IR 05000245/1980002
| ML20002A561 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/16/1980 |
| From: | Chaudhary S, Albert Lee, Sanders F, Lester Tripp, Varela A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | |
| Shared Package | |
| ML20002A548 | List: |
| References | |
| 50-245-80-02, NUDOCS 8011200134 | |
| Download: ML20002A561 (22) | |
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U. S. NUCLEAR REGULATORY COMMfSS10N O
OFFICE OF INSPECTION AND ENFORCEMENT
REGION I
Report No.
50-245/80-02 Docket No.
50-245 License No.
OPR-21 Priority Category C
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Licensee:
Northeast Nuclear Eneroy Comoany P.O. Box 270
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Hartford, Ct.
06101 Facility Name:
Millstone Nuclear Enercy Station, Unit 1 Investigation At:
Corcorate Offices, Berlin, Ct. ; Plant Site, Waterford, Ct.
Investigation Conducted:
January 2-4, 1980; January 9-11, 1980; January 29-31,
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15i80 Feoruary 13-15, 1980; February 20-22 1980 Investigators: N//,J,n';eeV
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.1/Is /so S. X. Chauchary, Reactor Inspector
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W. F. Saricers, Reactor Inspector
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,_&&a/mv dgha y A. A. Varela, Reactor Inspector date hsCm M
NI6 l80 h A. J. Lee Senior Mechanical Engineer cate b
4thO M/bb L. E. Tr1ptf, Chief. ES Section 41 cate RC&E. Branch (Exit interview only)
Approved by: <.I.
ANd
/hh L. E. Tr1tm, Chief, Engineer 1ng Support date Section 11, RC&ES Branch
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I_nvest'gation Sumary:
Areas Investigated: Special announced investigation conducted by three regional based investigators of Isolation Condenser System piping, pipe support, and dry-well con-crete for their ability to withstand loads imposed by seismic, bicwdcwn, or water-hamer event. The investigators rwiewed stress reports of piping and pipe supports,
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witnessed tests and NDE examination of the piping and supports, visually examined
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cracked concrete, interviewed engineering and technical persennel, and conducted a
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technical evaluation of data and other information presented by the licensee to determine the structural adequacy of this system.
The investigation involved 174 investigator hours by three regional based investigators, 34 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br /> by a NRP. engi-neer and 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> by a regional based sectica chief at the licensee's corporate offices, the licensee's contractor's offices and the plant site.
Results: One item of nonccmpliance was identified.
(Infraction - failure to promptly identify, evaluate, and document a nonconfor nance.)
Region I Form 167 (August 1979)-
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SUMMARY OF FINDINGS
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A.
Allegations and Invc<tigation Findings The NRC representatives-investigated the allegations conveyed to the regional office via telephone on December 21, 1979, and January 8,1980.
The allega-tions and a summary of NRC. findings on each are as folicws:
1.
Allegation No. 1.1 The Isolation Condenser System is not capable of withstanding seismic, blowdown, and water-hammer loads because of loose anchor bolts in pipe supports.
The NRC investigation found that the licensee was aware of the loose anchor bolts, and had taken actions to repair these bolts.
However, the documentation of the inspection and the repairs was not in compli-ance with the requirements of 10 CFR 50, Appendix 8.
2.
Allegation No. 1.2 a
The Isolation Condenser System is not capable of withstanding seismic, blowoown, and water-hammer loads, because of high stresses in piping, pipe supports, and nozzles.
The NRC investigation found no information or evidence to indicate that there was any overstressing in the Isolation Condenser System.
3.
Allegation No. 1.3 The Isolation Condenser System is not capable of withstanding seismic, blowdown, and water-hammer loads because of concrete cracking in the drywell wall at penetration' X-10A.
The NRC investigators determined that the licensee was aware of the cracking of concrete in the-drywell wall in the sicinity o/ penetra-tion X-10A.
However, the investigators determined tnat t:.4 licensee's i
inspection and evaluation of these cracks after the water-hammer event were not adequate.
The basis of licensee's determination of the charac-teristic and the potential safety significance of the cracks was erro-i neously based on an earlier inadequate inspection and evaluation.
This was not in compliance with the requirement of 10 CFR 50, Appendix B.
4.
