ML20248D896

Application for Amend to License NPF-39,ensuring Design Level of Counting Certainty Maintained for Source Range Monitors.Document Entitled, Source Range Monitor Count Rate Vs S/N Ratio for Limerick Unit 1 Withheld (Ref 10CFR2.790)

ML20248D896
Person / Time
Site:	Limerick
Issue date:	08/03/1989
From:	Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML19292J403	List: ML20248D896 ML20248D910
References
NUDOCS 8908110163
Download: ML20248D896 (14)

Text

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10 CPR 50.90 l c ., .-

PHILADELPHIA ELECTRIC COMPANY NUCLEAR GROUP HEADQUARTERS .

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955-65 CHESTERBROOK BLVD.

WAYNE PA 19087 5691 (zt s) sso-sooo .

l August 3, 1989 Docket No. 50-352 License No. NPF-39 i'

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk l Washington, D. C. 20555  !

SUBJECT:

Limerick Generating Station, Unit 1 Technical Specifications Change Request i

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Dear Sir:

Philadelphia Electric Company hereby submits Technical Specifications Change Request No. 89-02, in accordance with 10 CFR 50.90, requesting an amendment to the Technical Specifications j (Appendix A) of Operating License No. NPF-39.

This submittal requests changes to the Technical )

Specifications (TS) to ensure the design level of counting certainty  !

is maintained at all times for the Source Range Monitors (SRMs).  !

Information supporting this Change Request is contained in I Attachment 1 to this letter, and the proposed replacement pages are contained in Attachment 2. Also enclosed is a document entitled, "SRM Count Rate vs. S/N Ratio for Philadelphia Electric Company Limerick Unit 1."- This document contains information that is proprietary to General Electric Company (GE), and-therefore GE requests that the document be withheld from public disclosure in  ;

accordance with 10 CPR 2.790(a)(4). As required by 10 CFR 2.790(b)(1) an application and affidavit to withhold this document from public disclosure is also enclosed.

In accordance with the provisions of 10 CFR 50.9, it was reported to the NRC on October 7, 1988, and by letter dated December 13, 1988, that the current provisions of Limerick Generating Station Unit 1 TS may lack sufficient conservatism. In that notification we 1

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committed)to.' provide an' assessment.of the safety implications ofL ~

,l, c.having, operated with.the existing TS,:and to submit TS changes-which-p,  ;,.,

. would; correct therexisting' situation.This' Change Requestiserves?to t

provide closure'of:these: commitments'

~Iflyou.have'any questions regarding1this matter, please

-contact-us.

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.Very.truly yours, a G. A.., Hunger, Jr..

Director

~ Licensing Section Nuclear Support DivisionJ Attachments-

.- Enclosures cc

W.- T. Russell, Administrator, Region I, USNRC T. J. Kenny,;USNRC Senior Resident Inspector, LGS T. ' M. Gerusky, PA Bureau of Radiation Protection j

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, . TECHNICAL SPECIFICATION CHANGE REQUEST 89-02

COMMONWEALTH OF' PENNSYLVANIA  :

ss.

COUNTY OF CHESTER  :

D. R'. Helwig, being first duly sworn,' deposes and says:

That he is Vice President of Philadelphia Electric Company, the Applicant herein; that he has read the' foregoing Application for Amendment of Facility Operating Licenses to ensure the design level of counting certainty is maintained at all times for the Source Range. Monitors, and knows the contents thereof; and that the statements and matters set forth therein are true and correct to'the best of his knowledge, information and belief.

Vice Pres nt Subscribed and sworn to before me this 8 d

day of 989.

i LE,kr ',)1fa& -

Notary Public NOTARIAL SEAL CATHERINE A. MENDEI Notary Public Media Boro. Delaware Co.

