ML20217F094
| ML20217F094 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 10/14/1999 |
| From: | Hutton J PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20217F098 | List: |
| References | |
| NUDOCS 9910200225 | |
| Download: ML20217F094 (19) | |
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PECO NUCLEAR ecco ceerov cemnemv 965 Chesterbrook Boulevard A Unit of PECO Energy Wayne.PA 19087-5091 October 14,1999 Docket Nos. 50-352 50-353 License Nos. NPF-39 NPF-85 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555
Subject:
Limerick Generating Station Units 1 and 2 Technical Specifications Change Request No. 99-05-0
Dear Sir / Madam:
PECO Energy Company is submitting Technical Specifications (TS) Change Request No. 99-05-0, in accordance with 10 CFR 50.90, requesting an amendment to the TS (Appendix A) of Operating License Nos. NPF-39 and NPF-85 for Limerick Generating Station (LGS), Units 1 and 2. This proposed change will revise LGS Units 1 and 2, TS Sections 2.2, " Safety Limits ana Limiting Safety System Settings" and 3.0/4.0,
" Limiting Conditions for Operation and Surveillance Requirements". The proposed changes are necessary to support LGS Modification P00224 which will install a new Power Range Neutron Monitoring System and incorporate long-term thermal-hydraulic :
stability solution hardware. The new Power Range Neutron Monitoring (PRNM) !
System is a digital based General Electric NUMAC system. The new system will i include reactor thermal hydraulic instability monitoring through the Oscillation Power !
Range Monitor (OPRM). The OPRM satisfies NRC Generic Letter 94-02, "Long-Term Solutions and Upgrade of Interim Operating Recommendations for Thermal Hydraulic Instabilities in Boiling Water Reactors."
Information supporting this TS Change Request is contained in Attachment 1 to this letter, and the proposed TS pages (including marked-up pages) showing the proposed l changes to the LGS Units 1 and 2 TS are contained in Attachment 2. This information !
is being submitted under affirmation, and the required affidavit is enclosed.
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@g$ (BOO \ ', n l 9910200225 991014 PDR ADOCK 05000352-P PDR l
r L
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October 14,1999 l Page 2 l
The PRNM System is scheduled for installation at LGS Unit 1 during the 1R08 3efueling Outage scheduled to begin on March 29,2000. The PRNM system is t
t$eduled for installation at LGS Unit 2 during the 2R06 Refueling Outage scheduled to begin on April 4,2001. We request that, if approved, the TS changes proposed l herein be issued by March 15,2000, for both units, and become effective as follows:
LGS Unit 1 - During the 1R08 Refueling Outage LGS Unit 2 - During the 2R06 Refueling Outage.
If you have any questions, please do not hesitate to contact us.
Very truly yours,
//
/i/RA ames A. Hutton irector- Licensing
Enclosures:
Attachments; Affidavit I
cc: H. J. Miller, Administrator, Region 1, USNRC (w/ enc.) ;
A. L. Burritt, USNRC Senior Resident inspector, LGS "
R. R. Janati, PA Bureau of Radiological Protection "
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r COMMONWEALTH OF PENNSYLVANIA :
- ss.
COUNTY OF CHESTER' :
J. J. Hagan, being first duly swom, deposes and says:
That he is Senior Vice President of PECO Energy Company, the Applicant herein; that he has read the foregoing Application for Amendment of Facility Operating License Nos. NPF-39 and NPF-85 for Limerick Generating Station Units 1 and 2, conceming Technical Specifications Change Request No. 99-05-0, " Power Range Neutron Monitoring System Replacement / Reactor Stability Modification," and knows the contents thereof; and inat the
. statements and matters set forth therein are true and correct to the best of his knowledge, information and belief, va-Mr V ' Firesident Subscribed and swom to before me this /
day.
of 1999. g Noia,v Prio
/ .
. Carol A.Wanon, Notary Pubue Myb niesMixYpiua Uy
.. , = - , , -
l ATTACHMENT 1
, LIMERICK GENERATING STATION
, UNITS 1 and 2 l
DOCKET NOS. 50-352 50-353 LICENSE NOS. NPF-39 NPF-85 TECHNICAL SPECIFICATIONS CHANGE REQUEST NO. 99-05-0
" POWER RANGE NEUTRON MONITORING SYSTEM REPLACEMENT / ;
REACTOR STABILITY MODIFICATION l
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I Supporting information for Changes - 15 Pages l
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Octob:r 14,1999 Docket Nos. 50-352
, 50-353 Attachment 1 Introduction PECO Energy Company, Licensee under Facility Operating License Nos. NPF-39 and NPF-85 I for Limerick Generating Station (LGS), Units 1 and 2, requests that the Technical i Specifications (TS) contained in Appendix A to the Operating Licenses be amended to revise TS Sections 2.2 and 3/4 and their associated TS Bases to reflect changes to support Modification P00224 for the installation of a digital Power Range Neutron Monitoring (PRNM)
System and incorporate long-term thermal-hydraulic stability solution hardware. The proposed changes to the LGS Units 1 and 2, TS are indicated by the markups on the affected TS pages (Attachment 2). This License Change Application provides a discussion and description of the proposed TS changes, a safety assessment of the proposed TS changes, information ,
supporting a finding of No Significant Hazards Consideration, and information supporting an Environmental Assessment.
