ML20044B862
| ML20044B862 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 03/05/1993 |
| From: | Link B WISCONSIN ELECTRIC POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| CON-NRC-93-034, CON-NRC-93-34 TAC-M68586, TAC-M68587, VPNPD-93-058, VPNPD-93-58, NUDOCS 9303110039 | |
| Download: ML20044B862 (13) | |
Text
,
- 'i :
Wisconsin Electnc POWER COMPANY 231 W fAchomt PO EL w 20a$ MMukee Wt 53201-2046 (414J 2212345 VPNPD 05 8 NRC 0 3 4 March 5, 1993 Document Control Desk 10 CFR 50.63 U.S.
NUCLEAR REGULATORY COMMISSION Mail Station P1-137 Washington, DC 20555 Gentlemen:
DOCKETS 50-266 AND 50-301 SUPPLEMENT TO 10 CFR 50.63. TAC. NOS.f68586 ANDr68587 LOSS OF ALL ALTERNATING CURRENT POWER POINT BEACH NUCLEAR PLANTS, UNITS 1 AND 2 In a letter dated October 3, 1990, the NRC transmitted the Safety Evaluation Report (SER) issued by the Nuclear Regulatory Commission Office of Nuclear Reactor Regulation for the Point Beach Nuclear Plant (PBNP) response to the Station Blackout Rule, 10 CFR 50.63.
In that SER, the NRC made the following recommendation for using the-gas turbine generator (GTG) at PBNP as an alternate AC power source:
t "The licensee should demonstrate using actual test data that the GTG can obtain and maintain a reliability of 0.95 or better.
This demonstration should be completed within a reasonable time period (approximately 2 years)."
In a letter dated November 8, 1990, we committed to demonstrate the i
achievability of 95% reliability of the GTG within two years.
In a letter dated July 23, 1992, we provided the actual test data for the GTG from June 15, 1990 through March-18, 1992 for NRC review.
During a meeting with the NRC staff on June 25, 1992, we l
stated our belief that the data demonstrated the GTG can obtain 95%
reliability.
In that letter, we also described some of the details of.our efforts to improve the reliability of the GTG since'1989, J
the major overhaul and upgrade that was being performed, our plan i
to establish a reliability program, and the post-overhaul testing i
program.
The overhaul and upgrade was completed in October 1992.
The GTG
)
reliability program was also implemented in October 1992.
Post-overhaul reliability testing began on October 27, 1992.
9303110039 930305
~
T\\ /
PDR ADDCK 05000266 g ;J e
p PDR A sums 7dHimahExm opta r
Narch 5, 1993 Page 2 l
The July 23, 1992, letter also stated that we would attempt to prove the post-overhaul reliability of the GTG by' performing 20 tests with 2 or fewer failures.
We stated that we would submit additional information about how we propose to meet the requirements of 10 CFR 50.63 if more than two failures occurred.-
The third failure occurred during a return to service tent on January 5, 1993.
A summary of the post-overhaul testing that has been performed to date is provided as Attachment 1 to this Jetter.
Our assessment of the reliability of the GTG and our plan for meeting the requirements of 10 CFR 50.63 are provided as Attachments 2 and 3 to this letter.
We plan to continue to maintain 95% as the target reliability for the GTG and to continue to use the reliability program to monitor, improve, and maintain the GTG reliability.
Also, we plan to remove the temporary diesel generator which was installed as a compensatory measure during the GTG overhaul.
We have reviewed the requirements for Alternate AC power
[
reliability.
A discussion of " sufficient reliability" (10 CFR 50.2) of an Alternate AC power source is provided as to this letter.
r Please review this information in accordance with 10 CFR 50.63 (c)
(3) and (4).
We would be pleased to answer any questions you may have.
Sincerely,
_,fV12' Almuv1)
W Bob Link Vice President Nuclear Power i
Attachments cc:
NRC Resident Inspector NRC Regional Administrator
)
l l
POST-OVERHAUL RELIABILITY TESTING
SUMMARY
Post overhaul testing of the GTG started on October 27, 1992.
The l
seventh consecutive successful test was completed on November 17, 1992.
The completion of seven consecutive successful I
tests is considered a demonstration of restored performance for power sources that have experienced 4 or more failures in the last 25 tests.
