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VERMONT YAN KEE NUCLEAR POWER CORPORATION'

SIEVENTY SEVEN GROVE STREET B.3.2.1

RUTLAND, VEMMONT 05701 WY 80-52REPLY TO:

ENGINEERING OFFICETURNPIKE ROAD

WESTBORO. M ASS ACHUSETTS 01581April 1, 1980 ve' era oas **>-s** sois

United States Nuclear Regulatory CommissionWashington, D.C. 20555

Attention: Office of Nuclear Reactor RegulationMr. T. Ippolito, ChiefOperating 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

Dear Sir:

Subject: NJREG-0578 Hydrogen Monitoring,

The Vermont Yankee Nuclear Power Corporation (VYtPC) has investigated therequirements of Recommendation 2.1.9 of Reference (b) and (c) regarding monitoringof the containment atmosphere for hydrogen content. The results of theinvestigation are detailed below: l

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1. The Vermont Yankee plant is presently equipped with a hydrogen monitoring )system which meets virtually all of the requirements of References (b) |and (c).

2. Additional factors e.g., location of the second detector, redundancy ofsample points, etc., make this system even more effective than the systemrequired 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 theexisting equipment to meet all of the recommendations of References (b) !and (c).

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5. Replacement of the system has been conservatively estimated at twohundred 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 significantcost on the consumers, of New England, for a relatively insignificant improvement inquality, is counter productive conidering the capability and quality of tneexisting system. As a result, VYNPC requests that you evaluate the acceptabilityof the existing system to satisfy the requirements of the referenced documents.The attached information provides a description of the existing CAD hydrogenmonitoring system and a comparison between the installed system and the proposedsystem required by References (b) and (c). To assist VYNPC in meeting the scheduleestablished for Category B items, your prompt response is requested. Should youhave any questions please contact us.

Very truly yours,

VERMONT YANKEE NUCLEAR POWER CORPORATION

W. F. ConwaManager of Operations

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Attachment A |

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HYDROGEN MONITORING SYSTEM

The Vermnt Yankee (VY) Containment Atmosphere Dilution (CAD) system wasinstalled in 1976. A description was submitted to the NRC on June 1, 1976 andTechnical Specification Proposed Change No. 41 was submitted on July 15,1976. For reasons not directly related to the CAD system, Proposed Change 41has not yet been approved by your office. However, it is the understanding ofVY that the delay does not reflect any concern with the adequacy of the CADsystem. The CAD sampling sub-system description is repeated here forconvenience. This describes the system as it will be operated once accepted.At present, some operational aspects are different. These differences arediscussed below. The attached drawing shows the configuration.

Sampling Sub-System

"The sampling sub-system, consists of piping and valves, two hydrogenr7alyzer cells, redundant air p m ps, and an air to air heat exchanger; thesecomponents are connected in a manner to provide three drywell and one torussampling points and a return line to the torus sample line. The single torussample line is provided with a valve configuration such that no single activefailure 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 wasselected to minimize the length of sample piping. The analyzer is remotelyoperated with read-out in the Control Room. A redundant hydrcgen analyzercell is mounted on the outside wall of the Reactor Building in an area whichis 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.

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Manual calibration equipment is provided to verify the accuracy of the janalyzer cells during normal surveillance. '

The valves in the sampling sub-system do not receive a PCIS signal sincethis 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 I

operated from the Control Room.

A second line, which branches off the sample inlet hea' der, goes to aradiation monitor which is isolated from the hydrogen sampling sub-system bytwo solenoid valves and from the containment by two solenoid valves in the I

return line to the torus. These solenoid valves will close on receipt of aPCIS signal.

lOn loss of power, all solenoid valves utilized in both the sampling

sub-system and the radiation monitor piping loop are designed to fail in theclosed position.

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The CAD sample sub-system is designated Safety Class 2. Since it is amodification to the existing Sample System, it was designed in accordance withthe requirements of ANSI B31.1. However, the new additions to the samplesub-system were designed and purchased to meet the requirements of SeismicCategory I Criteria. In addition, those portions of the existing samplesystem which were incorporated into the CAD System, were upgraded to meetSeismic Category I Criteria." i

At present the valves in the CAD sampling subsystem receive a PCISsignal. This will be removed upon approval of the proposed TechnicalSpecification 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 wouldconsider a power supply modification. Electrical Systems at Vermont Yankeeare not classified as lE but instead as Safety Class. The designations areessentially the same.

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

each with redundant valves, provide flow paths to a single passive air-to-airheat exchanger and to the first of two hydrogen analyzers. This analyzer,provided by Delphi is located inside the reactor building and is housed in acabinet which contains the sample pumps and the heat exchanger. This analyzermeasures concentration over the range of 0-10%, provides local indication, andis capable of being remotely operated from the control room, where it providesinput 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 poweredfrom a Safety Class power supply. This unit was seismically qualified bycomparison to a unit of very similar design. The similar unit was testedutilizing biaxial random motion, amplitude controlled in one third octaveincrements from 1.1 Hz to 33 Hz and 5% of critical damping.

The unit was environmentally qualified by exposing it to conditionssimilar to those which it will encounter in its installed location, for atotal period of 36 hours. -

Motive power to produce flow is provided by redundant pumps. Powersupply to each pump is separate, redundant, and Safety Class. Flow from thepunps is returned to the torus through redundant, single-failure-proof valvingwith 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 thetorus. This loop and analyzer is outside of the reactor building in an areathat would be accessible following a design basis accident. This locationprovides the ability to replace the detector without entering the reactorbuilding. This unit measures hydrogen concentrations over the range of 0-4%,provides local indication and a remote alarm output. This unit was purchasednon-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 readingswould be relayed to the control room.

Examination of the equipment and installation reveal some differencesfrom the recommendation of NUREG-0578. The table following displays wherethose differences occur.

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It is apparent that the ability to sample and record the containmenthydrogen concentration is readily available at VY. The system is redundant inall active components with the additional ability of replacing the externalanalyzer if found necessary.

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

Plant emergency procedures call for actuation of the air dilution systemto always maintain the hydrogen concentration in the containment below thelower explosive limit of 4%. Extended range instruments serve littlepractical purpose.

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TABLE I

Comparision of NRC Requirements forH2 Monitors with Present Units at Vermont Yankee

Requirements from October 30, 1979, HR Denton, Jr. Delphi MSA

Continuous Indication in Control Room Recorder LocalIndicatorOnly

0-10% Range- 0-10% 0-4%Operate under both negative & positive ambient press. Yes YesMeet design provision of Reg. Guide 1.97 See Below

1.97 Provisions

Powered from Class lE source Yes YesDirectly measure desired variable Yes YesSpecifically ident. on MCB Control Panels rio NoMeans for checking during Reactor Operation Yes YesMeet single failure criterion togetherQualified in accordance with RG 1.89 See Below

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l.97 Proposed Rev. 2 Additional Provisions

Seismic Qualification per RG 1.100 Yes* NoMust be Recorded Yes NoPeriodic Testing per RG 1.118 Yes Yes

1.89 Provisions

Qualified per IEEE-323-1974 1971* No

IEEE-323-1974 Provisions,

Environmental Qualified Yes* NoAging Qualifications No No

* Ses Text

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