My Commission Exoires S_eut. 4.1989 1

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, ~ ATTACHMENT 1 3

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-LIMERICK GENERATING STATION Docket.No. 50-352'

License No. NPF-39 TECHNICAL SPECIFICATIONS CHANGE REQUEST ~

" Source: Range Monitor Count Rate Curve" Supporting Information for Changes - 11 pages i

t Docket No. 50-352 l Philadelphia Electric Company, Licensee under Facility i- Operating License NPF-39 for Limerick Generating Station (LGS)

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1 Unit 1, hereby requests that the Technical Specifications (TS) {

contained in Appendix A of the Operating License be amended as $'

proposed herein to ensure the design level of counting certainty l is maintained at all times for the Source Range Monitors (SRMs).

The proposed changes are provided in Attachment 2 and are indicated by vertical bars in the margin of the pages viii, 3/4 3-60a, 3/4 3-60b, 3/4 3-88, 3/4 9-4. We request the changes proposed herein to be effective upon issuance of the Amendment. ]

l This Change Request provides a discussion and description of the proposed TS changes, a safety assessment of the proposed changes, information supporting a finding of no l Significant Hazards Consideration, and information supporting an Environmental Assessment.

Discussion of Description of Changes The LGS TS presently allow reduction of the minimum SRM count rate required for control rod withdrawal or core I alterations from the normal 3 counts per second (cps) to 0.7 cps as long as the signal-to-noise ratio is greater than or equal to 1

two. General Electric Company has advised us that this provision is non-conservative with respect to the design bases of the SRM system, in that utilization of this provision could result in a  !

reduction in counting certainty. In order to ensure that the design level of counting certainty is maintained, a change to the TS is proposed to incorporate a graph of SRM minimum count rate I

• Docket No. 50-352 versus signal-to-noise ratio such that reduction of the count rate required by TS (3 cps to 0.8 cps)fis accompanied by a corresponding increase in the signal-to-noise ratio (2 to 30).

The SRM system consists of four identical neutron detection channels. Each channel contains a miniature in-core fission chamber, a pulse preamplifier, an electronics drawer, and remote reading indicators. Each detector is equipped with a motor driven mechanism to allow retraction from the core at neutron flux levels above the SRM range.

The SRM system monitors thermal neutron flux over a range sufficient to observe core shutdown soarce level, approach to criticality, and overlap into the Intermediate Range Monitoring (IRM) system. The indicating range of the SRM may be extended by retracting the detectors from the core. The SRM system provides four channels of neutron flux level information displayed over a range of 10-1 to 10 6 cps (approximately corresponding to 10-9 to 10-2 of rated thermal power),

and four channels of flux level rate of change information displayed as reactor period over a range of -100 to +10 seconds.

The SRM fission chambers are operated in the pulse counting mode and produce discrete output pulses which represent the composite effect of thermal neutron flux and gamma flux at the detector. Due to the nature of the detector, the pulses produced by thermal neutrons are of much greater magnitude than those produced by gamma, although the number of gamma pulses may far exceed the number of neutron pulses. An electronic circuit performs a discrimination action based on the amplitude of these

Docket No. 50-352 pulses, thus providing:an output signal proportional _only to the I 1 neutron count' rate.  !

.The following changes to'the TS are proposed.

1) . Insert Figure 3.3.6-1 on page 3/4 3-60b,."SRM Count Rate 4 versus Signal-to-Noise Ratio."

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2) Revise: Table'3.3.6-2 on Page 3/4 3-60a, TS section 4.3.7.6 on I Page 3/4 3-88, and TS Section 4.9.2 on Page 3/4 9-4, to permit reduction of'the minimum required ~SRM count rate below 3 cps "provided the' Source Range Monitor has an observed count rate ^and. signal-to-noise ratio on or above the curve shown on Figure 3.3.6-1."

-3) Revise the index on Page viii to include. Figure 3.3.6-1.

Safety Assessment The necessity for maintaining a minimum count rate on the SRMs when~ operating at-pre-critical and low power conditions is, based on the most conservative evaluation which includes fresh

-fuel loaded in the initial fuel cycle with no neutron sources present. A multiplying medium with no neutrons present forms the

' basis for the accident scenario in which reactivity is gradually' but inadvertently added until the medium is in a supercritical configuration. The introduction of some neutrons at this point would cause the core to undergo a sudden power burst, rather than a gradual startup, with no warning from the nuclear l

instrumentation. While this scenario is of concern when a

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a reactor.is loaded with fresh fuel, it is of less concern when loaded with. irradiated fuel.