Allegation No. 1.4
.The Isolation Condenser System is not capable.of withstanding seismic, blowdown, and water-hammer loads because of damage to welds in piping and ancnor X-10A due to water-hammer.
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The NRC '..vestigators found no infor. nation or evidence to indicate that there was any damage in any piping or anchor welds in the Iso-lation Condenser System.
5.
Allegation No. 2
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Northeast Utilities Ser/ ice Comoany (NUSCO) has known these conditions for some time through an in-house stress analysis and inspection.
They, however, have failed to correct the deficiency and alleviate the unsafe condition.
No infonnation or evidence was found by the NRC investigators to indi-
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cate that NUSCO was aware of any deficiencies or unsafe conditions, or had suppressed or tried to suppress any adverse observation regarding system safety of the Isolation Condenser System.
B.
Conclusions None of the allegations were substantiated by the NRC investigatier..
One item of noncompliance with regulator / requirements was identified during the investigation.
A management meeting was held in Region I offices on March 13, 1980, with licensee representatives to discuss other concerns that developed during the course of this investigation. This meeting will be the subject of a separate inspection report (50-245/80-05).
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OETAILS
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A.
Introduction
~The investigation was initiated by NRC Region I as a result of the allega-tions received from an anonymous caller on December 21, 1979.
A subsequent allegation-(Allegaticn 1.4) was received in a second telephone call on January 8, 1980.
Following receipt of tna initial allegations, a series of telephone conver-sations were held between Region I and licensee engineering representatives on December 21 -1979. The licensee described followup inspection / evaluation
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activities that had been accomplished since the water-hammer event of December 19, 1979, and an earlier event in 1978.
NRC found that the licens-ee was aware of some concrete cracking.and spalling at the vicinity of the penetration and at the ceiling attachment of support X-10A (Allegation 1.3)
plus loose anchor bolts (Allegation 1.1) through their evaluation and follow-up activities.
Licensee representatives stated that they were unaware of any stress analyses that inoicated any piping or component overstressing.
At the same time these telephone conversations were being conducted, the Millstone NRC Resident Inspector also independently conducted a walkdown
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inspection of the Isolation Condenser System; reviewed drawings, inspection procedures and records; and interviewed licensee personnel at the plant site.
This ef fort supported and confirmed th_e.information received via telephone
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from licensee representatives as discussed above with respect to ' system damage.
NRC Region I contacted the licenses by telephone on December 26, 1979, to announce the initiation of further investigation efforts at the site and
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licensee engineering offices.
The licensee was also requested to provide documents and other pertinent information to NRC investigators upon their arrival at the plant site and at the licensee's corporate offices.
A pre-liminary list of documents and information considered pertinent by NRC Region I was transmitted to the licensee by Region I via telecopy to make them available to the Region I investigator during'the investigation.
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B.
Scope of Investigation The scope of the investigation included examination of design and analysis documents, interviews with personnel, review of records, direct observations of the system in the plant, and witnessing of inspection and~ tests-on the system piping and supports.
C.
Persons Directly Contacted and/or Interv?ewed during the Investication 1.
Northeast Utilities
- E. A. DeBarba,. Supervisor Generation Mechanical Engineering C. Glanding, Mechanical Engineer R. Hanschka, Mechanical Engineer b
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R. J. Herbert, Unit 1 Superintendent W. Hibberd, Mechanical Engineer
- J. M. Kufel, Superintendent of Nuclear Operations
- T. J. Mawson, Mechanical Engineer
- L. Nadeau, Mechanical Engineer
- J. F. Opeka, Station Superintendent M. Powers, Mechanical Engineer D. Robinson, Civil Engineer
- P. F. Santoro, Chief, Generation Mechanical Engineering K. Thomas, Plant Test Engineer 2.
Ebasco Services. Inc.
M. Seminatore, Engineer (by telephone)
3.
Teledyne Engineering Services R. D. Ciatto, Principal Engineer-P. Bangser, Engineer D. F. Landers, Vice President (by telephone)
L. Sempruicci, Engineer (* Persons attending exit interview)
D.
Investigation of Allegations 1.
Allegation No. I a.
Allegation The Isolation Condenser System is not capable of' withstanding seismic, blowdown, and water-hamer loads because of loose anchor bolts in pipe supcorts.
b.
NRC Investigation The investigator conducted a walk-down inspection of the system from the drywell penetration X10-A to isolation condenser tank.
