ML20100R510
| ML20100R510 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 04/03/1992 |
| From: | Beck G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9204160038 | |
| Download: ML20100R510 (13) | |
Text
.
PIIILADELPIIIA ELECTRIC COMPANY NUCLEAR GROUP HEADQUARTERS 955-65 CHESTERBROOK BLVD.
WAYNE, PA 19087-5691 (215) 640-6000 NUCLEAR ENGINEERING & $CRVICES DEfARTMENT April 3, 1992 Docket No. 50-352 License No. NPF-39 U.S.
Nuclear Regulatory Commission Attn: Document Contro'. Desk Washington, DC 20556
Subject:
Limerick Generating Station, Unit 1 N2H Recirculation Riser Nozzle to Safe End Weld Application of Mechanical Stress Improvement Process Gentlemen:
This letter is being submitted to request NRC approval for tne application of the Mechanical Stress Improvement Process (MSIP) to the N2H recirculation riser nozzle to safe end weld at Limerick Generating Station (LGS), Unit 1.
We are requesting NRC approval since the dimensions of the N2H nozzle to safe end weld indication exceed the MSIP applicability limitations specified in NUREG-0313, " Technical Report on Material Selection and Process Guidelines for BWR Coolant Pressurc Boundary Piping," Revision 2.
Our evaluation concerning the use of the MSIP was based on the guidance specified in NRC Generic Letter (GL) 88-01, "NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping," and GL 88-01, Supplement 1.
Subsequent inspections of the N2H nozzle to safe end weld region will continue to be performed in accordance with the LGS Technical-Specifications.
In our letter dated March 12, 1992, we indicated that we.would select one (1) of four-(4) corrective action alternatives for the N2H nozzle to safe end weld indication during the fourth LGS Unit 1 refueling outage which began on March 21, 1992.
The alternative selected would be based on the ultrasonic testing (UT) examination results of the N2H nozzle to safe end weld performed during this refueling outage.
The results of the UT examination performed during the fourth' refueling outage, indicated no appreciable crack growth since the last inspection.
Therefore, we are requesting to apply the MSIP to the N2H nozzle to safe end weld.
Following application of the MSIP, Crack Advance Verification System (CAVS) monitoring of'this weldment will be discontinued since the residual stress field in the N2H nozzle to safe end weld would no longer correspond to that in the CAVS specimen.
I 9204160038 920403 PDR ADOCK 05000352 y
l P
PDR q
1 1
U.S. Nuclear Regulatory Commission April 3, 1992 Document-Control Desk Page 2
,e v
.8 Post-MSIP application UT examinations will be performed on the N2H nozzle to safe end weld.
The results will be provided to the NRC.
The attachment to this letter provides our evaluation of the present condition of the indication and justification for proceeding with application of the MSIP to the N2H nozzle to safe end weld.
If you have any questions or require additiona) information, please do not hesitate to contact us.
Very truly yours, JG G. J.
Beck Manager Licensing Section Attachment cc:
T.
T. Martin, Administrator, USNRC, Region I (w/ attachment)
T. J. Kenny, USNRC Senior Resident Inspector, LGS (w/ attachment) 4
e t
Attachment INFORMATION SUPPORTING APPLICATION OF MECHANICAL STRESS IMPROVEMENT PROCESS FOR N2H RECIRCUIATION NOZZLE TO SAFE END WELD INDICATION Introduction During the second Limerick Generating Station (LGS) Unit 1 refueling outage in 1989, inservice inspections were performed on austenitic stainless steel piping welds.
These inspections revealed an indication in the N2H recirculation riser nozzle to safe end weld (see Figures 1 and 2).
This indication exhibited the characteristics of intergranular stress corrosion cracking (IGSCC).
This particular nozzle is 12 inches in diameter, and is a recirculation loop reactor vessel inlet.
In our letters dated April 3, 1989 and October 23, 1990, we provided detailed evaluations concerning the N2H nozzle to safe end weld indication.
In addition, Philadelphia Electric Company provided proposals and justifications for operating Unit 1 during the third and fourth operating cycles with the N2H nozzle to safe end weld in the "as-found" condition.
The. basis for justification was the use of an on-line crack growth monitoring system (i.e., Crack Advance Verification System (CAVS)) and the establishment of specific l
corrective action steps should the CAVS specimen crack growth exceed pre-established values.