Irradiated fuel continuously produces neutrons by I spontaneous fission of certain plutonium isotopes, by photo fission, and by photo disintegration of deuterium naturally' present in the moderator. The neutron production in irradiated fuel is normally great enough to meet the normal minimum SRM .

l count rate of 3 cps for the duration of a refueling outage, including the subsequent reactor startup. However, there'is a possibility that a minimum count rate requirement of 3 cps could not be satisfied following an extended reactor shutdown.

Providing a requirement of at least 3 cps as measured by the SRM assures that any transient, should it occur, begins at or above the initial value of 10-8 of rated power with the reactor critical as used in analyses of transient cold conditions. A review of Chapter 15, " Accident Analysis," (Section 15.4.),

" Reactivity and Power Distribution Anomolies", of the LGS Final Safety Analysis Report (PSAR), has confirmed the use of 10-8 of rated power with the reactor critical in analyses of transient cold conditions. Furthermore, the inadvertent criticality concerns evaluated in Chapter 15 (Section 15.4.1) take no credit I for the SRMs, since the SRMs are used for indication only. )

Since 0.8 cps, the lowest count rate shown on Figure 3.3.6-1, corresponds to approximately 8x10-9 of rated power, we have concluded thal reducing the downscale setpoint in accordance with Figure 3.3.6-1 will not invalidate the assumptions used in the transient analyses. Stipulating a

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. signal-to-noise ratio in accordance with Figure 3.3.6-1 assures that the SRMs are indeed responding-to neutrons and the neutron flux level with'the' reactor critical will be well above 10-8 i of rated: power due to cuberitical multiplication.

The curve presented in Figure 3.3.6-1 was derived.by j

General Electric Company specifically for LGS Unit 1. The a technical basis for this curve is presented in General Electric Company Report EDE-47-ll88, "SRM Count Rate vs S/N Ratio for 1 I

Philadelphia Electric Company, Limerick Unit 1," dated December J J

2, 1988. The curve ensures the same level of confidence at lower g

cps setpoints as is-provided at the nominal 3 cps setpoint. The  !

3 cps setpoint is based on an assumed signal-to-noise ratio of two, which yields a. statistical neutron monitoring confidence of 95% that the indicated signal is correct. At lower cps setpoints, a higher signal-to-noise ratio is required to maintain the same' level of counting certainty. The inverse relation between cps and signal-to-noise ratio depicted in Figure 3.3.6-1 ensures the 95% confidence level.

In accordance with the provisions of 10 CFR 50.9, we reported to the NRC on October 7, 1988, and by letter dated j i

December 13, 1988, that the provisions of the current LGS Unit 1 i TS may lack sufficient conservatism. The following evaluation provides our assessment of the safety implications of this issue.

In addition, the changes to the TS proposed herein provide closure of those actions committed to in the December 13, 1989 letter. 1 i

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l l Had.the'SRM setpoint been lowered to 0.7 cps,with a.

- signal-to-noise ratio of=two, as permitted by the provision l .

L currently in the TS, General ~ Electric Company has determined the confidence in the. accuracy of the SRM would be decreased to i

approximately 80%. That is, there would be a.20% chance of' false 1

detection and a 20% chance of non-detection of neutrons. Because L

L the SRM would still respond to neutron flux variations, and any -

' l observable neutron count rate on the SRM is sufficient to ensure i

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the transient analyses remain valid, operation at 0.7 cps with a signal-to-noise ratio of two would not have a significant impact on safety.

Information Supporting a Finding of No Significant Hazards Consideration We have concluded that the proposed changes to the LGS-TS, which ensure the design level of counting certainty is maintained at all times for the SRMS, do not constitute a significant hazards consideration. In support of this determination, an evaluation of each of the three standards set forth in 10 CPR S0,92 is provided below.