The seven consecutive successful test criteria is j
discussed in NUMARC 87-00 and Draft Regulatory Guide DG-1021.
l l
The first failure was the 13th countable start and load-run test on December 9, 1992.
The failure was due to the starting diesel being unable to accelerate the turbine.
The throttle solenoid was lubricated and subsequently replaced.
Tre second failure was the 16th countable start and load-run test i
on December 23, 1992.
The failure was due to a failure of the I
starting diesel battery.
The battery was recharged and subsequently replaced.
The third failure was during a return to service test on i
January 5, 1993.
This failure could be considered not countable by the reliability program guidance because return to service testing is normally not countable.
However, this failure was not l
attributable to the maintenance that was performed prior to the o
return to service and therefore this situation was judged to be a countable failure.
The maintenance performed just prior to the return to service was the verification of a relay setpoint.
The failure was due to a loose pulley on the speed changer gear box.
t The unit achieved 850 generator RPM, 50 RPM short of the i
synchronization speed.
The set screw on the pulley was tightened and locked in with another screw.
The fourth failure was the 22nd countable start and load-run test i
on January 18, 1993.
The unit tripped on high vibration and would not accelerate during subsequent restart attempts.
It was discovered that the throttle solenoid replacement (see the first i
failure above) changed the operation of the throttle such that the starting diesel will not accelerate when it is running in cool-down j
mode.
This change in operation was r t identified by the engineers performing the change and was'therefe.e not communicated to the operators.
The operators believed thA failure to start was a
[
malfunction of the solenoid.
This change in operation has been subsequently identified and communicated to the operators.
j Additional modification is being considered to re-establish the original mode of operation.
The attached " Gas Turbine G-05 Start and Load Reliability Database"
{
table provides additional details about the testing that has been performed.
For clarification, it should be noted that during the j
test on December 7, 1992, the load-run was not completed due to operator error.
The auxiliary power diesel output frequency was 1
i
+:-*-. -
h-
<u-e t
l I
adjusted improperly, which caused the GTG to trip.
This was not a countable failure because the reliability guidance being used i
i states that operator errors are not counted.
The successful start for this test was. valid and countable.
The counting of all subsequent start and load-run tests is affected by not counting this load-run.
The start and load-run test count is essentially the start attempt number minus one after the December 7, 1993 test.
A similar situation appears in the data on January 24, 1993.
The load-run was not completed due to a problem with the automatic load control circuitry.
The GTG was verified as operable in the manual mode, but the load and duration specification of 50% rated capacity (10 MWe) for one hour was not completed because it was determined that a precautionary shutdown was appropriate.
This was not a countable failure because the GTG was verified to be operable.
This test was not a countable load-run because the load and duration specification was not met.
Current Status of the Gas Turbine:
The gas turbine reliability program requires programmatic assessments for the 3 failures in 20 test trigger value.
These assessments have-been performed.
Nine specific reliability improvement recommendations have been generated and are being implemented.
The reliability program also requires increased test frequency for 4 failures in 25 tests.
The increased test frequency is 7 days or less and must be maintained until 7 consecutive tests with no failures is achieved.
The seventh consecutive countable test with no countable failure was completed on February 17, 1993.
Biweekly (twice per week) testing of the gas turbine is being continued as a requirement of the degraded voltage relay temporary waiver of j
compliance (see LER 93-001).
i 1
1 i
l l
l l
l l
l l
l
L E
i i 5 5 i
"j
}"
j 1 1 I
5
.5 E E o m 4
i a
m -
m y
y g
8 5 5 5 5 5
a m
-= 5 a
a D
k et
-C L
w 3
- ~
b e a C t C
E5 E
E' n
=
2 E
5E E
E t
3 n= =
=
h& C t
o e
=g 5% 8 EEl I
%S 2 2 2
=
2-8 5
n E
E af :.33. $
3 3
m E tt$
e 33 3 3 3 3
d 3 **
5 ljat t t t t
tt BR~ %
~
~
1%l aa -al
- l
-l a
a a a
m 4
[ E 5
t t t t t
t E~~
8
- 6 pa h t 888 8
?
S 3
?$5 t 5
5 uo aam a
o
-= =
=
u.
