ML20062M499

Provides Evaluation of Drywell to Wetwell Vacuum Breaker Valves,In Response to NRC .Matl Ordering & Mfg Schedules Expedited to Allow Mods to Vacuum Breakers Prior to Fuel Load

ML20062M499
Person / Time
Site:	Fermi
Issue date:	08/18/1982
From:	Tauber H DETROIT EDISON CO.
To:	Tedesco R Office of Nuclear Reactor Regulation
References
EF2---59-061, EF2---59-61, NUDOCS 8208200121
Download: ML20062M499 (5)

Text

{{#Wiki_filter:I Harry Tauber b I 4 Co structen DetTOit Es:lissc>r) REDE!!:~im August 18, 1982 EF2 - 59,061 i Mr. R. L. Tedesco Assistant Director for Licensing Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555 i

References:

(1) Enrico Fermi Atoniic Power Plant Unit 2 NRC Docket No. 50-341 (2) NRC Letter to H. Tauber from B. J. Youngblood, " Completion of Fermi-2 Containment Analyses and Modifications", dated March 23, 1982 (3) " Mark I Containment Program Structural Acceptance Criteria Plant - Unique Analysis Applications Guide", Task Number 3.1.3, Mark I Owners Group, General Electric Company, NEDO-24583, Revision 1, July 1979

Subject:

Evaluation of the Enrico Fermi-2 Drywell-to-Wetwell Vacuum Breakers This letter provides a report on the evaluation which was i conducted for the Fermi-2 vacuum breaker valves between the wetwell and drywell. This submittal is for.your review, and responds to Staff requirements provided in the Reference-(2) letter. Fermi-2 has twelve (12) GPE 18" O.D. drywell-to-wetwell-vacuum breaker valves. The general arrangement of the GPE valve design has been provided in the attached. Figure

1. 1.

The vacuum breakers would open after a postulated LOCA to vent non-condensables from the wetwell airspace into the drywell when the steam in the drywell begins to condense. The size and number of vacuum breakers has been determined to ensure that the Fermi-2 drywell vacuum conditions do not exceed the external pressure design limit (-2 psig) for the structure. Section 6.2.1.2.1.10 of the Fermi-2 FSAR provides a more detailed discussion of the vacuum breakers. f3 cot lER*%$wagggy PDR .~

I Mr. R. L. Tedesco August 18, 1982 EF2 - 59,061 Page 2 During the chugging phase of a LOCA, the pressure fluctuation in the suppression pool vent system may cause the vacuum breaker pallets to cycle open and closed. The cyclic impact of the pallet on the valve seat due to chugging in the vent system presented a loading condition which had not been previously included in the vacuum breaker valve design. Therefore, as part of the Fermi-2 Mark I Containment Modification Program, Detroit Edison.has re-evaluated the design of its vacuum breakers for this new loading condition. The forcing function utilized in the vacuum breaker design evaluation was obtained from a segment of the pressure-time histories measured in the Mark I Owners Group Full Scale Test Facility (FSTF) vent system and wetwell during one of the chugging tests. The FSTF pressure-time history data was adjusted to account for Fermi-2 plant-unique geometric parameters, such as vent / pool area ratio, drywell volume / vent area ratio, submergence head, etc., to establish the expected loading function. The design loading function was then established by applying a conservative safety factor of 1.6 to this plant-unique pressure-time history. The expected and: design loading functions _were applied to .an analytic valve dynamic model to determine the maximum pallet-to-seat impact velocity during chugging. The valve dynamic model included the effects of torque alleviation in the pallet assembly as a consequence of the flow or leak-age through the open valve. The predicted: maximum expected and design impact velocities during chugging for the Fermi-2 vacuum breakers were 4.0 and 7.6 rad /sec respectively. For completeness, the re-evaluation of the vacuum breaker valve design included the loading conditions, identified in the Reference (3) plant _ Unique Analysis Applications Guide, which.could be combined with the chugging load. The impact velocities for these other loading conditions were conservatively assessed using a single-degree-of-freedom l model to represent pallet _ movement. The resulting impact velocities for Safety Relief Valve, seismic and pool swell ' load conditions were found to be negligible with. respect to the predicted maximum impact velocity experienced during chugging. The' impact velocities predicted for the limiting design l loading conditions were utilized in dynamic structural impact analyses to determine the stresses in-the valve components. The analytical"modelideveloped for the analysis l treated the moving parts of the valve as a single-degree-of-l . freedom ~ system rotating about a pivot point'at the shaft l location. The results of the structural analyses predicted f that several valve components.would exceed the ASME code limits..These components were.the pallet, hinge arm,-hinge l arm utud and the shaft. The results'of additional analyses i l'

o August 18,edlh$3o Mr. R. L T EF2 - 59,061 Page 3 showed that utilizing available higher strength materials for these components would provide the necessary corrective action. The maximum allowable impact velocity corresponding to the ASME code allowable limit for Service Level A, for the higher strength materials, was determined to be 9.28 rad /sec. Therefore, corrective action instituted by a repair program to replace the appropriate valve components with ones made from higher strength materials would restore the valve to within ASME allowable limits for the predicted design impact velocity of 7.6 rad /sec. Accordingly, Detrcit Edison is currently proceeding with a program to replace the components that exceed the ASME code limits. The attached Table 1 lists the components, the exis-ting materials, and higher strength materials which will be utilized in manufacturing the replacement parts. A purchase order for the manufacture and delivery of the replacements has been issued. Detroit Edison has been seeking to expedite the material ordering and manufacturing schedules to allow the modifications to the vacuum breakers to be completed prior to fuel load. However, should the material delivery schedule be extended, the modifications to the valves will be completed following receipt of the replacement parts, but prior to the second fuel cycle. Utilizing the existing materials, the maximum allowable impact velocity to establish a safety margin of 2.0 against failure, for the critically stressed component, was determined to be 5.27 rad /sec. This value is greater than the expected impact velocity of 4.0 rad /sec. As such, the current vacuum breaker design would meet the Mark I Program Short Term Criteria. Therefore, in the event that the' vacuum breaker modification cannot be completed prior to fuel load, interim plant opera-tion through the first fuel cycle is justified. If you have any questions, please contact Mr. L. E. Schuerman, (313)-649-7562. Sincerely, / -/ 6 h 9 Attachment cc: :Mr. L. L. Kintner RMr. B. Little

T Mr. R. L. Tedesco Attachment - Table 1 TA3LE 1 LIST OF COMPONENTS REQUIRING HIGHER STRENGTH MATERIALS 1 Replacc..ent i Existing Material Material Comnonent Specification Specification Pallet SA-516 GR70 SA-564 Hinge Arm SA-516 GR70 SA-564 Hinge Arm Stud SA-320-B8 SA-564 Shaft SA-320-B8 SA-564

= SEE FIG. i." ._______---cr ~ \\ .. s I t-l \\ . ' j9 y y t ,-I_ o

s T

I M .w t.d t 1 /, \\ '~. ~~ \\ [ +- \\ SEAT P.ING f s i 'l y -{- + ,---o C \\ f "q i) ~ N F%LLET / + + s \\ N -- PALLE T # 4 (CLOSE POSITICN) + s t f i 1 ~~ Tp g \\_ _ _ _ _ _ _ _ _ 'M b SEE FIG. (PALLET STOP MAGNET LATCH STUD LOCATION YACO'JM BREAKER WALL (4 ?LCS) I FIGURE 1 CPE 18" VALVE CEO)lETRY l (CPE TYPE LD-?40-208) e 1 r -.}}