nine mile point unit 1 regulatory conference/public meeting ...outage schedule (loop/loca testing)...
TRANSCRIPT
Enc
losu
re 4
Nin
e M
ile P
oint
Uni
t 1
Reg
ulat
ory
Con
fere
nce
Los
s of
Shu
tdow
n C
oolin
g
Nov
embe
r 1, 2
013
ML1
3340
A09
1
NMP Participants
Enc
losu
re 4
Maria Korsnick
CNO, COO and
Acting CEO
Chris Costanzo
Site Vice Presiden
t Jim
Stanley
Plant G
eneral M
anager
John
Bou
ck
Manager, O
peratio
ns
Elliott Flick
Gen
eral M
anager, Fleet Engineerin
g Bruce Mon
tgom
ery
Manager, Fleet Nuclear Safety & Security
Terry Syrell
Manager, N
uclear Safety & Security
Jim
Vaughn
Shift M
anager
Larry Naron
Gen
eral Sup
ervisor –
Engineerin
g Gareth Parry
Indu
stry PRA
Con
sulta
nt
E. P. (C
hip) Perkins
Director, Licen
sing
Agen
da
Enc
losu
re 4
– Ope
ning
Rem
arks
Chris Costanzo
– Introd
uctio
n
Jim Stanley
– Summary of Event
and Timeline
John
Bou
ck
– Ad
ditio
nal Risk
Mitigatin
gBa
rriers
JimVaughn
– PR
A An
alysis of Event
Elliott Flick
– Lesson
s Learned
and
Conclusio
ns
JimStanley
– Que
stions
Team
– Closing Re
marks
Ch
ris Costanzo
E
nclo
sure
4
Nin
e M
ile P
oint
Uni
t 1 L
oss
of
Shu
tdow
n C
oolin
g
Reg
ulat
ory
Con
fere
nce
Intro
duct
ion
Jim
Sta
nley
Pl
ant G
ener
al M
anag
er
Introd
uctio
n
Enc
losu
re 4
We are extractin
g all of the
learnings from th
e event
– An
y un
planne
d loss of SDC
is significant and
doe
s not m
eet
our e
xpectatio
ns
– Actio
ns ta
ken to re
spon
d rapidly and thorou
ghly
• Fixed proced
ures to
prevent re
curren
ce
• Re
structured
NMP2
outage sche
dule (LOOP/LO
CA testing)
– Managing actio
ns with
in our Corrective Actio
n Program
We have new
data and inform
ation to sh
ow why th
e indu
stry m
etho
dology fo
r assessin
g hu
man
pe
rformance app
lied by NMP shou
ld be used
to
evaluate th
e sig
nificance of the
event
Introd
uctio
n
Enc
losu
re 4
Technical differen
ce between CE
NG and
NRC
Staff analysis
of sa
fety significance
– Diffe
rence is in how
CEN
G and
NRC
Staff are hand
ling HU
elem
ents
• CENG PRA
yields C
CDF 5.6E
‐8
• NRC
Staff PRA
invokes R
ASP HU limit an
d yields CCD
F 1.1E
‐6
• NMP be
lieves the RA
SP doe
s not fu
lly ta
ke into accou
nt other hum
an
elem
ents of this e
vent
– Ab
sent app
lying the RA
SP guidance HE
P flo
or of 1
E‐6, th
ere is
good
agreemen
t on CC
DF between CE
NG and
NRC
Staff
Summary: NMP be
lieves, based
on othe
r risk
mitigatin
g factors, th
is event is o
f a very low sa
fety significance ‐
Green
E
nclo
sure
4
Nin
e M
ile P
oint
Uni
t 1
Loss
of S
hutd
own
Coo
ling
Reg
ulat
ory
Con
fere
nce
Sum
mar
y of
Eve
nt a
nd T
imel
ine
John
Bou
ck
Man
ager
, Ope
ratio
ns
Summary of Event
andTimeline
Enc
losu
re 4
Ap
ril 16, 201
3, U1 was sh
ut dow
n for refue
ling
Rx
in cold shutdo
wn (M
ode 4), RV he
ad installed bu
t de
tensione
d – dryw
ell dom
e he
ad is off
– RP
V he
ad is vented – 6‐inch vent p
ipe
– RP
V level is a
t the
RV flange / T
ime to boil: Ap
proxim
ately 2 hrs
– #12 SD
C pu
mp was in se
rvice
– #11 and #13 SD
C pu
mps were available bu
t breakers w
ere racked
ou
t for LO
OP/LO
CA te
sting
– Pre‐job briefin
g to prepare for racking
in breakers
– Ope
rators were standing
by locally to
rack in breakers if n