The object of this visual inspection was to determine any obvious damage to piping, pipe 4apports, or other appurtanances to the system. The investigator noticed that there were indications of repair /retorquing of anchor bolts on supcorts ICH-4 and ICH-5.
On further inquiry, the licensee inforned the investigator that these anchor bolts were found to be loose in the inspection fol-lowing the water-hanner event of Cecember 19, 1979. However, the licensee had retorqued the bolts to the original torque value required for each bolt, and because the bolts were able to be retorqued to original value, they were not considered to have failed due to water-hamer stresses.
The licensee also indicated that the depths of embedment for the bolts were verified after
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retorquing, and the embedment meets the required criterion of depth for such bolts.
There were no other visible indications of structural damage and/or repair on the system piping and pipe supports.
c.
NRC Findings The NRC investigation showed that the licensee was aware of the loose anchor bolts and had taken actions to evaluate and repair these bolts.
The NRC investigation found that a proper evalua-
tion of the cause of bolt _ loosening was not carried out by the licensee before the retorquing was effected.
The repair performed by retorquing was not properly controlled and documented.
The repair instructions were issued on a plain sheet of paper without any traceability as to the originator, reviewer, date, or proper approval. The repair instruction specified that the bolts be torqued to meet the criteria specified in IE3:79-02, however, the inspector did not find any documentation verifying the actual torque value to which the bolts were tightened.
This is violation of critarion XVI of 10 CFR 50, Appendix B.
2.
Allegation No.1.2 a.
Allecation The Isolation Condenser System is not capable of withstanding scismic, blowdown, and water-hamer loads because of high stresses in piping, pipe supports, and nozzles.
b.
NRC Investigation The NRC investigators examined and reviewed the stress report,
associated computer out::uts and data to verify the substance of this allegation.
The investigators reviewed the following stress reports and associated documents:
1.
The original Ebasco analysis of Isolation Condenser sucply line.
2.
Stress report no.78-765.89 GM, Rev. 1, done by NUSCO in October, 1978.
3.
Stress report no. 79-162-150 GM, Rev. O, done by NUSCO in January 1980 for the purpose of incorporating results of IES:79-14
Stress report no. 79-162-151 GM, Rev. 1, done by NUSCO in February 1980, with corrected input for geometry and seis-mic anchor displacemen.
5.
A stress analysis computer run identifiec is ICONS 2, done by NUSCO (preliminary).
5.
% stress analysis computer run identified as ICONSN, done by NUSCO (preliminary).
7.
TES drawing no. A5182, Rev. 3 for penetration X-10A.
8.
TES drawing no. A5182, Rev. 4 for penetration X-10A.
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Ebasco drawing no. 22040-3300A for penetration X-10A.
10.
Bechtel calculation sheets for support modification for penetration X-10A, dated June 8, 1979.
The investigators also examined and reviewed various other corre-spondences and documents relevant to the scope of this part of the allegation.
The investigators also conducted private inter-views with NUSCO engineering and technical personnel associated with and responsible for the stress analysis and engineering of the Isolation Condenser System.
NRC investigators made an inspection of the work in progress relative to the Isolation Condenser System at Teledyne Engineer-ing Services facility at Walham, Massachusetts to verify the technical adecuacy of analysis performed by TES for the modifica-tion of the pipe anchor at penetration X-10A.
c.
NRC Findings Based a the examination and review of the documents, and dis-cuss en with NUSCO engineering personnel, and also the direct inspection of as-built system in the plant, the investigators'
findings are as follows:
1.
There was no apparent overstress found in original analysis by Ebasco Services.
2.
Review of stress report 78-765-89 GM, Rev. I did not show any discrepancy in the analyses, and stresses were found to be within allowable limits.
3.
Review of stress report no. 79-162-150 GM and 79-162-151 GM disclosed that NUSCO has used the currently allowable stresses of 5 and S in the ASME B&PV Code instead of the more con-serv $tiveB931.1pipingcodetowhichtheplantiscommitted.
However, it was found that the difference in final allowable stresses computed by both methods was quite insignifican.
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l I-The valve weight used in an earlier analysis was consider-ably higher than that used in these analyses.
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NUSCO presented acceptable documentary evidence to support i
the as-built condition and lower valve weight.