Discussion and Description of the Proposed Chanoes The proposed Technical Specifications (TS) Change Request involves changes to LGS, Units 1 and 2, TS Sections 2.2 and 3/4 and their associated TS Bases for the installation of a digital Power Range Neutron Monitoring (PRNM) System and incorporation of long-term thermal- .
hydraulic stability solution hardware. Similar systems have been installed at Nine Mile Point Unit 2; Browns Ferry Units 2 and 3; Hatch Units 1 and 2; and Fermi Unit 2. This system is also scheduled to be installed at Peach Bottom Units 2 and 3.
The NRC issued Generic Letter (GL) 94-02, "Long-Term Solutions and Upgrade of Interim Operating Recommendations for Thermai Hydraulic Instabilities in Boiling Water Reactors",
which requires PECO Energy Company to develop and submit to the NRC a plan for long term stability corrective actions. In response to GL 94-02, PECO Energy Company committed to implement the long-term solution designated as Option Ill in NEDO-31960-A (including Supplement 1), "BWR Owner's Group Long-Term Stability Solutions Licensing Methodology."
The Option lil stability solution will be implemented as part of the Power Range Monitoring (PRM) System replacement modification (No. P00224) based on the NUMAC PRNM Retrofit plus Option 111 Stability Trip Function Topical Report NEDC-32410P-A (G-080-VC-00044). This modification consists of replacing the existing PRM System (including the Average Power Range Monitor (APRM) System, Rod Block Monitor System, and the Local Power Range Monitor (LPRM) System excluding the detectors and signal cables) with General Electric's (GE)
Nuclear Measurement Analysis and Control (NUMAC) Power Range Neutron Monitoring (PRNM) System. The NUMAC PRNM System utilizes the Oscillation Power Range Monitor (OPRM) detect-and-suppress function to implement Option Ill.
During the first operating cycle following installation of the new PRNM System, the OPRM will be fully operational except for the stability-related trip functions and some alarm functions.
The OPRM trip functions will be de-activated in order to perform on-line testing, tuning, and data collection of the instability detect and suppress algorithm. During the first cycle, PECO Energy will continue to implement the Interim Corrective Actions specified in NRC Bulletin 88-07 Supplement 1, to detect and suppress power oscillations as committed to in PECO Energy letter from G.A. Hunger to USNRC dated September 9,1994. Once armed, the existing 1
q Octob5r 14,1999 Docket Nos. 50-352 50-353 Attachment 1 operator actions for immediate exit and manual scram when in Regions 1 and 2 of the Power to Flow map will no longer be required.
L The Units 1 and 2 Technical Specification changes (including markups) associated with this modification are provided as an attachment. The significant TS Action Statement changes are i as follows:
p _ PRNM System -
i A. APRM Related RPS Instrumentation Functions l
A.1 Functions l 1
' The "APRM Neutron Flux - Upscale, Setdown" scram function will be retained with a slight name change to "APRM Neutron Flux - Upscale (Setdown)".
The "APRM Flow Biased Neutron Flux - Upscale" scram function and "APRM High Flow !
Clamped Neutron Flux - Upscale" scram function will be replaced with the "APRM J l Simulated Thermal Power - Upscale" and "APRM Neutron Flux - Upscale" scram ;
' functions. i The "APRM Downscale" scram interlock will be eliminated.
The "APRM Inop" trip function will be retained but will be changed somewhat to reflect ,
the new NUMAC PRNM System equipment and to delete the minimum LPRM detector !
count from this trip. The minimum LPRM detector count will be retained in the Trouble <
alarm and administratively controlled as to when to declare the APRM inoperable.
A new " pseudo" APRM trip function entitled "2-Out-Of-4 Voter" will be added. !
A.2 _ Minimum Number of Operable APRM Channels The required minimum number of operable APRM channels will change from four to three channels. ;
~A new requirement for minimum number of 2-out-of-4 voter channels will be added; all four 2-out-of-4 voter channels must be operable.
The minimum number of operable LPRMs per APRM channel required for APRM
- l. channel operability will increase from 14 to 20 per APRM channe: and from 2 to 3 for each of the four LPRM axiallevels per APRM channel.
