ML20248B734

Rev 1 to ES199800777, Engineering Evaluation

ML20248B734
Person / Time
Site:	Calvert Cliffs
Issue date:	05/27/1998
From:	BALTIMORE GAS & ELECTRIC CO.
To:
Shared Package
ML20248B729	List: ML20248B725 ML20248B734
References
ES199800777, ES199800777-R01, ES199800777-R1, NUDOCS 9806010370
Download: ML20248B734 (4)

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ATTACHMENT (1) 1 ENGINEERING EVALUATION ES199800777, Revision No. I l

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1 9906010370 980527 PDR ADOCK 05000318' p PDR Baltimore Gas and Electric Company Calvert Cliffs Nuclear Power Plant May 27,1998 l

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ATTACIIMENT 24, ENGINEERING EVALUATION ESP No.: ES199800777 Supp No. 000 Rev. No. 0001 Page 1 of 4

' REASONS FOR ENGINEERING EVALUATION:

Issue Report IR3-002-371 documents that crosion has caused a thru-wall opening at a 1" NPS half-coupling in the Salt Water System. This half-coupling is utilized for instrument 2-SW-5205-Tl which is located on the salt water inlet piping (Line No. 24"LJ-1-2009) leading to No. 21 Component Cooling Water Heat Exchanger. Specifically, the crosion has occurred at the toe of the fillet weld of the half-coupling.

Leakage of the subject half-coupling was also detected during the 1997 RFO (Ref. Issue Report IRI-050-986).

MEU evaluated this condition, and concluded that it was acceptable; however, repair of the leaking half-coupling during the refueling outage was rcquired to meet Generic Letter 91-18 requirements, and therefore, the evaluation was only written to be valid for Modes 5,6, and Defueled. The leak is now occurring during power operation; therefore, the evaluation must be expanded to include Mode 1 Conditions. Also, based on MEUs interpretation of the NDE Inspection Report, erosion is now being detec'ed on the header pipe itselfin the area near the half-coupling. The affcct of the expanded area of crosion on the stnictural integrity of the SSC must be assessed.

This Evaluation is valid for all modes.

DESCRIPTION OF CIIANGE(S):

This evaluation provides rationale that the 24"LJ header pipe integrity is not compromised, that the consequences ofleakage are acceptable.

DETAILED EVALUATION OF CIIANGE(S):

A. Structural Intecrity This section of the evaluation documents that the 24"LJ header pipe integrity is not compromised by the thru wall crosion.

Analysis Methodology Paragraph 104.3.1 of ASME B31.1-1967 discusses requirements for branch connections. The concern is that a pipe having a branch connection is weakened by the hole made in it. In order to compensate for this opening, additional metal around the hole, referred to as reinforcement, is required.

When a half coupling is used, the metal provided by this fitting is automaticallyjudged to provide ad equate reinforcement so no calculational evidence is required to dxument that adequate reinforcement exis s (Ref. ASME B31.1-1967, para.104.3.l(c)2.). However, in the situation addressed in this issue report, erosion hat gone through the wall completely at one point, and significant erosion around the entire half-coupling circumference at that axial location is suspected as well. Therefore, it is not appropriate to credit the reinforcement provided by the half coupling.

As a result, an analysis will be performed to show that even if the half coupling were not present, there is still adequate reinforcement available from the adjacent pipe wall thickness to satisfy the ASME B31.1 reinforcement requirements. j The reinforcement calculation approach was chosen since it provides a reasonable means of assessing the impact of the through-wall defect on the structural integrity of the flawed piping, given the geometry of the flawed area and the mechanism of the flaw initiation. The reinforcement calculation method was chosen over the "through-wall flaw" and " wall thinning" approaches outlined in NRC GL 90-05 since these methods do not address the presence l of the half-coupling opening in the pipe. The " wall thinning" approach would be appropriate for the l erosion / corrosion based type of flaw addressed by this evaluation; however GL 90-05 does not allow its use for through wall flaws. The "through-wall" approach is fracture mechanics based, but the proximity of the flaw to the I

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ATI'ACHMENT 24, ENGINEERING EVALUATION ESP No.: ES199800777 Supp No. 000 Rev.No. 0001 Page 2 of 4 half-coupling and the corrosion-based nature of the flaw do not support direct application of this method.

