigned a unique variable name. The calculation of LOCA frequency, including Monte Carlo merge operations are performed on Tabs “Intermediate FW_A”, “Intermediate FW_B”, “Intermediate RR_A”, and “Intermediate RR_B.” These intermediate calculation sheets are linked to the design information for FW Loop A, FW Loop B, RR Loop A and RR Loop B, respectively. Using the variable names as defined on Tab “Parameters,” each weld is assigned an appropriate failure rate (including uncertainty distribution as defined using a Crystal Ball “assumption”). Finally, an integrated calculation of LOCA frequency by leak threshold category (0 through 5) is performed on a separate spreadsheet, which is linked to the intermediate calculations. Each integrated LOCA frequency calculation is defined as a Crystal Ball “forecast.”

For the PWR Base Case, the original “PlantAWelds” includes a single spreadsheet with the ASME XI Class 1 Category B-F/B-J welds. In a first step to create a LOCA frequency model, each spreadsheet was split into two, one for the RC-HL and one for the pressurizer surge line. A third spreadsheet with the HPI/NMU weld listed was added to form a new Excel-file corresponding to the PWR Base Case LOCA frequency model.

D.6.2 BWR Base Case LOCA Frequencies at T = 25

Summarized in Table D.16 are the LOCA frequency uncertainty distributions that are derived for BWR Base Case Cat0 through Cat6 LOCA. The results are representative of Plant B after 25 years of operation (T = 25).