A new requirement for the maximum number of LPRMs per APRM channel that may ,
become inoperable (and bypassed) between APRM gain calibrations will be added; the new limit is 9 LPRMs per APRM channel. This aspect will be managed administratively.
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o Octob r 14,1999 Docket Nos. 50-352 50-353 Attachment 1 A.3 - Applicable Modes of Operation APRM Neutron Flux-Upscale (Setdown)
The requirement to be operable in OpCons 3(HOT SHUTDOWN) and 5 (REFUEL) will I be eliminated.-
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APRM Simulated Thermal Power-Uoscale This new scram function will be required to be operable in OpCon 1 (RUN) only.-
APRM Neutron Flux-Uoscale This new scram function will be required to be operable in OpCon 1 (RUN) only.
APRM Inoo The requirement to be operable in OpCons 3(HOT SHUTDOWN) and 5 (REFUEL) will be eliminated.
APRM 2-Out-Of-4 Voter This new scram function will be required to be operable in OpCons 1 (R.UN) and 2 (STARTUP).
A.4' Channel Check Surveillance Requirements APRM Neutron Flux-Upscale (Setdown) l The requirement will be changed from a frequency of every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> to every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
APRM Simulated Thermal Power-Upscale The requirement for this new scram function will be a frequency of every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. l 1
APRM Neutron Flux-Uoscale !
The requirement for this new scram function will be a frequency of every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
j APRM Inoo There will be no Channel Check requirements (i.e., no change). i S
APRM 2-06;-Of-4 Voter The requirement for this new scram function will be a frequency of every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
A.5 Channel Functional Test Surveillance Requirements A PRM Neutron Flux-Uoscale (Setdown)
The requirement will be changed from a frequency of every 92 days to every 184 days (6 months). A note will be added allowing operation for up to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> prior to test after entering Mode 2 (startup) from Mode 1 (run). The Channel Functional Test shall include both the APRM channels and the 2-out-of-4 voter channels.
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Octobar 14,1999 Docket Nos. 50-352
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50-353 l Attachment 1 l-APRM Simulated Thermal Power-Upscale The requirement for this new scram function will be a frequency of every 184 days (6 months) (without any specific requirement related to startup or shutdown). The Channel Functional Test shallinclude both the APRM channels and the 2-out-of-4 voter channels plus the flow input function, excluding the flow transmitters.
APRM Neutron Flux-Upscale The requirement for this new scram function will be a frequency of every 184 days (6
- months) (without any specific requirement related to startup or shutdown). The channel
' functional test shall include both the APRM channels and the 2-out-of-4 voter channels.
l APRM Inoo i The requirement will be changed from a frequency of every 92 days to 184 days (6 l months) (without any specific requirement related to startup or shutdown). The channel functional test shall include both the APRM channels and the 2-out-of-4 voter channels.
APRM 2-Out-Of-4 Voter The requirement for this new scram function will be a frequency of overy 184 days (6 months).
A.6 Jhannel Calibration Survaillance Requirements APRM Neutron Flux-Upscale (Setdown) l The Channel Calibration frequency will be changed from every 184 days (6 months) to every 24 months.
s APRM Simulated Thermal Power-Uoscale I l The Channel Calibration frequency for this new scram function will be weekly and every 24 months. The weekly Channel Calibration will consist of APRM adjustments and the l 24 month Channel Calibration will consist of equipment calibration. -The Channel Calibration at each 24-month interval will include the calibration of the flow input I function.
APRM Neutron Flux-Upscale
' The Channel Calibration frequency for this new scram function will be weekly and every l 24 months. The weekly Channel Calibration will consist of APRM adjustments and the
! 24 month Channel Calibration will consist of equipment calibration.
l' APRM inoo No change in requirement (i.e., no calibration applies).
APRM 2-Out-Of-4 Voter There will be no Channel Calibration requirement for this new scram function.
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Octob:r 14,1999 Docket Nos. 50-352 50-353 Attachment 1 A.7 Response Time Testing Surveillance Requirements The LPRM detectors, APRM channels, and 2-out-of-4 Voter channels digital electronics are exempt from response time testing. The requirement for response time testing of the RPS logics and RPS contractors (50 ms) will be retained by including a response time testing requirement for the new 2-Out-Of-4 Voter function.
APRM Neutron Flux-Upscale (Setdown)
There will be no Response Time Testing requirements for this scram function (i.e., no change).
APRM Simulated Thermal Power-Uoscale There will be no Response Time Testing requirements for this new scram function.
APRM Neutron Flux-Upscale There will be no Response Time Testing requirements for this new scram function.
APRM Inoo There will be no Response Time Testing requirements for this scram function (i.e., no change).
APRM 2-Out-Of-4 Voter The Response Time Testing requirement for this new scram function will be < 0.05 seconds. Response time will be measured from activation of the 2-Out-Of-4 Voter output relay.
