ML19259A747

Forwards Revised Response to Reactor Sys Branch Question 5 on License Application.Question Was Originally Included in FSAR by Amend 56 as Question 6.51.Discusses ECCS Intersys Leakage

ML19259A747
Person / Time
Site:	Sequoyah
Issue date:	12/29/1978
From:	Gilleland J TENNESSEE VALLEY AUTHORITY
To:	Varga S Office of Nuclear Reactor Regulation
References
NUDOCS 7901100256
Download: ML19259A747 (5)

Text

T TENNESSEE VALLEY AUTHORITY

, CH ATTANOOGA. TENNESSEE 374o1 500C Chestnut Street Tower II CEO 3 NIS Director of Nuclear Reactor Regulations Attention: Mr. S. A. Varga, Chief Light Water Reactors Branch No. 4 Division of Project Management U.S. Nuclear Regulatory Commission Washington, DC 20535

Dear Mr. Varga:

In the Matter of the Application of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328 Enclosed is TVA's revised response to Reactor Systems Branch question 5 on our application for the Sequoyah Nuclear Plant transmitted by your letter dated May 10, 1977, to Godwin Williams, Jr. This question was originally included in the Sequayah Nuclear Plant Final Safety Analysis Report (FSAR) by Amendment 56 as question Q6.51. It has been revised as informally requested by Glen Kelly of the NRC staff.

Very truly yours.

&G- Q '

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J. E. Gilleland Assistant Manager of Power Enclosure

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79011002sg An Equal Opportunity Ernployer

• ~ ' SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 RESP 0hbE TO ','fESTION 6. 51 Your response to question 6.51 on intersystem leakage is not satisfactory.

Discuss your ability to continuously monitor and alarm intersystem leakage between the RCS and the following interfaces:

1. Chemical Volume and Control System

2. Safety Injection System

3. Residual Heat Removal System

4. Upper Head Injection System

5. Cold leg Accumulators.

List alarms and setpoints. Andicate the total amount of leakage and volumetric flow required to actuate these alarms when the intersysten leakage is started from the worst initial conditions (i.e.. maximum total leakage before leakage is terminated or controlled). Provide the time span required to identify the leakage.

Response

ECCS Intersystem Leakage Leakrbe from the Reactor Coolant Svstem into low pressure portions of several ECCS lines is prevented by the use of two check vai.es in series.

The check valves are tested for leakage during the preoperational test program. The inservice test program under Section XI of the ASME Code and its application to surveillance of the check valves is under review.

The probability of a major leak through any pair of check valves will therefore be limited to approximately 5.5 x 10-9 per reactor year. This probability is low enough to clininate any concern for a major intersys-tem leak into low pressure ECC systems. However, means are available to continuously monitor and alarm intersystem leakage across the inter-faces between the RCS and the following: Cold Leg Accumulators (CLA) ,

Upper Head Injection System (UHIS), Chemical and Volume Control System (CVCS), Safety Injection System (SIS), and Residual Heat Removal System (RERS). Leakage into these systems can be detected both by monitcring for signs of incoming leakage and by monitoring the RCS for signs of out-going leakage. First, means provided to monitor incoming leakage will be described individually for each of the five system interfaces. Then means provided to monitor the RCS inventory for outgoing leakage will be described.

Q6.51-1

ECCS Inleakage

- 1. Intersyst'e= lea'kage across the two check valves in each of the four CLA lines would increase the liquid inventory in the respective four accu =ulator tanks. Ivo level sensors are provided on each accumula-tor, each having continuous indication and alar = availabic in the Main Control Roo= (MCR). Assu=ing that the initial accuculator level is at the worst condition, the total atount of inco=ing leakage before a high level alar = is annunciated at the setpoint of 130.3 inches would be 420 gallons. The total rise of the tank vater level would be 9.3 inches. The time span required to identify this leakage and also the leakages discussed across the check valves in the other syste=s is a function of the leakage rate across the check valves.

However, since level indication is continuously available in the MCR, indication of the increasing level would be available in the MCR at all tices. This contiauous indication is also available for the ceasured paraceter in each of the other systers.

2. Intersyste= leakage across the two check valves in anp of the four Uhls lines would increase the liquid inventory in the UHIS accumula-ter surge tank. Two level sensors are provided on the surge tank, each having continuous indication and alar = available in the MCR.