ecessary
as a plann
ed co
ntingency; th
ey were briefed with
PPE
staged
–
Workers were in th
e reactor cavity
at this tim
e
Nor
mal
RFO
con
ditio
ns
Summary of Event
andTimeline
Enc
losu
re 4
Loss of P
ower to
Battery Board (B
B) #12
14
44 (T
= ‐6
2m) to 15
45 (T
= ‐1
) – Co
ntrol board ann
unciation and iden
tification by
Ope
rators
– No eq
uipm
ent failures o
r faults
– SD
C pu
mp #12 continue
d to ru
n (verified
by Ope
rators)
– Metho
dical and
deliberate actio
ns to
restore po
wer to
BB
#12 Th
ere
wer
e no
equ
ipm
ent f
ailu
res;
SD
C in
ser
vice
Summary of Event
andTimeline
Enc
losu
re 4
Loss of Shu
tdow
n Co
oling
– 15
46 (T
= 0):
Closure of Static
Battery Charger (SBC
)‐171
A attempted
per N1‐OP‐47A, 125
VDC Po
wer Systems
• Mom
entarily en
ergized BB
#12 – bu
t immed
iately trippe
d • SD
C Pu
mp #12 trippe
d –
Orig
inal loss of D
C po
wer caused the high
suction tempe
rature re
lay to lose pow
er
– Trip
coil m
omen
tarily en
ergized whe
n BB
#12
ene
rgize
d tripping
SDC
pum
p #12
– 15
50 (T
= +4m
): Co
ntrol Roo
m Staff no
ted a change in critical
parameters:
– RB
CLC tempe
rature dropp
ed 6‐7 degrees
– 0 am
ps on SD
C pu
mp #12
• Iden
tified trip of SDC
pum
p #12 and en
tered N1‐SO
P‐6.1, Lo
ss of SDC
• Only took
4 m
inutes to
diagnose the prob
lem
Thro
ugh
cont
inuo
us re
view
of c
ritic
al p
lant
par
amet
ers,
O
pera
tors
reco
gniz
ed th
e lo
ss o
f SD
C in
4 m
inut
es
Summary of Event
andTimeline
E
nclo
sure
4
Re
covery
– 15
50 – 160
3: First steps
• Shutdo
wn safety risk re
view
ed
• Directed
racking in breakers for #11
and
#13
SDC
pum
ps
• Electrical prin
ts were review
ed and
quickly iden
tified the reason
the SD
C pu
mp
trippe
d –
1603
(T = +17
): SD
C pu
mp #11 started
(SDC
pum
p restarted in 17 min)
• Co
mmen
ced efforts to restore SD
C pe
r procedu
re
– 16
15 (T
= +29
m):
SDC pu
mp #13 started
– 16
20 (T
= +34
m): Coo
lant flow
through core re
stored
in accordance with
proced
ures ‐ total rise
in RPV
water te
mpe
rature: 30
degrees F
– 16
48 (T
= +62
m):
BB #12
pow
er from
SBC
171
A with
SDC
pum
p #12 no
w
available
– 16
56 (T
= +70
m): SO
P‐47
A.1 and SO
P‐6.1 exite
d (70 min after loss of SDC
) –
1711
: Breaker for BB #12 is closed
SD
C p
ump
rest
arte
d in
17
min
utes
Summary of Event
andTimeline
E
nclo
sure
4
Summary
– SD
C was not lost whe
n Ba
ttery Bo
ard #12 was disc
onne
cted
due
to a
HU error
– Loss of SDC
was diagnosed
in 4 m
inutes
– SD
C pu
mp was re
started in 17 minutes
– Co
olant flow th
rough core was re
stored
in 34 minutes
– There were no
equ
ipment failures o
r HU errors a
ssociated with
the loss
or re
startin
g of SDC
– Licensed
Ope
rators re
spon
ded in accordance with
standard practice,
training, procedu
res, and
pre‐establishe
d contingencies
– Ope
rators are re
gularly
traine
d on
loss of SDC
(including
simulator
scen
arios)
Pro
mpt
rest
orat
ion
of n
orm
al c
ondi
tions
E
nclo
sure
4
Nin
e M
ile P
oint
Uni
t 1
Loss
of S
hutd
own
Coo
ling
Reg
ulat
ory
Con
fere
nce
Add
ition
al R
isk
Miti
gatin
g B
arrie
rs
Jim
Vau
ghn
NM
P1 S
hift
Man
ager
PRA Co
ncep
t Overview
E
nclo
sure
4
Sh
utdo
wn
Coo
ling
RPV
Lev
el
Dia
gnos
e -
- Dia
gnos
e A
ctio