A.8 Logic System Functional Testing (LSFT) Surveillance Requirements There will be no LSFT requirements for the PRNM functions except the 2-Out-Of-4 Voter function. LSFT for that function will be required to be performed every 24 months.
A.9 Setpoints and Allowable Values Where justified by the setpoint calculations and the improved equipment performance specifications, Allowable Values will be adjusted. Those changes are marked in the Technical Specification markups.
B. APRM Control Rod Block Functions B.1 Functions The "APRM Neutron Flux - Upscale, Startep" rod block will be replaced with the "APRM Simulated Thermal Power - Upscale (Setdown)" rod block.
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Octobar 14,1999 i
Docket Nos. 50-352 50-353 f
t Attachment 1 The "APRM Flow Biased Neutron Flux - Upscale" rod block will be replaced with the l "APRM Simulated Thermal Powe. - Upscale" rod block.
l The "APRM Downscale" rod block will be retained but the name will be changed to "APRM Neutron Flux - Downscale" rod block.
1 The "APRM Inop" rod block will be retained as is.
The Reactor Coolant System Recirculation Flow "Inop" and "Comparator" rod blocks will be deleted. The Reactor Coolant System Recirculation Flow " Upscale" rod block will be made a subfunction of the APRM control rod blocks functions.
An APRM "LPRM Count Low" rod block function will be added.
B.2 Minimum Number of Operable APRM Channels i
The required minimum number of operable APRM channels will change from four to l three channels.
1 The minimum number of operable LPRMs per APRM channel required for APRM {
channel operabi:ity will increase from 14 to 20 per APRM channel and from 2 to 3 for .
, each of the four LPRM axiallevels per APRM channel. I A new requirement for the maximum number of LPRMs per APRM channel that may become inoperable (and bypassed) between APRM gain calibrations will be added; the new limit is 9 LPRMs per APRM channel. This aspect will be managed administratively.
B.3 Applicable Modes of Operation APRM Simulated Thermal Power-Upscale (Setdown)
This new rod block function will be required to be operable in OpCon 2 (STARTUP) or.ly.
APRM Simulated Thermal Power-Upscale This new rod block function will be required to be operable in OpCon 1 (RUN) only.
APRM Inoo The requirement for operability in OpCon 5 (REFUELING) will be ' !oted.
APRM Neutron Flux - Downscale This rod block function will be required to be operable in OpCon 1 (i.e., no change).
APRM Recirculation Flow- Uoscalg l This rod block function will be required to be operable in OpCon 1 (i.e., no change).
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Octobsr 14,1999 Docket Nos. 50 352 50-353 Attachment 1 APRM LPRM Count Low This rod block function will be requiad to be operable in OpCon 1 and OpCon 2.
B.4 Channel Check Surveillance Requirements There will be no Channel Check requirements (i.e., no change).
B.5 Channel Functional Test Surveillance Requirements APRM Simulated Thermal Power--Upscale (Setdown)
The frequency for this new rod block function will be every 184 days (6 months).
APRM Simulated Thermal Power-Upscale The frequency for this new rod block function will be every 184 days (6 months).
APRM Inoo
- The frequency will be changed from every 92 days to 184 days (6 months).
APRM Neutron Flux - Downscale The frequency will be changed from every 92 days to 184 days (6 months).
APRM Recirculation Flow- Uoscale '
The frequency will be changed from every 92 days to 184 days (6 months).
APRM LPRM Count Low The frequency of this new rod block function will be every 184 days (6 months).
B.6 Channel Calibration Surveillance Requirements APRM Simulated Thermal Power-Upscale (Setdown)
The frequency for this new rod block function will be every 24 months.
APRM Simulated Thermal Power--Uoscale The frequency for this new rod block function will be every 24 months.
APRM Inoo There will be no channel calibration requirements (i.e., no change).
APRM Neutron Flux - Downscale The frequency will be changed from every 184 days (6 months) to 24 months.
- APRM Recirculation Flow- Uoscale The frequency will be changed from every 184 days (6 months) to 24 months. !
l l l APRM LPRM Count Low j The frequency of this new rod block function will be every 24 months. j 1
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1-Octob:r 14,1999 Docket Nos. 50-352
. 50-353 Attachment 1 l l
l B.7 Resporse Time Testing Surveillance Requirements l
N/A i
i B.8 Logic System Functional Testing (LSFT) Surveillance Requirements N/A B.9 Setpoints and Allowable Values l Where justified by the setpoint calculations and the improved equipment performance specifications, Allowable Values will be adjusted. Those changes are marked in the Technical Specification markups.
l C. Recirculation System The reference to the APRM scram and rod block will be modified to include " Simulated Thermal Power - Upscale". '
PRNM Related RPS Technical Specification 3.3.1 Clarifications The following Technical Specification changes augment those described for the PRNM implementation. These clarifications have already been incorporated in the plants that have
. Improved Technical Specifications.
