ML20087E689

Forwards Results of Final Structural Evaluation of Prestressed Concrete Reactor Vessel During Decommissioning & Prestressing Tendons Detensioned

ML20087E689
Person / Time
Site:	Fort Saint Vrain
Issue date:	01/15/1991
From:	Warembourg D PUBLIC SERVICE CO. OF COLORADO
To:	Weiss S NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
P-92012, NUDOCS 9201220085
Download: ML20087E689 (5)

Text

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hPublic Service' r.O*-L..

January 15, 1991

- 1 Fort St. Vrain Unit No. 1 P-92012

=U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C.

20555 ATTN:

Dr. Seymour H. Weiss, Director Non-Power Reactor, Decommissioning and Environmental Project Directorate Docket No. 50-267

SUBJECT:

Results of Final-Structural Evaluetion of PCRV

REFERENCES:

1) NRC Letter, Erickson to Crawford, dated February 8, 1991 (G-91020)

-2) PSC Letter, Crawford to Weiss, dated April 26, 1991 (P-91118)

Dear Dr. Weiss:

i In Reference

_1, the-Nuclear Regulatory Comission (NRC)~ submitted a request for additional information regarding the structural integrity o f-

the Prestressed-- Concrete Reactor-Vessel

-(PCRV) during decomissioning, with the - prestressing tendons 'detensioned (NRC Question' No. 7).

Public Service Company of Colorado-(PSC) responded a

to tkis question in Reference 2, providing_ results of' the preliminary structural evaluation of the PCRV.

In its response, PSC stated that

" Detailed engineering analyses are currently in progress to confirm the structural integrity. of the PCRV based on this dismantlement app roach. '?

The final evaluation of the structural integrity of the PCRV,has-been completed and the results are attached.

Several differences exist between the results of the preliminary-evaluation and those of the fino, evaluation. An incorrect modular ratio _-was used in the' preliminary evaluation to calculate concrete and-reinforcing steel stresses by means of the " working stress" riie th oo.= The working stress method-is' consistent with the original

'PrRV concrete and reinforcement design-outlined

'- -FSAR Section-

. hen the modular ratio was corrected and the working stress 5 c.2.

W methoo applied, the revised concrete and reinforcement stresses

-changed.- most of ' which ' were lowered. The attached results of the final evaluation reflect the correct stresses and margins of safety.

The' -results of the preliminary evaluation, submitted in Reference 2, included evaluation of stresses resulting from an Opera ting Basis

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' - Janodry;15, 1991

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Earthquake..

The attached _ results of the final evaluation identify

-stresses lfrom both the Operating Basis and Design Basis Earthquakes.

- Should you have any questions regarding this information, please contact Mr. M. H. Holmes at (303) 620-1701.

Very-t'ruly yours, g{- JY-JYwdL f

Don W. Warembourg

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Manager, Nuclear Operations

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Attachment-cc: Regional-Administrator, Region IV-

.i Mr. J. B. Baird Senior Resident inspector..

-Fort-St. Vrain Mr. Rober6 M. ' Quillin. Director Radiation Control-Division Co;orado Department of Health-4210 East lith-Averge Denver,.CO 80220

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Results1of Final Structural Evaluation of the PCRV with the Tendons Detensioned for Decommissioning Public Service Company of Colorado's (PSC's) response dated April 26 1991-(P-91118) to question 7 of-the NRC's Request for Additional Information dated February. 8, 1991,_ provided the results of the preliminary structural evaluation that was performed to confirm the-structural integrity of the PCRV after tendons have been detensioned.

Subsequently, the final structural evaluation has been completed.

This--submittal provides 'an "odate of the stress values and the-margins of safety that were reported in the April 26, 1991 submittal.

No.te - that the-seismic results are now provided for both the Fort St.

Vrain (FSV)-Operating Basis' Earthquake (UBE) and the Design _ Basis Earthquake-(DBE),_rathe', than for the OBE alone.

- As stated in the April-26,-1991 submittal, the strcctural evaluation considered the detensioning and removal of all 2e cross head tendons, alt 90 vertical tendons, and all circumferential tendons from grouo C

-through group 19, in addition, it was conservatively assumed that all circuverential tendons (inner, middle and outer) were detensioned even though it is planned to only detension the inner and

. middle tendons Lin the top head and the inner tendons in the belt line region..To evaluate this modified structure, a simplified free-body lumped mass model fixert at the basement floor of the PCRV structure was ' developed for analys is with the STAAD-Ill/ISDS1 computer code.

