ML20217B607

Transmits Change to TS Bases Section B3/4.9.2,adding Info Re Role of Source of Power Supplied to One Source Range Neutron Flux Monitor in Determining Operability of Monitor in Mode 6

ML20217B607
Person / Time
Site:	Wolf Creek
Issue date:	09/19/1997
From:	Muench R WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20217B615	List: ML20217B607 ML20217B616
References
ET-97-0112, ET-97-112, NUDOCS 9709300088
Download: ML20217B607 (7)

Text

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W@) LF CREEKOPERATING C Rchard A Muench NUCLEAR Vee Presdent Engineering September 19, 1997 ET 97-0112 U. S. Nuclear Regulatory Commission ATTN Document Control Desk Mail Station P1-137 Washington, D. C. 20555 *

Subject:

Docket No. 50-402: Pevision to Technical Spec!fication Bases Section B3/4.9.2 for Source Range Neutron Monitor Power Supply Gentlemen This letter transmits a change to the Wolf Creek Generating Station (WCGS)

Technical Specification Bases. Attachment I provides background information and justification for the change. Attachment II provides a markup of the Bases page to be revised.

A copy of this Bases change, with attachments, is being provided to the designated Kansas State Official.

If you have any questions concerning this matter, please contact me at (316) 364-8831, extension 4034, or Mr. Richard D. Flannigan, at extension 4500.

.Very truly yours, Richar A. Muench RAM /jad Attachments I Background and Justification II Bases Markup Page ,Q hi!'

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cct V. L. Cooper (KDHE), w/a W. D. Johnson (NRC), w/a E. W. Merschoff (NRC), w/a J. F. Ringwald (NRC), w/a J. C. Stone (NRC), w/a 9709300000 970919

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P PDR PO. Box 411/ Burlington: KS 66839 / Phone (316; 364-8831 An Fouat Opportuvy Empyr M F HC VET

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Attachment I to ET 97-0112 Page 1 of 5 e

ATTACID4ENT I BACKGROUND AND JUSTIFICATION k

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Attachment I to ET 97-0112 Page 2 of 5 Background and Justifioation Proposed Bases Chang The proposed change to Technical Specification Bases Section B3/4.9.2 is to add the following sentence to the first paragraph in this section:

) "When any of the safety-related busses supplying power to the Source Range Flux Monitors are taken out of service, the corresponding Source Range Flux Monitor may be considered OPERABLE when powered from a temporary non-safety related source of power, provided the other Source Range Flux Monitor is powered from its nort..al power source." l This change will provide information concerning the role of the source of l power supplied to one source range neutron flux monitor in determining the OPERABILITY of the monitor in Mode 6.

]

Background

g' Wolf Creek Generating Station (WCGS) Technical Specification 3/4.9.2,

" Instrumentation," which is applicable only in Mode 6 (Refueling), requires two source range neutron flux monitors to be OPERABLE. WCGS Technical Specification 1.19, " OPERABLE - OPERABILITY," states:

"A system, subsystem, train, component or device shall be OPERABLE or have OPERABILITY when it is capable of performing its specified function (s), and when all necessary attendant instrumentation, controls, electrical power, cooling or seal water, lubrication or other auxiliary equipment that are required for the system, subsystem, train, component, or device to perform its function (s) are also capable of performing their related support f unction (s) ."

The source range neutron flux monitors provide indication and alarm functions only during Mode 6 operations. No protective functions are provided by the source range neutron flux monitors in Mode 6. The installed source range neutron flux monitors are part of the Nuclear Instrumentation System (NIS).

The detectors for these monitors are located external to the reactor vessel and detect neutrons leaking from the core. There are two sets of source range neutron flux monitors: (1) Westinghouse Source Range Neutron Flux Monitors, and (2) Gamma-Metrics wide range neutron flux monitors.

