ML19339C042
| ML19339C042 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 06/19/1980 |
| From: | Schnell D UNION ELECTRIC CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| Shared Package | |
| ML19339C036 | List: |
| References | |
| ULNRC-361, NUDOCS 8011170221 | |
| Download: ML19339C042 (7) | |
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UNION ELCCTRIC COMPANY 890s CRATBOT STRC CT - ST LOUIS June 19,-1980 an a s t e ne c a c o n C S S'
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$1 Loue s, eso. ess e s Mr. James G. Keppler, Director gg i {
Region III Office of Inspection & Enforcement U. S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137 ULNRC 361
Dear Mr. Keppler:
NRC QUESTIONS ON UE EMBED REPORT ADDITIONAL INFORMATION CALLAWAY PLANT In response to requests by NRC Region III representatives at a meeting at your offices on May 29, 1980 for additional input on the subject report we are submitting herewith one copy of the
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following information.
1.
BLUE-700, dated June 12, 1980, including all attachments.
2.
Daniel International Corp. Telecon Record Sheet, dated May 29, 1980, Acceptance Criteria Used for Inspection of Undercut Welds, including attachments.
3.
Daniel International Corp. Quality Control Procedure QCP-507, Rev. 5, Inspection'of Struc'tural and Misc.
Safety Related Welding.
In reference to our investigation to determine the exact number of embeds involved in the subject report, we are in the process of determining this count and expect to be completed in the first part of July.
Very truly yours,
.h.,
c M.
Donald F.
Schnell Manager - Nuclear Engineering DBS/sla cc:
E. Gallagher w/a c.,.
JUN 2 31980
'8013 y 7 0 221 -
SOLVING PROBLEMS THROUGH INVENTION & INNOVATION
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Bechtel Power Corporation I
Engineers-Constructors 15740 Shady Grove Road Gaithersburg. Maryland 20760 301-258 3000
. D. F. Schnell Manager - Nuclear Engineering Union Electric Company Post Office Box 149 JUN i 21980 St. Louis, Missouri 63166 BLUE-7 O O File: 0499.4/C-131 Bechtel Job Number 10884-001 SNUPPS Project Investigation of Welded Studs -
Additional Information Ref: 1. ULNRC 238 dated 3/10/78
- 2. ULNRC 349 dated 4/24/80
- 3. ULNRC 354 dated 5/23/80
- 4. AIF Program Report on Reactor Licensing and Safety, Vol. 2, No. 1, May, 1975 Encl: A. Cives Steel Company letter SL:367 dated June 10, 1980 B. Bechtel Surveillance Inspection Reports for Assignment 10466-C-131 Report Nos. 2, 3, 7, and 45 C. Sample Calculation for Manually Welded Plate Assemblies (EP 312)
D. Sample Calculation for Machine Welded Plate Assemblies (EP 512) -
Reduced Capacity Due to a Postulated Ineffective Stud E. DIC Memo -
Subject:
UE Inquiries -
Stud Welding
Dear Mr. Schnell:
This letter provides additional input reque.:ted by NRC Region III representatives at a meeting in their office on May 29, 1980. Specifically, this information includes:
1.
Documentation of the fabricator's stud welding practices for machine welded embed plates prior to June 9,1977.
RECElVED JUN 191980 D.F.SCHNELL
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t Bechtel Power Corporation Mr. D. F. Schnell 2
2 A sample calculation, including discussion of approach, for establishing the reduced capacity of machine welded plates due to a postulated loss of one weld. stud. Embed Plate EP 512A is used as a basis for this Miscussion.
3.
A sample calculation, including discussion of approach, to determine the reduced capacity of manually welded embed plates tspecifically embed plate EP 312) resulting from a postulated 1/16 and 1/8 inch undersize weld, as well as the analytical basis for accepting a 1/16 inch undercut on the shank of the anchor rod.
The following additional information is also offered as an aid to the NRC personnel in their' evaluation of the welded studs:
4 The effect of a maximum 1/32 inch undercut on the shank of manually welded machine weld studs.
5.
A discussion of the logic employed in the probability analysis for machine welded utuds.
Item I In' response to Item 1 above, the practice employed by the machine welded embed plate supplier for installation and inspection of machine welded studs prior to June 9, 1977 is su=marized in Enclosure A.
Enclosure B Provides examples of Bechtel inspection reports which indicate the review of welded studs (and stud bending) by the Bechtel inspector during the period in question.
