ML19305C763

Forwards Hydrogen Monitoring Sys Description.Util Has Investigated Requirements of Recommendation 2.1.9 of NUREG- 0578.Present Sys Meets Virtually All Monitoring Requirements.Replacement Would Be Expensive & Unnecessary

ML19305C763
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	04/01/1980
From:	Conway W VERMONT YANKEE NUCLEAR POWER CORP.
To:	Ippolito T Office of Nuclear Reactor Regulation
References
RTR-NUREG-0578, RTR-NUREG-578 SVY-80-52, NUDOCS 8004080238
Download: ML19305C763 (7)

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VERMONT YAN KEE NUCLEAR POWER CORPORATION SIEVENTY SEVEN GROVE STREET B.3.2.1 RUTLAND, VEMMONT 05701 WY 80-52 REPLY TO:

ENGINEERING OFFICE TURNPIKE ROAD WESTBORO. M ASS ACHUSETTS 01581 April 1, 1980 ve' era oas **>-s** sois United States Nuclear Regulatory Commission Washington, D.C.

20555 Attention: Office of Nuclear Reactor Regulation Mr. T. Ippolito, Chief Operating Reactors Branch #3

Reference:

(a) License No. DPR-28 (Docket No. 50-271)

(b) NUREG-0578 (c) NRC Letter, H.R. Denton to All Plants dated October 30, 1979 Attachnent: (A) Hydrogen Monitoring System Description

Subject:

NJREG-0578 Hydrogen Monitoring The Vermont Yankee Nuclear Power Corporation (VYtPC) has investigated the requirements of Recommendation 2.1.9 of Reference (b) and (c) regarding monitoring of the containment atmosphere for hydrogen content. The results of the investigation are detailed below:

1.

The Vermont Yankee plant is presently equipped with a hydrogen monitoring

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system which meets virtually all of the requirements of References (b) and (c).

2.

Additional factors e.g., location of the second detector, redundancy of sample points, etc., make this system even more effective than the system required by References (b) and (c).

3.

Since the system was designed prior to 1976, it does not meet certain requirements which have become, or are proposed for, regulatory requirements.

4 Vendor supplied information reveals that it is not possible to modify the existing equipment to meet all of the recommendations of References (b) and (c).

5.

Replacement of the system has been conservatively estimated at two hundred thousand dollars.

8004080238

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U.S. Nucl;;I Regul: tory Commission Page 2 Attention Mr. T. Ippolito March 31, 1980 It is the opinion of VYNPC that the imposition of this somewhat significant cost on the consumers, of New England, for a relatively insignificant improvement in quality, is counter productive conidering the capability and quality of tne existing system. As a result, VYNPC requests that you evaluate the acceptability of the existing system to satisfy the requirements of the referenced documents.

The attached information provides a description of the existing CAD hydrogen monitoring system and a comparison between the installed system and the proposed system required by References (b) and (c). To assist VYNPC in meeting the schedule established for Category B items, your prompt response is requested.

Should you have any questions please contact us.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION W. F. Conwa Manager of Operations LDM/kaf I

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Attachment A HYDROGEN MONITORING SYSTEM The Vermnt Yankee (VY) Containment Atmosphere Dilution (CAD) system was installed in 1976. A description was submitted to the NRC on June 1, 1976 and Technical Specification Proposed Change No. 41 was submitted on July 15, 1976. For reasons not directly related to the CAD system, Proposed Change 41 has not yet been approved by your office. However, it is the understanding of VY that the delay does not reflect any concern with the adequacy of the CAD system. The CAD sampling sub-system description is repeated here for convenience. This describes the system as it will be operated once accepted.

At present, some operational aspects are different. These differences are discussed below. The attached drawing shows the configuration.

Sampling Sub-System "The sampling sub-system, consists of piping and valves, two hydrogen r7alyzer cells, redundant air p m ps, and an air to air heat exchanger; these components are connected in a manner to provide three drywell and one torus sampling points and a return line to the torus sample line. The single torus sample line is provided with a valve configuration such that no single active failure could remove the torus sample point availability.

The primary analyzer, which measure the hydrogen concentration, is mounted in a cabinet located in an area of the Reactor Building which was selected to minimize the length of sample piping. The analyzer is remotely operated with read-out in the Control Room. A redundant hydrcgen analyzer cell is mounted on the outside wall of the Reactor Building in an area which is accessible after a LOCA.

The heat exchanger, a passive component, conditions the sample for analysis. Motive force for sample flow is provided by redundant air pmps.

.I Manual calibration equipment is provided to verify the accuracy of the j

analyzer cells during normal surveillance.

