ML20058H709

Discusses Integrated Plant Safety Assessment Sections 4.3 Re Wind & Tornado Loadings & 4.6 Re Tornado Missiles.Upper Reactor Bldg Structure Will Be Upgraded by Adding Cross Braces to Roof Framing

ML20058H709
Person / Time
Site:	Oyster Creek
Issue date:	11/15/1990
From:	Devine J GENERAL PUBLIC UTILITIES CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
5000-90-1990, C321-90-2003, NUDOCS 9011210252
Download: ML20058H709 (8)

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l GPU Nuclear Corix>rstion N 1wWE gay One Upper Pond Road Parsippany, New Jersey 07054  !

201 316-7000 TELEX 136-482 '

November 15, 1990 Writer's Direct Dial Number:

C321-90-2003

$000-90-1990 U. S. Nuclear Regulatory Commission [

Attention: Document Control Desk

, Mail Station Pl-137 Washington, DC 20555 "

Gentlemen Subjects Oyster Creek Nuclear Generating Station (OCNGS)

Docket No.'50-219 "

Integrated Plant Safety Asses 9 ment Sections 4.3, ;j Wind and Tornado Loadings, and 4.6, Tornado Missiles

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.The NRC staff's safety evaluation (SE) concerning the subject matters was transmitted to GPU Nuclear Corp.~on March 8, 1986. While the staff agreed with many of our analyses, the.SE identified a number of concerns which  !

affect the conclusions regarding.the plant's overall capability to- l withstand wind and tornado loads. Therefore, you requested that we l-

-re-evaluate the wind speed (i.e., exceedance probability) at which safe l shutdown could=be. achieved with appropriate ~ consideration of the structural failure modes, and conclude whether any modifications are ,

warranted tonincrease the plant's capability to withstand wird and tornado i loads.

. We have completed our re-evaluation and have decided to upgrade the upper i

reactor building structure by adding cross braces to theLroof' framing (See below for more details). GPUN believes that the proposed modification and the responses given below address the NRC staff'o concerns and resolve the

subject'SEP. topics.

A. Reactor Buildina Above the Oceratino Floor NRC Concern 1 Steel'tenelle strengths above yield were utilized *

j. . without1 consideration of structural stability that may become critical due to larger. deflections.

l~ GPUN Response Our analysis of the reactor building configuration after completion of L the: planned modification does not utilize steel tensile strengths L above yield. The results indicate that, after completion of this l

modification, the structural stability of the Reactor Building would be maintained at wind speeds up to 190 mph. O 1 9011210252 90111b l FDR ADOCK 05000219 II P \

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, . .;, y v uru rSuciear Corporation is a subsidary of General Pubhc Utilities Corporation l

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. C32,1-90-2003 Page 2 NRC Concern 2. If the roof deck or siding remains attached, simultaneous uplift 43d axial loads in the roof purlino should be evaluated.

OPUN Response Upon completion cf the proposed modification, the cross bracing will be adequate to transfer all applicable loads from the roof and siding to the main structural members. The roof purlins will not be relied upon to perform any structural function. If the purline were not adequate, the only consequence would be a loosening of the roof deck.

Buckling of the purlins would not degrade the overall structural l stability of the reactor building superstructure.

NRC Concern 3. Analysis of the metal siding system should account for possible buckling and the capacities of the connections should be examined. Furthermore, tests indicate that the siding capacity may be higher thun assumed and thus the siding may transmit loads to the steel fr2ces, therefore, loads applied to the steel frame from the roof deck and metal siding should be conaidered.

GPUN Responee our analysis of the metal siding system accounted for possible bu:kling and concluded that the capacities of the connections are higner than Lhat of the siding. Loads fully applied to the steel frame from the roof deck and metal siding were considered in the reanalysis and .83 was concluded that, after completion of the proposed modification, ti+ critical element can withstand wind speeds up to 190 mph, while the oeck and siding are assumed to be intact.

NRC Concern 4 Considering the three issues discusoed above, the licensee should re-examine the upper reactor building structure to determine its capacity and the potential effects on equipment within the building, in order to determine the limiting capacity for which safe plant shutdown can be assured.

gpUN Response As indicated above, GPUN re-examined the upper reactor building m structure to determine its capacity. In the reanalysis the metal siding and roof deck of the reactor building were assumed to be intact. Therefore, full loads from the roof dock and metal siding were conservatively applied to the stoel frame structure.

Results of our analysis indicate that the existing reactor building steel superstructure is capable of sustaining loads associated with a wind speed of 115 mph at the elevation of the roof deck. At this wind speed, calculated stresses in the connections of the reactor building cross bracing approach but do not exceed yield. Therefore, the existing structure will continue to perform its intended function at wind speeds up to 115 mph.

