ML19332E806

Forwards Response to Request for Addl Info on FSAR Section 3.8 as Followup from NRC Structural Audit at Facility During 890906-07.Stress Reported in FSAR Based on Conservative Evaluation Performed in Rev 0 of Calculation

ML19332E806
Person / Time
Site:	Comanche Peak
Issue date:	12/07/1989
From:	William Cahill TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TXX-89793, NUDOCS 8912130001
Download: ML19332E806 (14)

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. Log # TXX-89793 File # 903.8 r =

1UELECTRIC December 7, 1989 Executive Vkr President U. S. Nuclear Regulatory Commission i Attn: Document-Control Desk '

Washington..D. C. 20555

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SUBJECT:

COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)

DOCKET NOS. 50 445 AND 50-446 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION ON FSAR SECTION 3.8 >

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Gentlemen:

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.' During September 6-7, 1989, the NRC conducted a structural audit at CPSES. As a result of conversations after the audit, the NRC has identified two' Requests for-Additional Information (RAI's). TU Electric is providing a response to the RAI items-(see enclosure).

If you have any. questions regarding this submittal, please contact Carl Corbin

-at (214) 812-8859.

Sincerely,

{

WLyLa08lb William J. Cahill, Jr.  ;

By: M '

r RogerH5. Walker Manager, Nuclear Licensing CBC/smp

- Enclosure

-c - Mr. R. D. Martin, Region IV Resident Inspectors, CPSES (3) 8912130001 891207 PDR ADOCK0500g5 g3o A

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P. O. Box 1002 Glen Rose, Texas 76043-1002

.p. Enclosure toTXX*89793 )

Yl/g ' ,Pagel1 of 13 i Response to Request for Additional Information (Follow up from NRC Structural Audit at CPSES during September 6 7, 1989)

1 Part 1 RAI-items and response pg. 2 thru 5 Part 2 List'of references regarding pg. 6 High Strength Bolts Part 3 ' Design Criteria for_Handtight pg. 7 High. Strength Bolts

, 'Part 4 Typical Details of Handtight pg. 8 thru 12 H High Strength Bolted Connections Part 5 Calculated Stresses for Handtight pg. 13 ,

High Strength Bolts l l l l

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Enclosure to TXX 89793

,Page' 2 of 13- >

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION ITEM 1 l' A review of calculation 16345 CS(B)-171 (" Concrete Design Condensate Storage Tank and Refueling Water Storage Tank"), indicates that the L hydrodynamic load was calculated based on TID 7024 (" Nuclear Reactors ano Earthquakes," U. S. Atomic Energy Commission, Washington, D. C. August 1963. Chapter 6) which assumes the tank to be rigid. However, the seismic i profile indicates that the tank wall acceleration increases-with height P above the mat. What impact does this have on the TID assumptions? Since the calculated rebar-stresses are very close to the specified allowable stress, is the validation of the tanks adversely impacted?

RESPONSE

The maximum calculated stress (52.4 ksi) reported in FSAR Table 3.8 1 is L based on the conservative analysis of the tanks performed in revision 0 of the calculation. At the time of the audit, the schedule did not allow us to clearly present the results of the latest revisions to the calculation.

l The calculation concludes that of all load combinations specified for the l

design of Seismic Category I structures (FSAR Section 3.8.4.3.2), only three combinations will potentially control the design. These are:

Load Combination 1: U = 1.4D + 1.7L + 1.9 F ogo l- [FSAR Section 3.8.4.3.2 (1)(b)]

Load Combination 2: U = 0.75 (1.4D + 1.7L + 1.7To +1.7Ro+

1.9 Fogo)

[FSAR Section 3.8.4.3.2 (1)(e))

Load Combination 3:- U = D + L + To+Ro+Feqs

[FSAR Section 3.8.4.3.2 (2)(a))

When Revision 0 of the calculation was originated the seismic data for the tanks had not been validated and from review of the configuration of the i tanks (thickness of wall and amount of reinforcing steel) it was judged that they would have adequate-capacity. Conservative simplifying assumptions were made in the analysis for Revision 0 of the calculation and led to the conclusion that Load Combination 1 governed the design, and the maximum rebar stress was 52.4 ksi in the meridians direction of the wall.

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Enc o1'sure to'TXX 89793 .

