ML20117H563
| ML20117H563 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 05/06/1985 |
| From: | Gucwa L GEORGIA POWER CO. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.F.2, TASK-TM GL-84-23, NED-85-333, TAC-45139, NUDOCS 8505140335 | |
| Download: ML20117H563 (6) | |
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Georgia Power Company -
. 333 Picdmont Avqnue Attanta/ Georgia 30308 Tebphcae 404 5266526 Ma$ng Address:
Post Off,ce Box 4545
' Atlanta, Georgia 30302 Georgia Power L T.Gucwa try souttern ekxtrc system Manager Nuclear Engineering and Chef Nuclear Engneer 15578 May 6, 1985
-Director of Nuclear Reactor Regulation Attention: Mr. John F. Stolz, Chief Operating Rea'ctors Branch No.'A Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C.
20555 NRC 00CKETS 50-321, 50-366 OPERATING LICENSES DPR-57, NPF-5 EDWIN I. HATCH NUCLEAR PLANT UNITS 1, 2 REACTOR VESSEL WATER LEVEL INSTRUENTATION IN BWRs (GEERIC LElitH 84-23)
Gentlemen:
By letter dated Novenber 20, 1984, Georgia Fower Company stated that a complete response to Generic Letter 84-23 would be submitted by May 6,1985 In accordance with that commitment, Enclosure 1 is provided.
Please contact this office if you have any cuestions.
Very truly yours,
/ *[ Q-m L. T. Cucwa JH/jh Enclosure xc(w/ enc 1):J. T. Beckham, Jr.
H. C. Nix, Jr.
J. N. Grace (W C-Region II)
Senior Resident Inspector
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- GeorgiaPbwer A a
T ENCLOStRE 1 EDWIN I. HATCH NUCLEAR PLANT UNITS 1, 2 RESPONSE TO GEERIC LETTER 84-23
- REACTOR VESSEL WATER LEVEL INSTRUENTATION IN BWRs May 6, 1985 700176
GeorgiaPower d I.
INTRODUCTION In this report Georgia Power Company (GPC) proposes a plan and schedule for addressing the NRC staff position on BWR reactor vessel water level instrumentation as stated in Generic Letter 84-23.
II. BACKGROUE0_
Item II.F.2 of NUREG 0737 reouired a description of proposed additional instrumentation to detect inadeouate core cooling (ICC).
Revision 2 to Regulatory Guide 1.97 later identified core thermocouples as an acceptable means of satisfying Item II.F.2 in BWRs.
The BWR Owners Group (BWROG) ouestioned the effectiveness and need for core thermocouples.
An evaluation performed for the BWROG by S. Levy, Inc. (SLI) confirmed that the slow response time of core thermocouples would severely limit their usefulness as ICC detection devices.
That evaluation was documented in the report SLI-8121, " Thermal Analyses of In-Core Thermocouples in Boiling Water Reactors".
Following presentation of that report to the NRC staff, it was agreed by the staff and the BWROG that a general study responding to Item II.F.2 should be performed. The study was to address the adecuacy of existing reactor water level instrumentation during "off-normal" conditions as well as the general cuestion of ICC detection.
The staff agreed that ccre thermocouples would not be reouired if an acceptable program were implemented by the BWR Owners.
The study was performed by SLI for the BWROG and was documented in two reports.
The first report, SLI-8211 " Review of BWR Reactor Vessel Water Level Measurement Systems",
identified several areas for potential irrprovement of existing systems.
The second report, SLI-8218 "Inadcouate Core Cooling Detection in Boiling Water Reactors", demonstrated that reactor water level was a conclusive indicator of the adcouacy of core cooling and that, given the implementation of improvements to existing level instrumentation, additional ICC devices would have little or no benefit.
The staff has completed its review of SLI-8211 and SLI-8218.
Generic Letter 84-23 provides the staff position regarding reactor water level measurement system improvements.
The following sections address GPC's plans and schedule for addressing the staff position.
Hay 6, 1985 wn
k Georgialbwer h III. HATCH MODIFICATION PLANS GPC has actively participated in the BWROG effort.
Following completion of SLI-8211 and SLI-8218, a plant-specific evaluation of the Hatch reactor water level measurement systems was initiated.
The evaluation was performed by S. Levy, Inc. and addressed all of the generic concerns raised in the Owners Group study. The results of the Hatch-specific study are summarized as specific responses to the three categories of improvement identified in Generic Letter 84-23:
A.
