ML20207F464

Structural Evaluation of Vacuum Breakers (Mark I Containment Program),Dresden Station Units 2 & 3, Supplementary Technical Evaluation Rept

ML20207F464
Person / Time
Site:	Dresden
Issue date:	07/17/1986
From:	Carfagno S, Con V, Triolo S CALSPAN CORP.
To:	NRC
Shared Package
ML17199F979	List: ML20207F464
References
CON-NRC-03-81-130, CON-NRC-3-81-130 TER-C5506-324, TER-C5506-324-S01, TER-C5506-324-S1, NUDOCS 8607220546
Download: ML20207F464 (21)

Text

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, ENCLOSURE 2 SUPPLEMENTARY TECHNICAL EVALUATION REPORT F

NRC DOCKET NO. 50-237, 50-249 FRC PROJECT C5506 NRC TAC NO. -- FRC ASSIGNMENT 12 NRC CONTRACT NO. N RC-03-81-130 FRC TASK 324 STRUCTURAL EVALUATION OF THE VACUUM BREAKERS (MARK I CONTAINMENT PROGRAM)

Cc:'MONWEALTH EDISON COMPANY DRESDEN STATION UNITS 2 AND 3 TER-C5506-324 1

, Prepared for Nuclear Regulatory Commission FRC Group Leader: V. N. Con Washington, D.C. 20555 NRC Lead Engineer: H. Shaw l

July 17, 1986 This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or I- responsibility for any third party's use, or the results of such use, of any information, appa-ratos, product or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights.

Prepared by: Reviewed by: Approved by:

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CONTDJTS

, Section Title Page 1 INTRODUCTION . . . . . . . . . . . . . 1 1.1 Generic Backg.ound. . . . . . . . . . . 1 1.2 Vacuum Breaker Function . . . . . . . . . 2 2 EVALUATION CRITERIA. . . . . . . . . . . . 9 3 DESIGN LOADS . . . . . . . . . . . . . 10 4 STRESS EVALUATION . . . . . . . . . . . . 11 5 PLANT-SPECIFIC REVIEW: DRESDEN UNITS 2 AND 3 . . . . . 15 Background Information.

5.1 . . . . . . . . 15 5.2 Stress Anal'fsis Results . . . . . . . . . 15

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6 CONCLUSIONS. . . . . . . . . . . . . . 16 7 REFERDJCES . . . . . . . . . . . . . . 17 li L

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FOREWORD This Technical Evaluation Report was prepared by Franklin Research Center under a contract with the U.S. Nuclear Regulatory Commission (Office of Nuclear Reactor Regulation, Division of Operating Reactors) for technical I assistance in support of NRC operating reactor licensing actions. The technical evaluation was conducted in accordance with criteria established by the NRC.

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1. INTRODUCTION In a latter state of the generic resolution of the suppression pool dynamic load definition of the Mark I Containment Long-Term Program, a potential failure mode of the vacuum breakers was identified during the clugging and condensation phases of hydrodynamic loadings. To resolve this issue, two vacuum breaker owner groups were formed, one for those with General Precision Engineering (GPE) vacuum breakers, the other for those with Atwood-Morrill (AM) vacuum breakers.

The issue was not part of the original scope of the Mark I Containment Long-Term Program as described in NUREG-0661 [1]. However, vacuum breakers have the function of maintaining containment integrity and, therefore, are subject to Nuclear Regulatory Commission (NRC) review. In a generic letter dated February 3, 1983 (2), the NRC requested all affected plants either to submit the results of the plant-unique calculations which formed the bases for modifica- tions to the vacuum breakers or to provide the justification for the

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as-built acceptability of the vacuum breakers.

Franklin Research Center (FRC) has been retained by the NRC to evaluate the acceptability of the structural analysis techniques and design criteria

e used in the plant-unique analysis (PUA) reports of 16 plants. As a part of this review, the structural analysis of the vacuum breakers has been reviewed and documented in this report.

