ML17345B016
| ML17345B016 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 03/15/1983 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML17345B015 | List: |
| References | |
| NUDOCS 8303240316 | |
| Download: ML17345B016 (8) | |
Text
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ENCLOSURE 1
SAFETY EVALUATION REPORT WESTINGHOUSE ANALOG ROD POSITION INDICATION FOR SHUTDOWN NODES Introductf on Task Interface Agreement (TIA) 82-49 states that DSI will evaluate the bases for Westinghouse PMR rod posftfon fndfcatfon system accuracy requirements during plant operation fn Kodes 3. 4, and 5 (shutdown aedes).
In. a memorandum dated September 3, 1982 DRAB provided recomnendatfons regarding rod position fndfcatfon accuracy requirements to DSI.
The subject of the analog rod position indication system fn Mestfnghouse PMR's has Seen under review for the last year and one half.
Me have revfewed ORAB's reconmendatfons and the material submitted by two licensees, Beaver Valley and Sequoyah, including the Beaver Valley Power Station Unit 1 Analog Rod Position. Indication (RPI) System Special Report.
Me have met with Westinghouse on thfs subject several times and are currently revfewing their report on the Analog RPI System.
~kd The RPI system was orfgfnally installed so that there would be an accurate means of telling the locatfon of individual control rods during power operatfon fn order to avoid misalfgned rods.
The,Mestfnghouse safety analysis shows that a control rod mfsalfgnment.of +24 steps fs acceptable.
Since there fs a 12 step uncertainty, thfs leaves a requfre-~
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ment for no more than a +12 step fndfcated,misalignment..
Thus the Technfcal Specification requirement for individual control rods to be+
aligned with their banks within +12 steps.
The RPI system was not originally intended to be used fn the shutdown nodes.
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Calibration of the RPI system has been a, problem both during power operation and in the shutdown modes.
Yarious solutions.to the cali-bration problems for Nodes 1 and 2 (power. operation) have been worked out and presently the licensees have the +12 step accuracy requirement for Nodes 1 and 2.
The RPZ for each i'ndividual rod is calibrated at beginning of cycle at operatin'g temperature.
The calibration of the -RPIs is highly temperature sensitive.
Thus as the reactor cools down in Nodes 3, 4, and 5, the hot calibration becomes inaccurate and may be off as, much as 60 steps (total rod is 228 steps).
Thus the Technical Spec)fication which states that the RPIs and group demand counters must agree within +12 steps cannot be met as the plant cools down unless there were calibrations as' function of temperature.
If the plants wanted to operate in Modes 3,. 4, and 5 only with all the rods fully inserted the Technical Specification could be met because it does not apply to rods fully inserted.
However,; many plants prefer to operate with the shutdown banks "cocked" in order to have reactivity available ff needed.
They cannot meet the +12 step accuracy unless they recalibrate as temperature decreases.
Evaluation To prevent inadvertent criticality from Nodes 3,, 4, and 5, the licensee i's required to maintain the reactor in.a sub-critical.condition with keff c0. 99.
This is accompl ished thru boron concentration and tnsertion of control rods.
Calculation of the necessary boron concentration takes into account the position of the.contrel rods.
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Mhfle ft would be extremely useful to have the RPI system fndfcatfng rod positfons, ft is not possible to use the system accurately fn Modes, 3, 4, and 5.
ORAB recomnended a Technical Specfffcatfon that required the group demand counters and the RPIs to be operating fn Modes 3, 4, and 5.
The licensees indicates that. there was problem wfth the interpretation of the specificatfon and that ft led to unnecessary LERs.
Mestfnghouse has proposed a speciffcatfon whfch requfres only the group demand counters be operable and capable of determfnfng rod position for Nodes 3, 4. and 5.
In thfs way the analog system fs used for the Modes 1 and 2 where it was intended to be used and fs not required for Nodes 3, 4, and 5.
The group demand counters have proven to be extremely reliable over the 15 years they have been used.
They have proved to be. the most accurate means of determining rod posftion and are fn fact used to calfbrate the RPIs.
In additfon, the requirement that k << <0.99 for Nodes 3, 4, and 5 provides margin to inadvertent criticality.
Conclusion Based on our review we ffnd that the safety consideration of maintaining adequate sub-criticality can be accomplished by requiring that the group demand counters be used for rod: position indication.
The requirement to maintain a 12 step accuracy with the RPIs,fs not necessary.
Me conclude that the enclosed Technfcal Specfffcatfon which requires only the group demand counters for the shutdown modes fs the best solution for plants havfng the analog RPI system.
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A ENCLOSURE; 2..'EACTIVITY CONTROL SYSTEMS
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POSiiION INDICATION SYSTEM-SHUTDOMN LIMITING CONDITION FOR OPERATION 3.1.3.3 The group demand position indicator shall be OPERABL'E and capable of deter-mi'ning within + 2 steps the demand position for each shutdown control or part length rod riot fully inserted.
APPLICABILITY:
MODES 3+8, 4~8 and 5*8 ACTION:
Mith less than the above required group demand.position indicators(s)
- OPERABLE, inmediately open the reactor trip system breakers..
SURVEILLANCE REOUIREMENTS 4.1.3.3 Each of'he above required group demand position indicator(s) shall be determined to be OPERABLE by movement of the associated control rod at least, 10 steps in any one direction at least once per 31 days..
Nth the reactor trip system breakers in the closed position.
f See Spe'cial Tes Exception 3.10.5
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