ML20077S555

Safety Evaluation on Insp,Analysis & Repair of Recirculation Sys & RHR Sys Piping

ML20077S555
Person / Time
Site:	Peach Bottom
Issue date:	09/01/1983
From:	Office of Nuclear Reactor Regulation
To:
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ML20077S544	List: ML20077S542 ML20077S555
References
NUDOCS 8309220128
Download: ML20077S555 (8)

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UNITED STATES i?

5, a,,.,,f i NUCLEAR REGULATORY COMMISSION i

WASHINGTON, D. C. 2C555 i

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SAFET EVALUAT!0" BY THE 0:FICE OF NUCLEAR REACTOR REGULATION INSPECTION, A;iALYSIS Ai:D REPAIR OF THE

! 4cj PESCH 30TT0!1 Uf:IT 3 RECIRCULATICM SYSTEM

j AND RESIOUAL riEAT RE;iOVAL (RHR) SYSTEM PIPING I

PHILADELPHIAELECTRICCONPANY,ETAL.

DOCKET NO. 50-278 i

I Introduction During the current Peach Bottom Unit 3 refueling outage, Philadelphia Electric Company (PECo) performed augmented inservice inspection on a total of 112 Class 1 austenitic stainless steel piping welds, con-sisting of 77 welds in tihe Recirculation system and 35 welds in the RHR system, of which 40 were 12" riser welds and 72 were welds of 20" or larger in diameter.

The inspected welds include all the welds (91 welds) that were treated with Induction Heating Stress Improvement (IHSI).

The purpose of IHSI is to reduce the potential of susceptible welds to IGSCC.

Except for nine welds'in the 28" recirculation piping and three.9 elds in the RHR piping, all nonconforming welds in the recirculation and RHR piping systems were inspected in this outage.

Ultrasonic examina*

tion was performed on each of the 112 welds and additional radiographic J

examination using MINAC (Miniature Linear Accelerator) was performed on 20 12" riser welds where the riser pipes were cladded.

General Electric (GE) at King of Prussia, Sonic System International (a subcontractor of General Electric) and Scothwest Research Insti-l tute (SWRE) performed the UT examination for PECo.

Region I of NRC has determined that their UT procedures, calibration standards, equipment and IGSCC detection capabilities were satisfactorily i

demonstrated in accordance with I&E Bulletins 83-02 and 82-03, and the same procedures and technicues were used in this UT i

examination.

The results of the Ui examinations indicated that i

a total of 15 welds consisting of 1012" riser to elbow welds in the recirculation system and five :'C" riser to elbow welds in the l!

RHR systee-showed reportable linear indications.

All indications were in the weld heat-affected-zone (HAZ).

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In the 10 12" defective riser welds, all indications are oriented in axial direction.

The worst axial indication was reported in weld '

2-AHF-2 with a depth about 92% of wall thickness and a length about J

0.75 in.

In the five defective 20" PJIR welds, the indications are i

oriented predominantly in circumferential direction.

The worst t

circumferential indication was reported in weld 10-0-6 with a depth l

about 40% of wall thickness and a length about 32 inches.

i General Electric at San Jose performed the flaw evaluation for PECo in accordance with the new Code Section XI IWB 3600.

The new Code j

IWB 3600 provides flaw acceptance criteria for austenitic stainless l

steel piping based on the net section collapse approach which was approved i

by the ASME Code main cc=mittee this March, and is expected to be published later this year.

The results of the evaluation indicate-that 13 of the 15 defective welds (1012 riser welds and three 20" RHit welds) require weld overlay repair because the. final flaw sizes of these 13 welds at the end of an IG-month period (12,000 nours) woul.d exceed the new Code allowable limits.

However, PECo opted to weld overlay j

repair all 15 defective welds including the three 20" RHR welds whose final flaw sizes were shown to be within the new Code allowable limits at the end of in 1S-m66th period.

j General Electric performed the weld overlay repair on the 15 defective welds.

The minimum overlay thickness for the riser welds is 0.25" and for the 20" RHR welds it varies from 0.25" to 0.5".

The overlay thick-ness is designed to meet the Code allowable limits in the new IWE 3600 t

assumine the presence of through-wall cracks.

The length of the overlay varies ipproximately frcm 4 to 7 inches and is designed to reduce the j

stress at the end of the overlay acting on the crack location.

RHR welds 10-0-7, 10-0-10, a'nd 10-0-15 are bi-metallic welds (carbon steel to stainlesLs steel) and the over. lay is applied only to the stainless.

steel side of the welds.