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l* The first part of this report (Sections 1 through 4) consists of generic 2nformation that is applicable to all affected plants. The second part of the l

(s' report (Sections 5 and 6) provides a plant-specific review, which pertains to 1

i- the Dresden plant.

1.1 GENERIC BACKGROUND

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5 In 1980, the Mark I owners and the NRC became aware of the vacuum breaker

l. damage during full-scale test facility testing and of the potential for damage during actual LOCAs. Two vacuum breaker owner groups, General Precision l Engineering (GPE) and Atwood-Morrill (AM), were formed to develop action plan

[ for resolving this issue. In February 1983, the NRC issued Generic Letter u

83-08 (2), requesting commitments from affected utilities to provide l .

TER-C5506-324 analytical results. The licensees responded to the NRC request by developing appropriate force functions simulating the anticipated hydrodynamic loads, and then performing stress analyses that used these loads. With respect to loading, the NRC has reviewed and issued a staff position as indicated in Section 3. FRC's function is to review the stress analysis submitted by a

5 licensee.

1.2 VACTRIM BREAKER FUNCTION During steam condensation tests on BWR Mark I containments, the wetwell-l, to-drywell vacuum breakers cycled repeatedly during the transient phase of steam blowdown. This load was not included in the original load combinations used in the design of the vacuum breakers. Consequently, the repeated impact of the pallet on the valve seat and body created stresses that may impair its capability to remain functional.

A vacuum breaker is a check valve installed between the wetwell and the drywell. Its primary function is to prevent the formation of a negative pressure on the drywell containment during rapid condensation of steam in the drywell and in the final stages of a LOCA. The vacuum breaker maintains a wetwell pressure less than or equal to the drywell pressure by permitting air

!P flew from the wetwell to the drywell when the wetwell is pressurized and the 4

o b drywell is depressurized slowly.

': - A vacuum breaker can be internally or externally mounted. Figures 1 and 2 illustrate locations of vacuum breakers.

Schematics of typical GPE and AM vacuum breakers are illustrated in Figures 3 and 4.

A typical pressure differential vacuum breaker during a LOCA is provided

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in Figure 5.

Table 1 lists the various vacuum breaker types and the plants affected by them.

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TER {5506-324 Table 1. Vacuum Breaker Types and Affected Plants

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Vacuum Breaker Plant

[ GPE 18 In (Internal) Brown Ferry Units 1, 2, and 3 g Pilgrim Unit 1 Brunswick Units 1 and 2

_g Cooper l- Hatch Units 1 and 2 Peach Bottom Units 2 and 3

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TER-C5506-324 2.

f EVALUATION CRITERIA To evaluate the design of the vacuum breakers, the affected licensees follow the general requirements of NUREG-0661 [1] and those of " Mark I Containment Program Structural Acceptance Criteria Plant Unique Analysis Application Guide" (3]. Specifically, the requirements of the ASME Boiler and Pressure Vessel Code,Section III, Subsection NC for Class 2 Components,1977 Edition, including the summer 1977 addenda [4], have been used to evaluate the structural integrity of the vacuum breakers.

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3. DESIGN LOADS The loads acting on the Mark I structures and on the vacuum breaker are based upon the Mark I Program Load Definition Report (5) and the NRC Acceptance Criteria (1]. The loads acting on the vacuum breaker include gravity, seismic, and hydrodynamic loads. The hydrodynamic fercing functions were developed by Continuum Dynamics, Inc, (CDI). CDI used a dynamic model of a Mark I pressure suppression system, which was capable of predicting pressure transients at specified locations in the vent system. With this dynamic model and the full-scale test facility data, load definition resulting in pressure differential across the vacuum breaker disc was quantified as a function of time. This issue has been reviewed and addressed by the NRC (6].

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4. STRESS EVALUATION To determine structural integrity of the vacuum breaker, the licensees I have employed standard analytical techniques, the including finite element method, to calculate stresses of critical components of the vacuum breaker under various design loadings. Loads resulting from the hydrodynamic phenomenon were compared with those values specified in the ASME Codes [4].