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Wind cnd Torn d3 Lo dings, cnd 4.6, Torn:do M130ilco C32,1-90-2003 Page 3 To understand the impact of this condition on plant operation, the wind hazard probability curves for the Oyster Creek sito contained in the aforementionod NRC SER were reviewed. These curves provide the annual probability of exceeding a given wind speed at the Oyster Creek site. The wind speeds reported in these curves are the base wind speeds at 33 feet above grade. A wind speed of 115 mph at the Reactor Building roof is equivalent to a base wind speed of 95 mph.

Based on the information in the aforementioned SER, the probability of exceeding a 95 mph base wind speed at the Oyster Creek site is approximately 8x10' per year at the upper bound of the 95%

confidence level. At the median of the 95% confidence level, the probability of exceeding a 95 mph base wind speed is approximately 5x10~ per yrar. Since there is some level of margin in the design calculations and since the recurrence interval for a 95 mph base wind is approximately 1,000 years, we believe the existing structure provides a significant level of plant protection.

However, as shown in Table 1, the capacity of the existing structure is slightly less than that reported in the FSAR. The FSAR states that the maximum stresses remain less than 80% of yield at wind speeds up to 125 mph at the roof elevations. In addition, the probability of exceeding a 95 mph base wind speed is greater than the probability of eccurrence of other events considered in the design of Oyster Creek.

OpUN, therefore, proposes to upgrade the building by adding sixteen double angle cross braces to the bottom chord of the reactor building roof framing. This modification will enable the reactor building steel structure to withstand loads associated with wind speeds of up to 190 mph (approximately 5x10-6 per year probability of exceedance at the upper 95th percent confider.*e level) and provide further protection for the crane support from potential deflections of the building. Maximum stresses at this wind speed will approacn but will not exceed yield (See Table 2). As shown in Table 2, the probability of exceeding a wind speed of 190 mph at the Oyster Creek site is approximately 5x10-6 per year. In the staff's SER on the Diesel Generator vaults at Oyster Creek subjected to tornado generated load dated February 26, 1990, the staff stated that protretion from a turnado wind speed of 168 mph is acceptable. Therefore, CPUN proposes to modify the existing reactor building steel structure as discussed above. However, CPUN does not consider that an upgrade to a wind speed of lower probability would provide substantial additional protection (10CFR 50.109). OPUN is confident that the modified structure will provide a significant level of plar.t protection.

Engineering efforts for this modification are currently in progress.

Schedules for the upgrade will be addressed in the Oyster Creek integrated schedule.

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, C32,1-90-2003 Page 4 ERQ_gpacern.5. Crane stability from excessive deflection 6 should also be addressed if stool strengths higher than 1.6 x AISC allowables are utiliaed.

CPUN RecDonee Results of the reanalysis indicate that, after completion of the proposed modification, maximum calculated steel stresses will be less than 1.6 x AISC allowables assuming a 190 mph tornado wind. Relative displacement between the emot and west columns at the crane support locations will be negligible (0.25 inches). Therefore, the reactor building crane will not be derailed. In addition, horizontal drift of the reactor building steel structure at the crane support will be only approximately 0.50 inches.

D. Control RQ2m NRC Concern. Demonstrate that failure of the north wall due to combined wind and missile impact loading will nnt prevent safe plant shutdown.

CPUN Rennonse We have evaluated the ability of the north wall of the oyster Creek Control Room to withstand loads associated with the impact of the tornado generated missiles described in NRC Standard Review Plan 3.5.1.4 " Missiles Generated by Natural Phenomena." The 1490 pound utility pole described in the Standard Review Plan was determined to be the most critical missile. Standard Review Plan 3.5.1.4 requires this missile to be considered to a height of 30 feet above grade.

However, the analysis conservatively assumed that this missile would strike the center of the wall panel at an elevation of 32 feet above grade. Impulse-momentum methods and yield line theory were used to determine ductility ration. The test results conducted at Sandia Laboratories (EPRI NP-440 " Full Scale Tornado Impact") were used to develop the forcing functions.

The Control Room north wall is a 12 inch thick reinforced concroto non-loadbearing wall. Portions of the wall are cast-in-place concrete reinforced with #4 0 12 inches each way, each face. The remaining portions of the wall are 12 inch thick precant concrete panels with main reinforcement of #11 9 12 inches. Our analysis douonstrates that the cast-in-place walls have the lower capacity to withstand missile impact loads. Therefore, the cast-in-place walls were addressed in the analysis. The results of our analysis for the 12 inch cast-in-place walls are as followen

1. The Oyster Creek Control Room north wall 10 capable of withstanding the impact loads from 1490 pound utility pole missile generated by a tornado wind speed of 160 mph. The wall will experience moderate cracking and minor local partial penetration. However, collapse of the wall will not occur.

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2. The ductility ratio of the wall reinforcing was determined to be 12, which is acceptable per BC-Top-9-A Rev 2 " Design of structures for Missile Impact" by Bechtol Corporation. Since this wall is non-loadbearing, local v.amage and yielding of reinforcing will not jeopardite the structural integrity of the wall nor the control Room.

