ML19320B331

Submits Responses to NRC 800616 Draft Questions Concerning Containment Purge Valves.Comparison of Facility Purge Sys W/ Branch Technical Position Csb 6-4 Encl

ML19320B331
Person / Time
Site:	Farley
Issue date:	06/30/1980
From:	Clayton F ALABAMA POWER CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
NUDOCS 8007100185
Download: ML19320B331 (12)

Text

Alabama Power Company

. . 600 North 18th Street Post Office Boo 2641 Birmingham. Alabama 35291 Telephone 205 323-5341 L k -

hk c'^"S,1Cn, c Alabama Power June 30, 1980 ne scornern eutrc system Docket No. 50-364 Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention: Mr. A. Schwencer RE: (1) Letter Dated 9/27/79 to All Light Water Reactor Owners from D. G. Eisenhut, Division of Operating Reactors, NRC.

(2) Letter Dated 12/10/79 to Mr. A. Schwencer from F. L. Clayton, Jr., Response to Containment Purge Request, Farley Unit 1 (Docket 50-348).

(3) Letter Dated 2/5/79 to Mr. A. Schwencer from F. L. Clayton, Jr., Containment Purging During Normal Plant Operation.

Farley Unit 1 (Docket 50-348).

JOSEPH M. FARLEY NUCLEAR PLANT DOCKET No. 50-364 CONTAIhWENT PURGE VALVES Gentlemen:

This is Alabama Power Company's response to the draft (June 16, 1980) questions on containment purge valves. Each portion c ; the recommendations and enclosures is addressed separately.

NRC Request:

We recommend that the following actions be taken by the applicant:

(1) Provide a commitment in writing to maintain all containment purge and vent isolation valves greater than 3" nominal diameter closed whenever the reactor is not in the cold shutdown or refueling mode.

This requirement shall be in effect until such time as it is shown that these valves are operable under the most severe design basis accident flow condition loading and can close within the time limit stated in the license Technical Specifications, design criteria or

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U. S. Nuclear Regulatory Commission June 30, 1980 .

Containment Purge Valves Page 2 operating procedures. The operability of butterfly valves may, on an interim basis, be demonstrated by limiting the valve to be no more than 300 to 500 open (90 being full open) .

The maximum opening shall be determined in consultation with the valve supplier. The valve opening must be such that the critical valve parts will not be damaged by DBA - LOCA loads and that the valve will tend to close when the fluid dynamic forces are introduced. A brief explanation for this position is contained in Enclosure 1.

(2) Provide the details of a program that the applicant intends to implement for qualification of the purge and vent valves.

Enclosure 2 provides guidelines to be considered in the demonstration of valve operability.

A commitment to the interim position in (1) above, our review and acceptance of the program discussed in (2), and demonstration by the application of compliance with appropriate portions of 3tandard Review Plan (SRP) 6.2.4 Rev.1 and associated Branch Technical Position CSB 6.4 provide acceptable bases for resolution of this issue.

APCo Response:

Plant Farley's Containment Purge System consists of two flow paths as described in FSAR Section 6.2.3. The larger path (main purge) is through 48-inch butterfly valves. The smaller (mini-purge) utilizes 18-inch butterfly valves. All valves were supplied by Henry Pratt Company and are equippad with Bettis operators.

With regard to the 48-inch main purge valves, Alabama Power Company hereby commits to maintain the main purge valves closed whenever the plant is in modes 1, 2, 3 or 4 until valve operability is demonstrated. The valves will be opened only in modes 5 and 6 (cold shutdown and refueling) .

The 18-inch mini-purge valves have been analyzed by Henry Pratt Company and found to be fully qualified for the service. It is Alabama Power Company's intention to operate the mini-purge system in plant modes 1, 2, 3 and 4.

Information has been provided to the NRC on Unit I which demonstrates the operability of the mini-purge valves, specifically, attachment (1) to reference (3) provided a detailed comparison of the FNP Unit 1 purge system with Branch Technical Position CSB 6.4 and reference (2) provided further information concerning operability as requested by the NRC. This information is valid for Unit 2 and copies are attached.

U. S. Nuclear Regulatory Commission June 30, 1980 .

Containment Purge Valves Page 3 Enclosure 1 to NRC Request:

This enclosure presented a basis for blocking valves to less than full open. The data presented in the enclosure are consistent with the results of our discussions with the valve manufacturer. However, as the main purge valves will remain closed in modes 1-4 and as the mini-purge valves are fully qualified, such valve blocking is not necessary for Plant Farley. .

