ML19296A932

Responds to NRC 791117 Request for Addl Info Re Containment Purge & Venting Sys.No Specific Provisions Exist to Prevent Debris Entrainment Through Purge & Vent Valves.Probability of Occurrence Is Considered Negligible

ML19296A932
Person / Time
Site:	Cooper
Issue date:	02/08/1980
From:	Pilant J NEBRASKA PUBLIC POWER DISTRICT
To:	Ippolito T Office of Nuclear Reactor Regulation
References
LQA8000060, NUDOCS 8002190483
Download: ML19296A932 (3)

Text

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LQA8C00060 GENERAL OFFICE P. o. BOX 499, COLUMBUS, NEBR ASKA 68601 Nebraska Publ.ic Power D.

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ic t rete ~ o~ei.uise ..sei February 8,1980 Director, Nuclear Reactor Regulation Attention: Mr. Thomas A. Ippolito, Chief Operating Reactors Branch No. 3 Division of Operating Reactors U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Containment Purge and Venting System Cooper Nuclear Station NRC Docket No. 50-298, DPR-46

Reference:

1) Letter from T. Ippolito to J. Pilant Dated November 17, 1979

Dear Mr. Ippolito:

Reference 1 contained a request for additional system information which was necessary for the staff to complete the lo'.g term containment purge and venting system safety evaluation. The fol.'owing are the District responses to this request.

Reauest No. 1 Discuss the provisions made to ensure that isolation valve closure will not be prevented by debris which could potentially become entrained in the escaping air and steam.

Response

There are no specific provisio"a to prevent debris entrainment through the purge and vent valves at CNS; however, the probability of such an occurrence is considered negligible for the following reacons:

1. Two valves, located outside of the drywell, are in series on the 20" line and both would need to be affected by material caught in ene seating surface.

2. The design of BWR containment components minimizes materials of the type which could become debris during an accident.

Request No. 2 Discuss the provisions made for testing the availability of the isolation function and the leakage rate of the isolation valves, individually, durin teactor operation.

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002190 Yb

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Thomas A. Ippolito February 8,1980 Page 2

Response

The primary containment purge and vent valves are cycled weekly to verify valve operability. The logic for the isolation is functionally tested monthly. The entire system is operationally tested every six months by initiating an isolation to verify that all applicable valves function properly.

The leakage rates of the valves are tested annually during local leak rate testing. These tests pressurize the volume between two valves and determine the combined total leakage rate for both valves by the pres-sure decay method. The leakage rate for two valves is conservatively attributed to each valve of the pair. This method can be used during operation, but is only used after repair of a valve to determine if the repair is acceptable. Leakage rate for individual valves cannot be determined during operation without totally impairing a purge or vent line for a significant time.

Request No. 3 Specify the amount of containment atmosphere released through the purge and vent isolation valves for a spectrum break sizes during the maximum closure time allowed in your Technical Specifications.

Response

As discussed in CNS FSAR Section V-2.4.6, the Technical Specification closure time limit of 15 seconds ensures that the containment purge and vent valves will be closed before significant amounts of fission products are released from the reactor core under design basis accident conditions.

Because the amount of radioactive material in the reactor coolant is small, a sufficient limitation of fission product release will be accom-plished since the isolation valves are closed before the coolant drops below the top of the core. The small amount of activity which would be released with the containment atmosphere during the 15 second drywell pressure ramp can be qualitatively compared to the large amounts of -

activity which is assumed to be released in the higher pressure main steam line break analysis. This analysis (FSAR section XIV-6.5) assures that the 10CFR100 offsite dose requirements are met with an assumed main steam line isolation valve closure time of 10 seconds.

Request No. 4 Provide an analysis to demonstrate the acceptability of the provisions made to protect structures and safety-related equipment; e.g., fans, filters, and ductwork, located beyond the purge system isolation valve.s against loss of function from the environment created by the escaping air and steam.

Response

There are no specific provisions installed at CNS to protect equipment downstream of the valves from damage by escaping air and steam. The probability of accident of such severity occurring concurrent with the

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Thomas A. Ippolito February 8, 1980 Page 3 small period of time each year that CNS opens the purge and vent valves is considered negligible. NPPD has previously committed to limit purge valve operation to times as low as achievable in order to permit oper-ation of the station.

Request No. 5 For the containment purge isolation vslves, specify the differential pressure across the valve for which the maximum leak rate occurs. Pro-vide test results (e.g., from vendor tests of leakage rate versus valve differential pressure) which support your conclusion.

Response

The valve manufacturer (Allis-Chalmers) has informed NPPD that the butter-fly valves utilized at CNS were tested for leakage at the A-C plant prior to shipping to ensure that the valve is leak tight. Each valve was tested with air under water and the valve is considered leak tig if no air bubbles are observed for a period of 5 minutes. The valves are rated at 125 psi and the above test was performed at 75 psi. The periodic local leak tests discussed in the response to No. 2 are periodically performed at approximately 58 psi. This range of pressures assures adequate sealing capability for the valves.

Should you have any questions or require additional information, please contact me.

Very truly yours,

,0. v n

/s/' ay M. Pilant h Director of Licensing and Quality Assurance JDW/cmk