ML20087G950
| ML20087G950 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 08/11/1995 |
| From: | Denton R BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-M87189, TAC-M87190, NUDOCS 9508170265 | |
| Download: ML20087G950 (5) | |
Text
d Rostar E. DEVION Baltimore Gas and Electric Company
, Vice President Calvert Cliffs Nuclear Power Plant Nuclear Energy 1650 Calvert Cliffs Parkway Lusby, Maryland 20657 410 586-2200 Ext.4455 Local 410 260-4455 Baltimore August 11,1995 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Document Control Desk SUI 1 JECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 Response to Request for Additional Information - Evaluation ofIsolation Provisions for the Senice Water System (TAC Nos. M87189 and M87190)
REFERENCE:
(a)
Letter from NRC to R. E. Denton (BGE), dated n. : I,1995, Request for Additional Information - Evaluation of Isolat.. Jrovisions for the Senice Water System (TAC Nos. M87189 and M87190)
The response to the questions posed in Reference (a) are attached.
Should you have questions regarding this matter, we will be pleased to discuss them with you.
Very truly yours, I
RED / PSF /bjd i
Attachment cc:
D. A. Brune, Esquire T. T. Martin, NRC J. E. Silberg, Esquire P. R. Wilson, NRC L. B. Marsh, NRC R. I. McLean, DNR D. G. Mcdonald, Jr., NRC J. H. Walter, PSC
[k 9508170265 950811
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ATTACllMENT (1) l l
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION -
EVALUATION OF ISOLATION PROVISIONS FOR TIIE
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SERVICE WATER SYSTEM (TAC NOS. M87189 AND M87190)
NRC Ouestion No. I:
Provide a qualitative estimate for the ranges of naturalfrequencies of the NSR portion of the SRWpiping and ensure that the piping will be outside the resonance of the Calvert Chffs seismic design input motion.
BGE Resnonse:
Piping Natural Frequencies Estimates of piping natural frequencies were made during the development of seismic fragilities in support ofIPEEE efforts at Calvert Cliffs Nuclear Power Plant (CCNPP). At that time, service water (SRW) piping located in the Turbine Building was evaluated for potential system vulnerabilities. A potential seismic interaction was investigated and resolved during this process.
The resolution of this particular issue required developing a localized estimate of the piping system's frequency. This estimate is believed to be indicative of the frequency ranges of the balance of the SRW piping in the Turbine Building.
This particular seismic interaction concerned a small bore branch line off a large bore pipe. The large bore pipe's motion is determined by the motion of a still larger diameter header. The header is water-filled and supported by rod hangers varying in length from 3' to 8'. The effective hanger length in the area of the interaction was determined to be about 4'.
Piping spans are less than the ANSI B31.1 maximum length span for this diameter pipe. The piping run is very long with no lateral restraints near the area of concern, so the piping behaves as a single degree of freedom system whose lateral stiffness is determined by restoring action (pendulum effect) of the rod hangers. The best estimate of piping frequency for the large bore header was determined to be about 0.5 liz. Subsequently, the calculated displacement of -0.7" at the point of the potential interaction was found to be relatively small when compared to the clearance provided.
Based on this evaluation and the configuration of the balance of the non-safety-related (NSR) portion of SRW piping and supports in the Turbine Building, it is estimated that the natural frequencies for the majority of the piping lie within a range of 0.5 to 15 liz, i c., less than what would be considered the rigid range.
Resonant Frequencies ofDesign Input Motion Resonant frequencies of the CCNPP Turbine Building seismic input motion are also in the range of 1 to 15 liz. " Realistic Median Centered" in-structure response spectra (ISRS) were developed using as a basis the NUREG/CR-0098 84th percentile non-exceedance ground response spectrum anchored to the design basis safe shutdown earthquake peak ground acceleration (PGA) of 0.15g.
As suggested by the SQUG Generic Implementation Procedure (GIP), realistic equipment damping values given in the NUREG and EPRI Report NP-6041 of 5% were used as the basis for the response spectra. Using these 10% peak shifted ISRS, for evaluations below the 45' ground level, horizontal peak accelerations up to 0.65g's occur over a range of 2 to 4 liz.
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l ATTACIIMENT (1)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION -
EVALUATION OF ISOLATION PROVISIONS FOR TIIE SERVICE WATER SYSTEM (TAC NOS. M87189 AND M87190_)
Resolution While these estimates show that the NSR SRW piping system range of natural frequencies do not fall outside the resonance of the Calvert Cliffs seismic design input motion, experienced-based engineering judgment indicates that inertia from seismic events does not cause failure in welded steel piping. Piping with little or no seismic design has performed quite adequately during earthquakes up to 0.9g's PGA (Reference EPRI Report NP-5617, Volume 1). Considering inherent ruggedness of steel piping in general (Reference ASME Code Case N-411), the occurrence of a severe seismic event is not expected to result in a large pipe rupture.
