ML19247A462
| ML19247A462 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 04/16/1979 |
| From: | Fieno D Office of Nuclear Reactor Regulation |
| To: | Kniel K Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19247A452 | List: |
| References | |
| NUDOCS 7907310587 | |
| Download: ML19247A462 (4) | |
Text
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- '.h APR 16 7373 MEMORANDUM FOR:
K. Kniel, Chief, Core Performance Branch, DSS FROM:
D. B. Fieno, Leader, Reactor Physics Section, CPB, DSS
SUBJECT:
MEETING UITH WESTII;GHOUSE 01 THE PART 21 NOTIFICATI0ti CONCER: LING THE SII;GLE ROD DROP ANALYSIS A meeting was held in Bethesda on April 12, 1979 between the NRC and Westinghouse (W).
The purpose of the meeting was to discuss a Part 21 notification by W concerning the analysis of the single rod drop event.
The single rod drop is a DNB-limited transient considered to be a Condition II event, that is, a moderate frequency transient.
The calculated consequences for this event are dependent upon whether the reactor is being operated in an '.utomatic or manual rode.
The meeting was concerned primar-ily with the analysis of the single rod drop event with the reactor in the automatic mode.
The analysis in the SARs for the single rod drop event with the reactor in a manual mode remains valid.
This analysis indicates ti.at the DNB limit is not exceeded.
If a single rod drop event occurs when the reactor is in the automatic mode, the reactor control systen responds to both the reactor power drop (mismatch between turbine power and reactor power) and the decrease in the core average temperature and attempts to restore both quantities to their original values.
This restoration of reactor power by the reactor control system may result in some pcuer overshoot depending upon the excore power signal that is used.
For the SARs this analysis has been performed using a point kinetics.lodel to track the core power time-dependent behavior.
In 2-and 4-loon '{ plants the power signal to the reactor control system is auctioneered fro ~ an ong the four excore detectors to obtain a high value.
This results in a pe..er overshoot of the magnitude predicted in the SAR.
In a 3-loco " pl. nt tv situation is screuhat dif ferent in that the reactor control systa. cbtain: its pcwer signal from a dedicated excore detector.
Recent spatial analyses by. indicate that for a dropped red in the core quadrant adjacent to the dedicated excore detector, the power overshoot is greator N n the value coi'ulated by the cetheds used in the SAR.
This could ' hen lead to exceeding the L'B limit.
For the SAR analysis, n'o credit e
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. APR 16 E73 fo the negative flux rate trip for the plants which have this t-atJr", credit is taken for the turbine runback and rod stop for thu a
,ionts shich have this feature except. for the Indian Point-3 4-icop plant.
These recent 'd calculations which c'odel spatial effects have considered, one other things, different fuel cycles and times in fuel cycles.
Based on these calculations, H has proposed changes to the high negative flux rate trip setpoints to assure that all dropped rod events result in a reactor trip.
The negative flux rate trip setpoint would be decreased from 5 percent to 3 percent and the rate-lag time constant would be decreased from 2 seconds to 1 second.
In summary, the following points are noted:
(1)
It was stated by the Westinghouse representatives that present experience shows that a dropped rod generally results in a reactor trip for a W plant if it has the present negative flux trip circuit and setpoint.
(2)
The SAR analysis for 2-and 4-loop plants remains valid; however, the Technical Specification chances recenr. ended by the Westinghouse representatives for plants whicn have negative flux rate trips should be made to provide added conservatism pending a mora thorough analysis and review.
(3)
For 3-loop E plants, which have a negative flux rate trip, a change to the tvip setpoint should be made to provide additional assurance that a trip will result as a consequence of a rod drop.
This change is in a conservative direction from a safety standpoint.
Also, W analysis shows that the change recccrended will not trip the plant in a spurious way as a result of normal operational maneuvers and, therefore, should not affect the reliability of the plant staying on line.
(4)
For W plants without a negative flux rate trip, the turbine runback and rod stop feature of the control system, which were approved at the time of review, is relied on to avoid DNB in the dropped rod transient for all plants except Indian Pcint-3.
(5)
W is cor.nitted to provide the NRC with a topical report on this natter in about 6 ronths.
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- APR 16 7979 r3eting attendees is provided.
Slides presented at the meetinP 1, ', o
- leble in the Core Performance Branch office.
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Daniel Fieno, Leader Reactor Physics Sect.
Core Performance Branch Division of Systems Safety
Enclosure:
Attendance List cc:
- 9. Mactson/F Schroeder R. Fraley, ACRS (16)
DOR, DSS, DP:1, & DSE ads SD & RES ads IE (3)
P. Check S. Weiss L. Kopp W. Brooks M. Dunenfeld H. Richings R. Schemel J. Rosenthal P. Kapo S. Diab D. Fieno t;RC PDR Central File TiRR Rdg. File CPB Rdg. File S
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ENCLDSURE Meeting Attendees April I?, 1979 NRC Westinghouse Daniel Fieno DSS /CPB Dennis Richardson Karl Kniel Mike Hitchler Larry Kopp Rclando Perez W. L Brooks M. Dunenfeld H. Richings R. Scher:e1 J. Rosenthal DOR /RSB P. Kapo*
S. Diab
art-time attendance 488 284
.