(Crane Co.
drawing no. 142652; valve shipping invoice no. 4280 from
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Chapman Division of Crane Co. dated July 31, 1969)
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4.
The computer run identified as ICONS 2 was designed to find j
the high stress points in case of a water-hammer incident to facilitate in-service inspection.
To achieve this, i
two simultaneous loads of 50,000 lbs. and 25,000 lbs. were arbitrarily applied at two support locations where water-i hammer induced loads were expected to act.
The support stiffners in the direction of applied loads were not con-
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sidered in the computation for conservatism.
The analytical approach and the basic technical rationale underlying this approach was found acceptable by the NRC investigators.
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The computer run identified ICONSW did not reveal any dis-crepancy in analytical approach or show any overstress in
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the system.
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The other relevant documents, correspondence or drawings did
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not disclose any discrepancy or overstress condition in this'
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system piping, pipe supports, and nozzles.
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The investigators found no evidence or information to indicate j
that there was any overstrecsing in the Isolation Condenser
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System.
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3.
Allegation No. 1.3 a.
Allegation i
The Isolation Condenser System is not capable of withstanding i
seismic, blowdown, and water-hammer loads because of concrete cracking in the drywell wall at penetration X-10A.
b.
NRC Investiaation-
The investigator visually examined the containment drywell wall in the vicinity of penetration X10-A.
Several cracks were easily
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noticeable from the floor level.
Also, there was some spalling
of concrete in the ceiling at the point of support attachment.
In response to the investigator's inquiry, the licensee indicated i
that these cracks on the wall.had been observed in Juae 1979 i
during routine inspections, and were evaluated and considered insignificant surface cracks due to concrete drying and shrink-age. The licensee provided a letter from Ebasco Services Inc.
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to NUSCO covering inspection and evaluation of the cracks in i
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support of the above statement.
The licensee indicated that there was no indication of any additional damage in these areaa after the December 1979 event.
This determination was made by evaluation and comparison with the damage observed in June 1979.
However, the evaluation by Ebasco only identified two cracks on the wall and did not explain the methed of crack evaluation and the basis of such conclusions. After a closer reexamination of the cracks and spalling in concrete, the investigator questioned the adequacy and validity of Ebasco's evaluation. At this time the licensee suggested a telephone call to Ebasco Services, Inc.
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for obtaining the background infornation and further clarifica -
tion of the crack evaluation.
In the conference call established by the licensee, the investigator was informed by tne Ebasco engi-neer responsible for the evaluation in question that:
1.
There was no visible damage present 'n the, ceiling (spall-ing) at the time of June 1979 inspection.
2.
He did not observe any horizontal crack in the drywell wall.
3.
The inspection was not a close examination, rather it was done from the floor level under poor lighting conditions.
4.
The conclusions were based on his judgement.
3.
The inspection was oriented more towards the pipe support structure than the structural soundness of concrete.
In light of the above infonnation, the investigator did not acept Ebasco's evaluation of the cracks as adequate and valid, and requested the licensee to provide some better evaluation of con-crete damage than the Ebasco letter. The licensee did not pro-duce any other inspection, examination, and/or evaluation support from the records. Therefore, the licensee indicated that a cen-sultant would be called in to reinspect and reevaluate the con-crete cracks and other apparent damage.
Pursuant to the above commitment, the licensee called in Tele-dyne Engineering Services (TES) for the work.
TES engineers arrived at plant site in late evening of January 3, 1980, and initiated an inspection and examination of cracked concrete and other damaces. The investigator witnessed the inspection and exa-mination of the support by licensee and their consultant TES. The investigator noted that the design drawing for the support showing the anchor bolt tyce, size, and embedment length was not avail-i able for inspection of the support. The investigator was informed that the licensee had not been able to locate the applicable
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drawing.
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At the conclusion of this examination the licensee informed the investigator that the licensee considers the cracks and spalling a scrious matter, and TES would evaluate the results of this inspection and recommend any required follow-up actions.
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The following morning the investigator was informed by the Resident Reactor Inspector, and later by licensee that the support X-10A has been determined to be inoperable due to concrete damage, and the licensee had initiated the following actions:
1.
Isolated the Isolation Condenser System.
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Reduced reactor power to 40% of the maximum operating level.
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Requested TES to further evaluate the pipe support X-10A, and recommend modifications.
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Initiate further NDE of the pipe support structure at TES request.
