ML20076G846

Forwards Evaluation Results Demonstrating as-built Acceptability of Wetwell/Drywell Vacuum Breakers on Mark I Containments,In Response to Generic Ltr 83-08

ML20076G846
Person / Time
Site:	Hatch
Issue date:	06/09/1983
From:	Gucwa L GEORGIA POWER CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
GL-83-08, GL-83-8, NED-83-336, TAC-57156, TAC-57157, NUDOCS 8306160267
Download: ML20076G846 (16)

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. . Georgo Power Corrp ny 333 Piedmort Avenue Atlanta, Georgia 30398 Telephone 404 526 6526 Maihng Addrew Post Off.ce Box 4545 AtlMta. Georgia 30302 Georgia Power L. T. Gucwa the southem e%tre syste_>m Chief Nuclear Ermneer Power Generation Departncent 2D-83-336 June 9, 1983 Director of NJclear Reactor Regulation Attention: Mr. John F. Stolz, Chief Operating Reactors Branch No. 4 Division of Licensing U. S. RJclear Regulatory Commission Washington, D. C. 20555 NRC 00CKETS 50-321, 50-366 OPERATING LICENSES DPR-57, NFF-5 EDWIN I. HATCH NUCLEAR PLANT UNITS 1, 2 WEWELL/DRYWELL VACUlN BREAKERS ON MARK 1 CONTAIMENTS Gentlemen:

In response to your request in MC Generic Letter 83-08, we hereby submit the results of an evaluation which demonstrates the as-built acceptability of the Plant Hatch Units 1 and 2 wetwell/drywell vacuum breakers.

Should you have any questions regarding this subject, please contact this office.

Sincerely yours, 8T S c~a L. T. Gucwa WEB /CRP/mb xc: J. T. Beckham, Jr.

H. C. Nix, Jr.

J. P. O'Reilly (W C- Region II)

Senior Resident Inspector

/ No 9306160267 d30609 PDR ADOCK 05000321 P PDR

i INVESTIGATION OF PLANT HATCH WETWELL/DRWELL VACUDI BREAKERS Introduction Mark I Program tests were performed in the Full Scale Test Facility (FSTF) to determine LOCA related chugging and condensation oscillation loads.

During chugging, a GFE vacut.m breaker was observed to open partially or fully on a cyclic basis. Post test physical examination of the vacuum breaker showed: 1) evidence that the pallet opened fully and impacted the valve body in the full open position 2) evidence of seat, gasket and pallet hinge damage which may also have been due in part to pallet misalignment during installation.

No apparent effect was observed on the wetwell pressure during any tests due to vacuum breaker actuation. However, cycling of the vacuum breakers such as observed during the chugging phase of LOCA tests could result in vacuum breaker damage.

The vacuum breaker oscillation experienced in the test facility is more severe than that of an operating plant primarily because of the difference in the drywell volume / vent area ratios. This ratio is approximately a factor of two smaller in the test facility than in a typical plant.

As this ratio increases, the pressure fluctuations (due to chugging) which cause vacuum breaker actuation decrease. Figure 1 shows the GPE vacuum breaker installed in a typical Mark I Plant. The GPE vacuum breaker installed in Plant Hatch is shown in Figure 2.

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GPE Vacuum Breaker Program As a result of the FSTF experience, a GPE vacuum breaker program was implemented to include 1) development of an analytical model for predicting local stresses'in selected vacuum breaker component parts 2) development of plant unique valve dynamic models for predicting pallet impact velocity and 3) the performance of tests of unmodified GPE vacuum breakers.

A finite-element stress analysis of the GPC vacuum breakers was performed using the computer program ANSYS. Figures 3 and 4 show plate elements to model pallet response and beam elements for the shaft and hinge arm respectively. The results of the ensuing analysis have shown that stress is a linear function of pallet impact velocity and that the impact is elastic for velocities in the Mark I vacuum breaker range.

The foregoing considerations have been used to develop Table 1 which shows component stress levels for 18 inch GPE vacuum breakers as a function of pallet impact velocity. Additionally, modification guide lines as dictated by Table 1 parameters are shown in Table 2. It is noted that for impact velocities less than about 4.5 radians per second no modifications are required.

In order to predict plant unique vacuum breaker functions, a methodology was developed using FSTF pressure time history data during chugging and adjusting the vent system and wetwell pressures to account for plant unique geometry. The procedure used in development of this model follows.

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2. ALL DEGREES OF FREEDOM COUPLED 5 yff BETWEEN NODES 6 AND 4 EXCEPT ROTATION ABOUT x AXIS. FULL RESTRAINT AN ALYTICAL MODEL FIGURE 4 DETAILED VACUUM BREAF.ER HINGE MODEL

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a TABLE 2 MODIFICATION DECISION GUIDELINES FOR 18-INCH GPE VACUUM BREAKER IMPACT VELOCITY (rad /sec) ACTION Less than 4.5 no~ action required 4.5 to 9.3 Material upgrade Greater than 9.3 Use a snubber Assumptions:

- Material upgrade consists of material with 70 ksi code allowable

- Loads other than chugging contribute less than 5% of allowable stress

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1. Develop a dynamic model of the vent system, steam water interface and pool slosh with the condensation rate of the interface unknown.