D.1 Provision for channel surveillance to demonstrate channel operability .
A new " Note (n)" will bo added to Table 3.3.1-1. Reference to the note is added along with the " note (a)" reference in the " MINIMUM OPERABLE CHANNELS PER TRIP SYSTEM" column heading in Table 3.3.1-1. The note will allow retuming a channel or inp system to the untripped condition under administrative control for up to two hours to perform the required surveillance tests provided trip capability is maintained. This note will apply to all functions in the Table.
D.2 IRM operability requirements in Modes 3,4 and 5 Table 3.3.1-1 and Table 4.3.1-1 IRM operability and surveillance requirements in Modes 3 and 4 will be deleted. IRM operability and surveillance requirements in Mode 5 will be modified by adding a reference to the existing " Note (i)* which will require operability only if a control rod is withdrawn with an exception to this requirement for control rods withdrawn per Specification 3.9.10.1 and 3.9.10.2. Table 3.3.1-1 Action 2 will be deleted.
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Octob:r 14,1999
- Docket Nos. 50-352
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50-353 Attachment 1 L D.3 NMS shorting link removal requirements Table 3.3'.1-1 Note (c) will be deleted along with the "*" footnote referencing Specifications 3.9.10.1 and 3.9.10.2.
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Bagg; PRNM System The bases for the above listed Technical Specifcation changes are documented in Section 8.0 of the NUMAC PRNM Licensing Topical Report (LTR) NEDC-32410P-A including Supplement '
1 (both of which have been approved by the NRC) with the following exceptions:
Section 3/4.3.1 - APRM Related RPS Instmmentation Functions
' Deletion of Note "g"for Table 4.3.1.1-1 (adjust flow channel to conform to calibrated flow)
The LTR discusses in detail the aspects of the PRNM equipment that are improved, and the justification for eliminating Note "g" relative to drift of the PRNM equipment. !
However, the justification included in the LTR does not address the potential impact of !
changes in the core flow / recirculation flow ratio, either as a result of changes in power - !
distribution over the cycle or due to the potential for operating at a higher rod line than !
that used for flow calibration. Note "g" applies to flow as an input to the STP - Upscale !
' flow biased) scram.' There is no safety credit assumed in any analysis for the STP -
Upscale flow biased scram function. FurthG based on Reference 9, to the extent the flow biased scram is included in analysis, it is included as drive flow. Therefore, deletion of Note "g", and the potential increased difference be%een indicated drive flow and core flow will have no safety impact on the STP - Upscale flow biased scram !
function. I Setpoints and Allowable Values The improved performance specifications for the PRNMS equipment compared to the
. current equipment provide additional margin between the setpoints or allowable values and the corresponding analyticallimits or design basis values. Part of that margin will be " consumed" to offset the effects of increased surveillance intervals. The remaining margin, where available, is used to justify relaxing the Allowable Values The LTR does not address how to determine the Allowable Value (AV) for the STP -
Upscale or Neutron Flux - Upsca!e trip functions when they replace the "APRM Flow Biased Neutron Flux - Upscale" and "APRM High Flow Clamped Neutron Flux -
Upscale" trip functions as part of the modification. The LGS modification will retain the l Analytical Limit for the "APRM High Flow Clamped Neutron Flux - Upscale" trip as the
( "APRM Neutron Flux - Upscale" Analytical Limit since those two functions are !
equivalent. Based on this Analytical Limit, the Allowable Value for the "APRM Neutron i
9 !
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Octobsr 14,1999 Docket Nos. 50-352 50-353 Attachment 1 Flux - Upscale" function has been calculated based on the improved specifications of
~ the PRNM system. The value is shown in the Tech Spec markups.
There is no specific safety credit for the "APRM Flow Biased Neutron Flux - Upscale" scram in the original design, nor for the "APRM Simulated Thermal Power - Upscale" scram in the replacement PRNM. Therefore, the Allowable Value for the "APRM Simulated Thermal Power - Upscale" trip function is based on engineering judgment to -
balance benefits of providing additional margin for transients initiated at reduced flow conditions and the potential for inadvertent trips. Based on engineering judgment, a design bases " analytical limit" of 2% lower than the analytical limit for the "APRM Neutron Flux - Upscale" trip function has been established. Therefore, the "APRM Neutron Flux - Upscale" trip function analytical limit of 121% results in an "APRM Simulated Thermal Power- Upscale" trip function analytical limit of 119%. The design bases for the STP flow biased scram equation has been established to provide the same " flow intercept" (approximately 81% rated flow) as the current equation for the "APRM Flow Biased Neutron Flux - Upscale" scram. With those limits, the Allowable Values for the clamp and flow biased portions of the "APRM Simulated Thermal Power
- Upscale" scram have been calculated using the improved performance specifications of the PRNM. Those calculated values are included in the Tech. Spec. markup.