These values were based on structural integrity margins.
The NRC approved Unit 1 operation with the N2H nozzle-to safe end weld in the "as-found" condition for third and fourth operating cycles by letters dated May.2, 1989 and November 20, 1990, respectively.
The CAVS specimen crack growth did not reach any of the pre-established corrective action step values during cycle 3 operation.
In addition, ultrasonic testing (UT) examinations performed during the third refueling outage on the N2H nozzle to safe end weld showed a small change in the existing indication.
The information provided in the following discuscion details our evaluation of the N2H nozzle to safe end weld indication and our justification for proceeding with the application of the Mechanical Stress Improvement Process (MSIP) to the N2H nozzle to safe end weld.
Deccription cf 1992 Inspection Results of N2H Nozzle to Safe End Weld-As dcccribed below, the UT examination of the N2H nozzle to safe end weld performed during the fourth Unit i refueling outage, which began on March 21, 1992, was similar to the inspections performed during the previous refueling in 1999 and 1990.
The UT examinations performed during the 1939 and 1990 refueling outages,-were conducted by General Electric (GE) Company using the " Smart UT" system.
The UT Attachment examinations performed during the fourth-refueling outage were.again conducted by GE; however, a more sophisticated automatic " Smart 2000 UT" system was used.- The " Smart 2000 UT" system isibased on. digital technology, whilc the " Smart UT" system was: based:on: analog technology.
The following similarities regarding the application of-these two (2) systems for examination of the N2H nozzle to safe end weld are described as follows, o
Identical Electric Power Research Institute (EPRI) qualified inspection procedures were used.
o The same type and desigialof 45 degree and 60 degrae refracted longitudinal (RL) wave transducers were used, o
Similar calibration and scan sensitivities were used for both the 45 degree and 60 degree RL examinations.
Similar scan parameters were used.
o Furthermore, the manual verification Ond-sizing techniques used duplicated those performed during the 1989 and 1990 refueling outages as described below.
Identical-EPRI qualified procedures.
o The same 60 degree RL wave transducer was used.
j o
i The same high angle,-70 degree RL wave examination was o
performed.
The same EPRI-type sizing blocks-were=used.
o Additionally,_the same EPRI qualified: Level III GELindividual-was
-involved in evaluating the results.of-the-UT examinations forcallithree (3) refueling outages.
As discussed in our October 23, 1990oletter, the presence or; absence of loose " crud" on the nozzle annulus could affect the UT baseline noise level.
To minimize'any differences.between the:last examination and the one performed during.the current 11992 refueling outage, the nozzle annulus was.hydrolazed-priorJto the examination.:
This also reduced personnel radiation exposure duringEthe examination process.
Figure 3 depicts the results of-the-'1992!UT examination 'as compared-to the 1990 UT examination results.
The 19921results show a.O.411nch extension in the circumferential length with a 0.48 inch deep; cusp at' 38.5. inches.
Minor changes were also noted in depths;of the'previously identified cusps, the maximum of.which was'an' increase.of 0.03 cinches.
The' minor changes in the-indication length 1andfcusp depths are within.
.-.i..
Attachment the tolerances for the UT examinations.
It is likley that new cusp at 38.5 inches was present during the 1990 UT examination; however, this cusp was not detected at the time.
The basis for this conclusion is that known IGSCC crack studies have shown IGSCC crack morphologier to be very typical of the pattern depicted in the 3992 examination results.
Therefore, when the two (2) plots arc evaluated in their entirety, there appears to be no appreciable change to tne N2H nozzle to safe end weld indication from that measured in 1990 to the present results.
CAVS Results and Reactor Water Chemistry The cumulative crack growth for the Alloy 182 CAVS specimen for the fourth cycle of Unit 1 operation was 0.036 inches.
Considering the possible degree of error in both the CAVS and UT measurments, the CAVS results are comparable to those reported by the current UT examination.
With the application of the MSIP, CAVS monitoring will be discontinued since the residual stress field in the N2H nozzle to enfe end we]d would no longer correspond to that in the CAVS specimen.
As depicted in Figure 4, reactor water chemistry for the fourth Unit 1 operating cycle was maintained within the EPRI guidelines (i.e.,
conductivity < 0.2 uS).
We will continue to strive to maintain reactor water chemistry within the EPRI guidelines and continue with implementation of the Condensate / Filter Demineralizer Optimization Program at LGS.
