ML20212G424
| ML20212G424 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 01/09/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20212G418 | List: |
| References | |
| NUDOCS 8701200457 | |
| Download: ML20212G424 (8) | |
Text
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UNITED STATES y
g NUCLEAR REGULATORY COMMISSION 5
l W ASHINGTON, D. C. 20555
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT N0. 11 TO FACILITY OPERATING LICENSE NO. NPF-38 LOUISIANA POWER AND LIGHT COMPANY WATERFORD STEAM ELECTRIC STATION, UNIT 3 DOCKET NO. 50-382
1.0 INTRODUCTION
By applications dated August 29, and September 25, 1986, as supplemented by letters dated October 1, and October 23, 1986, Louisiana Power and Light Corrpany (the licensee) requested changes to the Technical Specifications (Appendix A to Facility Operating License No. NPF-38) for the Waterford Steam Electric Station, Unit 3.
The proposed changes would:
(1) add a power reduction curve to be used following a full or part-length control element assembly (CEA) misalignment; (2) revise the shutdown marain whenever all full-
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length CEAs are fully inserted into the core; (3) revise the special test exceptions on shutdown margin; and (4) allow credit for the log power trip during physics testing.
2.0 DISCUSSION l
The proposed changes to the technical specifications requested by the licensee are in four areas as described below.
2.1 Control Element Assembly Misalianment (NPF-38-34)
The proposed change would revise ACTION statements "c" and "d" to Technical Specification 3.1.3.1, " Moveable Control Assemblies, CEA Position". The reason for this change is to impose new requirements on power reduction during the period from 15 minutes to one hour following a full or part-length CEA misalignment. This change would reduce the inward CEA deviation penalty factors currently provided by the CEA Calculators (CEACs) to the CPCs to a value of 1.0.
The reduction of these penalty factors will reduce the sensitivity of the CPCs to CEA drops and to electironic noise which can be interpreted in the logic as a rajor CEA deviation and will, therefore, eliminate some unnecessary reactor trips.
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'- 2.2 Shutdown Marain with CEAs Inserted (NPF-38-40)
The proposed change (NPF-38-40) would revise Technical Specificatior.s 3.1.1.1 and 3.1.1.2, "Boration Control, Shutdown Margin;" 3.1.2.4, "Boration Systems, Charging Pumps-Operating;" 3.1.2.6, "Boration Systems, Boric Acid Makeup Pumps-Operating;" 3.10.1, "Special Test Exceptions, Shutdown Margin;" and the associated Bases. These changes revise the requirements for shutdown margin and, consequently, for boration of the reactor coolant system (RCS) whenever all full-length control element assemblies (CEAs) are fully inserted into the core during Cycle 2.
2.3 Test Exception - CEA Insertability (NPF-38-41)
The proposed change would mcdify Technical Specification 3/4.10.1, "Special Test Exceptions, Shutdown Margin". This specification currently allows shutdown margin to be reduced to less than the normal operating shutdown margin requirements during low power physics testing provided that certain conditions are met. One of these conditions (Surveillance Requirement 4.10.1.2) requires that all control element assemblies (CEAs) not fully inserted into the core be shown to be capable of full insertion when tripped from at least the 50% withdrawn position within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior to reducing shutdown margin to less than the normal operating requirements. The requested revision would allow this surveillance to be perfomed within seven days prior to margin reduction instead of within the prior 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
2.4 Test Exception - Reactor Coolant Loops (NPF-38-42)
The proposed change would revise Technical Specification 3/4.10.3, "Special Test Exceptions, Reactor Coolant Loops," by allowing credit for the log power trip for protection against power transients initiated at low power levels instead of relying solely on reduced reactor trip setpoints in the linear power channels.
3.0 EVALUATION The proposed changes to the Technical Specificatiens requested by the licensee and described in four areas above, are evaluated below.