Enclosure 2 to NRC Request:

This enclosure pre n nts a set of eight major considerations for establishing the operability of the purge valves. This information was previously transmitted to Alabama Power Company in regard to Farley Unit 1 by Reference 1. Reference 2 provided a response to these considerations.

The Unit I response also applies to Unit 2. A copy of Reference 2 is attached.

If you have any further questions concerning this matter, please contact us.

Very truly yours, j dl .? A-F7 LOC 1Yyt - .

FLCJr/TNE:aw 4

Attachments cc: Mr. R. A. Thomas Mr. G. F.' Trowbridge Mr. L. L. Kintner Mr. W. H. Bradford

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December 10., 1979 Docket No. 50-348 Director .r*

Office of' Nuclear Reactor Regulation g ,.

U. S. Nuclear Regulatory Conmission Washington, D.C. 20555 F

Attu: Mr. A. Schwencer -

Dear Mr. Schwancer:

J. M. FARLEY NUCLEAR PLANI CONTAItO!ENT PURCE TitisisinresponsetoyourletterdatedOctober 23, 1979 concerning operability of, containment purge valves. ,

- i F Alaba:a Power Company.is conducting a qualification progran on the .

main (48-inch) containment purge valves used at Farley Nuclear Plant.

Alabama Power Conpany conmitted, by letter to you dated August 7,1979, to maintain these valves closed in modes 1, 2, 3, and 4 until their operability

- can be demonstrated. The qualification progra:2 for the 48-inch valve is 1 currently in progress. ,

Alabara Power Conpany's operability verification program has been com-plated on the Farley 18-inch mini-purge. valves. ,

A detailed analytical analysis was performed by the valve manufacturer (Henry Pratt Co.) which demonstrated that the 18-inch Henry Prate Conpany valves with the Bettis valve operators are capable of closure without loss of structural inte3rity during' LOCA conditions in conjunction with seismic, and other loads. The following guidelines were incorporated into the -

analysis.

1. Valve closure time during a LOCA vill be less than or equal to the no flow time demonstrated during shop tests, since fluid dynamic ef f ects tend to close a butterfly valve. Tc ts shoved that the 18-inch valves close within 2.5 to 4 seconaa.

2. The analysis t 7nsidered the direction of flow which is the direc-tion resulting in the greatest torque.

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Page 2 December 10, 1979

3. The worst case sms determined to be a single valve closure

. with pressure on one side and acnospheric pressure on the other. -

4. Containment back pressure wi11 have no effect on closing '.

since the same back pressure will be present at the inlet side of the cylinder and the differential pressure will be -

, the same during normal operation. ,

5. Farley purge valves do not have accumulators. . ,

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6. Torque limiting devices only apply to electric motor operators which were not furnished on purge valves for '

Farley Nuclear Plant. .

7. The effect of upstream and downstream piping was ignored as a conservative approach. -

8. , For compressible fluid flow, the effects of valve orientation relative to the pipe line are considered to be insignificant.

The analysis consisted of a static analysis of the valve components demonstrating that the stress levels under combined seismic and LOCA con-U- ditions are less than 90 percent of yield strength of the materials used.

The valve operator structural evaluation was based on the operators -

ability to resist the reaction of LOCA induced fluid dynamic torques.. ,

Sealing caterials include EPT material on a 304 stainless steel '

surface. Melded EPT sc.ats have a maximum cumulative radiation resistance of 1X108 rad at a maximum temperature,of 3500F.

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. Valves at outside ambient temperatures below 0 F could 'oe affected due to ther=al contraction, however, during a LOCA the valve temperature would be high which tends to increase sealing. Also, ter.paratures below 00F in the geographical area where Farie; Nuclear Plant is located are rare.

Concerning debris, the purge supply and exhaust lines are protected i by registers. -

l Based on the results of the analysis as outlined above, Alabana Power Company's position remains that continuous purging during plant operation with the 18-inch (mini-purge) valves is safe under all accident conditions.

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Director of Nuclear Reacccr Regulation Page.3 .

December 10, 1979 -

Further information on the 48-inch main purge valve analysis will La supplied when available. ~

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Yours very truly,, ,

F. L.'Clayton, .- #

FLCJr/TNE:bhj .

. cc: Mr. R. A. Thomas --

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ATTACHMENT 1 (OF REFERENCE 3) ,

COMPARISON OF FARLEY PURGE SYSTEM WITH BRANCH TECHNICAL POSITION CSB 6-4 The following is a comparison of the Farley purge and Mini-Purge system with BTP CSB 6-4, Part B. The BTP requirements are reproduced herein for cla ri ty. ,

GENERAL: .