A. The proposed changes do not involve a significant increase in the probability or consequences of an accident previously evaluated The proposed changes reduce the minimum SRM count rate required to permit core alterations during reactor refueling and withdrawal of control rods during reactor startup. The proposed count rate is still within the

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Docket'No'. 50-352 design range of the SRM and specifying a signal-to-noise ratio assures-the SRMs are responding.to thermal neutron flux. No hardware changes are required to the-SRM system, therefore' malfunction of an SRM will still produce the required' control rod withdrawal blocks.

The applicable accidents related to the proposed change are those involving SRMs during reactor startup (control rod drop accident (RDA) and continuous control' rod withdrawal, and those' involving SRMs during reactor refueling (i.e., control rod removal error during refueling, a second control rod. removal or withdrawal, fuel insertion with the control rod withdrawn, and a control rod removal without the fuel removed). No credit is taken for the SRMs in any of these' accidents.

The RDA is the more limiting accident during reactor startup. Chapter 15 (Section 15.4.9) of the FSAR assumes an initial condition of 10-8 of rated power with the reactor critical in the analysis of transient cold conditions including the RDA. Therefore, reduction of the minimum SRM' count rate required to permit withdrawal of control rods as shown in Figure 3.3.6-1 still ensures that criticality will be achieved well above 10-0 of rated power. Accordingly, this proposed change does not affect the probability of consequences of previously evaluated accidents.

I The nuclear characteristics of the core assure that the reactor is subcritical even at its most reactive l

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condition with the most reactive control rod withdrawn during refueling. 'When the mode switch is in-REFUEL, only one control rod can be withdrawn. Selection of a second control rod initiates a control rod block,

+5ereby preventing the Lithdrawal of more than one control rod at a time. Therefore, the refueling interlocks prevent any condition which could lead to inadvertent criticality due to a control rod withdrawal error during refueling. Further, the mechanical' design of the. control rod, incorporating the velocity limiter, does not physically permit the upward removal of the control rod without the simultaneous or prior removal of the four adjacent fuel assemblies, thus eliminating any hazardous condition. In addition, the refueling interlocks require that all control rods must be fully inserted before a fuel assembly may be inserted into the core.

B. The proposed changes do not create the possibility of a new or different kind of accident from any accident previously evaluated.

No hardware modifications are required to implement this change. The design functions of the SRM system are not being changed. The only effect of this proposed change  !

is a reduction in the minimum count rate required for j control rod withdrawal and reactor core alterations.

The reducted minimum count rate, which must be accompanied by a corresponding increase in signal-to- I i

, Docket No. 50-352 I noise ratio, will continue to assure that all transients begin above 10-8 of rated power,-thereby maintaining ,

i the validity of the PSAR analysis.

I C. The proposed changes do not involve a significant reduction in a margin of safety.

The normal requirement of at least 3 cps assures that any transient, should it occur, begins at or above the initial value of 10-8 of rated power with the reactor critical as used in analysis of transient cold conditions. In fact, any observable neutron count rate on the ERM is sufficient to ensure the analysis remains valid. Therefore, reduction of the minimum count rate from 3 cps to the values shown in Figure 3.3.6-1 will not reduce this margin of safety becauce any transient will still begin at or above 10-8 of rated power with the reactor critical. Further, the SRMs are not required to ensure the margin of safety as analyzed in Chapter 15 of the PSAR.

Information Supporting an Environmental Assessment An environmental assessment is not required for the changes proposed by this Change Request because the requested changes conform to the criteria for " actions eligible for categorical exclusion" as specified in 10 CFR Sl.22(c)(9). The requested changes will have no impact on the environment. This

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' Change, Request does:not involve a significant hazards

, consideration as. discussed in the preceding section. .This Change-b

' Request does"not involve a'significant change in the types or

significant--increase in.the amounts of any effluents that may be

-released offsite. In addition, this Change Request does not

. involve a significant increase.in individual cr cumulative occupational radiation. exposure.

Conclusion:

'The Plant' Operations Review Committee and the Nuclear Review Board have. reviewed these proposed changes to the TS and

,have concluded that they do not involve an unreviewed safety question or a significant hazards consideration, and will not-endanger the health and safety of the public.

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