STAFF POSITION-HIGH ORYWELL TEMPERATURE EFFECTS
" Improvements to plant (s) that will reduce level indication errors caused by high drywell temperature.
These improvements include prevention of reference leg overheating or reduction of the vertical drops within the drywell.
(Vertical drop should be measured from the condensation pot to the drywell exit point. Maximum drop would allow an indicated level at the bottom of the normal operating range when actual level is just above lower tap for worst flashing condition.)
Those plants for which the vertical drop in the drywell has already been minimized will not have to make additional changes for the drywell heating effect."
RESPONSE
Due to significant vertical drops of level instrument sensing lines within primary containment, the Hatch units would be susceptible to level indication errors in the event of a high drywell temperature condition.
These errors would be detected by the Hatch Safety Parameter Display System (SPDS), however. The SPDS uses sanpled data from nine level sensors for water level measurement.
Water level intnrmation available to the operator includes:
1.
A bar graph d! splay and digital reading of current level; 2.
A time history plot of water level; and 3.
Separate bar graph displays for the nine sensors.
May 6, 1985 i rann.
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m GeorgiaPower d The water level signals from the nine sensors are corrected for instrument line fluid density changes and vessel fluid density changes.
The instrument line fluid densities are estimated from sensed drywell temperatures and the vessel fluid density is estimated from sensed vessel pressure.
A single value for vessel level is calculated using a weighted average of the nine corrected values.
The SPDS provides a warning message to the operator if conditions for instrument line flashing are approached, although flashing errors can not be corrected.
The onset of flashing can be significantly delayed and the operator burden thereby reduced, however, by insulating level sensing lines within the drywell. GPC plans to install insulation on the reference legs serving the wide range
(-150 to
+60")
instruments.
This will provide the operator with additional time to correct the cause of the high drywell temperature.
8.
STAFF POSITION-MECHANICAL EQUIPMENT RELIABILITY
" Review of plant experience relating to mechanical level indication coulpment. Plant experience shows that mechanical level coulpment is more vulnerable to failure or malfunction than analog coulpment.
A number of plants have already connected analog trip units to their level transmitters to improve reliability and accuracy.
Those plants that use mechanical level indication coulpment should replace the mechanical level indication coulpment with analog level transmitters unless operating experience confirms high reliability."
RESPONSE
To improve the reliability and accuracy of certain plant instrumentation, CPC has elected to install Analog Transmitter Trip Systems (ATTS) in both Hatch units. ATTS installation has included Icvel instrument replacement.
C.
STAFF POSITION-PROTECTIVE SYSTEM LOGIC
" Changes to the protection system logic that may be needed for those plants in which operator action may be reouired to mitigate the conscouences of a break in a reference leg and a single failure in a protection system channel associated with an intact reference leg.
Changes will generally result in additional transmitters to satisfy the single failure criterion.
This improvcinent, under evaluation by NRC, may be needed in plants where an analysis has demonstrated a vulnerability."
RESPONSE
GPC will respond to this issue following completion of the NRC staff evaluation.
Kay 6, 1985..
h0f fl
s 1-GeorgiaPower IV. IMPLEENTATION SCTOULE 3
A.
HATCH UNIT'1 i
The SPDS will be fully implemented by June 1986.
Reference leg' insulation will be installed during the refueling outage currently scheduled for spring 1987.
The rartions of ATTS applicable to this issue have been installed.
B.
HATCH UNIT 2 The SPOS will be fully implemented by June 1986.
Reference leg insulation will be installed during the refueling outage currently scheduled for fall 1986.
The portions of ATTS applicable to this issue have been installed.
V.
CONCLUDING
SUMMARY
In Generic Letter 84-23 it is stated that:
" Implementation of the first two categories of improvements (high drywell tenperat'Jte effects and mechanical coulpment reliability) will give increased assurance that the level instrumentation will provice the inadeouate core cooling instrumentation reouired by NUREG-0737 ItensII.F.2 and thereby satisfy tt.ls reouirement."
GPC believes that the aforementioned modifications, when implemented, will give Accreased assurance that the level instrumentation of the Hatch units provides adeouate ICC instrumentation, and will therefore complete Item II.F.2 for Plant Hatch.
s MAY 0 61985 1
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