Engineering judgment was based on GE Licensing Topical Report NEDC-32410P-A,
" Nuclear Measurement Analysis and Centrol Power Range Neutron Monitoring (NUMAC-PRNM) Retrofit Plus Option ll1 Stability Trip Function," which used the i
methodology documented in NEDC-31336, " General Electric Instrumentation Setpoint Methodology," to establish appropriate Allowable Values and setpoints that have analytical bases. NRC approved NEDC-31336 in a Safety Evaluation Report (SER) transmitted by letter dated February 9,1993, from B. Boger (NRC) to D. Roare (GE).
The NUMAC-PRNM equipment performance specifications are described in NEDC-32410P-A. T' e NRC accepted NEDC-32410P for referencing in license applications in L
an SER transmitted by letter dated September 5,1995 from B. Boger (NRC) to D.
Reigel (GE).
Deletion of APRM operability requirements during shutdown margin testing per
- Specification 3.10.3.
! lhe LTR discusses deletion of all operability requirements in the RPS Specification for APRM in Mode 5. It also addresses in general cases where plants allow Shutdown Margin Testing in Refuel Mode and include an APRM operability requirement during those tests (e.g., ISTS 3.10.8). However, the LTR does not discuss cases where current Technical Specifications include both a requirement for SRM operability with shorting links removed (as is the case for LGS Specification 3.10.3) and APRM (as is the case for LGS current Specifica+ ion 3.3.1). The current LGS requirement for APRM operability during performance of Shutdown Margin Testing per Specification 3.10.3 was essentially a " retained" requirement as part of LGS Technical Specification Amendment 41/7 (LGS Units 1/2). With that amendment, all APRM Mode 5 operability requirements were deleted except during performance of Shutdown Margin Testing per Specification 3.10.3. That amendment included a complete discussion of the relative 10 I
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f Octobtr 14,1999 Docket Nos. 50-352 50-353 Attachment 1 sensitivity of the SRM and IRM functions compared to the APRM function, and j- concluded that the SRM and IRM, particularly operating in non-coincidence mode (shorting links removed), is much more sensitive to detecting local criticality that might result due to errors during refueling. The only reason stated for retaining the
. requirement for APRM operability during Shutdown Margin Testing per Specification 3.10.3 is a statement in the UFSAR Description Section 7.2.1.1.4.1 (RPS Instrumentation and Control) that says that ". . . contacts from each SRM are combined
. with IRM and APRM trips to produce a noncoincident reactor NMS trip via removal of the RPS " shorting links." That amendment states that there are no other FSAR claims l
. or " requirements" for APRM operability in Mode 5.
The basis in Amendment 41/7 for retaining this APRM operability requirement was an incorrect interpretation of the purpose of the UFSAR descriptive statement. The UFSAR description was intended to state that shorting links are removed and then describe 'he result of such removal. In the current PRM design, removal of the shorting links does, as described in the UFSAR, connect the APRM in noncoincident mode, but that is simply a convenience in the original design since it would have been more difficult to design the circuit so that removing shorting links did not include the APRM.
Since Specification 3.10.3 includes a specific requirement to assure SRM operability and to remove shorting links, since IRM operability is required by Specification 3.3.1, and since removal of shorting links per Specification 3.10.3 will also connect the IRM trips in noncoincident mode, both the SRM and IRM scram functions will be operable in noncoincident mode during performance of Shutdown Margin Testing per Specification 3.10.3. Therefore, even if the maximum number of IRM and SRM channels are bypassed, these systems will provide an RPS trip before any APRM trip will occur.
Consequently, deletion of the requirement for APRM operability during performance of Shutdown Margin Testing per Specification 3.10.3 has no safety impact. As part of the PRNM modification as described in the PRNM LTR, the APRM contribution to the noncoincident mode RPS input is deleted; therefore, the UFSAR description will be revised.
Section 3/4.3.6 - Control Rod Block Instrumentation The Reactor Coolant System Recirculation Flow " Upscale" rod block will be made a subfunction of the APRM control rod blocks functions instead of being deleted.
Although not required to meet any licensing commitments, for consistency with other
- APRM rod block functions, the new APRM LPRM count low rod block will be added as a subfunction of the APRM rather than controlling the function by other procedures only.
Section 3/4.4.1 - Recirculation System The LTR did not inc!ude any discussion of the Recirculation System Tech Spec changes. This Tech Spec section must be revised to be consistent with the APRM Tech Spec changes implemented for PRNM.