Assu=ing that the initial surge tank level is at the worst condition, the total arount of inco=ing leakage before a high level alar = is annunciated at the setpoint of 15 inches would be 200 gallens. The total rise of the surge tank water level would be 12.7 inches.

3. There are no intersyste= leakape proble=s of practical concern in the CVCS because of the high syste= design pressure for the inter-facing CVCS piping and because the CVCS will generally be at a higher pressure than the RCS to provide the normal charging and seal injection functions.

4. Intersyste= leakage across the two check valves in each of the four SIS cold leg injection lines or across the two check valves and one normally closed gate valve in each of the four SIS hot leg injection paths would increase the pressure in those segnents of the lines. A separate pressure sensor is provided in each of the two SIS pump dis-charge lines with indication centinuously available in the MCh. The twe-pu=p discharge lines are connected with a nor ally open crossover line so a pressure increase in this segrent would be detectable by either sensor. Three pressure relief valves are also proviced for these SIS lines. When the pressure in the line reached 1,750 psig, the relief valves would discharge a total of 60 gpn to the pressuri-cer relief tank. Discharge into this tank would increase the tank level, pressure, and temperature. A level sensor is provided on the tank having both continuous indication and alar = available in the MCR. Assu=1ng that the iaitial pressuricer relief tani Jevel is at the worst condition, the total a=ount of incoming leakage before the Q6.51-2

e high Icvel alarm setpcint at 88 inches is reached would be 4,600 gallons.,The total rise in the t'nk water level would be 32.5 inches. A pressure sensor is provided having both continuous indica-tion and alarm available in the MCR. Assuming that the pressurizer relief tank pressure and level are at the worst conditions, the total amount of incoming Icaiage before the high pressure alarm setpoint at 8 psig is reached would be less than 1,400 gallons (neglecting teuperature effects for conservatism). The total rise in the tank pressure would be 5 psig. In addition, a temperature sensor is provided having both continuous indication and alarm in the MCR. The high temperature setpoint is 112.5 F.

5. Intersystem leakage across the two check val as in each of the four RHRS cold leg injection lines or across the two check valves and one normally closed gate valve in each of the two RHRS hot leg injection paths would increase the pressure in those segments of the lines. A separate pressure sensor is provided in each of the two RhRS pump discharge lines having both continuous indication and common alarm available in the MCR. The high pressure alarm set oint is 575 psig.

The two-pump discharge lines are connected with a aormally open crossover line so a pressure increase in this segment would be detectable by either sensor. Three pressure relief valves are al a provided for these RHRS lines. If the presrure in the lines reached 600 psig, the relief valves would discharge a total of 820 gpm to the pressurizer relief tank. Leakage into this tank is monitored continuously as described for the SIS leakage.

RCS Outleakage At steady state power operation, intersystem leakage from the RCS would reduce the RCS inventory and also affect RCS inventory control operations.

Monitoring of the RCS inventory and the inventory control operations would enable significant leakage from the RCS to be detected. If signs of this significant leakage were not observed in the primary containment, it could be assumed that it was intersystem leakage and possibly inter-system leakage into the ECCS. Monitoring the RCS would not aid in identi-fying the leakage path. At steady state, intersystem leakage from the RCS would cause the pressurizer 1cvel to drop which would automatically increase the CYCS charging pump flow rate. A flow element is provided in the common discharge of the three charging pumps with indication in the MCR. The CVCS Volume Control Tank (VCT) level would drop due to increased charging flow rate. A le el sensor is provided on the VCT having both continuous indication and clarm in the MCR. The operator could detect a change in the indication of VCT level corresponding to a loss of approximately 30 gallons. When a low level setpoint was reached, auto-matic makeup from a primary water makeup pump would te initiated.

Indication is provided in the MCR for operation of the makeup pumps.

If the level continued to drop, a low level alarm setpoint would be reached.

In addition to monitorin sthe inventory control operations, an RCS inventory balance is performed at least once every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> during steady state operation in accordance with the Technical Specifications.

If the leakage detection methods described above indicate that the ECCS check valves have excessive leakage, the permanent test lines provided in Q6.51-3

the system design could be used to determine the amount and identify the location of the leakage. If the RCS leakage limits in the Technical Specifications were exceeded by these check valves, and the leakage could not be reduced to within allowable limits in the time allowed, the reactor would be brought to cold shutdown and the valves would be repaired and retested to ensure the integrity of the double check valve isolation system.

Q6.51-4