For illustration purposes, a schematic drawing of the moving parts of all components other than the actual disc of the Atwood-Morrill valve and of the corresponding finite element model are shown in Figures 6 and 7, respectively.

The model in Figure 7 was used to investigate the dynamic response following impact.

A typical model for stress analysis of the vacuum breaker disc is shown in Figure 8. Loading inputs to this model are the displacement time histories f.

that v ee obtained from the impact model analysis.

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5. PLANT-SPECIFIC REVIEW: DRESDEN UNITS 2 AND 3

5.1 BACKGROUND

INFORMATION o Vacuum breaker type: 18-in Atwood and Morrill (external) f=

o Vacuum breakers are mounted on an +txternal header connecting the suppression chamber and the vent line.

o There are two external vacuum breakers on six'of the eight vent lines.

o The vacuum breaker valves have been modified by changing the cast aluminum disc to wrought aluminum discs with stainless steel posts.

5.2 STRESS ANALYSIS RESULTS I After the modification to wrought aluminum disks, the vacu.m breakers at the Dresden plant were analyzed using an ANSYS finite element computer model.

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The stress results of this analysis indicated that all stresses were within allowable limits as defined in the ASME Boiler and Pressure Vessel Code,Section III, Subsection NC for Class 2 components,1977, including the summer 1977 addenda. Therefore, no further modifications were planned for the vacuum breakers at Dresden Units 2 and 3. Following this analysis, the load evaluation was refined (7) and lower loads (in terms of pallet impact velocities) than had originally been calculated were predicted. The refined analysis shows that vacuum breakers at the Dresden plant will not actuate during the chugging transient. The Licensee conducted its structural analyen

- si based on an impact velocity of 0.8224 radians /sec [8). Since stress is proportional to impact velocity, the Licensee's results are conservative with respect to the refined loading criteria.

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6. CONCLUSIONS A review has been conducted to determine the structural integrity of the vacuum breakers at Dresden Units 2 and 3. The design loads associated with the hydrodynamic phenomena have been reviewed and addressed by the NRC in I Reference 6. This review covured only the structural analysis of the vacuum breaker, and the following conclusion is drawn from the review:

o The analytical methods used to evaluate stresses of critical components have been reviewed and judged to be adequate; the

! structural analysis indicates that the existing ~ vacuum breaker design is acceptable and no additional modifications are required.

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7. REFERENCES

1. NUREG-0661

" Safety Evaluation Report, Mark I Containment Long-Term Program Resolution of Generic Technical Activity A-7," Office of Nuclear Reactor Regulation, USNRC July 1980

2. D. G. Eisenhut "USNRC Generic Letter 83-80, Modification of Vacuum Breakers on Mark I lI. Containment" February 2, 1983

3. NEDO-24583-1

" Mark I Containment Program Structural Acceptance Criteria Plant Unique Analysis Application Guide," General Electric Co., San Jose, CA October 1979

4. American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section III, Division 1, " Nuclear Power I, .

Plant Components," New York, 1977 Edition and Addenda up to Summer 1977

5. NEDO-21888 Revision 2

. [- " Mark I Containment Program Load Definition Report," General Electric Co., San Jose, CA November 1981 1,

6. D. B. Vassallo, NRC Letter with Attachment to H. C. Pfefferlen, BWR Licensing Programs, GE

" Evaluation of Model for Predicting Drywell to Wetwell Vacuum Breaker

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Es Valve Dynamics" December 24, 1984

7. " Improved Dynamic Vacuum Breaker Valve Response for Dresden Units 2 and 3, Revision 0," Con:inuum Dynamics, Inc., Princeton, New Jersey,

. September 1982

8. B. Rybak Letter with Attachments to H. R. Denton (NRC)

Subject:

Modification of Vacuum Breakers on Mark I Containment Generic

. Letter 83-08 July 12, 1983 t

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