(Cetails of support modification are discussed in Section E.3 of
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this report)
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NRC Findings:
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l The NRC. investigation found that the licensee P
'ot conducted a proper and complete evaluation of the crac.
drywell wall concrete, and had failed to verify the basis Idequacy of the evaluation carried out by Ebasco Services, Inc.
This is a vio-lation of 10 CFR 50, Appendix 3, Criterion XVI.
4.
Allegation 1.4 The Isolation Condenser System is not capable of withstanding a.
seismic, blowdown, and water-hammer loads, because of damage to welds in piping and anchor X-10A due to water-hammer, b.
NRC Investigation
'l The NRC investigators inspected and examined the welding in sup-
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port X-10A in particular and in the system piping and other suo-ports in general.
Visual examinations were performed on -the welds.in the piping anchor 1 assembly of penetration X-10A.
This anchor is located at elevation 79.75 on the outside wall of the primary contain-ment wall (drywell). The records of the visual examination per-formed by the licensee using procedure NU-VT-1, Rev. O, were also reviewed as follows:
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ICBC-E-1-2 ICBC-E-2-2 ICBC-E-1-3 ICBC-E-2-3 ICB L'- E-1-4 ICBC-E-2-4 ICBC-E-2-1 ICBC-E-2-5 ICAC-E-1-1 ICAC-E-2-1 ICAC-E-1-2 ICAC-E-2-2 ICAC-E-1-3 ICAC-E-2-3 ICAC-E-1-4 ICAC-E-2-4 Additional visual examinations were trformed by the investigator for indications of service induced tracks resulting from the water-hammer events and the resulting stresses.
These inspections and examinations covered the system from the X-10A anchor support base plate outside the drywell to the Isolation Condenser because this portion of the system had experienced the major part of the water-hammer event.
Specific attention was directed to the heavy restraints ICH-4 and ICH-5 which had suffered the apparent loosen-ing of anchor bolts.
None of the inspection and examination dis-closed any apparent indication of weld or structural distress, and all the welds were judged to be sound.
However, to further inhance the confidence in the soundness of welds, magnetic par-ticle examinations were requested by NRC and performed by the licensee on welds that join the structural steel to the vertical and overhead bolted base plates.
These welds were examined by DC-MT techniques.
The investigators observed that the welds were cleaned of paint and other foreign materials prior to the exami-nation, witnessed these examinations, and verified that the per-sonnel carrying out the examination were qualified to the cequire-ments of SNT-TC-1A in the level-2 and level-3 categories.
These tests revealed two indications which were evaluated and resolved as weld bead anomalies frcm original construction.
They see not considered to be related to the water-hamnar or ot:M+ over-stress conditions.
Both indications were removed and tre welds were considered acceptable by NRC investigators.
The investigators also reviewed the licensee's inspection and evaluation of welds after the water-hammer event.
The licensee conducted an inspection and evaluation of the system using the in-service inspection standards of the plant.
The in-service inspection standards included U1 examination of welds which were categorized as high stress welos in the high energy pipe whip restraint program.
The welds identified in this program were the four 16 inch diameter elbow welds between supports ICAC-E-1-3 and ICAC-E-1-4 at elevation 79.75, and the 14 inch diameter welds on both sides of the outt3ard isolation valve (V-16-2) of the system.
The investigators witnessed the calibration of UT instru-ments and the calibration of the test system to establish test
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parameters.
Observations were made of the examination techniques including direction of scanning and evaluation of results.
After the examination, a recheck of the test system calibration was made.
The investigators found no discrepancies in the whole process.
c.
NRC Findings Based on the above findings, the conclusio'ns of the investigators are as follows:
1.
The welds in the Isolation Condenser piping have not suffered any deterioration due to high stresses caused by water-hammer events.
The licensee has assured the soundness, serviceability, and acceptability of welds by proper inspections and adequate evaluations.
2.
The welds in the pipe sucport X-10A have not suffered any damage due to high stresseu of water-hammer or otherwise.
The, investigators' direct observation, review of documents, and dis-
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cussions with engineering and technical personnel revealed that the licensee has carried out an extensive program of inspections and evaluation concerning the soundness of welds in piping and pipe sup-ports of the Isolation Condenser System.
No information or evidence was found to indicate that there was any i
damage in any piping or anchor welds.