2. Use measured drywell pressure to determine the condensation rate.

3. With the condensation rate determined, predict unsteady pressures at other vent locations to validate the model.

4. Use the condensation source at the vent exit to drive dynamic models to determine plant unique vacuum breaker forcing functions.

The details of the vacuum breaker model development are found in CDI Technical Note 82-31 " Mark 1 Vacuum Breaker Improved Valve Dynamic Model" -

September 1982. TN 82-31 was submitted to the NRC for review in accordance with General Electric letter of October 28, 1982 to D. B. Bassalo from H. C.. Pferiferlin on the same subject.

The vacuum breaker model was applied to each Mark I plant to derive a

. pallet impact velocity. Parameters for development of the forcing function as applied to Plant Hatch are shown in Tables 3 and 4 for Hatch 1 and Hatch 2 respectively. Vacuum breaker characteristics are identical for both plants, thus, Table 5 is representative of both Hatch 1 and Hatch 2. Finally, Tables 6 and 7 show the maximum pallet design impact velocity response of 1.26 radians /sec for Hatch 1 and 0.12 radians /second for Hatch 2, leading to the conclusion that no vacuum breaker modifications are required for Plant Hatch.

TABLE 3 Forcing Function Parameters for Hatch 1 Parameter -Value Used-In Computation Vent / pool area ratio 0.045 Drywell volume / main vent 532.87 ft*

area ratio (ft)

Main vent area /downcomer area' O.99 Main vent length (f t) 37.32 Header area /downcomer area 1.47 Header length'(ft) 15.0 ft 2

Downcomer area (ft)2 3.01 ft Downcomer length (f t) 10.8 ft Submergence head (ft) 3.67 ft water

• - Value used even though Hatch 1 is 586.42-ft.

The value used in the computation (532.42 f t) leads to more conservative results.

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, TABLE 4 Forcing Function Parameters for. Hatch 2 A

Parameter Value Used In Computation Vent / pool area ratio 0.045 Drywell volume / main vent 532.87 area ratio (f t) -

Main vent area /downcomer area 0.99 Main vent length (ft) 37.32 Header area /downcomer area 1.47 Header length (ft) 15.0 Downcomer area (ft2 ) 3.01 Downcomer length (ft) 10.8 Submergence head (f t watier) 4.0

, TABLE 5 Vacuum Breaker Characteristics for Hatch 1 and 2 Vacuum breaker type 18" GPE Internal System moment of inertia (Ib-in-s 2) 20.08 System moment arm (in) 10.86 Disc moment arm (in) 11.468 System weight (lb) 49.84 Disc area (in2) 375.83 System rest angle (rad) 0.06109 -

Seat angle (rad) 0.05236 Body angle (rad) 1.391 Seat coefficient restitution 0.6 Body coefficient restitution 0.6 Magnetic latch set pressure (psi) 0.25'

TABLE 6 VACUUM BREAKER VALVE RESPONSE FOR HATCH 1 EXIMUM IMPACT NUMBER MAXIMUM OPEN1NG VELOCITY OF ANGLE (rad /sec) IMPACTS (2) (rad) (3)

Expected Loading Function (1)

No flow effects 1.39 2 0.005 Flow effects 1.07 1 0.004 Design Loading Function (4)

No flow effects 1.64 Flow effects 1.26 (1) Submergence head is taken as 1.59 psi.

Vacuum breaker assumed to be mounted at the main vent-header junction.

(2) Seat impacts above 1 rad /sec.

(3) Body impacts do not occur.

(4) Design impact velocity is 1.18 times the expected impact velocity.

TABLE 7 VACUUM BREAKER VALVE RESPONSE FOR HATCil 2 MAXIMUM IMPACT NUMBER MAXIMUM OPENINO VELOCITY OF ANGLE (rad /sec) IMPACT (2) (rad) (3)

Expected Loading Function (1)

No flow effects 0.13 0 0.0002 Flow effects 0.10 0 0.0002 Design Loading Function (4)

No flow effects 0.15 Flow effects 0.12 (1) Submergence head is taken as 1.73 psi.

Vacuum breaker assumed to be mounted at the main vent-header junction.

(2) Seat impacts above 1 rad /sec.

(3) Body impacts do not occur.

(4) Design impact velocity is 1.18 times the expected impact velocity.

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c Unmodified CPE vacuum breaker tests were run to 1) show the linearity of the analytical model, 2) confirm the accuracy of the analytical results and 3) identify analytical conservatisms. The results of these tests confirmed the linear correlation between pallet impact velocity and stress. Also, good agreement was shown to exist between stresses predicted by analysis and by test. Analytical predictions were shcwn to be conservative.

Conclusion Since this study illustrates that the pallet impact velocities of Plant Hatch's Unit 1 and 2 wetwell/drywell vacuum breaker do not exceed the allowable pallet impact velocities, no modifications of these vacuum breakers are required. Operability of the vacuum breakers without significant degradation is predicted as a result of this study.