The Westinghouse source range neutron flux monitors employ BF3 detectors (SE-N1-0031 and SE-NI-0032) operating in the proportional region of the gas filled detector characteristic curve. The source range neutron flux monitors monitor the neutron flux in counts per second. The instrument range covers six decades of r.eutron flux (1 to 1E+6 cps). These monitors also provide continuous visual indication in the control room and each can provide audible indication in the control room and containment.

The Gamma-Metrics wide range neutron flux monitors employ fission chamber detectors (SE-NI-0060 and SE-NI-0061) and provide indication of neutron flux from reactor shutdown to reactor full power level (source range through power range). One of these wide range monitors provides continuous indication in the control room to a strip chart recorder, the other monitor provides visual indication through meters on the control board panel in the control room, and both monitors provide input to the plant computer, to allow operators to monitor core flux. The Gamma-Metrics wide range neutron flux monitors are not subject to Technical Specification 3/4. 9.2 but would be available to provide

Attachment I to ET 97-0112 Page 3 of 5 backup indication in the event one or both of the Westinghouse source range neutron flux monitors became inoperable.

The normal source of power to the source range neutron (BF ) detectors comes 3

off the 120 VAC vital busses NN01 and NN02. The Gamma-Metrics wide range neutron flux monitors are powered from NN01 and NN04 The attached figure provides a sittple one-line diagram for the B Train, which is typical of both trains. These busses are powered from safety-related 480 VAC busses, either directly through a 480/120 VAC SOLA transformer or their associated 125 VDC batteries / chargers (NKil/NK21 or NK12/NK22, respectively) through an inverter.

WCGS Technical Specification 3.8.3.2, "Onsite Power Distribution Shutdown,"

requires only one of the two safety-related onsite power distribution divisions to be OPERABLE in Mode 6. This means tbst the safety-related source of power to one of the source range neutron detectore is allowed to be unavailable in Mode 6 if that division or train is rendered inoperable for maintenance during an outage.

In 1996 WCNOC recognized that removing one train or division of safety-related power under Specification 3.8.3.2 would affect the corresponding source range neutron detector required to be CPERABLE by Specification 3.9.2, WCNOC investigated this concern and concluded that it would be acceptable to power the affected source range neutron detector from a non-safety related power source when in Mode 6, since Specification 3.8.3.2 required only one division of safety-related busses to be OPERABLE in Mode 6 and that the affected detector would be able to perform its required function under these conditions. To address this, WCNOC initiated a technical specification clarification (T5C 002-96), which allowed the operator to declare the detector af fected by a division outage Oh'RABLE when powered f rom a non-safety related powar source during refueling outages. In NRC Inspection Report 96-21, the NRC identified this clarification as a change to the requirements of Technical Specification 3.9.2, in that the Technical Specification definition of OPERABILITY includes a requirement for electric power, which the NRC interprets as referring to the normal safety-related power supply, even though Specification 3.9.2 itself does not refer to the power source. As a result of the NRC's position, WCNOC voided TSC 002-96 in October 1996. In letter WO 97-0017, dated January 22, 1997, WCNOC agreed with the NRC's position that Technical Specification Clarification 002-96 was not conservative. However, WCNOC has researched this issue further and has concluded that powering one source range neutron detector from a non-safety related power source in Mode 6 does not pose a safety concern, is necessary in order to conduct maintenance on the power distribution busses and components during Mode 6 operations involving core alterations or positive reactivity changes, and the normal safety-related power source to the detector is not necessary, in Mode 6, for the detector to perform its specified function (provided the detector can be powered from an alternate source).

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[ Justification l

I Powering one of the source range neutron detectors from a non-safety related power source is not a safety issue as a source range channel in Mode 6 provides monitoring and alarm capability only. In Mode 6 the reactor trip breakers are normally open (may be closed for short periods for maintenance or testing). During most of Mode 6 the reactor vessel head is removed and the control rods are not capable of being automatically withdrawn. The source range neutron flux monitors do not provide a reactor trip function in Mode 6.