Deep bed condensate filter /demineralizers have been installed to enhance the Optimization program and are expected to be operational during the next operating cycle currently scheduled to begin on June 5, 1992.
MSIP Apolication Assessment and Flaw Evaluation for the N2H Nozzle to Safe End Weld The MSIP is a stress improvement process acknowledged by the NRC as indicated in NUREG-0313, " Technical. Report on Material Selection and Process Guidelines for BWR Coolant Pressure Boundary Piping," Revision 2.
Application of the MSIP replaces the tensile "as-welded" residual stresses in the inside surface of the weldment with a zone of compressive residual stresses.
Prior NRC approval is required before we can proceed with application of the MSIF to the N2H nozzle to safe end weld since the dimensions of the measured indication exceed applicability limitations specified in NUREG-0313.
If the NRC approves this request, we plan on proceeding with the application of the MSIP to arrest crack growth and to prevent further damage due to IGSCC.
An inelastic finite element analysis was performed to verify that the extent of the compressive stress zone, as well as the magnitude of the compressive stresses generated by the application of the MSIP, will be large enough to arrest crack growth even when operating loads are superimposed on the nozzle to safe end weldment. __
m.
Attachment An axisymmetric finite element:model'of the nozzle toisafe end weld was generated and the ANSYS finite element! code was used for performing the-inelastic analysis..The analysis included simulation of the "as-welded" residual stresses,.followed by application ~of MSIP and normal operating loads, to obtain the state of stress in-the weldment during operation.. The-normal operating; loads-applied to_thecmodel.
Included internal pressure,_ piping loads-(i.e., deadweight and_ thermal expansion) and steady-state _ temperature.
The' stress distribution (i.e., post-MSIP application.plus operating loads)-through the pipe wall at the indication-location obtained from this analysis is illustrated in Figure'5...The anal'jais, as 1 illustrated by this figure, shows that the compressive stress none extends to approximately 53% of the wall thickness, which is well beyond thel depth ofLthe; indication.
Therefore,-following application of:theTMSIP to the N2H nozzle-to safe end weld,_any;further crack growth:will be arrested.
A flaw evaluation to verify theistability of'the crack was also performed.
The flaw-evaluation was based on the American Society of Mechanical Engineers *ASME)iCode,Section XI, IWB-3642iwhich'related to 3
the net pipe section collapse criterion. 'A failure assessment _. diagram which defines the combination ofJcrack depth =and. length at-which pipe collapse occurs was developed 1for the applied stress levels during.
operation and:used to assess the safety margins lto: failure.- AllJ primary loads including : seismic. loads were considered in this evaluation.
The-resulting. failure' analysis' diagram is'provided in Figure 6.
The curves. depicted in this figure.were obtained'by-using safety factors of-3.0 for normal operating conditions land l'.5 for emergency and faulted conditions in accordance with IWB-3642.
The current NUREG-0313 criteria for stressoimprovement of~ cracked welds and the compressive stress 1 zone generated'by. application.of the_MSIP have-also been plottediir. this figure.
In addition, an assessmentLof1the effecteoffthejapplication'of.the MSIP on the_ piping system was? performed based onnthe' guidance specified-
~
in Paragraph 5.of Supplement l to.NRC Generic Letter (GL)_'88-01, "NRC-i Position on:Intergranular Stress Corrosion Cracking'(IGSCC)iin.BWR Austenitic Stainless-Steel Piping." -Application ~ofLthe MSIP does r cause any shrinkage of the piping: system; innfact, it results=in an.
L elongation.
Furthermore, this_changefin axialElength.is an order of e
magnitude smaller than axial shrinkage _due to' weld overlay and.is' nondetectable'under field conditions-at the piping supports.-
Typically,.the elongation is approximately 10l mils, and therefore,~ will' not adversely impact the piping _or supports.
l L
-AMitional Testina A UT ' examination will be performed following the. application of the MSIP,-prior to startup-from the refueling-outage.
The results of this examination will beiused as the baseline for future examinations of'the N2H nozzle to-safe-end weld area.
.The post-MSIP UT results willibe forwarded to the'NRC.as part of the LGS Unit 1 post outage Inservice Inspection (ISI) report.
~4-
,.u.