==
o-x o
r x
83ACRAGR3SaGGRREEERRGaMA%SSRSRSRS3GX333333GGGREEE o6 gudddddddddd&& dad &dddddddddddddddddddddddddddddddds e o" a
Mh
!P88AARS%CctRRSS8888888888888888888888888888888888 g:ddadddddddddddddddd&&didada;;;;;;;&dadddddddddddda e-a
-o 2
0824cS4ECRS88888888SSRSSSSSSRSRSRSSRSSSSSSSERRS888 M
gaddddddddddddddddddddddddddddddddddddddddddddddddd M
M
- 8RACEMGR$3OR338GG%GGGRGGS3RG3SGGGSSSU5SMRRSEU3G4G a
Badd&dadddddddddddddddddddddddadddddddddddddddddddd o
A:
- i
'y aandadaddddddddddddddddddddddddddddddddddddddddddddd i
e4 o i
4 4
o M
a faddddddddddddddddddddddddddddddddddddddddddddddddd a
Jc
{ """*""****"***202"000$00$$b$$282REEEENNQ4Q4$522%
e O
OeN 4
g nnnnn nnn nnnnn n 44 wo i
-f g.
2 g:AAAAAMRRRASSSGGGG00303 3
.g 1
gashnm3G0cscsuS3sa~ mass.
W" t
fM C
a u
-em m
mmm N
5g R
8 1
-'E o
wwwweeeeeeeeewNNNNNNNN m %%
N nnannm8seOusenee hn;;ng munnat===nunnn======nu i
z-ODeweewwweeveveeOOOOOOOO
\\
b t
i
e e
se tu e
in l
))
))
)
)
)
t))dn
)
m s
ee e
e e
t eeai e
s e
tl l
l t
oll om l
e 0
t bb b
b b
rbbl b
t 1
u sa a
a a
haa 0
a un n
in r
t t t
t t
ttt e2 t
o mm eu m n
n umlbn m n
i i m r
u t
m r
oo ro o
o eooai o
t 0
e cc uc c
c scct c
0 r
1 l
e nt 1
a r
t t i t t
t idoooa o
t t ur t
t n
o oo ao o
o n
s i t
nn F n n n
nnct n
i e
ae((
(
(
(
g( (
s
(
r t
rl y
n t e t
r ett t rt t
t i tt or t
r e
a pt ss es s
es t ssn(
s a
r t
ooee t e e
re ree(
e t
u s
rtt t t t
ut att p
t s
s e
dh a
l t
di e
s r
eT ee B e e i e seeer e
r e
t cc c
c ac cct t c
r l
eli n
P e
l evvi ti i
fi
,iie i
ev v v
nvvl n v o
s psrr sr r
rr orrpo r
l e
meee ee e
ee i
eeni e
it i
lO cD D
n a
ca oiss i s s
gs t ssot s
a o
r oo o o ao roo r
o
)
t ib e
g t gtt gt t
ht ibtt tb t
s h n on n
c oi t
ir L
it t rr t r r
dr rr r
V t
ninn n n n
vnnnv n i
ua h
r t ruu ru u eu huudh u
t u
g w
a sat t at t
et gt t ag t
tr i
o t
et ee t e e
pe i eeoi e
e C
M L
s T5RR sR R
sR MRRLH R
n c
Ll 0000000000000000000000000000000000000000000 Al A0000000000000099999988888777766677777888999 2
T e N
9 OR 111111111111 111 0000000000000000000000000000 9
T 1
0 1
ts o
0i 0000000000000000000000000000000000000000000 P
o At A0000000000000000000000000000000000000000000
(
n Oe N
LR 111 1111 111111 11 1111111111111111 111111111111 e
id s i a
l b
S a
t Ti 0000000000000000000000000000000000000000000 a
Rt A0000000000000009999988888777766677777888999 D
A e N
T R 111 1111111111110000000000000000000000000000 y
S t
i l
ib Li 0000000000000003333488999556633333445566778 a
At A0000000000000009999988888888888888888888888 i
T e N
l OR 11111111111111100000000000000000000C0000000 e
T R
e d
v a i o
t Di 0000000000000000000000000000000000000000000 L
a At A0000000000000000000000000000000000000000000 Oe N
l d
u LR 111111111111111111111 1111111111111111111111 n
m a
u C
t rt T
f.