5.
Allegation No. 2 a.
Allegation Northeast Utilities Services Company (NUSCO) have known these conditions for some time through an in-house stress analysis and inspection.
They, however, have failed to correct the defi-ciency and alleviate the unsafe condition.
b.
NRC Investigation The investigators reviewed and examined the stress reports and analyses performed by NUSCO (discussed in detail in Section 0.1, allegation 1.2 of this report).
The engineering and technical personnel associated with these analyses were separately and privately interviewed.
The investigators also reviewed related correspondence and records maintained by NUSCO in their corporate l
offices in Berlin, Ct.
The investigation determined that the ana-lyses and stress reports did not disclose any stress concentration which was outside the code allowable limits.
The inspection of
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the'information (discussed in detail, in Section 0.1, allegation 1.3).
c.
NRC Finding Based on the above findings, the investigators concluded as follows:
There was no information or evidence found to substantiate that any of the in-house stress analysis performed by NUSCO revealed any stress concentration outside the code allowable in pip!ng or pipe supports, or indicated any. unsafe condition of the system.
The investigators
confimed by direct observation of the licensee inspections that t
there was no indication of unsafe condition'or deterioration in the system that could have been revealed by_ inspection.J Therefore, the investigators found nothing to indicate that the lihensee and NUSCO had any knowledge of any unsafe condition in the system.
No evidence
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or information was found to indicate that NUSCO suppressed or tried-to suppress any _ adverse observation regarding system safety of the
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Isolation Condenser System.
E.
Investicator Identified Items
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Ouring the conduct of this investigation, several other items of concern were identified by the investigators.
Some of these concerns were minor,
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and were resolved by more information presented by licensee. However,
i a few of these concerns required a detailed followup by new analysis,
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evaluation, and in some cases, modifications in the existing structural design or re-design of the pipe support at penetration X-10A as follows:
1.
Drilled in Excansion Anchor Bolts While evaluating the structural integrity of concrete supporting the
penetration X-10A, the investigators discovered that the base plates-attached to the wall of drywell were not anchored by cast-in-olace
" Williams Rock Bolts", rather, the bottcm row of anchor bolts were drilled in expansion anchors.
The' license was unaware of this vari-ance in as-built condition of the support. Becausa of this oversight, the drill.ed-in anchor bolts in the support had not been included in the evaluation process for such bolts pursuant to IES:79-02.
The investigators also discovered that due tc this discrepancy, the as-built system evaluation carried out for IES:79-14 was inaccurate.
It also became evident to the' investigators that this discrepancy was not identified in _IES:79-14 program because the detailed drawings of
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the anchor were not used in the as-built verification inspection.
The licensee subsequently located a detail drawing for the support and corrected the errors in IEB:79-02 and 79-14 evaluations.
2.
Structural Design of Anchor at X-10A In reviewing the structural design of penetration X-10A anchor, the investigators-became aware of two apparent design errors.
During the initial design of the support anchor, the design load combination included a high energy pipe rupture" load. However, in structural
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design of the support and sizing of the structural members, only a fraction of the high energy pipe rupture loads were taken in account.
Therefore, th: pire support anchor was not sized, fabricated or erected to meet the original design assumptions and criteria.
Furthermore, in the licensee's evaluation of the system stresses, this load was not considered in combination with nomal operating loads.
Hence, the apparent factors of safety ccmputed by the licensee for the support were in error. However, once this omission was identified, the licens-ee referred this discrepancy to their consultants for resolution and recomendation for corrective acticn.
Teledyne Engineering Services, the licensee's consultants, reanalysed and reevaluated the new information and concluded that the anchor in fact was undersized to resist the assumed design loads and moments.
To correct this deficiency, TES re:cmended an extensive modification of the support anchor with additional structural elements to enhance the load carrying capacity and structural integrity of the support.
The load conditions and ccmbina; ions for which the support was modi-fied were discussed and agreed to by NRC during conference telephone calls between the licensee and NRC (IE and NRR). The load condition which the support was modified to meet, and resultant factors of safety are as follows:
Condition 1 = Normal Operation + CBE Condition 2 = Normal Operation + HEpB The factors of safety:
(Pu/P)
Condition 1 > 4
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Condi tion 2 > 2
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In performing the analysis for condition 2, TES apolied all High Energy: Pipe Break (HEPB) loads simultaneously assuming that they could be positive (+) or negative (-) except for Fx, which culd only be applied in -x direction. The conservatism of this approach j
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was acceptable to NRC. Consequently, the discrepancy was considered to be resolved for plant operational safety.