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< October 14,1999 ;
- l. Docket Nos. 50-352 L
1 - 50-353 Attachment 1 l
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. Safety Assessment I
! LGS Modification P00224 and its associated TS changes will not adversely affect the ability of the RPS and RBM systems to perform their intended function. The replacement system has improved channel trip accuracy and channel indicated accuracy. The proposed changes do not cause a plant parameter for any analyzed event to fall outside of acceptable limits. The .
- i. . Surveillance Requirements and their frequency of performance will assure reliability of the RPS and RBM systems. Consequently, the proposed modifications and associated TS changes will not adversely affect the health and safety of the public.
Information Sucoortina a Findina of No Sionificant Hazards Consideration We have concluded that the changes to the Limerick Generating Station (LGS) Units 1 and 2 Technical Specifications (TS), which will revise TS Sections 2.2, " Safety Limits and Limiting Safety System Settings " and 3/4, " Limiting Conditions for Operation and Surveillance Requirements," and their associated TS Bases to install a new Power Range Neutron Monitoring (PRNM) System and incorporate long-term thermal hydraulic instability monitoring, do not involve a Significant Hazards Consideration. In support of this determination, an
, evaluation of each of the three (3) standards set forth in 10 CFR 50.92 is provided below.
~ 1. The proposed TS chanaes do not involve a sianificant increase in the probability or consecuences of an accident oreviousiv evaluated.
As discussed in the Nuclear Measurement Analysis & Control (NUMAC) PRNM Licensing
- Topical Report (LTR), the NUMAC PRNM modification and associated changes to the TS involve equipment that is designed to detect the symptoms of certain events or accidents and initiate mitigating actions. The worst case failure of the equipment involved in the L modification is a failure to initiate mitigating action (scram or rod block), but no failure can )
l cause an accident. The PRNM replacement system is designed to perform the same ;
operations as the existing Power Range Monitor System and meets or exceeds all !
L operational requirements. Therefore, it is concluded that the probability of an accident j previously evaluated is not increased as a result of replacing the existing equipment with i the PRNM equipment. !
The PRNM System reduces the need for tedious operator actions during normal conditions j
' and allows the operator to focus more on overall plant conditions. The automatic self-test
- . and increased operator information provided with the replacement system are likely to
- i. reduce the burden during off-normal conditions as well. The replacement equipment ;
qualifications fully envelope the environmental conditions, including electromagnetic
~
interference, in the LGS control room.
. The replacement equipment has been specifically designed to assure that it fully meets the
- response time requirements in the worst case. As a result, due to statistical variations resulting from the sampling and update cycles, the response time is typically faster than 12 ,
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Octob;r 14,1999 Docket Nos. 50-352 l .
50-353
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Attachment 1 1 required in order to assure that the required response time is always met. Setpoints are !
changed only when justified by the improved equipment performance specifications and by i setpoint calculations which show tnat safety margins are maintained. There is no impact to the Control Rod Drop accident analysis because the PRNM System maintains all existing system functions with a reliability equal to or better than the existing Power Range Monitor System.
j I
The replacement equipment includes up to 5 LPRM inputs on a single module compared to
{
one per module on the current system. Up to 17 LPRM signals are processed through one i preprocessor. The recirculation flow signals are processed in the same hardware as the '
LPRM processing. The net effect of these architectural aspects is that there are some single failures that can cause a greater loss of "sub-functionality" than in the current system. Other architectural and functional aspects, however, have an offsetting effect.
Redundant power supplies are used so that a single failure of Reactor Protection System (RPS) AC power has no effect on the overall PRNM System functions while still resulting in a half scram as does the current system. Continuous automatic self-test also assures that if a single failure does occur, it is much more likely to be detected immediately. The net effect is that from a total system level, unavailability of the safety-related functions in the I replacement system is equal to or better than the current Power Range Monitor System.
Based on the extensive and thorough verification and validation program used in the PRNM design and field operating experience, common cause failures in software controlled functions are judged to not be a significant failure mode. However, in spite of !
that conclusion, means are provided within the system to mitigate the effects of such a failure and alert the operator. Therefore, such a failure, even if it occurred, will not increase the consequences of a previously evaluated accident.
To reduce the likelihood of common cause failure of software controlled functions, thorough and careful verification and validation activities are performed both for the requirements and the implementing software design. In addition, the software is designed to limit the loading that external systems or equipment can place on the system, thus significantly reducing the risk that some abnormal dynamic condition extemal to the system can cause system functional performance problems due to processing " overload" (i.e.,
" slowing down" or stopping the processing).
As a conservatism, however, despite these verification and validation activities, common cause failures of software controlled functions due to residual software design faults are assumed to occur. Both the software and hardware are designed to manage the consequences of such failure (and also cover potential common cause hardware failures).
Safety outputs are designed to be fail safe by requiring dynamic update of output modules or data signals, where failure to update the information is detected by simple receiving hardware, which, in tum, forces a trip. This aspect covers all but rather complex failures where the software or hardware executes a portion of the overalllogic but fails to process some portion of new information (inputs " freeze") or some portion of the logic (outputs
" freeze").
