ML20056A075
| ML20056A075 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 07/30/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20056A072 | List: |
| References | |
| NUDOCS 9008030181 | |
| Download: ML20056A075 (6) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION i
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%.....jl E-WAssiNotoN. o. c. rosss SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
, SUPPORTING AMENOMENT NOS. 41 AND 7 TO FAClllTY OPERATING LICENSE NOS. NPF-39 AND NPF-85 PHILADELPH1A ELECTRIC COMPANY LIMERICK GENERATING STATION UNITS 1 AND 2 DOCKET N05. 50-352 AND 50-353
1.0 INTRODUCTION
By letter dated June 14, 1990, Philadelphia Electric Company (the licensee) requested an amendment to Facility Operating License Nos. NPF-39 and NPF-85 for the Limerick Generating Station, Units 1 and 2.
These proposed amendments would revise the Technical Specifications (T$s) to remove the operability requirements for the Average Power Range Monitors (APRMs) in Operational Condition 5 (OPCON 5), except while performing a shutdown margin demonstration in accordance with TS Section 3.10.3.
By definition, Operational Condition 5 is the Refueling Conditien, with the reactor mode switch in the shutdown or refuel position end with the reactor coolant temperature less than 140*F.
The requirement for the APRMs to be operable during a shutdown margin demonstration when the mode switch is in Startup as allowed by TS Section 3.10.3 will remain unchanged.
TS Section 3.10.3 is a Special Test Exception which allows operators to change the reactor mode switch from Refuel to Startup to perform a shutdown margin demonstration. The licensee is proposing to add the following qualification to the OPCON 5 APRM TS operability requirements, " Required to be OPERABLE only prior to and during shutdown margin demonstrations as performed per Specification 3.10.3."
This note is proposed to be added to TS Tables 3.3.1-1,
" Reactor Protection System Instrumentation," and 4.3.1-1, " Reactor Protection System Instrumentation Surveillance Requirements," and TS Tables 3.3.6-1, " Control Rod Block Instrumentation," and 4.3.6-1 " Control Rod Block Instrumentation Surveillance Requirements."
2.0 EVALUATION The Feutron Monitoring System (NMS) is composed of the following subsystems: SourceRangeMonitors($RMs)
Intermediate Range Monitors (IRMs)},localPowerRangeMonitors(LPPMs},AveragePowerRangeMonit (APRMs Rod Block Monitor, and Traversing Incore Probe. The purpose of the SRM, IRM, and APRM subsystems is to monitor local and core average neutron flux levels and provide trip signals to the Reactor Protection
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System (RPS)fu tontrol rod block portion of the Reactor Mar.ual Control System (RMCSI o ' squired.
The NHS provides local and core average power information te A reactor operator. The IRM and APFM are safety-related subsystems and provide safety functions, j
The SRM subsystem is corposed of four detectors that are inserted into the core during shutdown conditions. Although the subsystem is not i
safety-related, it is important to plant safety. The SRMs are ree.uired by the TS to be operational in OPCON 5.
During refuelirg cperations, the plant operator
- use the SRMs to ensure that neutron flux remains within I
an acceptable range.
Also, plant operators can monitor the SRMs for increates in neutron flux which may indicate that the reactor is j
approaching criticality.
The IRM subsystem is composed of eight incore detectors that are insert d into the core. The IRM is a five-decade instrument with ten ranges tha.
i are ranged up_during normal power increases. The IRMs are designed to j
monitor neutron flux levels at a local core location and provide protection against local criticality events caused by control rod withdrawal errors. The IRMs monitor neutron flux levels from the upper 1
portionoftheSRMrangetothelowerportionoftheAPRMrgnge, in terms of rated reactor power, the IRMs range from about 10' f of full reactor power to greater than 15% of full reactor power. The IRMs provide control rod block and scram functions at 108 and 120, respectively, of a 125 division scale.
The APRMs do not have incore detectors of their own but receive input i
from the t.PRM detectors A ich are located at various levels throug1out the core. The APRMs monitor core power from about 1% of full reactor power to 125% of full reactor power. The APRMs represent a core average power level while the IRMs and SRMs indicate a local power level.
In OPCON 5, the APRMs operate in the setdown mode to provide a control rod block and scram function at 121 and 15% core average power, respectively.
The safety design bases of the IRM subsystem is to generate trip signals to prevent fuel damage resulting from anticipated or abnormal operatienal transients that'could possibly occur while operating in the intermediate p yJr range. The safety design bases of the APRM subsystem is to wnerate trip signals in response to average neutron flux increases in time to prevent fuel e mage while the plant is in the operating power range. The independence and redundancy incorporated in the design of the IRM and APRM subsystems are censistent with the safety design bases of the NMS and RPS.
There are various levels of control to prevent inadvertent reactor criticality and fuel damage during refueling operations.
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1)
Licensed plant operators are trained to operate equipment and follow j
approved procedures.
l P) plant approved refuelir.g and maintenance procedures specify core alteration steps.
3)
SRMs indicate the potential for reactor criticality and generate a control rod block signal on high neutron flux levels. When shutdown margin has not been demonstrated. TS Section 3.9.2 requires the shorting links be removed so that the SRMs will operate in the 3
noncoincident scram mode to cause a reactor scram as necessary.
4)
Refueling interlocks prevent the removal of more than one control rod and prevent the insertion of fuel bundles into the core unless all control rods are fully inserted.
'5)
The IRMs and APRMs provide an indication of local power and average power, respectively.
IRPs and APEMs will provide red blocks and scram signals on high neutron flux levels.
