ML19263C289

Responds to NRC 781128 Ltr Re Containment Purging During Normal Plant Operation.Forwards Justification for Limited Purging Via 18-inch mini-purge Valves in Response to Branch Technical Position Csb 6-4

ML19263C289
Person / Time
Site:	Farley
Issue date:	02/05/1979
From:	Clayton F ALABAMA POWER CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
NUDOCS 7902130198
Download: ML19263C289 (12)

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M N N, a n Vce Pres acM Alabama POWCf the mulhem e!ecinc system February 5, 1979 Docket No. 50-348 Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Mr. Albert Schwencer Gentlemen:

JOSEPH M. FARLEY NUCLEAR PLANT-UNIT-1 CONTAINMENT PURGING DURING NORNAL PLANT OPERATION On January 9, 1979 Alabama Power Company responded to Mr. A.

Schwencer's letter dated November 28, 1978 concerning containment purging during normal plant operation for Farley Nuclear Plant, Unit 1. In the January 9 letter, Alabama Power Company committed to providing information concerning:

(1) justification for unlimited purging using the mini-purge (18 inch) system during power operation, (2) justification for limited purging using the main purge (48 inch) system, and (3) an evaluation of all safety actuation signal circuits which incorporate a manual override feature.

Justification for unlimited purging via the 18-inch mini-purge valves is provided in response to Branch Technical Position CSB 6-4 (En-closure 1). This detailed response to the BTP includes the following:

(1) verification that the valves are capable of closing against the dynamic forces of a design basis loss-of-coolant accident, (2) an evaluation of the imps t of purging during power operation of ECCS performance, and (3) an evaluation of the radiological consequences of a design basis accident.

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e Mr. Albert Schwencer PAGE TWO February 5, 1979 A review of the safety actuation signal circuits for the Containment Purge Systen has been performed. We have determined that overriding the safety actuation signals for the purge system containment isolation valves is not possible.

Justification for limited purging via the 48-inch main purge valves, including a demonstration (by test or by test and analysis similar to that required by Standard Review Plan 3.9.3) of the ability of the containment isolation valves to close under postulated design basis accident conditions, is addressed in our response to paragraph R.l.f of BTP CSB6-4 (enclosed).

A review of the design of all safety actuation signal circuits which incorporate a manual override feature was performed considering the follow-ing items:

(1) that overriding of one safety actuation signal does not also cause the bypass of any other safety actuation signal, (2) that suf ficient physical features are provided to facilitate adequate administrative controls, and (3) that the use of each manual override is annunciated at the system level for every system impacted.

The results of this review are as follows:

(1) We have verified that overriding of the safety actuation signal to any piece of equipment does not affect the safety actuation signals to any other equipment.

(2) (3) With exceptions, all manual overrides of equipment involving safety are alarmed in the main control room. These exceptions are as follows:

Each river water pump is provided with a breaker control switch located on the Main Control Board.

The control switch has three positions-maintained contacts. The three positions are: OFF - AUTO -

RUN. If a river water pump handswitch is placed in the "0FF" position the LOSP sequencer start signal to that pump is blocked. Failure of a river water punp to start during a LOSP is indi-cated by a sequencer step failure warning light and an alarm on the EPB annunciation system. It is an "immediate operator action" for a loss of offsite power to verify proper sequencer operation so that operator action can be taken for the pump start failure.

Mr. Albert Schwencer PAGE THREE February 5, 1979 Also, with a river water punp's handswitch in the "0FF" position and offsite power not avail-able, a low pond level signal is blocked to that pump. However, the same low pond level signal that initiates pump start also initiates a low pond level alarn to which the operator responds (by procedure) by verifying river water pumps running.

A technical specification change will be submitted in the near future to:

(1) provide surveillance requirenents for the nini-purge valvec (18 inch) as containment isolation valves, and (2) restrict the containment purge valves (48 inch) from being open in Modes 1, 2, 3, and 4 except for a maximum of 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year.

Yours very truly, F. L. layton, Jr.

FLCJr/TNE:bhj Enclosures cc: Mr. G. F. Trowbridge Mr. R. A. Thomas

ATTACliMENT 1 COMPARIS0N OF FARLEY PURGE SYSTEM WITil BRANCli fECilNICAL 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 BIP requirements are reproduced herein for cl a ri ty .

GENERAL:

Requi rement:

The system used to purge the containment for the reactor opera tional modes 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 opera tional modes of cold shutdown and refueling.

RysILon_sel The operation of 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 fil ter.

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.

Repir$ g nt:

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

(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 Assurance 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.

