ML20210R050

Safety Evaluation Accepting Revised Fermi-2 Control Ctr HVAC Sys Design Criteria in Design Criteria Document Submitted by Detroit Edison

ML20210R050
Person / Time
Site:	Fermi
Issue date:	08/22/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20210R033	List: ML20210R028 ML20210R050
References
NUDOCS 9709020270
Download: ML20210R050 (4)

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SAFET( EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE CONTROL CENTER HEATING. VENTILATION  ?

AND AIR CONDITIONING (CCHVAC) SYSTEM DETROIT EDISON COMPANY FERMI-2 DOCKET NO. 50-341

1.0 INTRODUCTION

in April 1989, the Senior Resident inspector at Fermi-2 identified certain concems regarding the structural integrity of the CCHVAC system at Fermi-2, which resulted in a Notice of l

Violation (50-341/89-011-02B(DRP)). The Detroit Edison Company (DECO, the licenue) responded to these concems in a Response to the Notice of Violation, dated November 29, 1989 (Ref.1), and supported this response with extensive desig,. calculations. The inspector reviewed these calculations and identified additional concems. The NRC staff in Region lli then referred these concems to the Office of Nuclear Reactor Regulation (NRR).

NRR staff reviewed the inspector's concems and was able to resolve some of the concems.

t However, issues related to the structural integrity or the leak tightness of the CCHVAC system under the combined loading f om dead weight, maximum negative pressure, and the Safe Shutdown Earthquake (SSE) remained unresolved. The staff sent DECO a request for additional information (RAI) in a letter dated March 3,1994 (Ref. 2).

DECO responded to the RAI in a letter dated June 3,1994 (Ref. 3). The licensee divided the RAI into 19 "NRC Concems" and attached extensive supporting calculations addressing each concem. The staff evaluated the responses to the coricems and concluded that some of the concems had been resolved but that othem i nained unresolved. In a letter dated December 7,1995 (Ref. 4), the staff provided its evaluation of the licensee's response and issued an RAI to DECO regarding resolving the remaining concems.

DECO developed an Integrcted Action Plan to resolve the remaining concems. This plan addressed both CCHVAC system operation and structural qualification issues. The NRC met with DECO at NRC Headquarters on February 7,1996, and d!scur, sed the staff concems and the integrated Action Plan. A follow-up meeting was held on March 1,1996. In a letter dated April 3,1996, (Ref. 5), the licensee submitted a Design Criteria Document and additionalinformation regarding the structural qualification of the CCHVAC system ducts and hangers. The licensee provided a revised version of the Design Criteria Document to the staff in a letter dated September 13,1996, (Ref. 6). The staff reviewed the !nformation in these two submittals and issued an RAI by letter dated October 25,1996, (Ref. 7). The Gf(f0Y 9709020270 970822 PDR P

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2 additionalinformation requested consisted of selected duct system eval'.:stion and qualification calculation packages, the large deformation finite element analysis of a " wye" i duc' conyction, a description of the required structural modifications, and the calculation of l the updated peak duct pressure. The licansee provided this information in a letter dated  !

November 8,1996, (Ref. 8). I 2.0 EV6LUATION  :

- 2.1 CCHVAC System Reevaluation As part of the integrated Action Plan, DECO updated the CCHVAC system pressure analysis

- and implemented a moolfication in plant operations to reduce the circulating fan speed.

Design calculations associated with this modification indicated that the maximum negative intomal duct pressures will be equal to or less than 14" water gage (WG) for recirculation line ductwork, and equal to or less than 6.5" WG for the remaining CCHVAC ductwork.- This represents a decrease from the original analysis, which calculated a recirculation duct maximum pressure of 22" WG, and equal to or less than 11" WG for the remaining CCHVAC ductwcrk. The reduced pressures were combined with the other loadinM n i the qualification L of the CCHVAC to the requirements of the structural design codes of record.

n 2.2 - CCHVAC Structural Reevaluation The major concems regarding the previous DECO calculations, as stated in Reference 2, can be summarized as follows:

The stress calculations were based on the thickness of costed instand of bare sheet metal.

Cross-sectional areas and moments of ineitia of rectangular ducts wsre based on full cross-sections instead of effective cross-sections. Geometric cross-sectional -

properties were not directly applicable to the structural analysis of thin-walled sheet metal structums.