0000000000000003333488999556633333445566778 t
R t_
A0000000000000009999988888888888888888888888 5
A e N
T R 1 111111111111 11 0000000000000000000000000000 5
S 0
-G e
s 01234556678901 222223444556667888888990123456 n
i s
11 1 1111111 1111 11 11 1 11 11112222222 w
a e
t E c r
$ c u
A u T
Ns
~
P sa D s 01234556678901222223444556667888888990123456
~
G At 11 11111111 11 11 111111 111112222222 Op L me
+
t t
n A
s 0123455667890123333455566777899o9001 12345678 s
1111111111 1 111 11111t 122222222222 e
E c S c A u HS P
T g 01234556678901234445677889001233344556789012 R t_
111111111111 11222222222222222333 Am TSe t
t A
22222222222222222222222223333333333333333333 t
99999999999999999999999999999999999999999999 s
////////////////////////////////////////////
e 7781 3500779350279946133804561388147713804724 eT 22200011111223000011 22223000111 122220001 1 122
////////////////////////////////////////////
t af 0001 1 11 1 111111 222222222221 11 1 11 1 1 1 1122222222 Do 111111 11 11111111 111111 1110000000000000000000 w
GAS TURBINE GENERATOR REL1 ABILITY ASSESSMENT In our initial station blackout submittal to the NRC, in April 1989, we stated that pBNP would rely on alternate AC power from the gas turbine generator-(GTG) that exists at the site.
At that time, the reliability of the GTG was reported to be about 0.91.
We also stated that additional testing and maintenance requirements would be implemented to improve the GTG's reliability.
t In July 1989, we began testing the GTG in a mode similar to the way
~;
it would be started during a station blackout.
The GTG has an auxiliary power diesel generator that starts automatically when power to the gas turbine is lost.
The new mode of testing included securing power to the GTG, allowing the auxiliary power diesel to start, then starting and running the gas terbine with its support systems powered by the auxiliary power dies.el.
During these initial tests, the auxi'le.ry power diesel failed several times by tripping on high temperature.
This failure causes the gas turbine to trip due to the loss of its support systems.
A l
main problem causing the high temperature trip was believed to be inadequate ventilation near the auxiliary power diesel.
A modification to the gas turbine building ventilation was completed in June 1990.
After the ventilation modification was completed, another test was attempted.
The test failed due to the auxiliary power diesel trip on high temperature.
The auxiliary power diesel high temperature trip circuit was recalibrated and the setpoint was raised.
The technical manual for the auxiliary power diesel allows the higher setpoint.
The GTG was tested after the recalibration of the high temperatura trip on the auxiliary power diesel.
The test was successful, but the maximum outside ambient air temperature that i
day was only SS'F.
Another test was performed during warmer weather.
This test failed due to the auxiliary power diesel high l
temperature trip.
In June of 1990 we started to perform monthly station blackout tests.
(The attached Gas Turbine Generator G-05 Start and Load j
Reliability database starts at that time).
The failure of the auxiliary power diesel during a long duration test in hot weather was not yet resolved, but the problem had been minimized to the extent that the GTG could be run for at least 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> during cool weather and about 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> during hot weather.
Long. duration testing was suspended until the auxiliary power diesel high temperature trip problem could be resolved.
After further study, it was determined that the temperature sensor and the trip circuitry should be upgraded.
In March of 1991 a change to the high temperature trip circuit for the auxiliary power diesel was completed.
On July 18, 1991 an eight hour test was i
completed.
The maximum outside ambient air temperature was ~86*F.
This test confirmed that the auxiliary power diesel high temperature trip problem had been resolved.
In_ July 1991, a GTG reliability team was formed.
In the last quarter of 1991, problems with the starting circuits for the l
i starting diesel and the auxiliary power diesel were corrected.
Also, the station blackout QA program was finalized and applied to l
the gas turbine and other station blackout equipment.
In April 1992, during an internal fiber-optic scope inspection of the GTG, we discovered component degradation and wear.
After consultation with Westinghouse, tha. GTG manufacturer, we declared the GTG out of service and began preparations for a major overhaul of the GTG.
The major overhaul and upgrade was completed in October 1992.
The i
GTG reliability program was implemented in October 1992.