Region I 'of f4RC has confirmed that the weld i

l overlay repairs were performed in accordance with the qua'lified and approved procedures consistent with ASME Code requirements.

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i 3-l During the overlay of RHR weld 10-0-6, a circumferential through-wall crack about 2 inches in length was found.

PECo indicated that the reason the original UT examinatica missed this through-wall circum-a ferential crack is due to the presence of an oversized crown on the subject weld which prevented a proper UT examination of the upper portion of the weld.

This through-wall crack did not affect the adequacy of the overlay repair because the overlay was desicned for a fully circumferential through-wall crack. The licensee submitted i

l by letter dated August 30, 1983, its evaluation and justification i

for those welds in the Recirculation, RHR, Reactor 'Jater Cleanup (RMCU) and Core Spray Systems which have not been inspected during t

-his cutage.

.J Evaluation

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We reviewed the licensee's submittals including General Electric's overlay design analysis to support the. continuing service for an 18-month period (12,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />) of the 15 overlay repaired weids.

t General Electric's overlay design analysis is based on the consersative assumption that all cracks are through-wall cracks eliminates the concern regarding the uncertainties in the UT sizing and the IGSCC crack growth rate because they will not be considered in this analysi's.

The required minimum overlay thickness for each defective weld is calculated by using the methodology allowed in the new IWS 3600 to meet the required Code safety margin.

For normal and upset condition, a safety margin of 3 is required and for the faulted and emergency condition, a safety margin of 1.5 is required.

Eecause the acceptable flaw in the normal condition based.on new IWS 3600 is more limiting, the acceptable flaw for the f aulted condition need not be cf.nsidered.

For RHR walds 10-C-5 and 10-0-6, the allowable flaw depth based on new IWS 3600-is conservatively cal.culated to be 75.5% anc 78.1% of wall.

thickness respectively.

This calculation assumes the flaws to be fully circu-ferential in length and through the original pipe " thickness in capth.

This assumption is very ccnservative because the worst repcrted i

UT irdication in these two welcs is about 4C f threagh-wai in depth

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and less than half of the full circumference in length.

GE's analysis has shown.that a minimum overlay thickness of 0.5 inch is more than 4

enough to make the assumed through-wall cracks (63% and 65% of the 9

l overlay repaired wall thickness) in these two welds meet the new calculated Code allowable limits (75% and 78%).

An allowable flaw j

depth of 82% was similarly calculated for RHR weld 10-0-7.

This weld 1

has a. worst reported flaw with about 35% of wall thickness in depth and about 7 inches in length.

With a minimum overlay thickness of q

0.35 inch applied to this weld, the assumed fully circumferential through-wall crack (73% of the overlay repaired wall thickness) is well within the new calculated Code allowable limit (82%).

The indications reported by GE on RHR welds 10-0-10 and 10-0-15 may be overcalls because both LMT and SWRE had examined the same two welds

.j and did not find any reportable indications.

Region I of NRC reviewed all the UT data recorded by the three UT teams and agreed with the LMT and SWRE's conclusion that there are no reportable indications in R,HR welds 10-0-10 and 10-0-15.

Mcwever, PEco decided to apply an overlay I

with a minimum ' thickness of 0.25 inch to these two welds to increase o

the Sofety ma.rgin in structural strength and to prevent any potential j.

leakage.

P We reviewed the weld overlay design calculation made by GE. We agree 3

with their conclusion that the overlay used will provide adequate

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reinforcement with the Code required safety margin for ~it least the next fuel cycle of cperation (12,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />).

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il GE also performed an evaluation of the overlay shrinkage effect by using a finite element model of the Recirculation and RHR piping

}l-systems.

The shrinkage was conservatively assumed to be 1/4 inch for the riser weld overlay and 3/8 inch for the RHR weld cverlay.

GE indicate &-that the maximum calculated nominal stress due to the s

h weld shrinkage is about 5000 psi and 16,000 psi in the Recirculation is l

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and RHR systems, respectively, which is well below the Code allowagle value of the yield strength (25 Ksi) of the material.

The subject shrinkage stresses are not expected to have any significant deleterious effect on the Recirculation and RHR piping systems.

i In its August 30, 1983 submittal pertaining to uninspected w;1ds, the licensee reported that for the Recirculation and RHR piping systems a total of 17 Class 1 non-conforming welds, of which 12 are in the large diameter lines (?.20") and 5 in small diameter lines (1E 6") were not UT examined during this outage.