n -
And
A
nd
- Act
ion
Or
CC
DF
Lost
SD
C b
ut n
ever
lost
RP
V le
vel m
ake-
up a
nd m
anag
emen
t
Three Success P
aths
with
Red
undancy
Enc
losu
re 4
Three Success P
aths with
Significant R
edun
dancy
– #1) N
ormal M
akeu
p – #2) Ide
ntify
Loss o
f SDC
& Restore SDC
– #3) Ide
ntify
Level Drop & Restore Le
vel
Re
minde
r: Successful identification of any of the
cues associated with
any of the
success p
aths (1
‐3)
yields a su
ccessful outcome (e.g., no
core damage)
Additio
nal M
itigatio
nRisk Factors
Enc
losu
re 4
#1 – BWR shutdo
wn level con
trol
– RP
V make‐up
: Co
nden
sate/feedw
ater sy
stem
–
RPV let‐do
wn: Reactor W
ater Clean
‐up System
–
Any lowering RP
V level due
to boil‐o
ff wou
ld have be
en im
med
iately
addressed by adjustin
g make‐up
or let‐dow
n –
This Ope
rator a
ction is the prim
ary barrier o
f maintaining
core inventory
at anytim
e du
ring shutdo
wn cond
ition
s
A d
edic
ated
Rea
ctor
Ope
rato
r was
act
ivel
y m
anag
ing
RP
V
leve
l dur
ing
the
even
t – th
ere
was
nev
er a
loss
of R
PV
leve
l co
ntro
l
Mainten
ance of R
PVLevelin Co
ldShutdo
wn
E
nclo
sure
4
M
onito
r Lev
el
Rai
se
Flow
Goi
ng In
Lo
wer
Flo
w
Goi
ng O
ut
Leve
l to
o O
r lo
w?
Loss
of D
C o
r SD
C h
ad n
o im
pact
on
abili
ty to
mai
ntai
n R
PV le
vel
Three Success P
aths
with
Red
undancy
E
nclo
sure
4
Three Success P
aths with
Significant R
edun
dancy
– #1) N
ormal M
akeu
p
– #2) Ide
ntify
Loss o
f SDC & Restore SDC
– #3) Ide
ntify
Level Drop & Restore Le
vel
Re
minde
r: Successful identification of any of the
cues associated with
any of the
success p
aths (1
‐3)
yields a su
ccessful outcome (e.g., no
core damage)
Additio
nal M
itigatio
nRisk Factors
E
nclo
sure
4
#2 – Ope
rators promptly re
cognize
d an
d diagno
sed the loss of S
DC. The
re
were many op
portun
ities fo
r the
m to
recognize the even
t in the CR
Tempe
rature Indicatio
ns
– Re
actor W
ater Clean
‐up
– Re
actor B
uilding Closed
‐Loo
p Co
oling – inlet a
nd outlet
tempe
ratures
SD
C System
Ope
ratio
n –
Loss of P
ump Am
perage Indicatio
n –
Loss of SDC
Pum
p Discharge Pressure
PP
C Large Screen
Disp
lays se
t up to m
onito
r critical param
eters
(screens disp
layed prom
inen
tly with
param
eter tren
ds atop pane
ls in
CR)
DA
‐426
7, RB 34
0 Fire Alarm
– Steam
wou
ld se
t off fire respon
se on
Refuel Floor
Vide
o #1
– Sim
ulator scenario
Ope
rato
rs re
cogn
ized
loss
of S
DC
in 4
min
utes
Additio
nal M
itigatio
nRisk Factors
E
nclo
sure
4
#3 – The
re wou
ld have be
en add
ition
al obvious indicatio
ns
outside the CR
of a
loss of S
DC
– He
ad was deten
sione
d and vented
and
there were workers on the
Refueling Floo
r; steam re
lease wou
ld have be
en noticed
–
Steam re
lease wou
ld have set o
ff on
e of many area
radiation mon
itors
(poten
tially prompting an
Alert declaratio
n)
– RP
Techs in the area
were continuo
usly m
onito
ring ED
s; th
ere are always
RP Te
chs o
n the Re
fueling Floo
r during RFOs
– Outage Co
ntrol Cen
ter (OCC
) staff were mon
itorin
g activ
ities on the
Refueling Floo
r by commun
ications and
via cam
eras
– Vide
o #2
– Emergency Co
nden
ser O
peratio
ns – what d
oes 4
0,00
0 gallons
of water boil‐o
ff look
like?