- LPage'3 off13 Subsequent revisions to the calculation were made to remove confirmations and to address audit questions. The results of these evaluations demonstrated the conservatism of the original evaluation. Conservative assumptions.made in Revision 0 to obtain the design forces include: (1) the magnitude"of the seismic acceleration used to determine all horizontal loadings was based on the acceleration at the roof of the tank (2) the OBE accelerations were assumed equal to the SSE accelerations, and (3) the hydrodynamic loading was approximated as a uniform weight constant over the height of the water, accelerated by the acceleration corresponding to the roof elevation. Comparisons of the total base shear and moment, due i,

to the hydrodynamic loading, was calculated in accordance with the TID procedure and the results from the conservative approximation demonstrated that the loads used were much greater than required by the TID. 1 To address the above NRC question, the three governing equations were reevaluated-with the above conservatisms removed. That is, the validated seismic data was considered, the variation of seismic acceleration with height was considered, and the hydrodynamic loading was evaluated with the pressure profile derived in the TID except the acceleration used to determine the magnitude of pressure corresponds to that at the elevation of the mass center of the fluid; not of the base mat.

The-results demonstrate that due to the reduction in seismic loadings, '

Load Combination 2 would be the gcVerning load. combination. The corresponding maximum rebar stress would be 42.05 ksi in the meridians direction of the wall. The predominant loading in Load Combination 2 is.

thermal. The governing thermal condition is when the temperature of the fluid is maximum (1200 F) and the outside temperature is l minimum (00 F).

L In summary, the stress reported in the FSAR is based on the conservative I evaluation performed in Revision 0 of the calculation. The evaluation performed in response to the above question has shown that the original H ' analysis was adequate and that the reported stress could be lowered to 42.05 ksi in the meridians direction of the wall. The corresponding ,

allowable stress would be 54 ksi.

TU Electric has reviewed the evaluation of the only other Seismic Category I concrete tank (i.e., Reactor Make-Up Water Storage Tank). Similar conservatisms were used in this evaluation completely offsetting the effect of the tank wall acceleration on the hydrodynamic forces and resulting in lower stresses. Thus the original analysis is also appropriate for this tank.

. Enclosure toiTXX-89793

.Page 4 of 13 ITEM 2 FSAR pages 3.8 12 and 3.8 82 allow the use of non-pretensioned high I strength bolts when supported by an engineering analysis. What are the i design criteria for non-pretensioned bolts, where they are used and why are they used.

RESPONSE

Non pretensioned high strength bolts are used in connection details where movement of the connecting parts is required. In most cases, the movement is caused by the design thermal conditions. The structures utilizing these bolts are the rotating platform and polar crane runway girders, moment and pipe whip restraints, heat exchanger supports, miscellaneous hoists / monorails and platforms. These are all Category I structures except that the miscellaneous hoists / monorails and platforms may be either Category I or II.

L Review of literature (page 6 of this er. closure) on the behavior of high strength bolts indicates that the key factor that could affect the design of the bolts is fatigue loadings. Thus, the design allowables for the non pretensioned high strength bolts are based on fatigue considerations and are shown on page 7 of this enclosure. Two sets of allowables are

considered, the service condition (i.e. dead plus live load conditions)

! .and the factored load condition (loading combinations which include seismic loads). Prying action is considered in the design of these bolts and modified AISC shear tension interaction equations are used to account for combined shear-tension effect.

The service load allowables are based on a reduced endurance limit of the l bolt materials. These endurance limits were developed based on the I

fatigue loading consideration of the bolts and the root radii of the thread. A parametric study was also performed to study the effects of  !

various root radii on the endurance limit in order to obtain lower bound limits. Derivation of the service load allowables is documented by -

u calculation. ,

The factored load allowables are based on 14,400 fatigue load cycles on L the bolt materials. The number of load cycles (14.400) was based on a l twenty times increase in the seismic load cycles of 720 as specified in the CPSES FSAR Section 3.78.3.2. The use of the twenty times increase in -

load cycles in the development of fatigue design basis criteria is consistent with the design philosophy in codes, such as the ASME code.

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' Enclosure to'TXX-89793 ,

Page 5 of 13 Typical details of these non pretensior;ed high strength bolted connections are shown in pages 8 thru 12 of this enclosure. These bolts were-installed'with jam nuts or with their tareads staked so that the nuts would not be backed out of the thread. The use of the non pretensioned bolts in pipe' whip restraints is prinarily to hold crushable material in place, i.e., they have no significant load carrying function. In the' case of the polar crane and the rotating platform runway ~ girders, these bolts were installed primarily for lateral support and must allow the structures to expand under thermal load conditions.

.Page 13-of this enclosure shows the typical stresses in these bolts under the service and factored load conditions.