The APRMs are not necessary for safe operation of the plant during OPCOM 5 because the IRMs will gererate an RF5 scram or control rod block if neutron flux increeses to the applicable setpoint. The IRMs are required by TS to be operational in OPCON 5.
The IRMs are a safety-related subsystem of the NMS and are designed to indicate and respond to neutron flux increases at local core locations. The APRMs are designed to monitor and respond (scram and/or control rod block) to a core average neutron flux level.
The most likely reactivity insertion transient expected during refueling would be a core alteration type event, e.g.,
control rod withdrawal or fuel assembly insertion into the core. A core alteration event would result in a local core criticality transient readily detected by the-IRMs and/or SRMs.
The IRM subsystem is designed and calibrated to respond to a neutron flux level that is significantly less than the flux level monitored by the APRMs.
For exam sensitive range,ple, during refueling, when the IRMs are on their most the IRMs will generate a scram signal at less than 0.01%
core average power while the APRMs will generate a scram signal at 15%
core average power. The IRM subs to the Refueling Interlocks (RIs)ystem acts as a backup protet. tion system during refueling.
Ris are required to be operational during refueling operations in OPCON 5.
They are not safety-related but are designed such that a sir 3 e 1
component failure does not cause an interlock failure.
The purpose of the RIs is to restrict the movement of the control rods and the operation of the refueling equipment to reirforce operational procedures that prevent the reactor from becoming critical during refueling operations.
Ris require that all control rods be fully inserted into the core prior I
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4 to allowing reactor operators to select and withdraw a single control rod. Other His will prevent the withdrawal of a contrn1 rod if the fuel leaded refueling platform is over the core. Also, the Ris require an "all-rods in" signal before allowing a fuel loaded refueling platform to go over the core.
T$ and plant operating procedures allow only one control rod to be withdrawn or removed at a time while the plant is in OPCON 5 and the mode switch is in " Refuel." The core loading pattern is designed to 4
ensure that the core is subcritical by a specified margin with the most reactive centml rod at the full out position.
Withdrawal of one control rod would not cause criticality and the event would not register on the APRMs.
The design of the control rod drive system reduces the probability of a control rod error during refueling.
For example, the latching action of the collet finger assembly serves to block the index tube in place. The velocity limiter physically prevents the control blade from being removed from the core with fuel in place.
The licensee concluded that the APRMs are not necessary for safe operation of the plant while operating in OPCOP 5 with the mode switch in
" Refuel" for the following reasons.
The IRMs are a safety-related subsystem of the NMS and are required by TS to be operable in OPCON 5.
The IRMs will generate an RPS Scram or control rod block if neutron flux increesed to the applicable setpoint.
The IRMs and SRMs are designed and calibrated to be more sensitive to neutron flux than the APRMs.
The IRMs are designed to monitor local core events while the APRMs provide a measure of core average power condition. The IRMs can monitor and react to the most events expected during refueling, i.e., probable reactivity control rod withdrawal or fuel insertion.
The IRMs would detect and respond (control rod block or reactor scram) to an inadvertent criticality event before the APRMs would provide a trip function.
The withdrawal of only one control rod in OPCON 5 is permitted by the "one-rod-out" interlock while in " Refuel." The core is designed to be suberitical with one rod out.
The withdrawal of a second control rod or inadvertent addition of a fuel bundle in OPCON 5 is precluded by refueling interlocks, refueling procedures, and administrative controls.
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I The APRMs will still be required to be operationel during a shutdown margin demonstration performed in OPCON 5 (a special test exception in the TS).
The SRMs are required to be operational in OPCON 5.
The transient analysis discussed in the FSAR does not require the APRMs to be operatioral in OPCON 5 to mitigate an undesirable operational or transient condition.
The licensee also perforried a review of Sections 7.0 and 15.0 of the FSAR, the results of which were discussed in the application.
The intent of the review was to identify conditions when the APRMs and IRMs were required to be operable to mitigate unacceptable consequences of inadvertent operatienal or transient conditions.
The licensee reviewed various postulated scenarios. The results of the review concluded that should assumed operator errors occur, followed by postulated equipment malfunctions, there were adequate systems end interlocks without the APPMs to preclude potential inadvertent criticality or violation of a safety limit.
We have reviewed the licensee's analyses end agree with their evaluations. We conclude that monitoring of neutron flux levels, administrative controls, plant procedures, refueling interlocks, and SRM and IRM protective features provide and maintain the defense-in-depth design and operation which precludes the need for the APRMs to be operable in OPCON 5 wit', the mode switch in " Refuel." The proposed, charges to the TSs are acceptable.
3.0 ENVIRONM5NTAt. CONSIDERATION P
These araendments involve a change to a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes to the surveillance requirements.
The staff has determined that these amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite and that there is no signifi-cant increase in individual or cumulative occupational radiation exposure.
The Commission has presiously issued a proposed finding that these amendments involve no significant hazards consideration and there has been no public comment on such finding. Accordingly, these amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement nor environmental assessment need be prepared in connection with the issuance of these amendments.
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4.0 CONCLUSION
The Com'ssion made a proposed determination that these an.endments involve no significant hazards consideration which was published in the Federal-Register (55 FR 26291) on June 27, 1990 and consulted with the Commonwealth of pennsylvanie.
No public comments were received and the Comonwealth of pennsylvanie did not have any coments.
The staff has concluded, besed on the considerations discussed above, l
that:
(1) there is reesonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner and
[2) such activities will be conducted in compliance with the ComIssion's regulations and the issuance of these amendments will not be inimical to the common defense and the security nor to the health and safety of the public.
Dated: July 30. 1990 Principal Contributor,:
R. Clark i