A lo
ss o
f SD
C w
ould
hav
e be
en v
ery
obvi
ous
Additio
nal M
itigatio
nRisk Factors
E
nclo
sure
4
There were statem
ents in th
e Septem
ber 2
3, 2013,
letter needing
clarification:
SDC Pu
mp Hi Tem
p Staff:
Ope
rator
missed it
NMP: A
nnun
ciator is silent due
to battery loss;
there was no alarm
PPC Displays
Staff:
Ope
rator
missed it
NMP: N
ot re
levant to
ana
lysis
Bus #
12 Failure
Alarm Log
Staff:
Ope
rator
missed it
NMP: N
ot re
levant to
ana
lysis
It is
not
cre
dibl
e fo
r the
Ope
rato
rs to
mis
s th
e lo
ss o
f SD
C
Additio
nal M
itigatio
nRisk Factors
Enc
losu
re 4
Co
nclusion
s regarding recognizing an
d restoring
SDC:
– Loss of SDC
wou
ld be ob
viou
s – Actio
ns are well procedu
ralized
and
traine
d on
– De
mon
strated respon
se indicates c
rews a
re well prepared
to re
spon
d to a loss of SDC
and
take action be
fore RPV
level is e
ven challenged
– IF th
is fails, the
re are even more indicatio
ns and
contingencies to respon
d to a loss of level in a BWR
Sta
ff re
cogn
izes
acc
epta
bilit
y of
man
ual a
ctio
ns
Three Success P
aths
with
Red
undancy
Enc
losu
re 4
Three Success P
aths with
Significant R
edun
dancy
– #1) Normal M
akeu
p – #2) Identify Loss of SDC
& Restore SDC
– #3) Iden
tify Level D
rop & Restore Level
Re
minde
r: Successful identification of any of the
cue
s associated
with
any of the
success p
aths (1
‐3) yields
a successful outcome (e.g., no
core damage)
Additio
nal M
itigatio
nRisk Factors
E
nclo
sure
4
#4 – The
re were many CR
instrumen
ts available that wou
ld
have indicated a loss of level
Multip
le Level Indicatio
ns (1
3)
– ‘K’ panel Flange ‐3 to
+3 ft flange level
– Fuel Zon
e Water Level Ch. 11 and 12
‐240
‐100”
*Reg Guide
1.97]
– ‘K’ panel GEM
AC 0‐100
” –
‘E’ panel GEM
AC 0‐100”
– ‘F’ panel Ch. 11/12
Yarways 0
‐100
” *Reg Guide
1.97]
– ‘F’ panel Ch. 11/12
GEM
AC 0‐100
” –
‘F’ panel Level Chart Recorde
r 0‐100
” –
‘F’ panel Ch. 11/12
LoLoLo ‐33‐100” *R
eg Guide
1.97]
PP
C Large Screen
Disp
lays se
t up to m
onito
r critical param
eters
(screens disp
layed prom
inen
tly with
param
eter tren
ds atop pane
ls across th
e Co
ntrol Roo
m)
DA
‐426
7, RB 34
0 Fire Alarm
– Steam
wou
ld se
t off fire respon
se on
Refuel Floor
Any
sin
gle
indi
catio
n w
ould
hav
e tri
gger
ed th
e ne
cess
ary
Ope
rato
r res
pons
e
Additio
nal M
itigatio
nRisk Factors
E
nclo
sure
4
Be
low are th
e 24
separate aud
ible alarm
s associated
with
RPV
Level (all available to th
e Ope
rators during the event):
– F1
‐4‐3/F4‐4‐6 Clear (RP
S Hi Lv
l, 95
”)
– F2
‐3‐3 Clear (R
PV Hi/L
o level, 83”)
– F2
‐3‐3 Alarm
(RPV
Hi/L
o level, 65
”)
– F1
‐1‐3/F4‐1‐6 Alarm (R
PS RPV
Low
Level, 53”) *
EOP/SO
P En
try+
– F1
‐2‐1/F4‐2‐8 Alarm (R
PS Auto Trip, 53”)
– F2‐4‐2/F3‐4‐3 Alarm (A
TWS Ch
. 11/12
Troub
le, 5”)
– F1
‐2‐3/F4‐2‐6 Alarm (R
PS RPV
LoLo level, 5”) *
SOP En
try+
– F1
‐3‐2/F4‐3‐7 Alarm (V
essel Isolatio
n, 5”)
– F1
‐3‐5/F4‐3‐4 Alarm (C
ontainmen
t Isolatio
n, 5”)
– F1
‐4‐6/F4‐4‐3 Alarm (R
PS Core Spray Au
to Start, 5”)
– F1
‐4‐2/F4‐4‐7 Alarm (M
ain Steam Auto Isolation, 5”)
– F1
‐4‐4/F4‐4‐5 Alarm (EC Au
to Initiation, 5”)
– F1
‐3‐3/F4‐3‐6 Alarm (R
PS Le
vel LoLoLo, ‐1
0”)
Vide
o #3
– M
ultitud
e of CR indicatio
ns (n
ext)
Any
sin
gle
annu
ncia
tion
wou
ld h
ave
trigg
ered
the
nece
ssar
y O
pera
tor r
espo
nse
E
nclo
sure
4
0