-Enclosure to TXX-89793

'Page 6 of 13' i

Technical References Utilized in the Development I of Design Allowables for Non Pretensioned l High Strength Bolts l .

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1. Rumpf, John L. and Fisher, John W.: Calibration of A325 Bolts, Journal of j the Structural Division, ASCE. December 1963  !

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2. Sterling, Gordon H.: Troup, Emile W. J.: Chesson, Eugene: and 1

Fisher, John W.: Calibration Test of A490 High-Strength Bolts Journal of the Structural Division, October 1965 )

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3. Munse. William H., Research on Bolted Connections ASCE Transactions Paper l No. 2839 )

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4. Munse W. H.: Peterson, K. S.: And Chesson, E.: Strength of Rivets And Bolts in Tension. Journal of the Structural Division, ASCE, March, 1959 1

I. 5. Lewitt, C. W. And Munse. W. H.: Riveted And Bolted Joints: Fatigue of Bolted Structural Connections, Journal of the Structural Division ASCE, February, 1963

6. Chesson, Eugene: Faustino, Norberto L. And Munse, W. H.: High Strength Bolts Subjected to Tension and. Shear, Journal of the Structural Division, ASCE, October, 1965 L 7. Aerospace Structural Metal Handbook,1981 Publication, (Formerly AFML-TR '68-115) e L

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Enclosure to'TXX 89793  ;

-Paga 7 of-13 DESIGN CRITERIA FOR HANDTIGHT HIGH STRENGTH BOLTS l

Handtightened high strength bolts (ASTM A325, A449 or A490) may be used where connections are required to slip provided-the design satisfies the other AISC i bolting requirements and the criteria below:

1. The allowable bolt tension F t, shall not exceed the values specified i below:

BOLT ALLOWABLE BOLT TENSILE STRESS. F+ (ksi) I MATERIAL SERVICE LOADS

• FACTORED LOADS **

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l A325 15 30 l' A449 15 30 A490 18 40  :

11. The shear tension interaction shall not exceed the following:

l BOLT ALLOWABLE BOLT TENSILE STRESS. Ft (ksi)

MATERIAL SERVICE LOADS

• FACTORED LOADS **

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A325 Ft = 19 - 1.6(fv) 1 15 Ft = 40 - 1.6(fv) 1 30 l 'A449 l

Ft = 19 - 1.6(fv) 1 15 Ft = 40 - 1.6(fv) 1 30 l l A490 ft = 23 - 1.6(fv) 1 18 Ft = 50 - 1.6(fv) 1 40 l l

! iii. ASTM A449 bolts.shall be limited to 1 1/2" and less. "

Where Ft - allowable bolt tensile stress including the effects of prying l

action fy- calculated shear stress i i.

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ENCLOSURE T0-TXX-89793 PAGE 8 0F i SLOTTED HOLES (VERT.)

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-ROTATING PLATFORM CONNECTIONS SIMILAR FIGURE 1 POLAR CRANE / ROTATING PLATFORM RUNWAYS w

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l ENCLOSURE TO TXX-89793

.PAGE-9-OF-13

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ENCLOSURE TO TXX-89793 l PAGE .10 0F 13

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ENCLOSURE TO TXX-89793 l PAGE 11 0F 13 I t

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! ENCLOSURE TO TXX-89793 PAGE 12 0F 13

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E;c?ostre to TXX 89793

• Page 13 of 13 CALCULATED STRESSED FOR HANOTIGHT HIGH STRENGTH BOLTS Commodity Typical ft Max. (ksi) Ft (ksi)

Descrintion Details Service (1) Factored (2) Service factored Polar Crane Figure 1 7.82 23.47 15.00 30.00 Rotating Figure 1 (A325) 3.01 28.9 15.00 30.00 Platform (A490) 1.53 16.70 18.00 40.00 Platforms & Figure 2A. 2B Negligible 23.09 15.00 30.00 Stairways Hoists & Figure 3 14.7 23.4 15.00 30.00 Monorails Heat Exchanger Figure 4 14.7 (3) 14.7 15.00 30.00 Supports Moment Figure 5 16.74 38.0 18.00 40.00 Restraints Pipe Whip Figure 6 Negligible -- Negligible -- -

Restraints (4) (4)

NOTES:

1) Excluding seismic loads unless noted otherwise

2) Including seismic loads

3) Includes seismic loads (conservative)

4) Handtight bolts for pipe whip restraints are only used to hold crushable material until pipe rupture occurs; bolt is not required to resist rupture loads

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