ML20199B012
| ML20199B012 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 01/21/1998 |
| From: | Reid D VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BVY-98-08, BVY-98-8, TAC-M99802, NUDOCS 9801280157 | |
| Download: ML20199B012 (13) | |
Text
_
VERMONT YANKEE NUCLEAR POWER CORPORATION 185 Old Ferry Road, Brattleboro, VT 05301 7002 (802) 257-5271 January 21,1998 BVY 98-08
\\ J U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555
References:
(a)
Letter, USNRC to VYNPC, Request for Additional Information Regarding the Emergency Diesel Generator Skid Mounted Piping - Vermont Yankee Nuclear Power Station (TAC NO. M99802), dated November 20,1997 (b)
Letter, VYNPC to USNRC, VY Response to Request for Additional Information Regarding the Emergency Diesel Generator Skid Mounted Piping, BVY 97-172, dated December 19,1997
Subject:
Vermont Yankee Nuclear Power Station License No. DPR-28 (Docket No. 50-271)
VY Response to Request for AdditionalInformation Regarding the Emergency Diesel Generator Skid Mounted Piping, Question 3 (TAC NO M99802)
Reference (a) requested additional information about the operability determination completed by 7
the Vermont Yankee Nuclear Power Corporation (VYNPC) on the subject piping. Reference (b) 9 responded to the request and provided answers to all but question 3. The response to that question required summarizing information from previous submittals into a single response. The descriptions in this response are our best attem'>t to describe in words information contained in pictures.
Attachment (1) provides responses to question 3 contained in reference (a). Should there be any questions please call Gautam Sen at 802-258-4111.
Sincerely, VERMONT YANKEE NUCIIAR POWER CORPORA 110N N
$ 1 $0h h b 271 p
PDR Donald A. Reid Senior Vice President, Operations cc:
USNRC Region 1 Administrator USNRC Resident inspector - VYNPS I 4" t y
' u t
n l
,k,((, of
,i, ' '
USNRC Project Manager - VYNPS Vennont Department of Public Service
_2
VERMONT YANKEE NUCLEAR POWER CODPORATION Docket No. 50 271 January,2,1,1998 fage1of12-
- q TABLE OF CONTENTS 1
RAI 3 Response Table 1 - Compiled RAI 3) Responses Figure 1 - Layout of Lube Oil Piping Figure 2 - Standardized Identification of Weld Joint Sections Figure 3 - Typical Overlay Weld Joint Configuration Figure 4 - Typical method Used to Determine Effective Weld Joint Penetration Figure 5 - Dctail of weld Joint Number 2 i
Figure 6 - Detail of Weld Joint Number 3 -
Figure 7a - Detail of Weld Joint Number 8 Figure 7b - Expanded View of Crack Location for Weld Joint Number 8 i,
VERMONT YANKEE NUCLEAR POWER CORPORATION Docket No. 50. :51 J,anuary,2.1,199a Page 2 of12 Response to RAI 3 RAI 3) Provide a sketch with dimensions specified for each weldjoint where cracks were found; and also label each sketch to show: (a) type of components, (b) seal weld, (c) overlay weld, (d) slags that initiate the crack, (e) location of shrinkage crack and fatigue crack, (f) length (OD and ID) and depth of crack, (g) repair weld, and (h) location of the crack that was weld repaired.
VYNPC Response - YAEC memorandum PSD 303/97 dated October 9,1997 discusses the results of metallurgical examinations on the sectioned lube oil piping removed from the "B" Diesel. The memorandum identifies that there were found to be one (1) through wall crack in weld joint number 2, one (1) small root crack in weld joint number 3, and two (2) small root fissures in weld joint number 8. The memorandum discusses in detail the through wall crack, the small root crack, and one of the two root fissures. Based on further discussion with the author of the memorandum, the following conclusions are made relative to these two small root fissures in weld joint number 8: (a) the discussion within the memorandum is applicable to, and bounds, both defects, (b) they are both characterized as stable micro fissures that developed during the original vendor fabrication process, and (c) neither fissure is attributed to fatigue effects, or indicates any presence of fatigue growth. The RAI 3) response that follows will address the three (3) defects discussed in memorandum PSD 303/97 for which available information exists.
Figure 1 depicts the layout of the lube oil piping and indicates the weld joint designations.
Figure 2 illustrates the sectioning identification used for each weld joint. The orientation for this figure is looking down the piping run from the filter towards the engine. For example, concerning weldjoint number 2, the 270 degree azimuth is representative of a segment at the inside radius or " crotch" of the elbow.
All welded joint " scal" welds are comprised of partial penetration welds. Subsequent weld passes, or " overlay" welds were placed directly over and to the side of each seal weld and consist of double crowned weld beads. A typical overlay weld joint is shown in Figure 3. The methodology used to determine the effective penetration depth at each joint is shown in Figure 4.