Vide
o #
3-
Mul
titud
e of
CR
Indi
catio
ns
CE
NG
a
join
t ven
ture
of
I C
onst
olla
tlan
..•
.. e
oF
E:n
wgy
" '
Additio
nal M
itigatio
nRisk Factors
Enc
losu
re 4
#5 – Ope
rators co
uld ha
ve initiated
make‐up
with
a CRD
pum
p from
the
Control Roo
m
– This is contrary to
the Septem
ber 2
3,
2013
, letter w
hich con
clud
es field actio
ns
are requ
ired. This is on
ly true
during no
n‐
emergency, normal ope
ratio
ns.
– Ope
rator a
ctions are includ
ed in
the
proced
ure and traine
d on
in th
e sim
ulator.
– Actio
ns are straightforw
ard and regularly
traine
d on
.
Additio
nal M
itigatio
nRisk Factors
Enc
losu
re 4
#6 – The
re were a nu
mbe
r of o
ther sy
stem
s available to th
e Ope
rators fo
r RPV
coo
ling an
d make‐up
–
Eleven
(11) sy
stem
s were available with
varying
make‐up
capacity
in excess
of an estim
ated
65 gpm boil‐o
ff rate
– Loss of B
B#12
restricted 5 of th
e system
s for 68 min after loss of SDC
–
Ope
rators are traine
d on
all 11
system
s in a variety of sim
ulated
accident
scen
arios, includ
ing loss of SDC
events
– Ope
rators are traine
d to use th
ese system
s in accordance with
clear, w
ell‐
written proced
ures
– NRC
Staff’s Inspectio
n Manual Part 9
900: Te
chnical G
uidance (see
C‐4)
recognize
s manual actions are accep
table in place of autom
atic sy
stem
s with
written proced
ures and
training
on those proced
ures beforeh
and
Any
sin
gle
mak
e-up
sys
tem
wou
ld h
ave
prov
ided
suc
cess
Additio
nal M
itigatio
nRisk Factors
Enc
losu
re 4
#7 – Core Spray (w
ith autom
atic initiation) was re
stored
to
availability 8.5 ho
urs into even
t –
Could have been restored
with
in 15 minutes – since SD
C had be
en
restored
, restoratio
n of Core Spray was in
accordance with
pre‐
planning
–
Core Spray re
stored
prio
r to the 9‐ho
ur projected
RPV
level reaching
top of active fuel
– Ha
d the Ope
rators fa
iled to ta
ke action to re
store SD
C or diagnose and
manually in
ject, C
ore Spray wou
ld have injected
autom
atically prio
r to
uncoverin
g fuel based
on the tim
eline of th
e even
t –
Not re
cognize
d in Sep
tembe
r 23, 201
3, letter
Had
NM
P re
cogn
ized
Cor
e S
pray
sys
tem
ava
ilabi
lity
and
com
mun
icat
ed th
is e
arlie
r to
NR
C S
taff,
a P
hase
3 a
naly
sis
may
not
hav
e be
en n
eede
d
Additio
nal M
itigatio
nRisk Factors
Enc
losu
re 4
#8 – The
re were many licen
sed Ope
rators in
the plan
t at the
time
of th
e even
t –
In add
ition
to th
e licen
sed staff (2 RO
s & 3 SRO
s), the
re were 5 SROs/4
ROs/2 additio
nal licen
sed managers in and in close proximity
to th
e CR
du
ring this even
t –
It is typical for add
ition
al licensed
personn
el to
be in th
e plant d
uring
outages
– Clarificatio
n to th
e Septem
ber 2
3, 201
3, letter: There is recognize
d value
of th
e extra licen
sed pe
rson
nel
• NURE
G/CR‐12
78 (Sectio
n 18
) credits fo
ur licensed
CR pe
rson
nel as the
minim
um group
to add
ress events
• NURE
G/CR‐12
78 (Sectio
n 19
) recognizes the
value
of add
ition
al
licen
sed pe
rson
nel for re
covery actions
Add
ition
al s
taffi
ng is
not
cre
dite
d in
PR
A a
naly
sis
Additio
nal M
itigatio
nRisk Factors
Enc
losu
re 4
– NRC
Staff agrees th
at th
ere may be adde
d worth to
add
ition
al
person
nel, bu
t ‘the analyst kno
ws o
f no othe
r guidance on
whe
n, how
, or if to cred
it additio
nal personn
el’.