3.1 Control Element Assembly Misalionment (NPF-38-34)
Currently, if a single full-length or part-length CEA is inserted beyond the other CEAs in its group by a specified distance (inward CEA deviation event), the core protection calculator (CPC) algorithm applies two penalty factors to the departure from nucleate boiling ratio (DNBR) and linear heat rate (LHR) calculations. The first is a static penalty factor which is applied upon detection of the CEA deviation. The second is a xenon redistribution penalty which is applied linearly as a function of time over a one hour period following the detection of the deviation. The maximum inward CEA deviation event is the drop of a full-length CEA from its normal position.
For this limiting event, the imposition of the DNBR and LHR penalty factors previously resulted in a reactor trip to assure that the DNBR and fuel centerline melt specified acceptable fuel design limits (SAFDLs) would not be '
violated.
Asaconsequenceofthecoreprotectioncalculator(CPC) improvement program, which has been reviewed and approved by the staff, an inward CEA deviaticn event would not be accompanied by the application of the CEA deviation penalty factors.
Instead, the expected margin degradation for the event is accounted for by reservino sufficient margin in the DNBRlimitingconditionforoperation(LCO)basedonthemostlimiting inward CEA deviation event, the CEA drop.
For Cycle 2, the limiting CEA drop was found to cause a radial peaking increase of 9.0%.
Xenon redistribution during the first 15 minutes following the drop caused an additional increase of 4.3%, resulting in a total peaking distortion of 1.137 (1.09 x 1.043). The LCOs will be set to maintain at least this much margin to the SAFDLs for Cycle 2.
The licensee has also determined that the additional distortion due to xenon redistribution during the period from 15 minutes to one hour after the drop is less than 1.2.
The power penalty due to this peaking is less than the power penalty imposea by the proposed Technical Specification Figure 3.1-1A.
If the combination of the static and xenon redistribution penalties exceeds the reserved required overpower margin, a power reduction in accordance with this figure is required.
The staff has reviewed the reanlaysis of the single full-length CEA drop event presented by the licensee for Cycle 2 and finds the results are acceptable since they meet the required NRC criteria regarding SAFDLs.
Since this event requires the maximum initial margin to be maintained by the LCOs, the staff finds the proposed changes acceptable.
For other than single CEA deviation events, such as CEA subgroup drops, the CEA position-i related penalty factors for downward deviations are still used by the CPCs as in the Reference Cycle (Cycle 1) to provide a trip when necessary.
3.2 Shutdown Marcin with CEAs Inserted (NPF-38-40)
The mest significant change due to the proposed amendment is the reduction in required shutdown margin during Modes 2 through 5 when all full-length CEAs are fully inserted into the core. The shutdown margin requirements vary throughout the fuel cycle as a function of fuel depletion and RCS temperature. The most restrictive condition occurs at end of cycle and is associated with a postulated steam line break accident at no-load operating temperature and the resulting uncontrolled RCS cooldown. As the RCS temperature decreases, the potential RCS cooldown and the resulting reactivity transient are less severe ano, therefore, the required shutdown margin also decreases. The licensee has proposed a new Figure 3.1-0 which shows the required shutdown margin as a function of cold leg temperature when all CEAs are fully inserted.
These shutdown margin requirements vary from 1% at low temperatures to 4.15% for ccid leg temperatures above 500'F. The shutdown margin requirements when any CEA is not fully inserted remain the same as current values in Technical Specification 3.1.1.1.
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4 Two diverse, independent CEA position indication systems are available at Waterford 3 to provide CEA position information to the operator; the pulse counting CEA position indication system and the reed switch CEA position indication system.
In addition, a light display is provided on the reactor turbine generator board in the main control room to indicate the fully inserted position of each CEA. Therefore, the staff finds that the operator has sufficient indication when all CEAs are fully inserted.
By definition, the shutdown margin assumes that the CEA of highest worth is always fully withdrawn (stuck out). When the actual shutdown margin is calculated at Waterford 3, the highest worth CEA is assumed to be stuck out to be consistent with the definition. However, in the safety analyses supporting this Technical Specification change request, the licensee has taken credit for the situations when all CEAs are fully inserted.