The piping in questions is generally of welded steel construction. There are some bolted flange joints and some of the small branch lines for small relief valves have threaded joints near the relief valve portion of the vent line. He ANSI B31.1 piping is supported by rods, spring cans, rigid supports under valves at valve stations, slides on trapeze and rigid supports, an occasional rigid restraint, and so forth. The piping is typically supported in a flexible manner normally found in a fossil fueled power plant or other heavy industrial facility. This is typical construction even for facilities located in earthquake-prone regions.
Finally, while a seismic event may result in swinging of the piping, the vast majority of pipe to pipe or pipe to structure spatial interactions can be considered beneficial. This is because they ensure the pipe dynamic response is nonlinear and prevent the resonant buildup of motion.
NRC Ouestion No. 2:
Explain the basis andprocedure)or identifying thefive potential break locations.
HGE Response:
Dynamic testing, under the Nuclear Regulatory Commission (NRC)/EPRI piping and fitting reliability joint test program, and actual carthquake experience (Reference EPRI NP-5617) has shown that scismic inertial motion does not result in rupture of welded steel piping and that spatial interactions with respect to large bore piping do not have any negative effects on piping.
Therefore, the area of concern was reduced to checking the NSR SRW piping for excessive anchor movement, primarily on small branch lines. This is the credible failure mode that could cause loss of pressure boundary in the SRW system.
Accordingly, the SRW piping in the Turbine Building, including all small bore and large bore branches, was visually inspected. An overall description of the SRW piping system is provided in response to Question No.1. The inspections were conducted in a manner reflecting the EPRI guidelines that are endorsed by the NRC in NUREG-1407. While these guidelines are not directly applicable to piping systems, the guidance on the conduct of seismic walkdowns and anRsis of 2
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1 ATTACIIMENT (1) l RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION -
I EVALUATION OF ISOLATION PROVISIONS FOR Tile SERVICE WATER SYSTEM (TAC NOS. M87189 AND M87190) results is relevant. Based on the engineering judgment of the walkdown team, the following three areas ofsusceptibility were investigated:
1.
Branch lines with threaded connections to main pipe or equipment - Considering adverse spatial interactions and seismic inertial motion, this condition, if existing, was identified as having the potential to leak due to the inherent weakness of a threaded connection in bending when compared to welded steel piping.
2.
Branch lines with restrain _t.s - Imposed forces and moments due to differential seismic anchor movement between a restrained branch line and its header could result in failure at I
the welded joint between the branch line and the main pipe.
3.
Branch lines with the potential to impact or become hard bopM - This could be any branch line which might be susceptible to impact with a structural member or other interference due to movement of the main pipe with a resulting failure at the welded joint between the branch line and the main pipe.
Of the five potential break locations identified, one was a combination of situation Nos. I and 2, one was similar to situation No. 2 and three were similar to situation No. 3.
$RC Ouestion No. 3:
Explain the basis and procedurefor concluding that the 7'urbine Building would maintain its integrity durmg a seismic event.
BGE Response:
The Turbine Building was originally designed to satisfy the defined requirements of a Seismic Class 11 structure. The building is an integrated steel stmeture, with metal siding, supported on reinforced concrete foundations.
Class 11 structures are designed in accordance with design methods of accepted codes and standards insofar as they are applicable. Wind design (25 psf zone) is in accordance with the Uniform Building Code (UBC), with a one-third increase in the allowable stresses. Seismic design is in accordance with the UBC. Seismic forces were based on Seismic Probability Zone 3 multiplied by a ratio of 0.08/0.30. A one-third increase in allowable stresses was not allowed. All of the structural steel columns, beams, and roof trusses of the building have been designed as independent members and in accordance with American Institute of Steel Construction, Inc.
(AlSC) Specifications. The Turbine Building is constructed below grade from the turbine deck down to its base mat.
In addition, taking the position stated in the NRC -endorsed GIP, it is a fact that large commercial / industrial stmetures, such our steel constructed Turbine Building, have behaved very well during strong motion earthquakes with seismic ground motion in excess of 0.9g's. They have 3
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ATTACilMENT (1)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION -
EVALUATION OF ISOLATION PROVISIONS FOR TIIE SERVICE WATER SYSTEM (TAC NOS. M87189 AND M87190) retained their structural and system integrity with the exception of localized damage due to insufficiently anchored equipment. Facilities which were built to the requirements of basic code construction 1. :ve been found to have the ability to sunive seismic-induced loadings and stresses well in excess of the original allowables.
Therefore, the Turbine Building at CCNPP has the ability to sunive an safe shutdown earthquake without the potential for damage to its piping systems.
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