The measurement was made by extending an imaginary line across the outer surface of the joint's adjacent two components and measuring from this baseline to the effective root of the joint.
These measured values are not reproduced herein but are available in materials previously sent; refer to Attachment D, pages 2 and 3, of calculation VYC-1695. Detailed information as to the size (i.e., depth or thickness) of the overlay welds has not been obtained as the evaluations performed in VYC-1695 conservatively ignored any contribution of strength that they provide.
Note that the mechanical testing summarized in VYC-1695 demonstrates that considerable joint strength is achieved b, the weld overlay feature.
VERMONT YANKEE NUCLEAR POWER CORPORATION Docket No. 50-271 January,21,1998 51 age 3 of12 All defects reported and discussed in memorandum PSD 303/97 emanate from slag pockets resulting from the original fabrication process by the supplier, Fairbanks Morse. All slag pockets are located on the inner diameter of the joined components at the effective root of the partial penetration seal weld.
Shrinkage cracks are attributed to each of the three (3) defects. The shrinkage cracks emanate off of a slag pocket in each case and are likely to have initiated as a result of high residual weld stresses during cooldown. An additional contributor is likely to be the poor geometry resultant ofjoint fitup and preparation. The only fatigue striations associated with the cracks were found in weldjoint numbers 2 and 3. The small micro fissures found in weldjoint number 8 were characterized solely as shrinkage with no evidence of fatigue.
The circumferential length of each of the cracks can be found in the enclosed Table 1 using information reproduced from memorandum PSD 303/97. The through wall crack identified in weld joint number 2 was identified using flourescent liquid penetrant examination applied to the outer surface of the joint and represents the outer diameter (OD) length. No attempt to measure the length of this crack ca the inner diameter (ID) of the section was pursued. However, as was demonstrated in the linear clastic fracture mechanics (LEFM) evaluation performed in our initial RAI response letter, BVY 97-172, a through wall crack on the order of 4.0 inches in length remains structurally stable assuming the total wall thickness is on the order of 0.2 inches. No other surface cracks were identified as a result of performing the flourescent liquid penetrant examination on the remaining sections. The cracks found in weldjoint numbers 3 and 8 were very small embedded cracks which were not associated with the OD of the sections. These cracks, emanating from the ID at the weld root were detennined to be of finite length as shown in Table 1.
There have been no weld repairs performed on anyjoints with defects as discussed above. At the present time, the lube oil piping sections between the engine and filter for both the "A" and "B" Diesels have been replaced in their entirety with new piping which conform to the requirements of ANSI B31.1. All section butt welds used full penetration details and were performed by qualified VYNPC personnel using approved procedures.
Relative to item RAI 3)(h) above, the only weid repair performed on lube oil piping associated with either diesel generator is that which was previously reported in our initial letter, BVY 97-172 [ refer to VYNPC Response to RAI 4)]. The location of this leak was in weld joint number 2 in the vicinity of the 270 degree azimuth (refer to Figures 1 and 2 enclosed) adjacent to where the thrcq h wall crack discussed above was found.
VERMONT YANKEE NUCLEAR POWER CORPORATION Docket No. 50-271 January,21,1998 i' age 4 of12 TABLE 1 Compiled RAI 3) Responses Weld
_(a)
(b)
(c)
(d)
(e)
(f)
(g)
Joint Component Type Seal Overlay Slag Location Location of Length OD/ID Repair l
No.
Weld Weld Shrinkage and (inches) -
Weld i
Fatigue Crack 2
Straight Tube-to-Partial Double Root of Partial Across OD<5/8 N/A 45 deg. Elbow Pen.
Crown Pen. Weld (270)225 ID Not i
and (180)225 Available L
Figure 5 l
3 45 deg. Elbow.
Partial Double Root of Partial (270)315
<3/8 N/A to-Straight Tube Pen.
Crown Pen. Weld Figure 6 OD/ID is N/A 8
Straight Tube-to-Partial Double Root of Partial
-(180)l35 0.045 N/A Straight Tube Pen.
Crown Pen. Weld Figure 7 OD/ID is N/A Notes: [each column in Table 1 corresponds to the " letter" designation of the RAI 3) question, as applicable)
- 1) RAI3)(a) - Component Types are as shown in the layout of Figure 1 enclosed; also refer to Attachment D, page 1 of VYC-1695 previously submitted.
- 2) RAI 3)(b)- All seal welds are partial penetration. Figure 4 enclosed provides an example of
. how penetration depth was measured; also refer to Attachment D, page 2 and 3 of VYC-1695 previously submitted for additional information related to measured depths.
- 3) RAI 3)(c) - Typical overlay configuration is shown in Figure 3 enclosed.