Reinforcement Analysis Required reinforcement (in square inches) for a branch connection at a right angle to the header pipe, per ASME B31.1-1967 para 104.3(d)2.(b), is given by:

required reinforcement = 1.07

• ta

• d i where ta = required wall thickness of the header pipe d i = 1.78" (ANSI B16.11 - 1980, Table 4) Note that the although the diameter for a 1" half coupling is 1.049",1.78" is consenstively assumed to be the OD of a 1" half coupling. This will consenatively account for header pipe erosion. _

From para 104.1.2(a), the formula for minimum required pipe wall thickness is:

ta = (P

• D. ) / 2 [ SE + 0.4P ] + A where P = 50 psig (Ref M-601 for LJ-l Pipe Class)

D. = 24" (Re. Tube Turns, page B19)

SE = 12,800 psi (Ref ASME B31.1, assuming A-53 welded pipe)

A = 0.0091

• 3 = 0.0273 square inches Note that A is calculated based upon the following. There was a similar occurrence on this section of the header during the 1997 Unit 2 RFO. A UT was performed and found that the minimum wall thickness was 0.389 inches.

A UT was performed this outage, and the minimum wall thickness was found to be 0.280 inches. This is a reduction of 0.109 inches in 12 months, which results in an crosion rate of 0.0091 inches / month. Replacement of the header spool piece is scheduled for early July. Assuming a 3 month further erosion, the w211 thickness is calculated as:

ta = (50

• 24 ) / 2 [ 12800 + 0.4(50) ] + 0.0273 (0.0091

• 3 = 0.0273 inches) ta = 0.G741 inches Therefore, the value for the required reinforcement area is:

1.07

• 0.0741

• 1.78 = .142 square inches Available reinforcement (in square inches) for excess pipe wall thickness in the header pipe is 6i ven by (refer to ASME B31.1-l%7 para 104.3(d)2.(c)) ,

A1 = d2 (T6 - ta ) l where di = half width reinforcing zone and is the greater of di and Tb +Th + d i /2 d2= 1.049, the inside diameter of a 1" half coupling ta = 0.0741 (calculated above)

Th = nominal wall thickness,0.280 inches Therefore, A1 = 1.049" (0.280" - 0.0741") = 0.215 square inches Since the available reinforcement area without the half coupling (0.215 square inches) is greater than the required reinforcement area (0.142 square inches), the header pipe qualification is not adversely impacted by the eroded half coupling. Note that this evaluation is good for three months after the date of this evaluation.

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ATTACHMENT 24, ENGINEERING EVALUATION ESP No.: ES199800777 Supp No. 000 lRev.No. 0001 Page 3 of 4

. B. Leak Rate Computation.

Evaluation of the safety significance of the leakage detected on the half-coupling requires that the worst case leak rate which might develop be computed. The worst-case leak rate is computed by assuming the entire half-coupling I

crodes away. The outside diameter of the half-coupling (1.78 inches per ANSI B16.11-1980, Table 4) is therefore assumed to be the diameter of the leak opening from the salt water system.

Though evidence of crosion on the salt water header pipe is indicated by the ultrasonic examinations of the pipe there is still a minimum of 0.280 inches of wall-thickness intact. Also, as seen in reinforcement calculation performed above, even if the erosion of the header pipe is assumed to continue there is still adequate wall-thickness to maintain structural integrity of the header pipe.

The following equations are used to calculate the flow from a square edged orifice in a pipe wall (Crane Technical paper 410, eq. 3-21).

