Watts Bar Unit 2 Startup
Simulations with VERA
John Ritchie
Tennessee Valley Authority
Andrew Godfrey
Oak Ridge National Laboratory
Joint IC/SC Meeting
Oak Ridge National Laboratory
October 11, 2016
2
– Dec. 2015 – Fuel Load
– May 23, 2016 – Initial criticality
– June 3, 2016 – On the grid
Watts Bar Nuclear Plant – Unit 2
• First new nuclear
plant in U.S. since
1996 (WB1)
• Traditional four-loop
Westinghouse PWR
• 3411 MWth initial
rated thermal power
• Current burnup:
~30 EFPD
Image courtesy of TVA
Notable
Dates:
3
WBN2 Cycle 1 Design
• 193 Westinghouse RFA2
17x17 fuel assemblies
– 12’ active fuel height
– IFM spacer grids
• Three enrichment regions
– 2.1%, 2.6%, 3.1%
• Low enriched 6” axial blankets
• IFBA/WABA burnable poisons
• ~400 EFPD cycle length
Radial Slice through
WBN1 Reactor Vessel
17x17 Assembly Layout with IFBA and WABA
Images courtesy of TVA
5
Power Ascension Testing
6
Power History for PAT
Turbine generator
coupling making
excessive noise
(5/28/2016)
Automatic trip and
safety injection on
steam pressure
low (6/5//2016)
Automatic trip from
Lo-Lo level in
number 4 steam
generator
(6/20/2016)
Planned 10% load
rejection
Manual trip due to
low steam
generator levels
caused by a loss of
feedwater flow
from main
feedwater pump
(8/23/2016)
Planned loss
of offsite
power trip
from 30%
(7/14/2016)
Loss of bushing
cooling due to
excessive
hydrogen leak,
unable to exceed
75% power
Turbine trip from a
main bank
transformer failure
(8/30/16)
50% load rejection
Turbine trip
(6/26/2016)
Planned
trip from
outside of
MCR
(8/3/2016)
8
VERA Methods
• MPACT
– 2D/1D deterministic neutron transport based on MoC/SP3
– 47g ENDF/B-VII.0 subgroup library
– 50 axial planes in the fuel/ 58 tota l
– 4,234 parallel spatial domains
• COBRA-TF
– Two phase coolant T/H
– 14,000 channels
– Cross flow between channels
– 193 parallel domains (4 per assembly)
• ORIGEN
– Explicit isotopic depletion and decay
– 263 isotopes in 1.9 million regions
• BISON
– Volume average full temperature tables as a functions of power
and burnup
• SHIFT (BOC HZP only)
– Continuous-energy Monte Carlo neutron transport
– Doppler broadening and thermal scattering treatments
– Massively parallel demonstrated up to 300,000 processors
HZP BOC Fission Rate
Distribution in WB2
(quarter core)
10
0.6% 0.8%
3.1%
-0.7%
3.1%
0.8% 1.0%
-0.7%
0.9%
-10%
-8%
-6%
-4%
-2%
0%
2%
4%
6%
8%
10%
D C B A SD SC SB SA Total
Ba
nk
W
or
th
D
iff
er
en
ce
(%
)
RCCA Bank
Startup Results*
Measured MPACT
Difference
Shift
Difference
Initial Critical Boron Concentration (ppmB) 1089 -14 -2
Isothermal Temperature Coefficient (pcm/ºF) -5.31 -0.15 --
Total Worth Error < 1%
*Measurements courtesy of TVA
Control Bank Worths
11
Miscellaneous Evaluations
• Applications of VERA providing higher fidelity
capabilities than current methods
Effects of Primary and Secondary Source Rods
On Full Core Radial Power Distribution in WBN2
Fission distribution for shutdown
margin calculation, All-Rods-In +
Worst Stuck Rod Out
12
Power Ascension Testing
• Power escalation began May 23, 2016
• Plan requires ~90 days from criticality to commercial
operations
• TVA has provided power history data and measurements
• VERA has been used to follow the startup procedure with
hourly statepoints
• Oak Ridge Leadership Computing Facility has supported
all calculations over the last 3½ months with priority on
Eos supercomputer
• Comparisons to measured data have included:
– Critical boron concentrations at operating conditions
– Subsequent critical conditions after shutdowns
– Measured neutron flux distributions at certain checkpoints
The Largest Simulation Ever Performed by CASL!
