ML19320D295
| ML19320D295 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 07/01/1980 |
| From: | Crouse R TOLEDO EDISON CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| 1-147, IEB-79-02, IEB-79-2, NUDOCS 8007210216 | |
| Download: ML19320D295 (5) | |
Text
'4 776 e
a AI 4
+
TOLEDO EDISON Docket No. 50-346 Rcsano P CAJU5E License No. NPF-3
$217'""
141912 % *221 Serial No. 1-147 July 1, 1980 Mr. James G. Keppler Regional Director, Region III Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137
Dear Mr. Keppler:
IE Bulletin No. 79-02, dated March 8, 1979, and subsequent supplements and revisions, requested that we review and verify the pipe support base plate designs using concrete expansion anchor bolts for the Davis-Besse Nuclear Power Station Unit No. 1.
Attached is the current status of our work related to IE Bulletin No. 79-02.
All modifications to nonaccessible supports will be completed by the end of the current refueling outage as required by Supplement No. I to IE Bulletin No. 79-02, dated August 20, 1979. We have clso addressed the concerns of Mr. I. T. Yin, of your staff, raised in OI&E Inspection raports Nos. 50-346/79-24 and 50-346/79-33 concerning the adequacy of tne torque values, lubricated vs. nonlubricated, for wedge-type anchor bolts.
This closes out all outstanding items on IE Bulletin 79-02 except for the accessible base plate flexibility analysis for which the current status is attached. This effort will be completed by November 1, 1980.
Yours very truly, ff a : ^ '
db e/3 RPC:CLM cc:
United States Nuclear Regulatory Commission Office of Inspection and Enforcement Division of Reactor Operations Inspection Washington, D.C.
20555 THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO. OHlO 43652 8007210 2.16 UUL 7 1880
Dock 2t Ns. 50-346 License No. NPF-3 5 Sarial No. 1-147 July 1, 1980 A REPORT ON PIPE SUPPORT BASE PLATE DESIGNS USING CONCRETE EXPANSION ANCHOR BOLTS Response to NRC IE Bulletin 79-02 Davis-Besse Nuclear Power Station Unit 1 I.
Introduction All licensees for nuclear power plants were required to evaluate the design practices cnd installation procedures used for concrete expansion anchors and pipe support base plates in accordance with NRC IE Bulletin 79-02, dated March 8,1979 and subsequent cupplements and revisions.
This report is to be considered in conjunction with our original response of July 6,1979 (Serial No.1-78) and the additional response of December 7,1979 (Serial No.1-108).
It presents a current status of the base plate flexibility analysis and of the field
_ mod.' fications which have resulted from this review.
All terms, names, organizations cnd references previously defined remain unchanged.
As required by Supplement 1 to Revision 1 of the Bulletin, all pipe supports, located in normally inaccessible areas and having a factor of safety less than original design factors of safety, have been redesigned and will be repaired prior to start-up of the unit.
II.
Base Plate Flexibility Analysis A.
' Engineering Status Our previous responses to the Bulletin provide a description of the analytical 1
' techniques used to evaluate the effect of base plate flexibility on anchor bolt loads. Currently, this analysis is complete on 90% of the total number of pipe supports within the scope of the Bulletin.
This percentage includes 100%
of the supports located in the normally inaccessible areas. The remaining 10% are all located within normally accessible areas and are being analyzed as revised loads are generated by IE Bulletin 79-14 reanalyses.
B.
Status of Field Repair As a result of the flexibility analysis described above, all pipe supports having an anchor bolt factor of safety less than the design value will be redesigned and subsequently repaired to correct these conditions. Revised designs for all pipe supports located within the normally inaccessible areas have been issued and the modifications will be completed prior to starting up from the current refueling outage. After restart of the unit the only remaining supports requiring modification will be located in the normally accessible areas.
Redesign of these supports will be issued by November 1,1980, and all necessary field repairs will be complete by February 1,1981.
l L
i i
4,* -
', III.
Inspection / Testing Program A.
General g
In response to Item 4(c) of OI&E Inspection Report No. 50-346/79-33, a supplemental inspection was developed to verify the existance of lubricant for all wedg's-type anchor bolts without torque / lubricant certification. A statis-tical sampling plan was initiated, but when the preliminary findings could not conclusively substantiate the use of thread lubricant during installation of those anchor bolts without certification, and when acceptable anchor bolts were being damaged during disassembly, it as decided to terminate the sampling inspection and inspect / test 100% f those bolts located within the normally inaccessible areas and which did not previously have torque /
lubricant certification.