Q = 236 di ' C (AP/p )in C = Ca/ (1-p')"'

p = di / d2 where Q = Volumetric Flowrate (gpm) di = Inside diameter of Orifice d2= Inside Diameter of Header Piping C = Orifice Flow Coefficient C4 = Discharge Coefficient of the Orifice The header pipe is 24" W pipe (wall thickness = 0.375") therefore 2d is 23.25 inches. With di equal to 1.78 inches it is seen that p is 0.08. Using the figure provided on page A-20 of Crane, and assuming turbulent flow the Orifice Flow Coefficient is 0.6. The minimum density occurs at the maximum temperature (90?F) and is 62.116 lbm/ft'. Conservatively using the design pressure of Class U pipe ( 50 psig) as the driving pressure through he orifice yields the following worst-case flowrate:

Q = 236 (1.78)2 (0.6) (50 / 62.I16)"' = 402.52 a 403 gpm  !

l This flow rate is a conservative estimate of the worst-case leakage that could result from a complete failure of the 1" NPS half-coupling at 2-SW 5205-TI.

C. Flooding Imnact.

BGE Calculation No. M-90-173, Rev. O evaluates the potential for flooding the Unit 1 & 2 CCW pump Rooms (Room Nos. 201 & 208). This calculation shows that the worst-case direct flooding results from a critical crack in a 14" Safety i Section Line concurrent with fire protection actuation. This event results in a flowrate of approximately 2852.0 gpm. The evaluations per rormed in conjunction with the development of ES-001 Rev. O

" Flooding" demonstrate that no safety-related equipment in the CCW Room or any other room would be impacted

.o ATTACHMENT 24. ENGINEERING EVALUATION ,

ESP No.: ES199800777 Supp No. 000 Rev.No. 0001 Page 4 of 4 by this event. Therefore, the 403 gpm leakage resulting from the complete failure of the 1" NPS half-coupling is bounded by existing evaluations.

D. Imoact on Component Cooling Water (CCW) Heat Exchaaer Performance.

The CCW heat exchangers use Salt Water to remove heat from the Component Cooling Water svstem. During normal plant operation only one heat exchanger is required for cooling service; hewever, during the post-R AS phase of a lhCA, both CCW heat exchangers are assumed to be available. The impact of a 403 gpm salt water

!- leak (computed above for complete loss of half-coupling) in the supply header to one of the beat exchangers is evaluated for its impact on heat removal from the Component Cooling Water System during the post-RAS phase of aLOCA.

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As described in Section 9.5.2.3 of the UFSAR, salt water flow to the CCW heat exchangers is throttled post-RAS, and this action is prescribed in step V.I.c.(2) of EOP-5 (" Loss of Coolant Axident"). The minimum flow per header pre-RAS is found from Section 9.5.2.3 to be 17,230 gpm (16,830 + 400) while the nummum post-RAS header flow is 15,400 gpm (9,500 + 400 + 5,500). From this it is seen that the salt water flow is throttled approximately 1830 gpm, and therefore, a salt water leak of approximately 403 gpm can be recovered by reducing the amount of throttling. The amount the Salt Water flow is to be throttled is already based on Operator action as seen in Step V.I.k of EOP-5 which instructs that the Salt Water flow to be adjusted to maintain a Component Cooling water flow of 120'F, or less. Therefore, the operators will be adjusting salt water flow to maintain CCW System temperature. Any salt water leakage can be compensated for by increasing the salt water flow prosided the leak rate doesn't exceed the total amount the flow had been throttled. As shown above there is plenty of margin between these two values (403 vs 1830 gpm).

E. Potential loss of Tenuereture Ind%tian.

2-SW-5205-Tl provides local SW inlet temperature indication for 21 CCW heat exchanger. This parameter is not critical to the safe operation of either the SW or CCW systems. The primary indication of SW inlet temperature is from CW001, in addition there are alternate indications of SW inlet temperature from the SRW heat exchangers and No. 22 CCW heat exchanger. As a result the potential loss of temperature indication due to the failure of this Tl does not present a safety concern.

F. Eauioment Soravdown.

The effect of spray on nearby equipment will not impact safety related functions. This is based on the limited number of components in the vicinity (2SW-5260 limit switches, 2SW5173 solenoid, accumulator for 5174), and the low driving pressure (30 psig) out of the orifice.

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