_. _, _ a._,w
-Attachment Future examinations of the N2H nozzle to safe end weld will be performed in accordance with the requirements of the LGS Technical Specifications Section 4.0.5 and the guidance specified-in GL 88-01 and NUREG-0313.
The application of the MSIP will result in recategorizing this weld, as specified in the guidance of GL 88-01, from Category F to Category E.
If no further indications are encountered following application of the MSIP, this weld will be scheduled for reinspection at the next Unit 1 refueling outage, and subsequent inspections performed every two (2) refueling outages, thereafter.
Conclusion The results of the flaw evaluation verified that the N2H nozzle to safe end weld indication will remain within an acceptable region of the compressive stress zone produced by the application of the MSIP.
This condition meets the safety margins specified in IWB-3642 as well as the allowable depth to wall thickness requirements of the ASME Code.
1.
'4 e
d,.
dw n..
k-
~
i s
, u...
(<.,
g I=
4 4 7
.wa M
E E
o, t,
m 1
3 q a ss G-~
y//
g a.u~
,.y i
3,.
/
i.?
1:
- M" :
1
=,.
0 ) ) h NN N
E fo 5
N -: -: n: 55 e
n u-laa -
w w
w
= a a
- sP
=
s G q q q 6
t' a -
d-m a
5 a
r ir n
r a
u !B re n
es.
e-
-o
=s 2
a z
a g
E wg 8
g* -
.9 g
-8w w
n a
m ww e ;a -
g x =e x
m U
6E S
,P e's.
se-o a
mw=
w w s-C: s-
--w-w w
ra s.
am
=.
e.
e
=, " e gar I..
m
=
- e. e e
.o
.-m
~
o
=
a a se e,s.R v,,i.
a
.m g
e w
=
0
{
<ed a
x M
Md Gag s
,s a
ww
.mm i
=
A
=Eh o"o r.
4 7
5a6
[4 l.
C 5:d f=
d
~s<p u
--~~
hd 3
-k
$$$a em /
[/a
=
/l w,_ "
q
- $M e *dd 4s
~<=
s w
3=
.M e
zg
.4
~
no<
e
=an s
b.
N h, '
'A fk h
a E=
- r..-
g
~
S=
/
w o
l'
.g
%y
~
=$
e g RE
- ,l " -
/
<t
.J m
.3-
+
c.
n o
8 =-
g d
ha.
N-
'4 dyh lsa N
N N
-s wnn w,_
e-we-g,$1 k
kW9-G m;- /
_=
g w
me
~ ~ < -
\\s m
.h g7d
=
- -. a..
N g
d
,_d A
w i
w a
- ;ja w G C 5
\\
- t.
a m,
- g--
. \\
9
~
.m
=
5 Msg
~
44.==
t.': a!
/
W:.
== --
--n gm*
Nig_
h-N$ $$.
Gf En
=.
=;;;;
= u!
e
/
==...
-a
/
=%ng*
c we e6 c
V 11MAA DW g
UE e
Aff3ff' s
OS "i. E a
= E 7 7.5 7 7.
2 =
- ffeff
=.
w M M., M M
.3 a==0 =
l 3
g t"
- T r
v+,
+-
..?
7N."."*'M
- y Py ey pT 'T 9 -
3
-a,..
- 1;
- l qr 4l
/
i
~
1\\
/
l l
/
/
508 Class 2 l
(
)[
/
316 L Stainless -Steel
[
j s.s.nciad 1
l
~ g\\'
~
~
- l L
ll 1989 UT Indication
(
Heat Treate'd)
- EE Alloy 182; Weld Butter; Non-a
,j EllE ' Alloy 82 Weld- (Non-Heat Treated)
M. Original Alloy 182 Butt. Weld (Non-Heat Treated)
'T y
L inc'onel 600 (Non-Heat Treated)
I' y.
182 Weld Butter (Heat-Treated Twice)
/
i-d_._ Original Alloy Fr,gure.
2.
4
.__m
~---
l REPORT NO.
SITE' I J HElzu" V-tr"'r I'-
INDICATION PLOT SHEET GENuclear Energy enosecr no: w *er.
SYSTEM: Eeac:rcs?.Ecocc.outT1mf COMPONENT ID NO: WE.4ED-I A-fltd CONFIGURATION: "h E+1D brttE
~..
.199o DAYA..
.s.
1...
........i....
..s..
.a.
...~...
- 4. c.y.............. ;.. e
.q....