3. While the entire spectrum A of tornado missiles described in Standard Review plan 3.5.1.4 (Missiles Generated Dy Natural Phenomena) was considered in the analysis, in actuality, at wind speeds of 160 mph only relatively light objects could be lifted 30 feet above grade. These lighter objects would not be capable  ;

of performing substantial structural damage. In addition, an +

object would have to be lifted 25 feet above grade to hit any portion of the subject wall.

In conclusion, the north wall of the Oyster Creek Control Room is capable of witnatanding the loads from a missile generated by a tornado wind speed of 160 mph without impact on the safety functions of any plar'. equipment or structure. Based on the NRR tornado hazard curve discusse) previously, the 160 mph wi probabilityofoccurrenceoflessthan10~gdspeedcorrespondstoa per year at Oyster Creek. ,

This probability level is considered congruent with the protection levels associtted with other severe natural phenomena, such as earthquakes atd flooding, and with postulated events, such as pipe break.

As stated pe sviously, the probability of exceeding a wind apeed of 160 mph at the !yster Creek site is less than 10-5 In the staff's SER on the Diestl Generators Vaults at Oyster Creek subjected to tornado generated loading dated February 26, 1990, the staff stated that protection from a tornado wind speed of 168 mph is acceptable. OPUN does not consider that an upgrade would provide substantial additional

! protection (10CFR 50.109). Thus, OPUN is confident that the existing control Room North well provides a significant level of plant protection and upgrading of this structure is not required.

C; Architectural Componente l

l NRC Concern Verify that architectural components, such as rollup doors, are not located such that damage to safe shutdown equipment could occur.

l OPUN Response

! During the integrated assessment, the staff identified several l components in the vicinity of tue mechanical equipment access opening of the reactor building that are potential targets for missiles penetrating the access rollup doors. As stated in Section 4.6.2 of IPSAR/NUREO 0822, CPUN agreed to evaluate the potential for and consequences of tornado-missile impact on components in this area rad provide protection, if necessary.

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-. C321-90-2003 1 Page 6 l OPUN letter dated June 7, 1985 provided the results of an evaluation I concerning the consequences of tornado missile damage to certain safety related components in the vicinity of the access rollup door.  !

The evaluation concluded that even with loss of certain components j near the access door, unaffected paths exist to achieve and maintain  !

safe shutdown. There are no other access doors or openings which I would permit damage to safe shutdown equipment due to tornado winds or j missiles.

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If you have any questions concerning this submittal, please contact Mr. j Michael Laggart, Manager, Corporate Nuclear Licensing at (201) 316-7968. I Ver trulyfy urs, y

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J. C. DeVine, Jr.

Vice President and I Director Technical Functions )

JCD/YN/ pip I l

ces Mr. William T. Russell, Administrator Region I U.S. Nuclear Regulatory Commission  ;

475 Allendale Road )

King of Prussia, PA 19406 NRC Resident Inspector Oyster Creek Nuclear Generating Station Forked River, NJ 08731 l

Mr. Alex Dromerick U.S. Nuclear Regulatory Commission Mail Station P1-137 Washington, DC 20555 l

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• TABLE 1 l Wind speeds and aswociated probabilities at which maximum calculated I stresses reach a design limit of 80% of yis1d as specified in the OCNGS  :

F8AR. j i

Reported in Existing Configurations ,

FSAR Configuration After Modification 9 RB Roof Elevation 125 mph 100 mph 169 mph

• Base Wind (33' Above 100 mph 85 mph 169 mph Grade) '

Upper Bound Annual 6x10'4 8x10~3 7x10-6 Probability of Exceed-ing Base Wind speed 0 95% Confidence Level  !

Median Annual 3x10-5 8x10'4 5x10*7 Probability of Exceed-ing Base Wind speed 0 .s 954 Confidence Level P

• At'this wind speed, tornado winds control hazard probabilities. For tornadoes, base wind speeds and wind speeds at the roof elevation are

!- approximately equivalent.

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• TABLE 2 Wind speeds and associated probabilities at which maximum cale"1 Lied stresses reach the yield point of the steel.

Reported in Existing Configurations FSAR Configuration After Modification e RB Roof Elevation 140 mph 115 mph 190 mph Dame Wind (33' Above 115 mph 95 mph 190 mph Grade)

Upper Bound Annual 8x10~6 8x10~4 5x10-6 Probability of Exceed-ing Base Wind Speed e 95% Confidence Level Median Annual 5x10-6 5x10-5 3x10~7 Probability of Exceed-ing Base Wind speed e 95% Confidence Level

• At this wind speed, tornado winds control hazard probabilities. For tornadoes, base wind speedn and wind speeds at the roof elevation are approximately equivalent.

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