ML20235C413
| ML20235C413 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Zimmer |
| Issue date: | 01/05/1978 |
| From: | Bates A Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| Shared Package | |
| ML20234A777 | List:
|
| References | |
| FOIA-87-40 NUDOCS 8707090412 | |
| Download: ML20235C413 (4) | |
Text
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g UNITED STATES f
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g NUCLEAR REGULATORY COMMISSION E
'f ADVISORY COMMITTEE ON REACTOR SAFEGUARDS j#
WASHINGTON. D. C. 20555 January 5,1978 i
ACRS Members
SUBJECT:
. REVIEW 0F ZIMMER PLANT FOR AN OPERATING LICENSE l
The NRC Staff (DSS) has asked that the ACRS be made aware of a significant change in the recirculation control system on Zimmer from plants previously i
reviewed for OLs. Zimmer is the first of the BWR 5 or 6 series reviewed for an OL and it has a valve control on recirculation flow. Prior BWRs reviewed were designed with pump speed control on the recirculation system.
The new control system has two distinct pump speeds, 25%(15Hz) and 100%
(60Hz). Flow in the recirculation line is controlled by adjustment of a flow control valve. The valve design allows flows between 6% and 100%
with a nearly linear response to valve movement between the minimum and maximum valve positions. Reactor startup requires a rather complicated procedure for switching between the high and low pump speeds. Startup is initiated with the flow control valve closed (6% flow area), the pump is switched on at 100% speed to initiate bearing lubrication flow and then is tipped back to 25% speed. Reactor power is brought up to about 35% by opening the flow centrol valves (increasing recirculation flow) and control rod withdrawal. At 35% power the flow control valve is 100% open and the pump is on low speed. The next step in increasing power requires that the flow valve be closed, the pumps switched to high speed, and the opening of the valve is again initiated. The system is interlocked to prevent the pump from being switched to high speed with the flow control valves.open. Switching of the pumps to high speed with the valves open would produce a rapid reactivity insertion as the additional flow reduces the void fraction of the Core.
The Staff has postulated the failure of the interlock along with an operator error that switches the pump to high speed without first closing the flow control valve. The Staff has asked that the utility analyze the resulting reactivity transient and determine that it is acceptable.
Attached is a copy of the portion of the draft SER dealing with the recirculation control system.
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i g description of confirmatory tests planned to assess the co ervatism-of their transient.' analysis.ethods. This must:be:res ved prior.to power operation.
The staff is per orming a generic study of
.e hydrodynamic stability characterist' s of LWRs under normal operation, anticipated transients, and acci ent conditions. The resul s of this study will be applied no the aff review and acceptance f stability analyses and analyti il me'thods now in use by the rp ctor vendors.
In the interim, t e staff concludes that pa ! operating experience, stabilf t ests, ar/J the inherent therma hydraulic characteristics of L' s provide a basis for accepting t Zimmer stability evaluation f normal operation and anticipated ransient events.
However, i order to provide additional margin stability limits, natural rculation operation of Zimmer wi be prohibited until the s f review of these conditions is complete.
%ny action resulting from the staff study will be applied to Zimer.
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Zimer-1 uses valve flow control rather than pump speed flow control j
as has been used on boiling water plants through the BWR/4. The principal modes of. normal operation with valve flow control low frequency motor generator (LFMG) set are summarized in the following.
The recirculation pumps are started on the 100% speed power source in order to unseat the pump bearings. Suction and block valves are 4
I
, 1 fully open and the flow control valve is in the minimum position.
When the pump is near full speed, the main power source is tripped and the pump allowed to coast down to near 25%. speed, where the LFMG set will power the pump and motor. The flow control valve is then 1
opened to the maximum position, at which point the reactor heatup and pressurization can commence. When operating pressure has been l
l established, reactor power can be increased. This power increase
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will follow a line within Region I of the power-flow map in Figure 4.4-1.
When reactor power is greater than approximately 30% of rated, the low feedwater flow interlock is cleared and the recirculation pumps can be switched to the 100% speed power source. The flow control-valve is closed to the minimum position before the speed change to i
prevent large increases in arc power and a potential flux scram.
This operation occurs within Region II of the operating map. The system is then brought to the desired power-flow level within the normal operating area of the map (Region IV) by opening the flow control valves and withdrawing control rods.
t An interlock has been installed for each pump to prevent system startup or transfer from 25% to 100% pump speed unless the flow control valve is in the minimum position.
The primary safety concern which requires this interlock is a sudden reactivity insertion due to sweeping the voids from the core should the transfer to 100% speed occur with the flow control valve in the maximum position. A discussion of the consequences of this event, which is a new transient
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applicable only to BWRs with valve flow control, will be discussed
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A in the SER to Ippendix H of the Zimmer FSAR.
p No vibration an loose parts monitoring ystem has been proposed for Zimmer-1. A y bration and loose par monitoring system, ac.ceptable
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to the staf, must be operational efore power operatioywill be permitted. We require a mini.um of two LPMS sensors tt each natural colle ion region.
Cr d deposition causes gradual flow reduct on in some LWR cores..
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pumppressuredrop,a/
However, measurement of core flow by jp nd core plate pressure op would provide uate indication of uch flow reduction, i such should occur,( Technical Specifica ions require that the ore flow be che every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> an APRM flow biased scram be recalibrates ery month. This fr uency is sufficient to detectcruddepositjoneffects. The ef s of crud buildup have n design calculation [ar 3 are not considered to been considered cause signif' ant problems (3.5 1s additional crud on fuel rods reduces t e MCPR by.009).
I A
Summary The thermal-hydraul'c design of the core for Zimme nit 1 was reviewed.
The scope of th review included the design teria, implementation of the design iteria as represented by tpe' final core design, and the steady-s te analysis of the core t tral-hydraulic performance.
The applicant's thennal-hydra ic analwses were performed using
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