....o...
.-l.. - -l
. zs :
.4 z.,....~..............
-.l
...l.
czs
.....l..
. zs **,.. -... 4
....a o......:. 1. _,........
3
..r..i........,...,........
.,....3..,.
.zs
.................. 4..............
1.
1
.l
.+
.t.
s
......,....... >.............. v........
.....i........a.....
u
...........b.,
........... _.................... ~....
........1..:..
- tes a c* rA....................
..........m...
.... :.... m.
.s
,..... :. m..........p.
..q...;...
a..
%.. 3.......
{,
. :...g.3..q...s4 o.... g.. y. 3.-
.... q..:.:...<......
4...-.
...........i............
'.r...,c..:...<......u...........>..<............t...>.4....i....:.....,.
....o.....
..>. a.. q........:....:....
o.
g. A.6.
4
.u..
.....s.
.45
.g g.
.zs..
.... i......gj.
. 3... [.
.. zs...
l
,[.
..:.. q
.m,,
.....,.........z..
....i.
....g o.
g
. 1 :.....:.
..g.,........
.g..
. [..
....._.l..
.,.. l..
..l :......
.i
..... -..... m a
. A..,
....: o....
.q...g.
,.. 4
- 4..
A
..=
o..:....:..
.e
..:... v. a... ;.
. o..
..4....
2
.. :.:. 4...;..... p..>..:...;.
- a................
f-f
.s l
31 9Z--
~01 Page
~
.w
'IC 5-3c-k e r wU Drawn Dy /
Level Date Review
~I evel Date Reviewed ny Tie:e Date ronw tar s.n.no Figure 3
, - - g_
~. -
m,,
i Limerick Generating Station ny) 0.6-
.v."r -
u.
A I
i
......................g.................b............................................... a.....................
x c
o,4 _
o A
l RA I
u.
b E
ha s
-- --- -- --------- ------------- ----- ------------- a 3
o.2-
A----
6
(
c:
0.0 i
y I
\\
l t_
7 "gq-10 0 -
m g-
"r
~ ~ " " " " " " " " " " " " " - '
l'.
"-"""""""-~-
- '"-~
' ~ ~ ~ ~ ~
O 75-O_
" - - - - - " - - " " " - - - - - - - ~ ~
M SO-
~-
e
.+.'".
2541..........................
T i
C g
-. - - ~ ~... ~...- - -....... ~ J.... -.~. -.. ~.- -.-.. - - -..........
D o-
.,.......,........,....................,................ c.......
J F
M A
M J
J A
S O
N D
J F
l 1991 1992 Figure 4 d
.g Post-MSIP + Operating Load Stresses GO g'
I l '.
we-l y TENSION
-j,
=l 1
=
ae - -
g.
,i
.l
,r' LEGEND' i 'e' e-j F.E.M.'Sg Stress L M
I.
y COMPRESSION
,e r
-ae.,
N Peig. FALLed Sg
,s' s
g
~%
,/
-40 i
i.
e.e
-e.a e.4 e.s e.a 1.e
/
'lJALL ' FRACTION ' FROM THE I.D.
1 AXIAL iSTRESS DISTRIBUTION THROUGH THE N'IZZLE WALL AT THE CRACK LOCATION -
- FOLLOWING MSIP WITH THE OPERATING LOAD 5 INCLUDED-(THE-SOLID LINE IS THE
-flNITE ELEMENT MODEL RESULT lAND THE DASHED LINE IS THE POLYNOMIAL' FIT).
w m.,
Figure'5
_,a
___y
FAILURE ANALYSIS DIAGRAM (SMAW)*
1.0 I
O. 8 --
3p, 1,5 b
0.s-
_ _ _ _A_S.M_E C _ ODE _LI _MIT _ _ _ _ _ _ _ _ __ _ w_ _
SF = 3.0
..________.......h__...____________.......
- 15 0.4-a MSIP COMPRESSIVE ZONE O
1992. INDICATION
\\
RESULTS' Y-h"'0.2 CURRENT g
.'0313s '
CRITERIA 00 F
i i
i O.0 0.2 0. 44 0.6 9.8 1.0.
NON-DIMENSIONAL CRACK LENGTH-(L/PI*D)
FAILURE ANALYSIS DIAGPAM Figure 6
- - Shielded Metal' Arc Weld 4
.