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Octob:r 14,1999 Docket Nos. 50-352 50-353 Attachment 1 To help reduce the likelihood of complex failures, a watchdog timer is used which is updated by a very simple software routine that in turn monitors the operational cycle time of all tasks in the system. The software design is such that as long as all tasks are updated at the design rate, it is likely that software controlled functions are executing as intended.
Conversely, if any task fails to update at the design rate, that is a strong indication of at least some unanticipated condition. If such a condition occurs, the watchdog timer will not be updated, the computer will be automatically restarted, and the system will detect an abnormal condition and provide an alarm and trip.
The information available to the operator is at least the same as with the current system and, in many cases, improved. No actions are required by the operator to obtain information normally used and equivalent to that available with the current equipment.
However, the replacement system does provide more directly accessible information regarding the condition of the equipment, including automatic self-test, which can aid the operator in diagnosing unusual situations beyond those defined in the licensing basis.
In summary, the reliability of the new PRNM Gystem and its ability to detect and mitigate abnormal flux transients have either remained the same or improved over the existing Power Range Monitor System. Since these postulated reactivity transients are mitigated by the new system as effectively and reliability as the existing system, the consequences of these transients have not changed. Therefore, the proposed TS changes do not involve a significant increase in the probability or consequences of an accident previously evaluated.
- 2. The proposed TS chances do not create the possibility of a new or different kind of accident from any accident previously evaluated.
LGS Modification P00224 uses digital processing with software (firmware) control for the main signal processing part of the modification. The remainder of the equipment in the modification uses conventional equipment similar to the current system (e.g., penetrations, cables, interface panels). !
l The digital equipment has " control" processing points and software controlled digital j processing where as the current system has analog and discrete component processing. l The result is that the specific failures of hardware and potential software common cause failure are different from the current system. The effects of software common cause failure are mitigated by hardware design and system architecture, but are of a "different type" of failure than those evaluated in the LGS Updated Final Safety Analysis Report (UFSAR).
Therefore, the replacement system may have a malfunction of a different type from those evaluated in the LGS UFSAR and this constitutes an unreviewed safety question.
However, when these PRNM failures are evaluated at the system level, there are no new effects.
LGS Modification P00224 involves equipment that is intended to detect the symptoms of certain transients and accidents and initiate mitigating action. The worst case failure of the equipment involved in the modification is a failure to initiate mitigating action (scram), but no failure can cause an accident. This is unchanged from the current system. Software 14 i
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Octob:r 14,1999 Docket Nos. 50-352 50-353 Attachment 1 common cause failures could result in the system failing to perform its safety function, but this possibility is addressed in Section 1, above. In that case, it might fail to initiate action to mitigate the consequences of an accident, but would not cause one. No new system level failure modes are created with the PRNM System.
Therefore, LGS Modification P00224 does not create the possibility of a new or different kind of accident from any accident previously evaluated.
- 3. The proposed TS chanaes do not involve a sianificant reduction in the marain of safety.
The PRNM System response time and operator information is either maintained or improved over the current Power Range Monitor System.
The PRNM System has improved channel trip accuracy compared to the current system and meets or exceeds system requirements assumed in setpoint analysis. The channel response time exceeds the requirements. The channelindicated accuracy is improved over the current system and meets or exceeds all of the system requirements.
The PRNM System was developed to detect the presence of thermal-hydraulic instabilities and automatically initiate the necessary corrective actions to suppress the oscillations prior to violating the Minimum Critical Power Ratio (MCPR) Safety Limit. The NRC has reviewed and approved the PRNM Licensing Topical Report (LTR) concluding that the PRNM System will provide the intended protection.
Therefore, LGS Modification P00224 does not result in a significant reduction in the margin of safety.
Information Supportina an Environmental Assessment An Environmental Assessment is not required for the changes proposed by this TS Change Request because the requested changes to the Limerick Generating Station (LGS), Units 1 and 2, TS conform to the criteria for " actions eligible for categorical exclusion" as specified in 10 CFR 51.22 (c)(9). The requested changes will have no impact on the environment. The proposed changes do not involve a Significant Hazards Consideration as discussed in the preceding section. The proposed changes do not involve a significant change in the types, or a significant increase in the amounts, of any effluents that may be released offsite. In addition, the proposed changes do not involve a significant increase in individual or cumulative occupational radiation exposure.
Conclusion The Plant Operations Review Committee and the Nuclear Review Board have reviewed these proposed changes to the Limerick Generating Station (LGS), Units 1 and 2, TS and have l concluded that the new digital equipment may have failure modes not considered at the time of I the original system review and is therefore an unreviewed safety question. However, the
! proposed changes will not endanger the health and safety of the public.
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