The i
3 failures out of 20 test trigger value indicated that 95%
reliability was not being maintained.
The reliability program provides guidance for monitoring reliability and taking appropriate actions for failures and trigger value exceedence.
The cumulative reliability of the GTG after the overhaul is about 88%.
The reliability of the GTG prior to the overhaul was about 72%.
This shows that improvement has been occurring.
Additionally, the evaluations required by the reliability program i
have been performed.
Specific reliability improvement recommendations have been generated and are being implemented.
We l
believe that these improvements will help continue to improve and maintain the GTG reliability.
l f
I 1
1 t
i j
1 "l
4
PLAN FOR CONTINUED IMPLEMENTATION OF 10 CFR 50.63 The letter to the NRC dated July 23, 1992 provided the pre-overhaul reliability data.
That letter stated that we believed the l
pre-overhaul test data demonstrated the achievability of 95%
reliability on the GTG and that our method for improving and maintaining the reliability of the GTG would be the reliability l
program.
Based on the summaries provided in Attachments 1 and 2, our belief that we have demonstrated the achievability of 95% reliability for the GTG, and that the GTG reliabilty program provides the method for monitoring, improving, and maintaining the GTG reliability, we plan to maintain the GTG as the AAC power source for Point Beach l
Nuclear Plant.
The target reliability will continue to be 95% as I
recommended by Reg Guide 1.155.
We plan to continue to use the GTG reliability program as the method for monitoring, improving, and
)
maintaining the reliability of the GTG.
j We will continue twice per week testing until the degraded voltage relay Technical Specification change is issued or until the NRC l
concurs that this compensatory action is no longer necessary.
The i
routine test frequency of the GTG is once per month.
We plan to remove the temporary diesel generator that was installed 1
for the GTG overhaul outage.
The temporary diesel generator was i
l installed as a compensatory measure during the GTG overhaul for l
10 CFR 50 Appendix R and 10 CFR 50.63 concerns.
The operability of i
the GTG is now being maintained.
Therefore, the temporary diesel is no longer necessary.
l l
l i
1 1
1 1.
DISDUSSION OF ALTERNATE AC POWER SOURCE " SUFFICIENT RELIABILITY" We have reviewed the requirements for AAC power reliability.
The l
following is a discussion of the results of this review.
10 CFR 50.2 Definitions, states that an AAC source must have sufficient capacity and reliability for operation of all systems required for coping with a station blackout.
Sufficient reliability is not defined.
The guidance documents for 10 CFR 50.63 (NUMARC 87-00 and Reg Guide 1.155) do not provide l
guidance on how to select a target reliability for Alternate AC power sources.
Section 3.3.5 of Reg Guide 1.155 states that the reliability of an AAC power source should meet or exceed 95%.
A basis for the 95% reliability is not provided.
NUREG-1032 " Evaluation of Station Blackout Accidents at Nuclear Power Plants:
Technical Findings Related to Unresolved Safety Issue A-44" is the report that represents the culmination of several technical studies undertaken by the Nuclear Regulatory Commission (NRC) staff and contractors to place a reliability and risk perspective on USI A-44 " Station Blackout."
This NUREG provides extensive evaluation of the expected frequency of the loss of off-site power, reliability of on-site emergency AC power sources (emergency diesel generators), and the redundancy of on-site emergency AC power sources.
These factors provide the basis for determining the duration of a station blackout.
This NUREG does not discuss the use of AAC power sources to cope with a Station Blackout.
10 CFR 50.63 was developed based on the probrbility of station blackout events.
A key aspect of this probt.bility is the reliability and redundancy of on-site emergency AC (EAC) power i
sources.
Reg Guide 1.155 provides 4 groupings of on-site emergency AC power redundancy (emergency AC power configuration) and 2 categories of on-site emergency AC power reliability.
Point Beach is a 1 out of 2 shared configuration which is classified in group "D."
Group D also includes 2 out of 3, 3 out of 4, and 3 out of 5 configurations (reference Reg Guide 1.155 Table 3).
Reg Guide 1.155 Table 2 provides EDG target reliability levels of O.95 and 0.975.
The target EDG reliability for PBNP was chosen to be 0.976.