Ten (8, 28" welds and 2, 22" welds) of the 12 uninspected large diameter welds were located ir the high radiation area (up to 10 R/hr on contact) and required removal of large cuanties of insulation. Thes'e welds were not examined based on ALARA considerations. The other two uninspected large diameter welds (24") in the RHR return loops were located between the penetration and the valve outside the drywell.

Because of physical restriction, these two welds cannot be UT examined.

Five small diameter uninspected welds i

were all weldolet welds which are not readily ultrasonically examinable, i

The licensee has inspected 72 large diameter (20" and above) welds and no defective welds were found for welds in pipes with a diameter of 22" or above.

Therefore, based on the results of this large sampling, we believe extensive l

cracking is not likely to be present in those 12 uninspected large diameter welds (E 22"). As a compensatory measure to ensure early detection of potential leakage in repaired and uninspected welds, the licensee has installed moisture sensitive tapes on 30 selected large diameter welds including 10 uninspected l

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large cie.neter -eics inside tne dry..all ar.c 5 uninspectec welcolet we'.cs.

l Based on the above discussico, we conclude that the 17 uninspected welds

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in the recirculation and RHR systems are not likely to be crackeo to the t

l extnet of compromising the safety of the plant.

Even if they were to crack I

through the wall fully, the resultant leakage would be detected by the moisture sensitive tape leak detection system.

The licensee did not inspect the non-conforming welds in the reactor water cleanup system (RWCU) (6") and Core Spray (10" and 12") piping systems during this outage.

There are non-conforming welds in the RWCU system which are not inspectable due to physical limitations.

There are 22 non-conforming welds in the two loops of the Core Spray system.

The licensee indicated that tne

..i portions of the Core Spray piping containing tne 22 non-conforming welds were operated at a temperature less than 200*F and are considered to be not susceptible to IGSCC.

We do not fully agree with the licensee's justification; however, we do believe the low temperature (6250*F) portions of piping are less susceptible to cracking.

4 We also note that the portion of the RWCU piping containing the 3 non-conforming welds in the RWCU piping system is isolaole and, therefore, will not impact tne integrity of the reactor coolant primary pressure boundary.

The licensee also indicated that they will install moisture sensitive tapes o'n these 3 welds in the RWCU system to ensure early detection of potential leakage.

Based on the above discussion, we conclude that the uninspected welds in the RWCU and Core Spray systems are not likely to be cracked to the extent

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'of compromising the safety of the plant.

Even if they were to crack througn the wall fully, the resultant leakage would be detected by the lea ( detection system.

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Leak Detection I

i Although a large pcr ion of the nonconforming stainless steel welds j.

in Peach Bottom Unit 3 was examined and all defective welds found were l

weld overlay repaired, not all welds were exanined and signifi-cant cracks could be present in welds that were not examined.

Because of this concern, it is prudent to improve the requirements for monitoring for unidentified leakage.

The required additional monitoring and tighter limits on unidentified leakage are summarized below:

(1) An additional operational limit on reactor coolant system leakage of an increase in unidentified leakage of two gallons / minute or more withi~n any 24-hour period or less (except during the first 24 ' hours after startup).

On exceeding this limit, the reactor should be placed in n cold shutdown condition within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for inspection.

(2) The leakage measured from each sump should be recorded every 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

(3) At least one of the leakage measurement instruments associated with each sump should be operable.

We conclude that implementation of the above measures will provide adecuate assurance that possible cracks in pipes will be detected before growing to a si e that will compromise the safety of the plant.

5c.- ary and Conclusions We have reviewed Philadelphia Electric Ccmpany's submittals regarding the actions taken or to be taken during this refueling outage on the inspection, analyses and repairs of recirculation and RHR piping system welds in _the Peach Bottom _ Unit 3_ plant.

This includes a description of the defects found, description of repairs, stress and fracture analysis.

1 We conclude that the Peach Bottem Unit 3 plant can be safely returned to power and operated in its present config'uration at least for one 10-

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l month fuel cycle (12,000 hour0 days <br />0 hours <br />0 weeks <br />0 months <br />.s) provided that the following items are satisfactorily completed:

(1) The, Code required hydrostatic test and nondestructive examination on overlay repaired welds should be satisfactorily completed prior to startup.

(2) The additional leak detection requirements as listed in the section on Leak De'tection should be properly implemented prior to startup.

Nevertheless, we still have concern regarding.the inng-term growth of small IGSCC cracks that may be present but not dete.ted during this inspection.

Therefore, we require that plans for inspection and/or modification of the recirculation and other RCPB piping systems during the next refueling outage be submitted for our review at least three montus before the start of the next refueling outage.

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