If, for example, the. stuck CEA were worth 1%, then a shutdown margin of 1% would mean that the core is actually subtritical by 2% (i.e., 1% shutdown margin plus the worth of the stuck CEA) since all CEAs have been verified to be fully inserted. The safety analyses used by the licensee to suppcrt this change were initiated with the core subcritical by 2% since all CEAs were assumed to be inserted.
The anticipated operational occurrences (A00s) and accidents that have the potential for being impacted by the proposed change are the steam line break, CEA withdrawal, CEA ejection, inadvertent boron dilution, and the startup of an inactive reactor coolant pump. The licensee has reevaluated these events for Cycle 2.
The staff agrees that these are the appropriate events to be evaluated and finds the results of these evaluations meet the appropriate NRC acceptance criteria as stated in the Standard Review Plan.
The proposed changes to Specification 3.1.1.1 and 3.1.1.2, therefore, are acceptable.
The proposed changes to Specifications 3.1.2.4, 3.1.2.6, and 3.10.1 are required in order to refer to the appropriate shutdown margin specification depending on whether or not all CEAs are fully inserted. These changes are editorial in r,ature and are required for consistency. They are', therefore, acceptable.
3.3 Test Exception - CEA Insertability (NPF-38-41)
This proposed change would enable low power physics tests to be accomplished i
without an additional trip to verify CEA insertability. The startup test program includes a CEA trip test before criticality in order to measure CEA drop times and demonstrated CEA insertability. Criticality is then achieved and low power physics tests are perfomed. Measurements of CEA worths are made later and may involve the reduction of shutdown margin l
as pemitted by Technical Specification 3.10.1.
Since these CEA worth l
measurements are performed several days after the CEA insertability tests are performed, the reactor would have to be tripped again to demonstrate CEA insertion capability and satisfy the current 24-hour
- criterior). The requested revision would, therefore, eliminate the necessity for an additional trip during physics tests by requiring CEA insertability to be verified within seven days prior to reducing shutdown margin instead of within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
The primary concern in extending the surveillance time period of verifying CEA insertability is whether or not there could be an increase in the probability of a stuck CEA over a seven-day period of time as compared to the present 24-hour time period. Consideration of the configuration of the components that are used in CEA insertion indicate that there is nothing which could cause a significant increase in the probability of a CEA to become untrippable since there is no significant change in the geometry of these components over the seven day period of low power physics testing.
The components considered include the fuel assembly (including foreign material buildup in the gap between the CEA and the guide tube), the CEA, the CEA extension shaft, the control element drive mechanism, and the upper guide structure. Surveillance requirements necessitate the CEA drop time of full-length CEAs be demonstrated through measurement prior to reactor criticality for specifically affected individual CEAs following any maintenance on or modification to the CEA drive system which could affect the drop time of those specific CEAs. Therefore, if any modifications were made which could affect CEA drop times and hence, trippability, following the previous verification of CEA tripability, a reverification is required. Also, since the CEAs will insert by gravity upon loss of power, the probability of a stuck CEA is not increased due to an electrical malfunction, if one were to occur during physics testing.
The staff concludes that the proposed change continues to provide assurance that all CEAs are trippable during low power physics testing and does not affect the amount by which shutdown margin may be reduced during this period.
It is similar to a change previously approved for Arkansas Nuclear One, Unit 2.
The proposed change is, therefore, acceptable.
The staff has reviewed the proposed surveillance requirement change to the k'aterford 3 Technical Specificetion associated with the shutdown margin special test exception. This change would allow a time duration of seven days following verification of CEA trippability during which time shutdown margin may be reduced to accommodate physics testing. The staff concludes that the proposed change is acceptable since it continues to provide assurance that all CEAs are trippable during low power physics testing and does not affect the amount by which shutdown margin may be reduced during the testing period.