Inputs to the analysis included NRt' Regulatory Guide 1.60 (December, 1973) design ~ response spectra normalized -to the (FSV) specific

" double design earthquake" (DBE) ground motions with Regulatory Guide 1.61 (October, 1973) damping values.

Specifically, the FSV OBE-

- grou'nd motions of 0.05g horizontal and 0.0339 vertical accelerations and DBE ground were. used in the analysis. ).a1 motions of 0.10 hcrizon and 0.0679 vertical 9

accelerations In addition, the concrete

-has 'a compressive Strength of f'c = 60C0 psi and the reinforcing steel Lwas-conservatively assumed to be Grade 40 steel with a Fy =

40,000 psi,;although the.FSAR indicates that it is probably Grada 60, or (better.L The damping values.used are 2% horizontal and vertical for the OBE and-2% vertical and 5% borizontal for the DBE.

-1.- STAAD-III/ISDS, Revision 14.0 is a general purpose structural

-analysis program _for' the-static and dynamic analysis of sat tically-determinate and indetenninate structures represented by a combination of., beam and/or plate elements.

It-is-a-proprietary code of__Research Engineers r Inc. of Marlton, N.J.,

Copyright-1991 1

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... Atthchment The modified structure was conservatively evaluated for the loadings i

produced bylthe dead weicht of the PCRV structure (assuming the PCRV is : flooded ~with. water),- PCRV internal components, the lifting

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operations' of the core. support floor, and OBE and DBE events, i

-The _resulting -forces 'and moments in each of the individual crors 1

sections of the PCRV were used to develop concrete compressive and reinforcingisteel tensile stresses.-

In the developnent of.the 1

concretoJand reinforcing steel stresses,- all vertical, cross-head and circumferential pre-stressing tendons were considered detensioned.

The resulting. concrete compressive and reinforcing steel tensile-1 stresses ~are provided below:

Concrete Reinforcing-Cross Compressive Steel Tensile.

Section.

Loading Stress (psi)

Stress (psil-Top Head DW 16.7 0,0 Lift 7.7 0.0-OBE' Seismic 2 22,0 10.2 2

LDSE Seismic -

25.1 23.7 Belt Line DW.

-134.6 0.0 Region-Lift.

6.1 0.0 OBE Seismic ^

298.9 814.8 DBE Seismic 2 381.5 1,268.0 To ' determine margins of safety,-the worst case load combinations of dead weight,- lift loads, and OBE and DBE-seismic events were-considered' -using the~ following equations, consistent - with the 3

'" Building Code 9equirements _ for Reinforced. Concrete,"_-ACI 318-83 (Revised l1986), American Concrete Institute, Detroit, Michigan:

U = 0,75 (1.4 DW + 1,7 Lif t + 1.87 OBE seismic)-

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3 EQ-2:

U2 = 0.75 (1.4 DW + 1.7 Lift + 1.4 DBE seismic) 2.-

Includes the effects of Dead Weight (DW).

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' The -: total? combined-concrete compressive stress was compared to the i

" limit Condition 2". compressive stress alloweble of 0,85 f'c or_.5100

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as _ outlined byx Section E.1.2.6.2. of the :F5V-TSAR.-

The-reinforcing steel-allowable _ tensile stress was considered to be 90%

- of thelyieldLstress of Grade 40' steel, oc 36,000 psi. -The margins of safety, where. margin = allowableLstress/ combined actual stress,- are summarized below:

Concrete Reinforcing Steel-Section EQ-1 E0-2 E0-1 Eg;?

Top _ Head' 87.6 95.0 2517 1447 Belt Line' Region 8.97 9.28 31.5 27.0 in summary, the structural evaluation has ' determined that the-resulting' concrete ~ compressive and reinforcing steel tensile stresses are well within ' allowable limits.

Furthermore, adequate margin of-safety exists for all loading. conditions specified.

The potential

-for _ cracking-of concrete in the _ modified top head and_ beltline

_ regions has been reviewed:and, considering the relatively low tensile 1

stress-in'a-conservative number of reinforcing bars, cracking due to tension in the concrete is not expected.

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