Additionally, the licensee made a comitment to review and evaluate other genetrations and pipe supports where a similar error might have been made, and to
' inform the NRC of the result of such review.
3.
Modification of Anchor at X-10A The modification of the support at penetration X-10A required two new
- elements to be attached to ceiling by plates attached to concrete by drilled-through anchor bolts attached to a coverplate on the floor above. However, during the installation of this base plate in the ceiling and the coverplate on the floor, it was discovered that there was a high incidence of cut rebars in the floor slab in the area of plate, and more seriously, the rebar arrangement in the slab did not conform to the design drawing which, certified the as-built rebar arrangements by the A/E (Ebasco Services, Inc.).
This discrecancy again required that a review and further evaluation of the integrity of support be carried out by the licensee.
The' investigators followed up this new development by reviewing the design documents, and through discussions with licensee and their consultants' personnel. Thc licens-ee initiated an independent review and reevaluation of this discrepancy with its consultants, TES and the original A/E.
Following is the sumary based on the investigators' direct observa-tion and the information provided by the licensee to the investiga-tors after review and evaluation:
1.
The slab thickness at elevation 82.75 is 2 feet thick in the vicinity of the anchorage of penetration X-10A; the balance of the slab is 1 foot thick.
2.
The installed rebar condition consists of number eight (8) bars at twelve (12) inches on centers each way, at top and bottom of the slab and in the middle.
3.
The design drawing (G-187811, Rev.1) called for number eleven (11) bars, six (6) inches on centers at the bottom of the slab, and number eight (8) and number eleven (11) bars alternately on six (6) inch centers at the top of slab.
4.
Several of the existing rebars were found to have been cut par-tially or completely, probably during the installation of the rock
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bolts fastening the plate to the underside of the slab.
5.
Masonry drawing G-187810 as revised reflected a 2 foot thick floor slab in area of X-10A (NOTE: reinforcement details are not indicated on masonry plan.) This drawing was not aporoved until June 10, 196. _
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Reinforcement drawing G-187811 (Rev.1) as revised reflected both 6.
2 foot thick floor slab and increased steel requi.ements for anchor X-10A ruptureL oads.
Bar bending schedule also revised.
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- This drawing was not' approved.until June 10, 1968, on or about the date of the concrete placement.
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7.
One to two weeks.before concrete placemer',.rebar mats were installed in the. slab, according to G-15/811 (Rev. 0), No. 8's at 12 inches top and bottom, both ways.
8.
Concrete placement SW and SE-section of floor slab at El. 82.75-was started on June 7, and was finished by June 10, 1968.
9.
The slab as-built at Elevation 82.75 in the area of X-10A sup-
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port anchor was not capable of withstanding the maximum design-pipe break load with the original anchor configuration.
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In light of the above observations and evaluation,_the licensee referred this matter to its consultant (TES) for resolution and recommendations.
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Based on'further reevaluation, the licensee initiated the following corrective action for the discrepancy:
1.
Additional sections of rebar were welded to cut rebars to make them continuous.
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Two' additional elements were installed connecting the top cover 2.
plate of the anchor to the drywell wall.
Two additional elements
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were provided from the underside of the slab base plate to dry-well wall.
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The additional structural elements were designed to support the f
anchor independently without transmitting any significant load to the floor slab.
4.
The licensee initiated a program.of design document raview to determine-if a similar condition exists at any other place in the plant.
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During the implementation of above corrective action by the licensee,
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the investigators observed the following:
1.
In rebar welding, weld procedures and welder qualifications:
were in conformance to ANS 012.1 and ACI-318,_Section 7.5.
2.
Weld simulated in placa test results fulfilled the requirements cf ACI-318.
3.
Concrete repair procedure was adequate to assure concrete
replacement.
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Quality control of the operation was satisfactory.
5.
The assumptions and techniques (finite element) used by TES for designing the modification of support were acceptable.
No noncompliance or deviation was identified by the investigators in this area.
4.
Develocment and Determination of Water-Hammer Loads Due to transient and unpredictable nature and the magnitude of water-hammer loads, it is very difficult to develop any realistic design criterion for stresses imposed by such events.