System

LOCA

Category

Uncertainty Distribution

Mean

5 % — tile

50%-tile

95%-tile

RR Loop A NPS12

Cat0

2.06E-06

9.72E-08

1.38E-06

6.28E-06

Cat1

1.33E-06

6.29E-08

8.95E-07

4.09E-06

Cat2

1.44E-07

6.04E-09

8.66E-08

4.73E-07

Cat3

5.81E-08

2.34E-09

3.51E-08

1.91E-07

Cat4

2.31E-08

9.08E-10

1.39E-08

7.54E-08

Cat5

N/A

N/A

N/A

N/A

RR Loop B NPS12

Cat0

2.07E-06

1.00E-07

1.36E-06

6.41E-06

Cat1

1.34E-06

6.45E-08

8.81E-07

4.15E-06

Cat2

1.44E-07

5.85E-09

8.65E-08

4.72E-07

Cat3

5.84E-08

2.26E-09

3.47E-08

1.95E-07

Cat4

2.31E-08

9.15E-10

1.40E-08

7.48E-08

Cat5

N/A

N/A

N/A

N/A

RR Loop A NPS22

Cat0

1.23E-06

4.88E-08

7.30E-07

4.07E-06

Cat1

8.58E-07

3.37E-08

5.12E-07

2.89E-06

Cat2

7.36E-07

2.42E-09

3.94E-08

2.57E-07

Cat3

2.95E-08

1.01E-09

1.60E-08

1.01E-07

Cat4

1.16E-08

3.94E-10

6.33E-09

4.04E-08

Cat5

4.72E-09

1.57E-10

2.52E-09

1.63E-08

RR Loop B NPS22

Cat0

1.24E-06

4.97E-08

7.26E-07

4.06E-06

Cat1

8.66E-07

3.39E-08

5.10E-07

2.88E-06

Cat2

7.37E-08

2.48E-09

3.95E-08

2.59E-07

Cat3

2.91E-08

9.77E-10

1.59E-08

1.01E-07

Cat4

1.18E-08

3.86E-10

6.36E-09

3.97E-08

Cat5

4.73E-09

1.56E-10

2.55E-09

1.67E-08

RR Loop A NPS28

Cat0

2.73E-06

1.31E-07

1.80E-06

8.41E-06

Cat1

1.91E-06

9.05E-08

1.24E-06

5.91E-06

Cat2

1.64E-07

6.27E-09

9.69E-08

5.38E-07

Cat3

6.54E-08

2.49E-09

3.92E-08

2.16E-07

Cat4

2.61E-08

1.03E-09

1.55E-08

8.65E-08

Cat5

1.05E-08

4.24E-10

6.20E-09

3.50E-08

RR Loop B NPS28

Cat0

2.76E-06

1.35E-07

1.82E-06

8.44E-06

Cat1

1.93E-06

9.31E-08

1.27E-06

5.92E-06

Cat2

1.65E-07

6.32E-09

9.73E-08

5.42E-07

Cat3

6.62E-08

2.57E-09

3.93E-08

2.18E-07

Cat4

2.64E-08

1.10E-09

1.56E-08

8.74E-08

Cat5

1.06E-08

4.40E-10

6.33E-09

3.40E-08

FW Loop A NPS12

Cat0

6.69E-07

2.78E-08

4.05E-07

2.20E-06

Cat1

4.34E-07

1.80E-08

2.61E-07

1.42E-06

Cat2

4.75E-08

1.61E-09

2.58E-08

1.61E-07

Cat3

1.89E-08

6.41E-10

1.03E-08

6.49E-08

Cat4

7.53E-09

2.62E-10

4.07E-09

2.53E-08

Cat5

N/A

N/A

N/A

N/A

FW Loop B NPS12

Cat0

6.83E-07

2.89E-08

4.16E-07

2.24E-06

Cat1

4.44E-07

1.90E-08

2.68E-07

1.45E-06

Cat2

4.86E-08

1.70E-09

2.64E-08

1.67E-07

Cat3

1.93E-08

6.58E-10

1.06E-08

6.71E-08

Cat4

7.75E-09

2.80E-10

4.20E-09

2.62E-08

Cat5

N/A

N/A

N/A

N/A

FW Loop B NPS14

Cat0

6.02E-08

1.52E-09

2.61E-08

2.26E-07

Cat1

4.19E-08

1.06E-09

1.84E-08

1.55E-07

Cat2

3.59E-09

7.64E-11

1.42E-09

1.37E-08

Cat3

1.45E-09

3.12E-11

5.69E-10

5.51E-09

System

LOCA

Category

Uncertainty Distribution

Mean

5 % — tile

50%-tile

95%-tile

Cat4

5.80E-10

1.19E-11

2.30E-10

2.21E-09

Cat5

2.32E-10

4.74E-12

9.11E-11

8.83E-10

FW Loop A NPS20

Cat0

8.43E-07

3.47E-08

5.08E-07

2.74E-06

Cat1

5.92E-07

2.37E-08

3.55E-07

1.95E-06

Cat2

5.08E-08

1.75E-09

2.75E-08

1.74E-07

Cat3

2.03E-08

7.15E-10

1.10E-08

6.83E-08

Cat4

8.10E-09

2.77E-10

4.33E-09

2.81E-08

Cat5

3.26E-09

1.12E-10

1.74E-09

1.13E-08

FW Loop B NPS20

Cat0

1.00E-06

4.40E-08

6.13E-07

3.24E-06

Cat1

7.014-07

3.01E-08

4.28E-07

2.12E-06

Cat2

6.03E-08

1.03E-09

3.32E-08

2.04E-07

Cat3

2.41E-08

8.45E-10

1.33E-08

8.00E-08

Cat4

9.64E-09

3.44E-10

5.27E-09

3.32E-09

Cat5

3.84E-09

1.38E-10

2.14E-09

1.31E-08

RR Total Loops A & B

Cat0

1.21E-05

3.02E-06

1.03E-05

2.70E-05

Cat1

8.24E-06

2.02E-06

6.98E-06

1.86E-05

Cat2

7.64E-07

1.40E-07

6.07E-07

1.92E-06

Cat3

3.07E-07

5.43E-08

2.44E-07

7.79E-07

Cat4

1.22E-07

2.22E-08

9.73E-08

3.06E-07

Cat5

3.05E-08

3.59E-09

2.19E-08

8.52E-08

FW Total Loops A & B

Cat0

3.26E-06

5.55E-07

2.60E-06

8.13E-06

Cat1

2.21E-06

2.72E-07

1.75E-06

5.56E-06

Cat2

2.10E-07

2.70E-08

1.54E-07

5.85E-07

Cat3

8.40E-08

1.10E-08

6.18E-08

2.30E-07

Cat4

3.36E-08

4.40E-09

2.47E-08

9.35E-08

Cat5

7.33E-09

3.95E-10

4.33E-09

2.44E-08

RR + FW Total

Cat0

1.53E-05

5.24E-06

1.37E-05

3.10E-05

Cat1

1.05E-05

3.51E-06

9.30E-06

2.14E-05

Cat2

9.75E-07

2.24E-07

8.24E-07

2.26E-06

Cat3

3.90E-07

9.00E-08

3.32E-07

9.05E-07

Cat4

1.56E-07

3.64E-08

1.31E-07

3.57E-07

Cat5

3.78E-08

6.43E-09

2.93E-08

9.73E-08

D.6.3 PWR Base Case LOCA Frequencies at T = 25

The PWR Base Case Cat0 through Cat6 LOCA frequencies including uncertainty distributions, are summarized in Table D.17. These results are representative of Plant A. a/A. b after 25 years of operation (T = 25).

System

LOCA

Category

Uncertainty Distribution

Mean

5 % — tile

50%-tile

95%-tile

RC Hot Leg (3-of-3); Plant A. a

Cat0

8.94E-07

4.84E-09

1.27E-07

2.88E-06

Cat1

6.65E-07

3.55E-09

9.39E-08

2.14E-06

Cat2

4.87E-08

2.10E-10

6.15E-09

1.49E-07

Cat3

1.83E-08

8.33E-11

2.42E-09

5.95E-08

Cat4

6.99E-09

3.03E-11

8.93E-10

2.21E-08

Cat5

2.55E-09

1.16E-11

3.29E-10

8.29E-09

Cat6

1.26E-09

5.44E-12

1.58E-10

4.04E-09

RC Surge Line Plant A. a

Cat0

1.44E-07

2.65E-09

2.98E-08

5.02E-07

Cat1

1.14E-07

2.13E-09

2.36E-08

3.94E-07

Cat2

9.60E-09

1.48E-10

1.88E-09

3.46E-08

Cat3

3.84E-09

5.78E-11

3.50E-10

1.35E-08

Cat4

1.44E-09

2.01E-11

2.77E-10

5.06E-09

Cat5

5.31E-10

8.23E-12

1.01E-10

1.87E-09

Cat6

N/A

N/A

N/A

N/A

HPI/NMU (2-of-2) Plant A. b

Cat0

2.72E-05

4.64E-07

6.90E-06

1.07E-04

Cat1

1.60E-05

2.62E-07

3.93E-06

6.09E-05

Cat2

2.33E-06

3.30E-08

5.40E-07

9.02E-06

Cat3

9.22E-07

1.28E-08

2.14E-07

3.59E-06

Cat4

N/A

N/A

N/A

N/A

Cat5

N/A

N/A

N/A

N/A

Cat6

N/A

N/A

N/A

N/A