Requirer.ent:

- The systen used to purge the containment for the reactor operational hodes of power operation, startup, hot standby and hot shutdown; i.e., the on-line purge system should be independent of the purge system used for the reactor operational modes of cold shutdown and refueling.

Response: ,

The operation 'f the Mini-Purge System, or On-Line Purge ~ System, is independent of the operation of the purge system used for the reactor operational modes of cold shutdown and refueling, although there is common ductwork and a common filter.

b' Figures 1 and 2 show the supply and exhaust, respectively, for the Mini-Purge System (18 inch) and the Containment Main Purge System.(48 inch). From these figures it can be seen that the Mini-Purge System has its own fans and isolation valves, which operate independently of the Containment Main Purge System. '

Recuirement:

1. The On-Line Purge System should be designed in accordance with the following criteria: *

(a) The performance and reliability of the purge system isolation valves should be consistent with the operability assurance program outlined in Branch Technical Position MEB-2, Pump and Valve Operability Assuranch Program. (Also see SRP Section 3.9.3) The design basis for the valves and actuators should include the build-

- ing of containment pressure -for the LOCA break spectrum, and the purge line and vent line flows as a function of time up to and during valve closure.

Response: ,

The mini-purge isolation valves are~ Seismic Category I, ASME Section III, Nuclear Class 2. The operability assuranse program for these

' valves is described in paragraph 3.9.4.1 of FHP FSAR which was

• reviewed and approved by the NRC.

2 Requirement: .

1.b: The number of purge and vent lines that may be used should be ,

limited to one purge line and one vent line.

Response

As shown in Figures'1 and 2 there is only one supply line and one exhaust line in the Mini-Purge System. -

Requirement:

. 1.c. The size of the purge and vent lines should not exceed about eight inches in diameter unless detailed justification for largen line .

sizes is provided.

Response

The size of the Farley mini-purge lines,18 inches in diameter, exceeds the 8 inches in-diameter called for in the Branch Tech-nical Position. The justification for the larger line size is provided below. , ,

One of the design objectives of' the Mini-Purge System was to allow 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> per week occupancy of the containment during power

. -- opera tion. In order to achieve this, it was determined that a C purge flow rate of 5,000 cfm was required. In order to provide the 5,000 cfm flow rate and taking into account fan de-sign, the optimum size of. the supply line and exhaust line was determined to be 18 inches in diameter.

A. discussion of the isolation valve closure capability and the radiological consequences of a LOCA are presented under Positions B.1.f and B.S.a. respectively.

Requirement: ,

l.d. The containment isolation provisions for the' purge' system lines-

, should meet the standards appropriate to engineered safety features; i.e., quality, redundancy, testability and other appropriate .

cri teria. .

Response

Ths isolation provisions of the Mini-Purge System meet the standards -

for engineered safety features. There are redundant isolation valves in both the supply and exhaust lines with one valve an "A" train and the other a "B" train in each line. These valves were designed to ASME Section III Class .2 nuclear requirements and have been seismically and environmentally qualified. ,

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Requirement: ,

1.e. Instrumentation and control systems provided to isolate the purge system lines should be independent and actuated by diverse parameters; e.g. , containment pressure, safety injection actuation, .

and containment radiation level. If energy is required to close the valves, at least two diverse sources of energy shall be pro-vided, either of which can affect the isolation function.

Response

The Mini-Purge System is provided with independent instrumentation and control systems for isolation which are actuated by diverse ~

parameters, specifically high radiation in the exhaust flow and ~

a containment ventilation isolation signal' (CVIS). .

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Figure' 2 shows the relative location of the containment purge -

radia tion monitors (RE-24A, B). Upon sensing high radiation in the purge exhaust line, these monitors generate an isolation signal

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which results in the closing of all four mini-purge isolation '

valves.

FSAR Figure 7.2-8 provides details. as to the various parameters wh.jch ,will ge.nerate a, CVIS. _Upon receip,t of a CVIS, all'four mini-

_,. .,__ .,pur_ge isolation valves,wil.l .close. .

Electrical power is not required for the isolation function other  ;

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, than to generate the isolation signal. The isolation valves are ~ l air operated valves which will close upon loss'of air and loss.of I power to the solenoid valves resulting in loss of air to the  !

operator.  ;

Requirement:

• 1.f. Purge system isolation valve closure times', including instrumen-

- tation delays, should not exce'ed five seconds. -

Response: .