The required response to a loss of a source range neutron flux monitor is to

immediately stop all operations involving core alterations or positive reactivity changes. A loss of ,ource range neutron flux detector high voltage l

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Attachment I to ET 97-0112 Page 4 of 5 is annunciated on the Main Control Board to ensure prompt discovery and response. The response to a loss of one source range neutron flux monitor is the same (i.e., compliance with the action statement in Technical Specification 3.9.2) regardless of the source of power supplied to the detector. Additional assurance of safety is provided by the fact that during Mode 6 the refueling cavity may be flooded above the vessel flange, providing maximum response time to potential incidents.

Applying the WCGS Technical Specification definition of VERABLE, a source range neutton flux monitor is considered OPERABLE when it is capable of performing its specified function and all necessary support systems it needs to perform that function are capable of performing their related support functions. The only specified function the source range neutron flux monitors have in Mode 6 is to provide redundant monitoring and alarm capability to detect changes in the reactivity condition of the core. In order to perform this functinn, ti e associated detectors have to be powered, and their normal source of power is from the 120 VAC Vital AC busses (NN01 and UN02). However, in Mode 6, as described above, one safety-related power division may be removed from service as allowed under Technical Specification 3.8.3.2 (also 3.8.2.2 allows one safety-related 125 VDC battery bank and associated charger to be out of service in Mode 6). The action required by both specificationo in the event both divisions are lost includes immediately suspending all operations involving core alterations or positive reactivity changes. This is the same action required by Specification 3.9.2 for the loss of one source range neutron flux monitor. Removing one power division under Specification 3.8.3.2 or one 125 VDC train under Specification 3.8.2.2 would affect the normal power supply to the associated source range neutron flux detector, since they supply power to the 120 VAC Vital AC bus powering the source range neutron flux detectors. Under these conditions, it is WCNOC's position that power may be supplied to the affected 120 VAC Vital AC bus from a non-safety related power source. This action would provide the power needed by the affected source range neutron flux detector in order to perform its specified function while complying with all requirements and allowances of Specifications 3.8.2.2, 3.8.3.2, and 3.9.2. In this particular situation it is WCNOC's position that the affected source range neutron monitor may be declared OPERABLE when its associated detector is powered from a non-safety related power supply, based on several considerations:

1) In Mode 6 the source range neutron flux monitors provide only monitoring and alarm functions. No reactor protection or accident mitigation actions are provided.

2) The opposite source range neutron flux detector will continue to be supplied from its normal safety-related power source.

3) In Mode 6 only one onsite power distribution division and one 125 VDC battery / charger train is required to be OPERABLE; the other onsite power distribution division and 125 VDC battery / charger train is not necessary to meet Mode 6 power requirements.

4) The source range neutron flux monitors are not credited in any design basis accident for accident mitigation activities.

5) Surveillance tests specified in Technical Specification 4.9.2 will continue to verify that the affected detector is performing its specified function while being powered from its alternate power supply.

6) The Train A Gamma-Metrics wide range neutron flux monitor would be available to provide backup core flux monitoring capability in the event of a loss of the temporary power supply to the Train B source range neutron detector.

At t achmerit I to ET 97-0112 Page 5 of 5 0

• FIGURE 1 - SOURCE RANGE NEUTRON DETECTOR POWER SUPPLY SIMPLIFIED DIAGRAM (THAIN B - TYPICAL *)

4100 VAC (safety related)(NB02)

Diesel Generator O

LJ 480 VAC non safety relateo f] I 480 VAC (safety related)(NG02)

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480 VAC (safety related)[NG04)*  !

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Battery NK12 l Temporary Powei Charger NK22 l l

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+ 125 VDC (safety related)

[NK02]

kj SOLA Transformer (safety related backup power Inverter

[XNN06)

[NN12) 120 VAC (safety related)

[NN02]

• On Train A, Charger NK21 and the SOLA Transformer are both Source Range powered from NG01.

Neutron Detector Otherwise, this figure is typical SE-NI-32 for both trains.

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ATTACID4ENT II BASES 14ARKUP PAGES

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