The valves in the sampling sub-system do not receive a PCIS signal since this sub-system is considered an integral part of the containment. These i

valves are used only to select an appropriate sample point and are manually operated from the Control Room.

A second line, which branches off the sample inlet hea' der, goes to a radiation monitor which is isolated from the hydrogen sampling sub-system by two solenoid valves and from the containment by two solenoid valves in the return line to the torus. These solenoid valves will close on receipt of a PCIS signal.

l On loss of power, all solenoid valves utilized in both the sampling sub-system and the radiation monitor piping loop are designed to fail in the closed position.

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The CAD sample sub-system is designated Safety Class 2.

Since it is a modification to the existing Sample System, it was designed in accordance with the requirements of ANSI B31.1. However, the new additions to the sample sub-system were designed and purchased to meet the requirements of Seismic Category I Criteria. In addition, those portions of the existing sample system which were incorporated into the CAD System, were upgraded to meet Seismic Category I Criteria."

i At present the valves in the CAD sampling subsystem receive a PCIS signal. This will be removed upon approval of the proposed Technical Specification change. Review of the system for purposes of this letter reveals that all the sample valves are powered from a single reliable power l

source. To guarantee single failure proof operation Vermont Yankee would consider a power supply modification. Electrical Systems at Vermont Yankee are not classified as lE but instead as Safety Class. The designations are essentially the same.

It can be seen that mult'ple means are available to perform the analysis of the hydrogen content of the reactor containment. Redundant sample points, i

each with redundant valves, provide flow paths to a single passive air-to-air heat exchanger and to the first of two hydrogen analyzers.

This analyzer, provided by Delphi is located inside the reactor building and is housed in a cabinet which contains the sample pumps and the heat exchanger. This analyzer measures concentration over the range of 0-10%, provides local indication, and is capable of being remotely operated from the control room, where it provides input to a recorder located on the back of the main control board. This unit-was purchased and installed as a seismic, Safety Class device and is powered from a Safety Class power supply. This unit was seismically qualified by comparison to a unit of very similar design.

The similar unit was tested utilizing biaxial random motion, amplitude controlled in one third octave increments from 1.1 Hz to 33 Hz and 5% of critical damping.

The unit was environmentally qualified by exposing it to conditions similar to those which it will encounter in its installed location, for a total period of 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

Motive power to produce flow is provided by redundant pumps. Power supply to each pump is separate, redundant, and Safety Class. Flow from the punps is returned to the torus through redundant, single-failure-proof valving with the power supply as described above. A second hydrogen analyzer, purchased from MSA, is installed in a by-pass loop in the return line to the torus. This loop and analyzer is outside of the reactor building in an area that would be accessible following a design basis accident. This location provides the ability to replace the detector without entering the reactor building. This unit measures hydrogen concentrations over the range of 0-4%,

provides local indication and a remote alarm output.

This unit was purchased non-safety related. Its method of operation was presumed to be as follows.

In the event of a failure in the first or primary detector, local readings would be relayed to the control room.

Examination of the equipment and installation reveal some differences from the recommendation of NUREG-0578. The table following displays where those differences occur.

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It is apparent that the ability to sample and record the containment hydrogen concentration is readily available at VY.

The system is redundant in all active components with the additional ability of replacing the external analyzer if found necessary.

The range of the external detector is less than the recommendation of MJREG-0578 but the external connection provides a sample point for laboratory measurement in the unlikely event of failure of both detectors and any replacement equipment which may be installed at the secondary sample point.

Plant emergency procedures call for actuation of the air dilution system to always maintain the hydrogen concentration in the containment below the lower explosive limit of 4%. Extended range instruments serve little practical purpose.

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TABLE I Comparision of NRC Requirements for H2 Monitors with Present Units at Vermont Yankee Requirements from October 30, 1979, HR Denton, Jr.

Delphi MSA Continuous Indication in Control Room Recorder Local Indicator Only 0-10% Range-0-10%

0-4%

Operate under both negative & positive ambient press.

Yes Yes Meet design provision of Reg. Guide 1.97 See Below 1.97 Provisions Powered from Class lE source Yes Yes Directly measure desired variable Yes Yes Specifically ident. on MCB Control Panels rio No Means for checking during Reactor Operation Yes Yes Meet single failure criterion together Qualified in accordance with RG 1.89 See Below l.97 Proposed Rev. 2 Additional Provisions Seismic Qualification per RG 1.100 Yes*

No Must be Recorded Yes No Periodic Testing per RG 1.118 Yes Yes 1.89 Provisions Qualified per IEEE-323-1974 1971*

No IEEE-323-1974 Provisions Environmental Qualified Yes*

No Aging Qualifications No No

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