Mcwever, due to the sensitivity of the Isolation Condenser System to water-hammer loads (three events in past six years) it is imperative that a reasonable criterion must be developed, and the system safety evaluated against this criterion.
Recognizingthissafetyconcern,thelicenseehasinitiah.edaprogram of developing such a criterion for water-hammer loads in the Millstone 1, Isolation Condenser System.
The licensee's consultant, TES, has ini-tiated a study by computer modeling of the system, generating various parameters for the criterion.
The method is based on " Time-Force History" analysis of water-hammer pulses in the system piping.
The investigators reviewed the work done in this area by TES at its Walham, Massachusetts offices.
The review consisted of discussion with TES engineers and inspection of some preliminary data generated in this effort.
The investigators did not ihqtify any apparent item of noncompliance in this area.
5.
Develocment of Pice Ruoture Load The investigators found that the licensee has also initiated a program for developing more realistic pipe rupture load for the Isolation Con-denser System.
In reviewing the design of the support, it was dis-covered that the pipe rupture load used by Ebasco during the initial design may have been arbitrarily derived by the design engineer, and vis unrealistically high.
No documentation, background design assump-tions, and/or technical justification was available in Ebasco Services'
files to support this load. The licensee contends that the support anchor can never be subjected to such a load as the structural abi-lity of the piping, i.e., the ultimate strength, is lower than the stresses assumed due to such a load combination, therefore the piping will fail before the stresses in the support ever reach the critical leve _
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The dynamic design analysis of the plant was carried out by the
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" static" equivalent method prevalent at the time. Therefore, it is
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more reasonable and realistic to develop a high energy pipe rupture load in accordance with present day criteria with more sophisticated and reliable methods acceptable to NRC.
This new pipe rupture load-will tue used to evaluate the Isolation Condenser System stresses by the currently acceptable dynamic analysis to satisfy the present criteria of NRC for an acceptable aralysis.
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Exit Interview.
The investigators met with licensee representatives (denoted in.Section C.1)
at the conclusion of the investigation on February 22, 1980.
The investi-gators summarized the scope and the findings of the investigation.
In response to the findings and concerns expressed by the investigators, the licensee made a commitment for a written submittal to Region I office for the items listed below.
The schedule of submittal as agreed to by Region I and the licensee is noted after each item.
1.
A detailed description of ' design errors in original Ebasco design involving pipe restraints at penetration X-10A.
The response will cover at least the following:
(3/31/80)
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Results of the licensee's investigation as to the circumstances
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surrounding these designLerrors.
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b.
The licensee's basis for providing assurance that similar design.
errors have not been made at other high energy pipe restaints (a's much as possible by 3/31/80, and remainder in ten months).
2.
A detailed description of cut reinforcing in the floor slab at the 82.75 foot elevation in the area of the containment penetration X-10A pipe restraint covering at least the following:
(3/31/80)
.rocedural requirements in effect during plant construction regarding the cutting and documentation of cut reinforcing.
steel, b.
Results of the licensee's investigation as to the circumstances causing the cut reinforcing steel.
3.
A detailed description of differences in the vf acement of reinforcing
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steel between as built' conditions and as-built drawings for the floor slab at the 82.75 foot elevation in the area of the containment pene-tration X-10A pipe restraint.
(3/31/80)
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Procedural requirements in effect during plant construction regarding the. verification of proper' implementation of reinforc-ing steel design requirements.
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Results of the-licensee's investigation as to the circumstances causing the differences between reinforcing steel design require-ments and the as-built conditions.
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The licensee's basis'for providing assurance that similar dif-ferences in reinforcing steel of other class one structures will not prevent those structures from performing their design
. functions.
4.
The effect of water-hammer stresses on the margin of safety of the
. pipe restaints presently provided for the Isolation Condenser System.
If modificatiors are found to be necessary, a schedule will be pro-vided.
(4/30/B0)
5.
The effects on the primary containment structure of the pipe stress forces transmitted by the present isolation condenser restraint to that structure at containment-penetration X-10A.
(3/31/80)
G.
Management Meeting i
A followup management meeting with the licensee was held in Region I offices t
on March 13, 1980, to discuss concerns that developed during the course of this investigation (see Inspection Report No. 50-245/80-05).
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