3.4 Test Exception - Reactor Coolant Loops (NPF-38-42)
In order to perform certain physics tests at low thermal power levels, it is necessary to bypass the core protection calculators (CPCs). The I
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measurement of control element assembly (CEA) worths, for example, requires inserting and withdrawing CEAs outside of the nomally prescribed sequence.
If the CPCs were not bypassed, they would genenate out-of-sequence penalty factors that would result in a reactor trip. Currently Technical Specification 3.10.3.b requires that the linear power level-high trip setpoint be decreased to less than or equal to 20% of rated themal power when the CPCs am bypassed during physics tests. The addition of Technical Specification 3.10.3.c is being proposed to allow credit for either the reduced reactor trip setpoints in the linear power channels (Technical Specification 3.10.3.b) or the log power trip (proposed Technical Specification 3.10.3.c) for protection against power transients during CPC bypass periods. Both the high log power trip and the high linear power level trip use the neutron flux power from the excore neutron flux ronitoring system as input. The high log power trip is provided to trip the reactor when the indicated neutron flux power reaches 0.257% of full power and has been found acceptable by the staff in assuring the integrity of the fuel cladding and the reactor coolant system bounnory in the event of an unplanned power transient from subcritical or low power conditions.
Therefore, the high log trip is an acceptable alternative to the hiah linear power level trip when the CPCs are bypassed during physics tests.
The CPC operating bypass permissive bistable must be increased to a value above the power level where physics testing is performed in order to bypass all four CPC channels without generatina a reactor trip. Since this same bistable also serves as the threshhold value for bypassing the log power trip (i.e., it is the minimum thermal power below which the log pcwer trip cannot be bypassed), setting it above the log power trip setpoint of 0.257% power removes the possibility of bypassing the log power trip. Thus, by bypassing all four CPCs as described in the proposed change, a type of electrical interlock is created that pmcludes the log power trip from being bypassed.
Therefore, the log power trip will provide the necessary protection in the event of an unplanned power excursion during physics testing precluding the need to change the high linear power setpoint. Also increasing the CPC operating bypass permissive bistable setpoint above the log power trip setpoint does not preclude the CFCs from perfoming a protective function.
That is, if the thermal power were to exceed the bistable setpoint (without causing a log power trip), the CPCs would automatically come out of bypass and, as necessary, trip the reactor. The staff, therefore, finds the proposed change acceptable.
4.0 CONTACT WITH STATE OFFICIAL The NRC staff has advised the Administrator, Nuclear Energy Division, Department cf Environmental Quality, State of Louisiana of the proposed detemination of no significant hazards consideration. No comments were received.
5.0 ENVIRONMENTAL CONSIDERATION
l This amendment involves changes in the installation or use of facility components l
located within the restricted area. The staff has determined that the amendment l
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- involves no significant increase in the amounts of ery effluents that may be released offsite and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued proposed findings that the amendment involves no significant hazards consideration, and there has been no public comment on such findings. Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuantto10CFR51.22(b),noenvironmental impact statement or environmental assessment need be prepared in connection with the issuance of this amendment.
6.0 CONCLUSION
Based upon our evaluation of the proposed changes to the Waterford 3 Technical Specifications, we have concluded that:
there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and such activities will be conducted in compliance with the Commission's regulations and the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
We, therefore, conclude that the proposed changes are acceptable, and are hereby incorporated into the Waterford 3 Technical Specifications.
Dated: January 9, 1987 Principal Contributor:
L. Kopp I
JAN 9 267
'SSUANCE OF AMEhDMENT NO. 11 TO FACILITY OPERATING LICENSE NP. NPF-38 FOR WATERFORD 3 DISTRIBUTION _.,,
f octet F11e 50-3823 D
"NRC PCR Local PDR PBD7 Reading FMiraalia JLee(5)
JWilson Attorney, OGC - Bethesda LHannon EJordan BGrimes JPartlow TBarnhart(4)
WJones WRecan ACR5 (10)
OPA RDiggs, LFMB DCrutchfield CThomas LKopp NLauben WRegan I
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