ML19329A509
| ML19329A509 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 10/13/1977 |
| From: | Woodruff R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| To: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| NUDOCS 8001060025 | |
| Download: ML19329A509 (5) | |
Text
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l K. V. Seyfrit. A/0. TP, RCI ;
MEMORANDUM FOR:
FROM:
TRIP REPORT /0CONEE POWER OSCILLATIONS
SUBJECT:
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Background
Operator Licensing, while conducting an oral examination at Oconee-3 The Licensee stated discovered that reactor power was oscille. ting.
that the oscillations originated in the secondary cooling system.
References 1 and 2 state that oscillation of secondary flow and pressure can occur in B&W steam generators and can cause variations in Reference 1 also states that power oscillations can reactor power.
be eliminated by adjusting an orifice assembly installed on the secondary side near the inlet to the tube bundle.
The steam generators are vertical tube and shell components with a Primary coolant is on the tube side and water box at each end.
secondary coolant is on the shell side. Feedwater is sprayed down-ward into the annulus fomed by the shall and the baffle: surrounding the tube bundle. The fdedwater spray aspirates steam into the annulus from ports for that purpose in the baffle. The lower part of the annulus contains preheated feedwater and condensed steam which flows thru feedwater ports at the bottom of the baffle. The orifice plate assembly is located in the annulus immediately above the feed-The water level in the annulus is detemined by the ~
water ports.
orifice setting, fe dwater flow, and reactor power.
Oscillations For Oconee Units 1, 2. and 3. the Licensee considers 0.25 hs.-tz power oscillations to be nomal in the power range from 40 to 70% when the l
i Following the first re-peak-to-peak amplitude is 1.5% of full power. fueling outage fo tions became progressively larger as shown in Flaure 1.
For Unit-3 the following parameters also oscillate at 0.25 Hz:
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Steam generator levels i
b.
Nedwater flows c.
Feedwater pump suction and discharge pressures l
d.
Reheater drain flow to the condenser e.
Reactor inlet temperature f.
Reactor average temperature i
i The control rods do not oscillate.
l Selected recorder charts from June, 1977, for water levels in the annuli of the steam generators were reviewed. The level in steam generator A oscillated 10 inches peak-to-peak, and in sceam generator 8, 4 inches peak-to-peak. At the same time, feedwater flow to steam generator A oscillated 0.2 million poinds/ hour over the flow range from 1.0 to 5.5 million pounds / hour. For steam generator B, the oscillation varied between 0.2 and 0.3 million pounds / hour in the same flow range. The feedwater flows for the two steam generators were 180% out of phase.
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Indicated reactor inlet and reactor average temperatures oscillated 3 F and 1 F, respectively. Actual oscillations would be larger because l
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i of the response time of the temperature sensors.
In addition, one set
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of drain valves in the reheater drain system were opening and closing at 0.25Hz.
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I, Steam Generator Perfomance t
Steam generator A is not performing as well as B as indicated by steam 0
temperatures. For A, the outlet steam temperature is 578 as compared to 598 F for B.
The saturation temperature is approximately 5400F. The 0
difference in perfomance may be related to orifice settings which in turn may affect the amplitude of the oscillation.
Testing The Licensee, with the assistance of BW, has perfomed a number of tests to detemine the cause of the increasing amplitude of the reactor power oscillation.
In these tests, various sections of the control system were placed on manual control. Although the reactor power oscillations were significantly reduced under certain conditions, the Licensee consf ders the results to be ambiguous and additional. work is planned.
The Licensee expects to shut Oconee= 3 down next month for refueling.
During the power reduction and the power ascension fcilowing refueling, the Licensee plans to perfom additional tests to detemim the cause of the increase in amplitude of the power oscillations. During the 1
i refueling cutage, the Licensee plans to inspect the adjustable orifices l
in both steam generators.
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OCT 131977 i K. V. Seyfrit l'
i Safety Review The Licensee's off-site committee has not reviewed the power oscilla-Further, the Licensee does not believe that the oscillations i
tions.
This belief is based on the
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constitute an unreviewed safet;y question.
fact that there is a limiting safety system setting on flux flow ratio.
When This settir.? limits reactor power to 1.07 times percent flow.
power and flow are matched, the peak-to-peak amplitude of the power However, if power were oscillation would be limited to less than 14%.
j reduced larger oscillation would be tolerated by the control system without tripping the reactor.
f The limiting safety system setting for flux flow ratio is based on consideration of DNBR resulting from a loss of flow accident and on thennal limits (linear power density and DNBR). To the best of our knowledge, oscillatory effects have not been considered.
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Followup after the Visit _
Following the trip to Oconee, the oscillations were discussed with one of B&W's control engineers who has been involved in the Oconee-3 tests.
In his opinion, the cause of the oscillations may be the control system e
He states that there is not a signi-for the secondary cooling system.
ficant difference between the Oconee-3 steam generators and the steam generators for Oconee-1 and 2.
He also states that all other operating j
B&W plants are operating in a stable manner.
Information obtained during and fo11 ewing the visit was described to i
l the Licensing Project Manager.
l Recomendations l
IE should monitor the efforts of the Licensee in resolving this l
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-prabproblem, specifically, the tests prior to shutdown of Unit-3 for-i I
refueling, inspection of the orifice assemblies, and tests perfonned during the power ascension after refueling.
If significant progress in identifying the cause of oscillation 2.
does not result from these tests and the Licensee's inspection.
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IE should send a cetrols er.gineer to.0conee to inspect the i
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Licensee's effort.
,,.j, If the amplitude of oscillation increases significantly, a transfeel / '? -
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of lead responsibility should be prepared. -
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OCT 131977 K. V. Seyfrit References 1.
BAW-10002. "Once-through Steam Gene,ator Research and Development Report." August. 1969.
2.
BAW-10002, Supplement 1. June,1970.
R. W. Woodruff Technical Programs, ROI. IE cc:
H. Thornburg. HQ
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