- 4) RAI 3)(c)- Refer to Figure 2 enclosed for crack location. Location is determined as follows:
number in parenthesis denotes the sectioned segment in terms of an azimuth and remaining number denotes face. For example, the crack in weld joint number 3 is located at the 180 degree segment on the 135 degree face.
- 5) RAI 3)(f)- As discussed above, the OD crack for the through wall defect in weldjoint number 2 is as tabulated; the ID crack is not available. The information tabulated for weld joint numbers 3 and 8 provide the length of the very small embedded cracks identified and is not associated with the OD or ID.
VERMO'NT Y ANKEE NUCLEAR POWER CORPORATION Docket No. 50-271 J,anuary,21,1998 l' age 5 of 12 l
CONNBCHON TO NN l
MAN VfE1V
'f (ao scale)
\\
"I I
O I
10NLDR LAYOUT OF LUBE OIL PIPING FIGURE 1
VERMONT Y ANKEE NUCLEAR POWER CORPOR ATION Docket No. 50-271 J.anuary,21,1998 Page 6 of 12 O'
<< s.
4 l
90' 270 l
l 4
4L,
- g*
180' STANDARDIZED IDENTIFICATION OF WELD JOINT SECTIONS FIGURE 2
__J
VERMOMT Y ANKBE NUCLEAR POWER CORPORATION Docket No. 50-271 January,21,1998 Page 7 of 12 5.T' r-Y.
. 4,, ',).
A_ '
4
.'A.
s i
\\
x.
4 3:s 9
4 Y$ff'L:
l y
- - u )il ;;
- r y!
.,..a r s,
.r
+
f Q
A' g
ya yt
-?
A c,; g._.
?
,n TYPICAL WELD JOINT CONFIGURATION (NOTE OVERLAY)
FIGURE 3
VERMONT Y ANKEE NUCLEAR POWER CORPORATION Docket No. 50 271 January,21,1998 Page 8 of 12 hj?ti H
p ?gQUp.fas.n,. s h-QQ g?'33QkMh?
wy.
ce:. cll;
-(.
5 j
.. a,n. A. s
- + 4t TYPICAL METHOD USED TO DETERMINE EFFECTIVE WELD JOINT PENETRATION FIGURE 4
VERMONT Y ANKEE NUCLEAR POWER CORPORATION l
l i
Docket No. 50-271 J,anuary,21,1998 Page 9 of12 TOUCil-UP WELD ORIGINAL WELD c.,
%.Q.;
bQ FATlGUE
=
bh$
.. %e e
- gy 13 wfi
.%Ws
.,. 5)N y
., R SHRINK CRACK w.
(-0.060")
jA, y spg r e r '
- m..,o,j, 7 y~U.,m,3
,g ;t; ;,.
s m9 a
y:
n,s.
.., vag l
'W f '5};,p
- 3;-Q ~'l TAin ;*r Eps: ;..
E, aJs
'i g:,ti,
- g s
re m; 1i' J
m....
- 4 ',(yg(e M;;&m
. ],
qw y.
.p, - ['
' ' 1. '
1
-g!
n;E
~,
a SLAG POCKET N:
~
-,-N:(;v..,fis
- 3;s c n
,2
,. ; t a. *n
.,e.,
$5:
l
.6nf((j ;_'; h ' ":
"((;%l?f^RB&
$34pg{t;di:h.g.
4.5" M T ff! = f d k(
ELBOW
,W ya w.;-%
1 Figure 5 l
l Detail of weld Joint Number 2
VERMONT Y ANKEB NUCLEAR POWER CORPORATION Docket No. 50 271 J})anuary,21,1998 age 10 of 12 m,,,,, gn -,,,e
.c
,,,4 i<
+
i
?
-* i.
s f[_
- o
?
p
- l'
'(
e
. v; g.
0
%j:
v e-i; t
+
s
\\
- g
- .
~
=*
p, s.... 4.,,
g-i
)
,y
^l 11.
q SHRINK CRACK T
(-0.057")
A-
~
=Y SLAG POCKET
.f.
.l 1,
Figure 6 Detail of Weld Joint Number 3
VERMONT YANKun NUCLEAR POWER CORPORATION l
Docket No. 50-271 January,21,1998 l' age 11 of 12 m,,,
,, _,q 1..
- dd.kOd u.s
- r. f;;1p.
xr y'
Figure 7a Detail of Weld Joint Number 8
VERMONT Y ANKEE NUCLEAR POWER CORPORATION Docket No. 50-271
/anuaq21,1998 Page 12 of12 l-SHRINKAGE CRACK l
(~.009")'
l V
'K t
l SLAG POCKET i'
t;-
4 i.
Figure 7b Expanded View of Crack Location for Weld Joint Number 8
__