Conclusion
: Thu
s, th
is conservative choice in th
e analysis will
inflate th
e risk associated
with
the even
t. With
a 1.1E‐6
prob
ability, m
ore realistic mod
eling if available wou
ld likely
drive the nu
mbe
r to less th
an th
e 1E
‐6 th
reshold for a
white
finding.
Add
ition
al fa
ctor
s w
ould
tend
to d
rive
PR
A a
naly
sis
resu
lts
even
low
er.
E
nclo
sure
4
Nin
e M
ile P
oint
Uni
t 1
Loss
of S
hutd
own
Coo
ling
R
egul
ator
y C
onfe
renc
e P
RA
Ana
lysi
s of
Eve
nt
Ellio
tt Fl
ick
Gen
eral
Man
ager
, Fle
et E
ngin
eerin
g
PRA An
alysis of Event
Enc
losu
re 4
Summary View
on PR
A:
– Either of two inde
pend
ent o
perator actions wou
ld prevent co
re
damage (restore SDC
and
maintain RP
V level)
– CE
NG and
NRC
Staff evaluatio
ns determined
no ‘dep
ende
ncy’
existed
for the
ope
rator a
ctions
– CE
NG and
NRC
Staff qu
antitative evaluatio
n of th
e individu
al
operator actions closely agree
– Re
sults diverge based
on NRC
assigning
a m
inim
um HEP
value
for the
two combine
d inde
pend
ent a
ctions:
• CE
NG:
EPRI / TH
ERP *
• NRC
Staff:
SPAR
‐H; R
ASP Vo
lume 1, Rev 2 (N
RC Staff Guidance)
*Referen
ce: Techn
ique
for H
uman
Error Rate Predictio
n (THER
P) is a te
chniqu
e used
in th
e fie
ld of H
uman
Re
liability Assessment (HR
A), for th
e pu
rposes of e
valuating the prob
ability of a
hum
an error occurrin
g througho
ut th
e completion of a sp
ecific task.
PRA An
alysis of Event
Enc
losu
re 4
Event w
as evaluated
usin
g standard PRA
techniqu
es
and principles
Mitigatio
n of th
is event req
uired Ope
rators to
eith
er:
– Re
store SD
C, or
– Maintain RP
V above top of active fuel
Initial plant con
ditio
ns (app
roximate):
– 2 ho
urs to bo
iling
in RPV
– 5 ho
urs low
‐low Level in RPV
– 9 ho
urs for inventory to re
ach top of active fuel
9 ho
urs
wer
e av
aila
ble
to ta
ke a
ctio
ns.
PRA An
alysis of Event
E
nclo
sure
4
Bo
th CEN
G and
NRC
Staff analysis agreed
: zero de
pend
ency
associated
with
the tw
o actio
ns
De
pend
ency factors con
sidered
: –
Same Crew
: a sh
ift tu
rnover wou
ld have occurred
prio
r to a projected
boil‐off to top of active fuel;
– Co
mmon
Cognitive: a variety of cue
s and
procedu
res a
pplied
– Same Time: cue
s occur over a
lengthy tim
e fram
e (hou
rs)
– Ad
equate Resou
rces: Extra personn
el alm
ost d
ouble the no
rmal
control roo
m com
plem
ent
– High
Stress: we classified this as a nom
inal stress event
– Same Locatio
n: strong
cue
s from both control roo
m and
refuel floo
r –
Timing: su
bstantial tim
e was available to act
Agr
eem
ent o
n ze
ro d
epen
denc
y - d
iffer
ence
s be
twee
n N
RC
S
taff
& C
EN
G a
naly
sis
of h
uman
per
form
ance
fact
ors.
