ML17341B597
| ML17341B597 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 01/06/1983 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17341B593 | List: |
| References | |
| NUDOCS 8301140493 | |
| Download: ML17341B597 (4) | |
Text
t SAFETY EVALUATION NODIFICATlONS TO TURBINE RUNBACK SYSTEM ENCLOSURE INTRODUCTION By letter dated August 10, 1982 and clarification dated September 7,
1982 the Florida Power and Light Company proposed to modify the Turbine Runback System for Turkey Point Units 3 and 4.
The modification would delete the flux rate input to the system in order to reduce the number of spurious runbacks.
The Reactor Physics Section of the Core Performance
.Branch has reviewed the proposal.
Our evaluation follows.
In the rod bank or single rod drop event a turbine runback to 70 percent of full power occurs when either a rod-on-bottom signal or a negative flux rate signal from one of the excore detector channels is received.
A failure in the detector channel then results in an unnecessary turbine runback.
-If the flux rate input is removed from the turbine runback circuit the only protection against rod drop events will be the rod bottom signal.
If one assumes a single failure to occur in the protection system (i.e., the failure of the rod bottom signal) then a runback will not occur when a single rod drops.
Protection for a rod bank drop will still be provided since in th',s case there are multiple rod bottom signals.
EVALUATION The single rod drop event has been reanalyzed for the Turkey Point reactor assuming that no turbine runback occurs.
The power mismatach input to the automatic rod control circu',try has been disconnected and the reactors are operated in the manual mode.
Thus no overshoot occurs-.when the reactor returns to power after the drop.
The return to power. occurs as a result of the reduction in the average moderator temperature.
The temperature reduction, in turn, causes a reduction
',n reactor pressure.
The:core stabilizes at essent',ally full power with the dropped rod fully inserted.
This case has.
been analyzed for normal temperature and pressure in the FSAR as the limiting rod misalignment case and shown to result in no violation of fuel thermal limits.
The effect of the reduction in temperature and pressure in the
~ dropped rod case has been analyzed by standard Westinghouse analysis methods..
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The increase in DNBR, due to the temperature reduction is greater than the decrease due to the pressure change.
The licensee concludes that the single rod drop event is bounded by the limiting rod misalignment event and thus has. acceptable consequences.
CONCLUSION I
Based on our review we concur with the licensee's conclusions.
This concur rence is based on 'the fact that the transient analysis is performed by the same calculational methods that were used in the FSAR analysis and that the consequences are acceptable.
We conclude that the proposed revision to the turbine runback circuitry is acceptable provided that the reactor remains in manual control'ode.
Principal Contributor:
W. Brooks
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