13
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
5/23 5/30 6/6 6/13 6/20 6/27 7/4 7/11 7/18 7/25 8/1 8/8 8/15 8/22 8/29 9/5 9/12
Co
re
P
ow
er
L
ev
el
(%
)
Date
Power History
Measured Power
Distributions
~2750 hours total
14
Bank D History
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0
23
46
69
92
115
138
161
184
207
230
5/23 5/30 6/6 6/13 6/20 6/27 7/4 7/11 7/18 7/25 8/1 8/8 8/15 8/22 8/29 9/5 9/12
Co
re
P
ow
er
(%
)
Ba
nk
D
P
os
iti
on
(S
te
ps
W
ith
dr
aw
n)
Date
15
Inlet Temperature History
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
530
535
540
545
550
555
560
565
570
575
580
5/23 5/30 6/6 6/13 6/20 6/27 7/4 7/11 7/18 7/25 8/1 8/8 8/15 8/22 8/29 9/5 9/12
Co
re
P
ow
er
(%
)
In
let
Te
m
pe
ra
tu
re
(F
)
Date
16
Zero Power Criticality Measurements
• Criticality Measurements taken at HZP conditions
following shutdowns
• Include various Bank D positions and transient Xenon-135
conditions
-14 -16 -17 -17 -20 -20 -22
-18
-2
-6 -7 -6 -9 -9
-12
-8
-50
-40
-30
-20
-10
0
10
20
30
40
50
1 2 3 4 5 6 7 Average
Cr
iti
ca
l B
or
on
D
iff
er
en
ce
(p
pm
B)
Criticality
MPACT
SHIFT
17
Boron Concentrations
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
650
700
750
800
850
900
950
1,000
1,050
1,100
1,150
5/23 5/30 6/6 6/13 6/20 6/27 7/4 7/11 7/18 7/25 8/1 8/8 8/15 8/22 8/29 9/5 9/12
Co
re
P
ow
er
(%
)
So
lu
bl
e B
or
on
C
on
ce
nt
ra
tio
ns
(p
pm
B)
Date
18
Boron Concentrations
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
650
700
750
800
850
900
950
1,000
1,050
1,100
1,150
5/23 5/30 6/6 6/13 6/20 6/27 7/4 7/11 7/18 7/25 8/1 8/8 8/15 8/22 8/29 9/5 9/12
Co
re
P
ow
er
(%
)
So
lu
bl
e B
or
on
C
on
ce
nt
ra
tio
ns
(p
pm
B)
Date
Measured
VERA
19
Boron Concentration Differences
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
-50
-40
-30
-20
-10
0
10
20
30
40
50
5/23 5/30 6/6 6/13 6/20 6/27 7/4 7/11 7/18 7/25 8/1 8/8 8/15 8/22 8/29 9/5 9/12
Co
re
P
ow
er
(%
)
So
lu
bl
e B
or
on
C
on
ce
nt
ra
tio
ns
D
iff
er
en
ce
s (
pp
m
B)
Date
Boron Difference = -19 +/- 8 ppm
HZP Bias = -18 ppm
20
Xe-135 Concentration
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.E+00
1.E-09
2.E-09
3.E-09
4.E-09
5.E-09
6.E-09
5/23 5/30 6/6 6/13 6/20 6/27 7/4 7/11 7/18 7/25 8/1 8/8 8/15 8/22 8/29 9/5 9/12
Co
re
P
ow
er
(%
)
Co
re
A
ve
ra
ge
X
en
on
-1
35
C
on
ce
nt
ra
tio
n
Date
21
Sm-149 Concentration
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.E+00
5.E-09
1.E-08
2.E-08
2.E-08
3.E-08
3.E-08
4.E-08
5/23 5/30 6/6 6/13 6/20 6/27 7/4 7/11 7/18 7/25 8/1 8/8 8/15 8/22 8/29 9/5 9/12
Co
re
P
ow
er
(%
)
Co
re
A
ve
ra
ge
S
am
ar
iu
m
-1
49
C
on
ce
nt
ra
tio
n
Date
22
Np-239 Concentration