Items 2 and 3 Sample calculations for the embed plates discussed in Items 2 and 3 above are included in Enclosures D and C respectively.
Item 4 Although the vast majority of machine welded stude are installed auto-matically with special " guns" under controlled conditions, there are a limited number of occasions where the studs may have either been installed or repaired by manual fillet welding.
As indicated by field Personnel in Enclosure E, such field welding was on a very limited basis.
UE has indicated. that the field practice in inspecting these limited number of studs for undercut was to use a 1/32 inch acceptance criterion on the shank of the stud in lieu of the more restrictive requirements of.01 inches as specified in AWS Dl.1-75 Para. 3.6.4 The result is that some reduction in the safety margins could occur on these isolated studs. However, in the unlikely case m
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Bechtel Power Corporation Mr. D. F. Schnell 3
that a maximm 1/32 inch undercut is postulated to extend around the entire perimeter of a stud, the revised stud capacity, as computed using the mininum specified yield strength, still would exceed the i
design requiremants.
Design drawings have been revised to clarify the design intent.
Item 5 The probability analysis for plates with machine welded studs presented in Reference 1 was prepared to evaluate the pott,ttial for failure of plates installed in concrete prior to the reinspection effort.
In order to establish this probability the analysis accounts for several f actors; the probability of a stud being ineffective (P1), the probability of a plate (which is assumed to have an ineffective stud) supporting a safety related attachment (P2), the probability of a load on a plate being of sufficient magnitude and at a location relative to an assumed failed stud to exceed the failure capacity of the plate (P ) and the probability of the plate to ever experience the attachment 3
design load (P ).
None of these factors in itself is representative of 4
plate failure. Rather the resultant probability against a single plate failure is the product of these factors, or:
P = [(Pt*P2
- P ',3 = P" 3 - P "'3
- P4)
J i
The factor (P ) is established from the reinspection data of 81,673 1
studs which were installed and shop inspected in the same manner as those studs on the plates in question. One could express the results of this reinspection in terms of a " Confidence Level" in a fashion similar to that employed by the NRC in IE Bulletin 79-02. This bulletin requires licensees to review concrete expansion anchors which serve essentially the same function as the embed plates in question. The acceptance criterion established in this bulletin was to have a 957.
confidence level that less than 57 defects exist. Using the formu-lations included in the bulletin (which are based on a 957. confidence level) and the reinspection results, less than 0.17. defects are idencified. Many of the plates support attachments which are not safety related. Although these plates share an equal probability of having ineffective studs there is no safety consequence. Plates retrieved from the laydown area prior' to June 9,1977 would have been taken from the same stock whether used for a safety related or non-safety related function. The f actor (P2) accounts for those plates which have safety related attachments.
The -factor (P ) addresses the effect the attachment load and its l
3 location have on a given plate, assuming the plate has an ineffective stud on or adjacent to the attachment location. Actual loads resulting from the attachment for each plate were determined.
In order to include the possibility.that the attachment may be at any location on the plate, the load was applied in each of 9 zones shown in Sketch la of the report (Reference 1). It is assumed the load has an equal possibility of being in any one of nine zones, hence P"3 = 1/9 This is a conserva-l tive assumption in that the load will normally be applied in the center l
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Bechtel Power Corporation 4
Mr. D. F. Schnell
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In f act a drawing revision since the report was prepared of the plate.
requires that the centroid of the attaching weld be within the middle third of.the plate. These applied loads were compared to the f ailure load in each zone of each plate aqsuming'the stud in zone I to be If the actual load exceeded the failure load a postu-ineffective.
laced failure was identified. The failure load is identified for each i
of these zones if any of the stresses reach the W-m specified For computational purposes the ineffective stud was yield stress.
assumed to occur in zone I.
A finite number of postulated failures were identified for zones I, II, III and VI as shown in the report (P'3).
Since the ineffective stud has an equal chance of occurring in any one of the four studs within a cluster the chance of it being in zone I is Conversely, zones IV, VII and IX have as equal chance one in four.
as zone I of having the load applied over a postulated ineffective Combining the random possibility of an ineffective stud at a stud.
given corner with the possibility that one of four corner zones could have a load over a postulated ineffective stud yield.s a f actor of 1/4 i
A similar argument holds for loads applied in X 4/1 = 1 (P"'3).