Resppnsg:

The mini-purge isolation valves are Seismic Category I, ASME Section III, Nuclear Class 2. The operability assurance program for these valves is described in aragraph 3.9.4.1 of FNP FSAR which was reviewed and approved b the NRC.

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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 Tiini-Purge System.

Requirement:

1.c. The size of the purge and ver t lines should not exceed about eight inches in diameter unless detailed justification for larger 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 /> Der week occupancy of the containment during power opera tion. In order to achieve this, it was determined that a purge flow rate of 5,000 cfm was reqcired. 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 6.1.f a nd B. 5.a , respec ti vely.

Requirement:

1.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

The isolation provisions of the Mini-Purge System meet the standards for engineered safety features. There are redundant isolation "A" valves in both the supply and exhaust lines with one valve an 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.

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 wi th independent ins trumentation and control systeas for isolation which are actuated by diverse parameters, specifically high radiation in the exhaust flow and

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a containment ventilation isolation signal (CVIS).

Figure 2 shows the relative location of the containment purge radia tion moni tors (RE-24A, B) . Upon sensing high radiation i the purge exhaust line, these monitors generate an isolation signal which results in the closing of all four mini-purge isolation valves.

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FSAR figure 7.2 'd provides details as to the various parameters wh_ict will genera te a CVIS. Upon receipt of a CVIS, all four mini-purge isolation valves _will_ close.

Electrical power is not required for the isolation function other than to generate the isolation signal . The isolation valves are air aperated valves which will close upon loss of air and loss of power to the so'enoid valves resulting in loss of air to the oper a tor.

Requirement:

1.f. Purge system isol< tion valve closure times, including instrumen-tatJon delays, should not exceed five seconds.

Response

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

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 discutsed 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. Ref erences 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

.. Butterfly Valves" by Turgut Sarpkaya, Paper #60-WA-105 from Trans-actions of the ASME Journal of Applied Mechanics.

Requirement:

1-9 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.e s po n s e :

The mini-purge and main purge supply and exhaust duct openings inside the containment are covered with " bird screen," preventing large pieces of material that ray break loose during a LOCA from entering the ducts and blocking isolation valve closure. The

" bird screen" is made from 1/2" mesh, .047" wire.

Requirement:

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

Res_ponse_:

Neither the Mini-Purge nor the Main Purge System was designed for temperature and humidi ty control within the containment. The system was designed for control of radioactivity levels wi thin the contain-r.ent as discussed in Position B.l.c. , above.

Requirement:

3. Provisions should be made to minimize the need for purging of the cor.tain-ment by providing containment atmosphere cleanup systems within the co nta i nment.

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, the pre-access filtration system is available for use in minimizing the need for purging the containment.

Requirement:

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.

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

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

Re_ qui rement:

5. The following analyses should be performed to justify 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 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 ptns e valves during the maximum interval required for valve closure. The radiological consequences should be within 10 CFR 100 guideline values.

Resppnse:

An analysis of the radiological consequences of a DBA LOCA during operation of the Mini-Purge System was performed. The method of 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 iodine spike of 60 ACi/gm I-131 dose equivalent.

The Mini-Purge System is operating with two 18 inch lines fully open, one tupply and on~e exhaust line. A' containment high pressure signal .will initiate isolation of the contsinment.within 0.8 seconds after the LOCA. The isolation valves will be fully 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 dependent; 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.

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

then added 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 Table 15.a-12 Incremental Total _ Lir:t_

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 Site Boundary (2 hrs.) 6.5 8.7 (10-3) 6.509 25 LPZ (0-30 days) 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:

5.b. An analysis which demonstrates the acceptability of the provisions made to protect structures and safety-related equipr.ent; e.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.

Response

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

Reauirement:

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 determination.

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 af ter inception of the LOCA. The Mini-Purge. System utilized during reactor operation consists of two 18-inch diameter lines. .It is. conservatively represented in this computc

• ion as follows:

1. A 5 second isolation valve closure time is assumed. During the 6-second period immediately following the LOCA, no credit is taken for the reduction in effective flow area which occurs while 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 system ducts is established immediately at the time of the LOCA.

A mixture of steam and air will be exhausted from the containment 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.

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 rates, critical flow was then conservatively assumed to be in effect from time zero.

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 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 magnitude on the calculated peak clad temperature is expected to be minor (less than 200F). When added to the curr~ent calculated peak clad temperature for a LOCA of 21580F, the results of this evaluation indicate that the Farley Plant meets 10CFR50.46 limits (22000F).even if the containmer.t is being purged at the time of a LOCA event.

REFERENCES:

(1) Shapiro, A. H., The Dynamics and Thermodynamics of Compressible Fluid Flow, Volume 1, p.185. .

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

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

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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