ML18009A622
| ML18009A622 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 07/31/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18009A621 | List: |
| References | |
| NUDOCS 9008080214 | |
| Download: ML18009A622 (8) | |
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i UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REGARDING THE SEISMIC DESIGN OF FLEXIBLE VERTICAL TANKS SHEARON HARRIS NUCLEAR POWER PLANT UNIT 1 CAROLINA POllER
& LIGHT COMPANY DOCKET NO. 50-400
1.0 INTRODUCTION
Surveys of damage during past earthquakes (NUREG/CR-4776) have repeatedly pointed out the damage susceptibility of large, above-ground, vertical tanks under earthquake loads.
The basic cause of damage has been identified as the inadequacy of the seismic analysis methods used for design of the tanks.
A number of safety-related, above-ground vertical tanks exist at the operating nuclear power plant sites.
The earlier, commonly used method of analyzing tanks for seismic response was based on the "Housner-Method,"
contained in TID-7024, "Nuclear Reactors and Earthquakes,"
dated August 1963.
During the discussions related to the resolution of Unresolved Safety Issue (USI) A-40, "Seismic Design Criteria," the method of analysis of an above-ground, flexible, vertical tank was identified as an important topic requiring technical resolution.
The resolution of the USI is contained in Revision 2 of Standard Review Plan (SRP) Sections 2.5.2, 3.7.1, 3.7.2 and 3.7.3.
The guidelines related to the seismic analysis of the above-ground vertical tanks are included in SRP Section 3.7.3.II.14.
Thus, at a number of nuclear power plant sites, licensees were required to ensure that the safety-related, above-ground vertical tanks are adequately designed.
Most of the licensees of newer plants have incorporated the flexible tank concept in the design of their above-ground tanks.
Some licensees have committed to evaluate their designs using the procedures developed by the seismic qualification utility group (SHRUG) under the resolution of USI A-46, "Seismic gualification of Equipment in Operating Plants."
Carolina Power
& Light Company (CP&L) is one of the four licensees requested to provide information regarding their above-ground vertical tanks.
Information related to the seismic design of the vertical, above-ground steel tanks of CP&L's Shearon Harris Nuclear Power Plant, Unit 1 (Harris),
was requested by Reference 1.
This evaluation addresses the seismic adequacy of the two safety-related, vertical tanks at the Harris site.
PDR ADOCK 5'0073'0080802g4-P 05000400 PDC j,'
- 2. 0 EVALUATION A typical tank evaluation consists of confirming:
(1) the appropriateness of the seismic analysis, (2) the adequacy of the tank shell and the roof
- supports, (3) the adequacy of the anchor bolts to hold the tanks against uplift, and (4) the adequacy of the foundation or the floor-slab.
The refueling water storage tank (RWST) and the condensate storage tank (CST) are located in the Tank Building at a floor elevation of 261.00 ft mean sea level (MSL).
The RWST is enclosed on four sides by reinforced concrete walls up to elevation 286.00 ft MSL with no roof slab.
The CST is fully enclosed by reinforced concrete walls and roof slab.
The horizontal and vertical design response spectra for the plant are based on Regulatory Guide 1.60 with zero period ground acceleration (ZPGA) of 0. 15g for safe shutdown earthquake (SSE) and 0.075g for operating basis earthquake (OBE).
The licensee has considered the appropriate floor responses to arrive at the tank-base excitations.
The tank seismic analysis models (TSAM) and the responses for RWST and CST are shown in Figures 1 and 2, respectively.
An examination of the TSAM indicates that the sloshing (convective) mode of fluid vibration is not considered a part of the models as delineated in the 'guidelines provided (Reference 1).
However, in calculating responses from the impulsive mode of fluid-tank vibration, the licensee considered the entire fluid mass rather than the effective fluid mass (which could be about 70K of the total fluid mass).
Also, the licensee has considered the effect of sloshing on tank roofs and roof support members.
Recognizing that (1) these calculations were performed (in 1981) prior to the NRC position (Reference 1), (2) the error introduced by these counterbalancing effects is not considered as significant, and (3) the overall safety margins are substantial, the calculated tank responses are acceptable.