. The mini-purge and main purge isolation valves are ' butterfly valves designed to close in less than 5 seconds against LOCA pressure.  !

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Specifically, the valve operators were sized to seat and unseat the valves with a differential pressure of 65 psig. The valves were shop tested by opening and closing the valves under a no flow no pressure condition with resulting closing times of 3 to 4 seconds. For reasons discussed below, the closing times for these valves will be no greater under flow conditions.

The fluid dynamic characteristics of butterfly valves tend. to produce operating torques that will close the valve. If the fluid dynamic effects were to be added to the operating tests the valve may actually close in a shorter time than those shown in a static test. References- for this phenomenon may be found in "A Contri-bution to the Study of Butterfly Valves" by D. Gaden from Water Power, December 1951 and " Torque and Cavitation Characteristics of r . ., . . _ - - - . -

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-  : Buttarfly Valves" by Turgut Sarpkaya, Paper 160-HA-105 fr:m Trans-  !

. actions of the ASME Journal of Applied Mechanics. l Requirement:

l.g. Provisions should be made to ensure that isolation valve closure will not be prevented by debris which could potentially become entrained in the escaping air and steam.

P.es conse: - -

l The mini-purge and main purge supply and exhaust duct openings inside the containment are covered with " bird screen " preventing large pieces of naterial that nay break loose during a LOCA from

- entering the ducts and blocking isolation valve closure. The ,

" bird screen" is made from 1/2" : =n, .047" wire.

Requirement: .

2. . The purge system should not be relied on for temperature and humidity con-trol within the.containman' -

Response

Ne.ither the Mini-Purge nor the Pain Purge System was designed for ,

- temperature and humidity control within the containment. The system r ,

was designed for control of radioactivity levels within the contain-cant 2.s discussed in Position B.1.c., above.

Rsquirement: ,

3 ', Provisions should be made to minimize the need for purging of the contain-ment by providing containment atmosphere cleanup systems within the containment.

Response

The Mini-Purge System is designed to maintain radioactivity levels in ~

the containment consistent with occupancy requirements without the use of the installed pre-access filtration system. However, ".2 pre-access filtration system is available for use in minimizing the need for purging the containment.

Requi rementi

4. Provisions should be made for testing the availability of the isolation function and the leakage rate of the isolation valves, individually, during reactor operation. .

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Provisions have been made for testing the availability of the isolation function and the leakage rate of the isolation valves during reactor ,

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operation. The valves are capable of being tested by safety train for availability of the isolation function; i.e., both "A" train valves would be tested simultancously as would both "B" train valves. The

- valves are leak tested by line; i.e., the supply line and the exhaust ~

line, by pressurizing between the closed isolation valves.

. Requirement: ,

5. The following analyses should be performed to ,iustify the Containment Purge System design: .

a. An analysis of the radiological consequences of a loss-of-coolant accident. The analysis should be done for a spectrum of break .

sizes, and the instrumentation and setpoints that will actuate the 4

' vent and purge valves closed should be identified. The source

- term used in the radiological calculations should be based on a -

calculation under the terms of Appendix K.to determine the extent of fuel failure and the concomitant release of fission pro-ducts, and the fission product activity in the primary coolant.

A pre-existing iodine spike should be considered in determining

• primary coolant activity. The volume of containment in which fission products are mixed should be justified, and the fission products from the above sources should be assumed to be released through the open purge valves during the maximum interval required for valve closure. The radiological consequences should be within -

10 CFR 100 guideline values. .

i~ Resoonse: ,

An analysis of the radiological consequences of a DBA LOCA during operation of the Mini-Purge System was performed. The method of t

analysis and the results are discussed below.

The analysis was performed in the following manner. Just prior to the LOCA, the reactor is assumed to be operating with 1% failed fuel.

- There is a pre-existing iodin. espike of 60 Aci/gm I-131 dose equivalent.  !

The Mini-Purge System is operating with two 18 inch lines fully open, -

ene supply and onb exhaust line. A* containment high pressuie signal.will initiate isolation 6f the c6ntiinri.ent within 0.8 secbnds after the LOCA. The isolation valves will be ful-1.y closed in the next 5 seconds (a total of 6.0 seconds was used in the analysis). The quantities of interest (e.g., blowdown, temperature, pressure) are all time depend:nt; therefore, the 6 second period was divided into 1 second intervals and the flow out the mini-purge lines was calculated based on the maximum conditions (density, temperature, pressure) for the interval. The activity released to the containment for an interval was based on the incremental blowdown for that interval. No credit for the purge filter was taken in this analysis.