This inspection / testing program is independent of our April-June 1979 inspection ef fort and the conclusion previously stated remains unchanged (i.e., "there exists a greater than 95% confidence level of there having been installed not more than f
5% defective anchor bolts").
B.
Normally Inaccessible Areas 1.
The inspection / testing program proceeded in the following manner. One sample bolt per base plate, selected by the field engineer, was disassembled by backing the nut of f far enough to ascertain previous lubrication.
a) If the sample anchor bolt was previously lubricated, the lubricant specified in the original installation specification was applied to the threads and the nut-washer interface.
The nut was then reinstalled and tightened to the lubricated torque preload as specified in the inspection procedure PDP-1.
All other anchor bolts on the same plate were then torqued to the same lubricated torque preload as the sample bolt.
b) If the sample anchor bolt was not previously lubricated, no lubricant was applied to the threads or the nut-washer interface.
The nut was reinstalled to the unlubricated torque preload specified in procedure PDP-1.
All other bolts on the same plate were then loaded to the same unlubricated torque preload as the sample bolt.
c) If lubrication or the lack of 1.ubrication was obvious by the ease or dif ficulty of torquing on an anchor bolt other than the selected sample bolt, the bolt was tested in accordance with either the lubricated or unlubricated bolt torque value as applicable.
2.
Since high radiation and physical limitations prevented a complete 100%
inspection of all anchor bolts in normally inaccessible areas, a statistical evaluation of the findings was prepared.
The method of parameter estimation described in our previous responses was used to evaluate the results.
By this method an upper confidence limit on the number of defects (D) in the total population (N) is constructed.
The acceptance criteria is a 95% confidence level that there are 5% or fewer defective anchor bolts in the total population. The total population was defined as all anchor bolts on those pipe supports for Q-listed
piping systems 2 1/2" and larger which are within inaccessible areas, and without torque / lubrication certification.
The actual sample size was 70.4% of the total population.
Randomness of the sample was governed by the reasonable accessibility of the anchor bolt.
Limits on accessibility were access restrictions due to high radiation levels or limited physical accessibility.
All nonconformances that were noted during the above inspection were documented on Toledo Edison Nonconformance Reports (NCR's) and forwarded to Bechtel Power !arporation for resolution. Engineering evaluation was performed for eas nonconforming condition and those anchor bolts which would not meet t1 factors of safety previously stated in the response to action item 2 (Serial No. 1-108) were considered " failures".
These items will be corrected during the current refueling outage.
All the original documentation for the testing program, including system identification; location; method of test; type of anchor bolt; test results; date of test; and signatures of reviewing engineer and Quality Control inspector, are maintained by Toledo Edison. The results of the inspection are listed below. Definition of symbols and terms are described in our previous responses.
Population (N) 416 Sample size (n) 293 Defective bolts (x) 9
, Statistical Inference:
CX=.01324 100% (1 -CX) = 98.67%
In conclusion, there is a 98.67% confidence in finding 5% or fewer defective anchor bolts in the total population described above.
C.
Normally Accessible Areas Based upon the results stated above for the recent inspection / testing program in the normally inaccessible areas, which reinforce the earlier findings presented in our December 7, 1979 report, there exists sufficient evidence to conclude that the anchor bolts in the normally accessible areas are accept-able as installed.
IV. Summary The base plate flexibility analysis effort for pipe supports located within the normally inaccessible areas is complete. All redesigns necessary to bring the installations within the design factors af safety have been issued and field repair will be coupleted during the current reiueling outage. The analysis and redesign effort for those p*.pe supports located within the normally accessible areas is l
currently in progress. Scheduled dates of completion are November 1, 1980 for l
issue of all necessary redesigns and February 1,1981 for implementation of all field repairs.
7
4
.In response to OI&E Inspection Report No. 50-346/79-33, the inspection / testing program
~
on anchor bolts located in the inaccessible areas without torque / lubricant certification obtained results upon which a high degree of confidence has been established that the installation of anchor bolts in the accessible as well as the inaccessible areas are acceptable.
e
.no i
~~~
- ~~
wn
..,..