ML20042B664
| ML20042B664 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 03/23/1982 |
| From: | Dale L MISSISSIPPI POWER & LIGHT CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0831, RTR-NUREG-831 AECM-82-88, NUDOCS 8203250502 | |
| Download: ML20042B664 (6) | |
Text
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MISSISSIPPI POWER & LIGHT COMPANY Helping Build Mississippi EdMAMiddB P. O. B O X 164 0. J A C K S O N.
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U. S. Nuclear Regulatory Commission
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Attention:
Mr. Harold R. Denton, Director 2)
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Dear Mr. Denton:
SUBJECT:
Grand Gulf Nuclear Station Units 1 and 2 Docket Nos. 50-416 and 50-417 File 0260/L-350.0 Submittal of Information on Transient Analyses AECM-82/88 The enclosed information is being transmitted by Mississippi Power & Light in response to an informal request for information from your Reactor Systems Branch. The enclosure discusses the effect on the minimum critical power ratio (MCPR) for a reactor feedwater controller failure includ-ing the loss of turbine bypass capability. This transient is not being analyzed as a credible FSAR Chapter 15 event but is presented for informational purposes to demonstrate the lack of dependence on the turbine bypass system during this transient.
This information also addresses concerns regarding the turbine bypass system as discussed in the Grand Gulf Safety Evaluation Report, NUREG-0831, Sections 15.1 and 16.0.
If you have any questions or require further informa-tion please contact this office.
Yours truly,
/
/['/L. F. Dale Manager of Nuclear Services SAB/JGC/JDR:ph Attachment I
cc:
Mr. N. L. Stampley (w/a) oO Mr. R. B. McCchee (w/a) 3 Mr. T. B. Conner (w/a)
Mr. G. B. Taylor (w/a)
/
Mr. Richard C. DeYoung, Director (w/a)
Office of Inspection & Enforcement U. S. Nuclear Regulatory Commission Washington D
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8203250502 82632.
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.siddle South Utilities System E
Attechment to AECM-82/88 4
BRANCH:
Reactor Systems CONCERN:
In the event that the turbine bypasa capability is lost, assurance should be provided that the critical power ratio will not drop below safety limits due to a simultaneous failure of the reactor feedwater controller.
In order to assure an acceptable level of performance for Grand Gulf, the NRC Staff's position is that the turbine bypass system be
' identified in the plant Technical Specifications with regard to availability, setpoints, and surveillance testing. See also SER Sections 15.1 and 16.0.
RESPONSE
The feedwater controller failure with loss of turbine bypass should not be considered as a credible transient event since separate iritiating events are required to simulate this multiple failure. However, to address this concern, an analysis was performed to determine the MCPR for this transient and demonstrate an adequate operating margin for such an event.
The initial sequence of events as shown on Table 1 are the same as was performed for the feedwater controller failure with bypass available. The subsequent failure of turbine bypass due to turbine trip will cause a faster system pressure buildup and quicker actuation of the safety / relief valves. This analysis was performed using the ODYN transient analysis code. The parameters used in this analysis are identical to those used in the ODYN analyses as presented in our submittal on this subject (AECM-81/400, dated October 19, 1981).
The results of this analysis provided a MCPR of 1.08 which is identical to that observed for thia event with bypass available.
Even though the reactor pressure and void reactivity is greater than with bypass available (See Figure 1), the change in CPR is only minimally affected due to a small change in heat flux. These relative increases noted are primarily due to the bypass failure and the resulting pressure buildup occurring after the scram. The control rod insertion speed for a BWR 6 is-fast enough to reduce scram reactivity to avert the increase in void reactivity caused by the increased pressure. The fast scram capability of Grand Gulf reduces the effect of turbine bypass failure on the MCPR's, and therefore, should not require any further consideration.
By virtue of the above discussion and the attached information, there is no need to identify the turbine bypass system in Grand Gulf's Technical Specifications with respect to availability, setpoints, or surveillance testing.
The results of the ODYN analysis for feedwater controller failure with bypass available is also attached (revised Table 15.1-3 and revised Figure 15.1-3) to allow comparison of both events. The revised table and figure will be incorporated in FSAR Amendment 55, April, 1982.
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Table 1 SEQUENCE OF EVENTS FOR THE FEEDWATER' CONTROLLER FAILURE (MAXIMUM DEMAND) WITH BYPASS FAILURE TIME SEC.
EVENT 0
Initiate simulated. failure of.130% upper' limit on.feedwater. flow;at sys'.2 design pressure of-1065 psig.
11.78 L8 vessel' level' set point initiates. reactor scram and trips main turbine and feedwater pumps.
11.79 Recirculation pump trip (RPT) actuated by stop.
r valve position switches, but main turbine bypass.
valves failed to open on turbine trip.
13.03 Safety / relief valves actuated due to high' pressure.
19.29
-Safety / relief valves close.
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TABLE 15.1-3 SEQUENCE OF EVENTS FOR FEEDWATER, CONTROLLER FAILURE WITH BYPASS.(FIGURE 15.1-3)
Time-sec Event 0
Initiate simulated failure of 130% upper limit on feedwater flow at the system design pressure of 1065 psig.
11.78 L8 vessel level set point trips main turbine and feedwater pumps and initiates reactor scram..
11.79 Recirculat. ion pump trip (RPT) actuated by stop valve trip fluid pressure transmitters and trip units.
11.88 Main turbine bypass control valves start to open due to turbine trip.
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13.57 Safety / relief valves open due to high pressure.
18.99 Safety / relief valves close.
30.0(esti Water level dropped to low-low water level set point (Level 2).
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TIME ISECl TIME ISEC1 MISSISSIPPI POWER & LIGHT COMPANY FEEDWATER CONTROLLER PAILURE, GRAND GULF NUCLEAR STATION MAXIMUM DEMAND UNITS 1 & 2 WIT 11 TURBINE BYPASS FIGURE 15.1-3 FINALSAFETY ANALYSIS REPORT Amendment 55, 4/82