Since a one in nine chance was assumed for the load to other zones.
be applied in a given zone, it is necessary to sum the result for all since no potential failures were identified for nine zones..In fact, zones IV, V, VII, VIII and IX (P"n3 = 0) the actual. summation includes l
indicates only the proba-only zones I, II, III and VI. Note that P3 bili ~ty of a plate f ailure for a postulated ineffective stud adjacent to the load point whichis asafety related attachment with the computed attachment load applied.
in itself is meaningless for it is cocnputed on the i
The factor P3 premise that every attachment is on or adjacent to an ineffective stud.
Furthermore, it is based on applying each attachment load in each of l
Realizing the nine zones to deliberately seek postulated failures.
that plates with safety related attachments have a combined total of approximately 2,500 studs, the reinspection results would suggest that 1
Of course only approximately two studs could be postulated to fail.
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these two studs may be located in areas of the place not affected by the attachment loads. The point is that one cannot isolate one f actor Rather, the independent of others in the probability analysis.
probability of a plate failure must consider all factcrs in concert.
An equally important consideration is the possibility of the plate
~ As one example, a significant ever experiencing the design load.
contribution to the losds imposed on the plate is dee to the seismic j
Dr. News. ark, in Reference 4 suggests that in combining the event.
safety margins u ted-to identify the seismic event and the multipli-of safety resulting from the critaria and analytical cation of margino methods imposed, a probability that the structure will ever experience the design loads may be in the order of 10-8 A probability of 10-4 was conservatively assumed in the report for this consideration.
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Bechtel Power Corporation
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Mr. D. F. Schnell 5
In sununary the probability of a plate failere is the product o'f the probability of having an ineffective stud, the probability of the plate with an assumed ineffective stud supporting a safety related Ioad, the probability of that load exceeding the plate capacity due to an assumed adjacent ineffective stud, and the probability of the attachment load actually occurring.
As provided in Reference 1, a total of 10 plates had multiple stud failures. Multiple stud failures on a given plate have no additional-effect on the probability analysis unless they occur on adjacent studs.
Four occurrences of adjacent stud failures can be identified from the i
data. No case exists where more than two studs failed within a stud cluster (the basis for design being a four stud cluster).
An analysis has not been conducted to evaluate the probability effect if a two adjacent stud failure were considered. Based on some simple comparisons we believe it is evident that this consideration will not substantially affect the results. The probability computation 03r a two stud failure is similar to that given above for a single stud i
failure, except that rather than considering the probability of a failed stud to the total number of studs inspected (P1) one must compare it to the total number of stud clusters available. Based on a total of 81,673 studs, at least 81,673/4 = 20,418 stud clusters exist.
Actually there are somewhat more than this number of stud clusters i
available since plates with more than 4 studs have studs that can be in more than one stud cluster. However, a similar equal increase in the number of cluster possibilities for the pair of ineffective studs also exists so that the effect is essentially self-cancelling. The 1~
or less than 1/4 the value result is that P1 becomas' 4
=
20,418 5,104 for the single stud failure.
An increase in the probability of P3 will occur. Although the cricu-lations have not been generated to establish magnitude of this increase firmly we believe it to be in the neighborhood of a factor of 2 to 4 All other factors remain essentially the same as for a one stud failure.
The net result is that the probability for plate failure due to a postulated multiple stud failure is of the same magnitude (exponent wise) as for a one stud failure i.e., the increase in P3 is approximately offset by the decrease in P.
l Since the probability for a one stud failure and a two stud f ailure are i
additive, the overall probability may at worst double. However the i
order of magnitude (exponent wise) remains essentially the 'same as presented in Reference 1 Ve truly yours, c.
EWT:bg Project gineerl.ng Manager cc:
N. A. Petrick i
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8 CHURCH STREET. GOVVERNEUR. NC YORK 13642 (315) 237 2200 TWE 510-257-6951 f
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June 10, 1980 SL: 367 Bechtel Power Corporation P.O. Box 607 Gaithersburg, MD 20760 Attention: Mr. Paul Divj ak
Reference:
SNUPPS Proj ect 10466-C-131 Miscellaneous Metals Centlemen:
In regard to Purchase Order Item No. 2 embedded plates with concrete anchors, we ' -ehy verify that Cives intent since the beginning of the pre n of these plates has been to
'ain a 360' fillet on the. chine welded studs.
If the appli. stud did not have 360*, the stud was either a) bend tested per AWS 4.30.1, or b) repaired per AWS 4.29.3, or c) replaced.
Very truly yours, CIVES STEEL COMPANY Northern Dixision L
/s _
Ted Totten Project Manager TT:sw CC: Dean W.
Parshley
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