Figures 3 and 4 indicate the combined responses from the two horizontal components of the earthquake as delineated in Regulatory Guide 1.92, "Combining Modal Responses and Spatial Components in Seismic
Response
Analysis."
Though a dynamic analysis was not performed to determine the responses of the tanks in the vertical direction, the licensee used 100K of the vertical static load (instead of some fraction of the dynamic responses) to calculate the most adverse combined responses, which is acceptable.
Overall dimensions and plate thicknesses of both the tanks are shown in Figures 1 and 2.
The tank shell and the supporting components (i.e., roof
- supports, anchor-bolt chairs) are fabricated from ASME SA-240, T304 material.
The 3 in. diameter anchor-bolts are fabricated from ASME SA-449 material.
The tanks are formed from cylindrical hoop sections with varying wall thickness.
These hoop sections are referred to as courses.
The maximum combined compressive stresses in each of the tank courses were computed for OBE and SSE loadings, and compared against the corresponding
allowables.
A minimum safety factor (i.e.,
a ratio of allowable stress to actual stress) for RWST under OBE loading in Course 1 was calculated as
- 1. 16.
The maximum tensile stresses in the anchor-bolts due to combined overturning moment was determined to be less than half the yield strength and the allowables of the bolt material.
The calculated stresses in chair bearing plates, gusset plates, weld stresses in chair to shell connections and the gusset plates to bearing plate connections were significantly less than the allowables.
The stresses in roof-support skirts and their welds with the roof and the cylinder were determined to be less than the corresponding allowables.
As the original designs of the tanks were performed considering tank flexibilities, there are no appreciable additional loads imposed on the supporting structures that would require reevaluation.
However, the licensee checked the original calculations and confirmed that the postulated loads are properly considered in the designs.
- 3. 0 CONCLUSION On the basis of, the review of the licensee responses and the site audit of licensee's engineering calculations, the staff concludes that the design and construction of the two safety-related
- tanks, the condensate storage tank and the refueling water storage tank, properly considered the effects of tank flexibilities and that the guidelines provided in Revision 2 of Standard Review Plan 3.7.3 are satisfactorily met.
Therefore, the tanks are acceptable.
REFERENCES 1.
Letter from E.
Adensam (NRC) to Lynn M. Eury (CP8L),
Subject:
"Seismic Design Consideration for Certain Safety-Related Vertical Steel Tanks (Request for Information)," June 1, 1989.
2.
Letter from L. Loflin (COL) to NRC (response to Reference 1),
October 3, 1989.
Dated: July 31, 199O
~Princi al Contributors:
H. Ashar R. Becker
REFUELINP
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Figure 1
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Figure 2
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h4iXlMUM RESPONSES OF R.W.S. TANI(
(Includes Max Response Caused By Sloshing Effect)
ZBE=4i Ho%"/P.
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MODEL DISPLAGEMENT AGI-ELERATION SHEAR
( FT )
GGEI=I=IGI".-NT
( KIPS)
MAX.
iViOIN/EI'lT
( KI T)
(1)
Horizontal Responses Represent the simultaneous effect of the two horizontal seismic excitations.
(2) maximum vertical displacement of wave for cvocal analyses caused by sloshing effect ~ 9. 7 7
MAXIMUM RESPON5E5 GF C.S. TANY.
(Includes Max Response Cause/
By Sloshing Effect) o,~ss4-p.033'.4-4
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MODEL DISPLACEMENT ACCELERATION SHEAR iViOIIEIIT
( FT )
GOEI=I=IGIENT
( KIPS}
( KFT)
(l) llorizontal Responses Represent the simultaneous effect of the two horizontal seismic excitations.
(2)
Maximum vertical displacement of wave for cvocal analyses caused by sloshing effect ~ ~
DISTRIBUTION
= Docket File NRC PDR Local.PDR S. Varga G. I,ainas E. Adensam H. Ashar T. Alexion A. Gody R. Rothman P. Anderson R. Becker OGC E. Jordan ACRS (10)
Harris File