PRA An
alysis of Event
E
nclo
sure
4
The RA
SP handb
ook references EPR
I Rep
ort 1
021081
Establish
ing Minim
um Accep
table Values for
Prob
abilitie
s of H
uman
Failure Events, for the
se type
of evaluations. From RAS
P hand
book:
– “EPR
I Rep
ort 1
0210
81 provide
s a m
ore de
tailed approach in
de
term
ining the level of d
epen
dence be
tween HF
Es and
app
lying
minim
um joint p
robabilities. Based
on the de
term
ination of th
e level
of dep
ende
nce, an analyst w
ill assign a joint H
EP of 1
0‐5 (lo
w
depe
nden
ce) o
r 10‐6 (very low dep
ende
nce). In ad
ditio
n, th
e repo
rt
states th
at, ―
if the crite
ria fo
r ind
epen
dent HFEs are met, it sho
uld
not b
e ne
cessary to employ
an alternative minim
um value
rather
than
the on
e calculated
.”
Min
imum
HE
P s
houl
d no
t alw
ays
be a
pplie
d.
PRA An
alysis of Event
Enc
losu
re 4
CE
NG and
NRC
Staff agree:
– Risk Calculatio
n (w
/o th
e RA
SP guidance 1E
‐6 quantificatio
n lim
it) is at least 5.6E‐8
Alignm
ent o
f SDC an
d RP
V injection
NRC
CCD
P CENG CCD
P
No Joint H
EP quantita
tive lim
it 6.1E
‐8
5.6E
‐8
Joint H
EP quantita
tive lim
it 1E
‐7
1.4E
‐7
1.6E
‐7
Joint H
EP quantita
tive lim
it 5E
‐7
5.4E
‐7
5.6E
‐7
Joint H
EP quantita
tive lim
it 1E
‐6 (u
sing RA
SP Handb
ook
guidance)
1.1E
‐6
1.1E
‐6
NR
C S
taff
& C
EN
G c
alcu
latio
ns a
re c
lose
.
PRA An
alysis of Event
Enc
losu
re 4
RA
SP guidance assig
ning
a 1E‐6 lim
it for m
ultip
le HFEs
– Co
mpe
nsates fo
r lim
itatio
ns in ability for e
xisting PR
A metho
ds
to evaluate the HE
P for h
ighly reliable actio
ns
– Ho
wever, 1E‐6 has n
o firm te
chnical basis
– Ap
plying
the lim
it do
es not disc
riminate be
tween cases w
here
there are many versus a single su
ccess p
ath
– Ap
plying
1E‐6 may not significantly affe
ct base CD
F/LERF
– 1E
‐6 was cho
sen as not to
dom
inate the risk results
App
lyin
g th
e m
inim
um H
EP
has
val
ue in
man
y ca
ses;
ho
wev
er it
is n
ot a
pplic
able
to th
is c
ase.
PRA An
alysis of Event
Enc
losu
re 4
Ap
plying
1E‐6 lim
it is inapprop
riate in th
is case
– Given
the pletho
ra of cue
s, it is inconceivable that th
e op
erators w
ould not have the correct p
lant status assessm
ent
– No mechanism
(cognitive or physic
al) can
be po
stulated
that
wou
ld re
sult in a failure to
respon
d in th
e tim
e available
– 1E
‐6 has no firm te
chnical basis
– 1E
‐6 is so
con
servative that it driv
es th
e ou
tcom
e of th
e SD
P
App
lyin
g th
e m
inim
um H
EP
sig
nific
antly
dis
torts
real
ity a
nd
is in
appr
opria
te in
this
cas
e.