A comparison of the risk of EAC power failure at Point Beach with other Group D EAC power configurations can be performed as follows:
1 This evaluation method is based on NUREG-1032 Appendix B which I
states that the modeling has been done on a generic level, but it could be made plant-specific by adjusting failure rate parameters to reflect site location, system design, and operational factors.
of an "i" outlof "j" The emergency AC power reliability (Risthprobabilitythat"i"out g3e diesel generator system, and P EAcl of "j" diesels will fail or be una/3vailable when required, P is theprobabilitythatasingledieselgeneratorwillfailor$e g
i unavailable when required, and P is the probability that "i" out of "j" diesel generators wil$CF[a/fl and be unavailable as a result of comLon cause when required) can be modelled as follows:
i
For a 1 out of 2 diesel conficuration:
REAcl/2 = 1 - [(PEDc) * + PecF2/23 I
For a 2 out of 3 diesel conficuration:
REAc2/3 = 1- [3(PEDc)8 + 3PccF2/3 + PccF3/33 The common cause factors will be considered of similar magnitude l
for this demonstration.
Therefore, the above equations simplify to:
l For a 1 out o[_2 diesel conficuration:
i REAcl/2 = 1 - (Pgog)8 j
For a 2 out of 3 diesel conficuration:
REAc2/3 = 1 - 3(PEDG)
From these equations, it can be seen that if the P is equal for the two EAC power configurations then the probabilkpgty that an EAC system will fail to meet its requirement is 3 times more likely for-the 2 out of 3 configuration when compared to the 1 out of 2 configuration.
Using 0.025 (which is 1 - 0.975) as the EDG failure rate (PEDG), the 1 out of 2 EAC system failure rate is (0.025)8 = 0.000625.
The EAC system failure rate for a 2 out of 3 configuration is 3-(0.025)2 = 0.001875.
The differences in failure probability for emergency AC power configurations in the same EAC power configuration group is not l
explained or accounted for in Reg Guide 1.155.
We believe that in order to evaluate " sufficient reliability" of an AAC power source, the reliability and configuration of the EAC power system should be considered.
If the Reg Guide 1.155 recommendation for a single, standard AAC power reliability (0.95) is applied, the probability-of failure of the EAC and AAC power systems for a 2 out of 3 configuration would be 3 times more likely than a 1 'ut of 2 configuration.
A 1 out of 2 EAC power configuration with a 0.85 AAC power reliability is essentially equivalent to a 2 out of 3 configuration with a 0.95 AAC power reliability.
Mathematically this can be shown as follows:
J l
For a 1 out of 2 dieLel confiauration with 0.85 reliable AAC:
I REAcl/2 = 1 - (Pgog)*-(PAAc)
=1-(0.025)2*(0.15) l 1
= 0.99990625 l
l For a 2 out of 3 diesel conficuration with 0.95 reliable AAC:
j REAc2/3 = 1 - 3 (Pgog)**(PAAC) = 1 - 3(0.025)8*(0.05)
= 0.99990625 q
Hote that the current post-overhaul cumulative reliability of the Point Beach GTG is about 0.88.
Although, as stated previously, we believe that the target reliability for the GTG is 0.95 and we are continuing to use the GTG reliability program to improve and
)
maintain the GTG reliability.
l Additionally, Reg Guide 1.155 states that there should be a minimum potential for common cause failure with the preferred or the blacked-out unit's onsite emergency AC power sources.
The AAC power source at PBNP is a different system than'the onsite emergency AC power sources.
The diverse AAC system at PBNP is less susceptible to common cause failure with the onsite emergency AC power sources than an AAC system that relies on the same power source as the onsite emergency AC power system.
A probabilistic safety assessment (PSA), to meet the requirements of Generic Letter 88-20, is being performed for Point Beach Nuclear Plant.
Preliminary results from this PSA show that the station blackout event is approximately 11% of the overall core damage frequency, compared to 38% for Large LOCA, 18% for Steam Generator Tube Rupture, and 14% for Medium LOCA.
The preliminary results show that the core damage frequency for station blackout is i
1.22E-05 per reactor-year.
Emergency diesel generator failure rate of 0.038 (success rate 0.962) and GTG failure rate of 0.35 (success rate 0.65) were used in the development of these preliminary results.
This shows that station blackout is not the predominant core damage event for Point Beach even when a GTG success rate of 0.65 is used.
J i
t
,