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This analysis resulted in incremental doses resulting from purg-ing while the plant is in operation. These incremental doses were

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then addsd to the doses presented in FSAR Table 15.4-12 (through Amendment 71). The resultant doses and 10CFR100 limits are ,

summarized below.

Thyroid Dose, Rem

- 10CFR100 Limit Table 15.4-12 Incremental _ Total _

Site Boundary (2 hrs'. ) 175 5.' 7 180.7 300 LPZ (0-30 days) 110 2.1 112.1 300 ,

Whole Body, Rem 10CFR100 Table 15.4-12 Incremental Total Limit 6.5 8.7 (10-3) 6.509 25 Site Boundary LPZ (0-30 days )(2 hrs.) 3.2 2.2 (10-3) 3.202 25 Therefore, the thyroid and whole body doses remain well below the limits of 10CFR100 for these accident conditions.

Requirement: , ,

1 5.b. An analysis which demonstrates the acceptability of the provisions rade to protect structures and safety-related equipment; e.g.,

g fans, filters and ductwork, located beyond the purge system isolation valves against loss of function from the environment created by

.. the escaping air and steam. .-

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Response

The radiological analysis was perfor=ed taking no credit for the purge filter. Therefore, this position is not applicable.

Requirement: '

5.c. An analysis of the reduction in the containment pressure resulting from the partial loss of containment atmosphere during the accident ~

for ECCS backpressure deterraination. ,

Response: ,

An analysis has been performed for the Joseph M. Farley Nuclear Plant based on the containment conditions defined.in the limiting FAC Analysis case (DECLG break, CD = 0.4) obtained using the February 1978 Westinghouse Evaluation Model. A containment isolation signal is received in that analysis within the first second after inception of the LOCA. The Mini-Purgo System utilized during reactor operation consists of two 18-inch diameter lines. .It is. conservatively represented in this computation as follows:

'l.

. A 5 second isolation valve' closure time is assumed. During the 6-second period immediately following the LOCA, no credit ,

l is taken for the reduction in effective flow area which occurs '

whi?. :: the valve is in the process of closing.

2. 'The frictional resistance association with duct entrance and exit losses, filters, ductwork bands and skin friction has not- .

been considered.

3. No. fan coastdown effects are considered.

4. 'No inertia is considered. Steady state flow out the purge syste'm ducts is established immediately at the time of the LOCA.

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. A mixture of steam and. air will be exhausted from the contain=ent through the purge lines during the 6. seconds that the isolation valves are assumed to remain open. The effect of the composition of the gas being exhausted on containment pressure has been bounded by investigating. the two extreme cases, air alone and steam lone. "

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Within several seconds of the inception of the LOCA, containment pressure will have increased to the point that critical flow will occur in the purge lines. To bound the calculated containment gas mixture exhausted through the purge lines, the critical flow rates of steam and air were calculated during the first six seconds of the CD = 0.4 DECLG break transient. Using these flow ra%, critical flow was then conservatively assumed to be in effect from time zero. i l

Equation (4.18) in Reference (1) was employed to calculate the '

critical flow rate of air through the Farley purge lines. Figure 14 of Reference (2) was applied to compute the critical flow rate

, of steam through the purge lines. The total mass released during the-6 seconds that the valves are presumed open is calculated as F

1711 lbs. air or 1235 lbs. steam. The impact on containment

. pressure at 6 seconds resulting from this loss of air or of steam is less than 0.25 psi in either case. The effect of a. containment pressure reduction of this niagnitude on the calculated peak clad temperature is excected to be minor '.less than 200"). When added to the c.urr~ent calculated peak clad temperature for a LOCA of 21580F, the resul ts of this evaluation indicate that' the Farley Plant meets 10CFR50.46 '. .mits (22000F).even if the containment is being purged.

at the time of a LOCA event.

REFERENCES:

(1) Shapiro, A. H., Th5' Dynamics and Thermodynamics of Compressible Fluid Flow, Volume 1, p.'85.,,

(2) 1967 ASME Steam Tables, p. 301. .

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Requirement:

5. d . The allowable leak rates of the purge and vent isolation valves should be specified for the spectrum of design basis pressures and flows against which the' valves must close.

Response: 4 The isolation valves were tested in accordance with 10 CFR Part 50 Appendix J and, when combined with the previous total leakage the result was found to be within allowable limits.

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