Conservatisms O
verstate
Risk & Dilute
Insig
hts
Enc
losu
re 4
+
Inaccurate Characterisa
tion of Risk
=
1E‐6 Quantita
tive lim
it conservatism
Overw
helm
ing indicatio
ns on Re
fuel floo
r and in th
e Co
ntrol Roo
m Con
servatism
+ CR
Staffing, Stress, Training
Co
nservatism
+ Multip
le indicatio
n and success p
ath
conservatism
+ La
yers
of
Crew
Turn‐over
Conservatism
Con
serv
atis
m
PRA An
alysis of Event
E
nclo
sure
4
HR
A mod
eling of actions with
very low probabilities is
challenging and the resulting
HEPs a
re very un
certain
Qualitative factors m
ust a
lso be considered
to give an
accurate assessm
ent o
f risk
De
fense in Dep
th / Co
nservative PR
A techniqu
es distort
risk pe
rspe
ctive
Risk‐in
form
ed decision
‐making must recognize th
e lim
itatio
ns of q
uantifying very re
liable, inde
pend
ent
human
actions
Ass
essi
ng p
lant
per
form
ance
sho
uld
reco
gniz
e qu
alita
tive
risk
miti
gatin
g fa
ctor
s an
d in
depe
nden
ce in
this
cas
e.
PRA An
alysis – LERF
Analysis
E
nclo
sure
4
Large Early
Release Frequ
ency (LER
F) ana
lysis
projects m
argin to pub
lic risk
– The NRC
Staff evaluatio
n assumes a large release occurs <2
hours a
fter RPV
level low
ers to the top of active fuel
– Co
mpu
ter m
odeling (M
AAP) co
nclude
s no appreciable
release be
fore 4.6 hou
rs
– CE
NG and
NRC
Staff agree that a Gen
eral Emergency
evacuatio
n could be
effe
ctively completed
in 2 hou
rs (less
than
half the
time be
fore a projected
early re
lease pe
r MAA
P pred
ictio
ns)
Ther
e w
as a
long
er ti
me
to p
roje
cted
rele
ase.
PRA An
alysis – Evacuatio
nStud
y
Enc
losu
re 4
Risk to
the pu
blic was very low; study
show
ed
evacua
tion could be
effe
ctively completed
with
in 1 hr
40 m
inutes
– Co
mmissione
d an
evacuation tim
e estim
ate analysis using
actual con
ditio
ns at the tim
e a Gen
eral Emergency wou
ld
be declared
– Used guidance in
NURE
G/CR‐7002, Criteria for E
vacuation
Time Estim
ate Stud
ies
Ther
e w
as ti
me
to e
vacu
ate
the
publ
ic.
E
nclo
sure
4
Nin
e M
ile P
oint
Uni
t 1
Loss
of S
hutd
own
Coo
ling
Reg
ulat
ory
Con
fere
nce
Less
ons
Lear
ned
and
Con
clus
ions
Jim
Sta
nley
G
ener
al P
lant
Man
ager
Conclusio
ns
E
nclo
sure
4
We are extractin
g all the
learnings from th
e event
– An
y un
planne
d loss of SDC
is significant and
doe
s not
meet o
ur expectatio
ns
– Taken Actio
ns – re
spon
ded rapidly and thorou
ghly
• Fixed proced
ure prob
lems to prevent recurrence
• Re
structured
NMP2
’s ou
tage sc
hedu
le (LOOP/LO
CA te
sting)
– Managing actio
ns with
in our corrective actio
n program
We have co
mmun
icated
new
data and
inform
ation to sh
ow why th
e indu
stry
metho
dology fo
r assessin
g hu
man
perform
ance
applied by NMP shou
ld be used
to evaluate the
significance of e
vent;
Conclusio
ns
E
nclo
sure
4
We be
lieve th
e CE
NG PRA
analysis
for N
MP1
is so
und
– CE
NG PRA
yields C
CDF 5.6E
‐8 fo
r this e
vent
– An
alysis based on
accep
ted indu
stry m
etho
dology
– Includ
es con
servatism
/provide
s a m
ore realistic picture of risk
– Po
tential hum
an errors a
re und
erstoo
d and mod
eled
– Ad
ditio
nal risk
mitigatin
g barriers
– Staff guidance (Part 9
900): accep
table to credit m
anual actions
– An
autom
atically initiated
system
(CS) was re
stored
prio
r to the
projected tim
e of 9 hou
rs (R
PV level to top of active fuel)
– Ope
rators never lost awaren
ess a
nd con
trol of R
PV level
Summary: NMP be
lieves, based
on ou
r analysis
and
other
risk mitigatin
g factors, th
is event is o
f a very low sa
fety
significance ‐ Green
Que
stions and
Closin
g Re
marks
E
nclo
sure
4