The maximum membrars plus bending stress under combined dead weight, intemal

)-~ pressure, and SSE loadmg exceeded the allowable stress (.9*Fy) specified in the HVAC construction standard ANSI /ASME-N509-1C80 (Ref 9). This standard was accepted as the HVAC standard for Fermi-2.

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The a!iowable stress was based on the ' minimum yield stress of structural steel, it should have been based on the minimum yield stress of the duct sheet metal.

The seismic analysis did not consider Seismic loading 4 the vertical direction.

The stress evaluation did not consider local panel response to seismic loading.

- The stress evaluation neglected consideration of potential stress intensification effects in " tee" and " wye" type duct connections.

3-To address these concoms, the licensee contracted with Raytheon, Engineers and Constructors to reanalyze the CCHVAC system ducts s'id duct supports subjected to the updated intomal pressure and to load combinations involving dead weight, intemal pressure and tri-axial site-specific SSE motion. The CCHVAC system was divided into 22 flexible systems and 37 rigid systems. The static and dynamic structural response of the systems was evaluated using standard finite element analysis of beam structures, accounting for the effective cross-sectional properties of rectangular ducts. The duct structures and the duct supports were analyzed using the public domain programs STARDYNE and STRUDL. All analyses and evaluations were performed in accordance with the licensee's Design Criteria Document. The ducts were qualified in accordance with the requirements of Section 5.10 of ANSI /ASME N509-1980, and the duct supports wera qualified in accordance with the AISC Specification,1970 and 1980 Editions (Ref.10).

- During the structural revalidation process, the contractor determined that the resuits for some i of the flexible CCHVAC systems exceeded the acceptance criteria. A number of structural modifications were required to correct these deficiencies. The systems requiring modifications were reevaluated until the appropriate design criteria were met. The modifications included the following:

the installation of four new duct supports, with associated base plates and anchor bolts, a

the addition of bracing members to sixteen existing duct supports, the adc! tion of stiffeners to a " wye" duct transMion segment, and the addition of a longitudinal connection between an existing duct and duct support.

The staff also reviewed the calculations that were submitted in Reference 8 and concluded that they were reasonable and were performed in accordance with commitments in the .

-- updated final safety analysis report (UFSAR) and the Design Criteria Document (Ref. 6)._ The staff concluded that the calculations are acceptable.

3.0 - CONCLUSION The staff has reviewed the revised Fermi-2 CCHVAC system design criteria in the Design Criteria Document and has determined that a:1 previous staff concems have been satisfactorily and reasonably addresced. The staff also finds that the revised design criteria conform with the UFSAR commitments for Fermi-2. The staff concems are therefore considered resolvad.

The staff has examined represen% calculations of the structural reevaluation and revalidation of the CCHVAC system, and finds them acceptable and in accordance with the Fermi-2 CCHVAC Design Criteria Document.

Principal Contributor: Mark Hartzman Date:

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4.0 REFERENCES

1, Letter dated November 29,1989, from W. S. Orser, DECO, to the NRC Document Control Desk,- Response to a Notice of Violation.

2.- - Letter dated Orch 3,1994, from T. G. Celbum, NRC, to D. R. Gipson, DECO, Request For Additional Information.

3. Letter dated June 3,1994, from D. R. Gipson, DECO, to the NRC Document Control

- Desk, Response to Request For Additional Information.

4. Letter dated December 7,1995, from T. Colbum, NRC, to D. R. Gibson, DECO, Safety Evaluation and Request For Additional Information.

5. Letter date April 3,1996, from D. R. Gipson, DECO, to the NRC Document Control Desk, Response to Request For Additional information.

' 6.-

Letter of September 13,1996, from D. R. Gipson to the NRC Docunant Control Desk, Supplemental Response to Request For Additional Information.

7. Letter dated October 25,1996, from A. J.- Kugler, NRC, to D. R. Gipson, DECO, i Request For AdditionalInformation.

8. Letter dated November 8,1996, frcm R. McKeon, DECO, to the NRC Document Control Desk, Response to Request For Additional Information.

9. American Society of Mechanical Engineters,' ANSI /ASME N509-1980, " Nuclear Power

- Plant Air Cleaning Units and Components," New York, N. Y.,1980,

10. American Institute of Steel Construction, " Specification for the Design, Fabrication and Erection of Structural Steel for Buildings," 7th and 8th Editions l 1970 and 1980.

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