ML19340A179
| ML19340A179 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 01/10/1974 |
| From: | Thies A DUKE POWER CO. |
| To: | Anthony Giambusso US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8001140771 | |
| Download: ML19340A179 (6) | |
Text
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AEC STRI SUTIC: 70' PART 50 SCCRET_
TERIAL (TatPOR.\\RY FCPJt)
CONTROL NO:
354 FILE:
FRCM:
DATE OF DOC DATE REC'D LTR MEMO RPT GTER Duke Power Company Charlotte, N. C.
A, C. Thies 1-10-74 1-14-74 X
.TO:
ORIG CC OTHER SENT AEC FDR vyy, A. Giambusso 1 siened CLASS UNCLASS PROP INFO INPUT NO CYS REC'D DOCKET NO:
XXX 1
50-270 DESCRIPTION:
ENCLOSU?2S:
Ltr trans the following.....
REPORT: investigations into the poss-ibility of a loose object in the icwer o Denotes Letter Only reactor vessel head and information DONOT REMOVE Supporting the continued operation ACKNOWLEDGED PLANT NAME
- 0conee Unit #2 (1 cy rec'd)
FOR ACTICN/INFORATION 1-15-74 GMC BUTLER (L)
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January 10, 1974 y
9 qi Mr. Angelo Giambusso
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l Deputy Director for Reactor Projects Directorate of Licensing f'
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Office of. Regulation 4
U. S. Atomic Energy Commission Ne, Washington, D. C.
20545 N7~..
Re: Oconee Unit 2 Docket No. 50-270
Dear Mr. Giambusso:
Please find attached for your Information and review a report con-cerning i e Ir.iication of 'a. possible loose object in the lower reactor assel head of Oconee Unit 2.
Extensive investigations and evaluations have been made and are sum.arized in the attached report..-Duke Power Company, the Babcock r. Wilcox Company, the on-site Station Review Committee, and the Nuclear Safety Review Committee have reviewed this information and have concluded that operation of Oconee Unit 2 can continue without endangering the health and safety of the public. When Unit 2 is returned to service, the extensive monitoring program also described in the attached report will be implemented.
Very truly yours, f>,
-A. C. Thies.
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7: JAN 11 1974 V Attachment ed; E
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Mr. Norman C. Moseley 3
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DUKE POWER COMPANY j,
OCONEE NUCLEAR STATION - UNIT 2
.Z" INFORMATION SUPPORTING THE CONTINUED OPERATION 0F OCONEE UNIT 2 VITH INDICATED PRESENCE OF A LOOSE OBJECT'
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IN THE LOWER REACTOR VESSEL HEAD g
Loose Parts investigation An indication of a possible loose object was observed on the loose parts monitoring system when Reactor Coolant Pump 2B1 was started while the reactor coolant system was in a naturai circulation mode at approximately 1900 psig and 400*F on January 4, 1974. The indication was of low magnitude, below the alarm setpoint on the loose parts monitoring system.
The indication was observed primarily on Channels 3 and 4, monitoring the incore instrument guide tubes near the lower reactor vessel head.
Indications, at a lower signal level, were also present on the steam generator upper tube sheet area channels.
Following unit cooldown, the following investigative actions /results were Observations were made taken to better define and characterize the noise.
with the LPM output, additional temporary accelerometers, and personnel in the plant using stethoscopes.
Various single and dual reactor coolant pump combinations were run.
1.
The noise was evidant in some single pump runs and during some dual pump runs some observers thought they could hear a faint sound.
It The was also heard on coastdowns from single and dual pump runs.
least one time, during the operation of each noise was present, at reactor coolant pump.
Pieces of hardware, such as bolts, nuts, washers, etc. were used to 2.
simulate the noise in the lower vessel head area of Unit 3 which was open and full of water.
A ball bearing of about 1/2" to 3/4" diameter most nearly simulated the noises detected in Unit 2.
Accelerometers were added to monitor the reactor coolant pump area 3
for possible noise source in the motor anti-rotation device or other Time delay analysis between the various sensors pump-related sources.
showed the noise was not coming from the reactor coolant pump area but f rom somewhere equi-distant f rom the four pumps.
Unit I reactor coolant pumps were run to determine if a similar noise 4.
could be detected. None were.
Time delay analysis data of the signals from the various loose parts 5
for pickup
_ monitoring system channcIs showed the following time sequence of the noise signal:
First, lower vessel head area; second, upper vessel There head area; and last, the steam generator upper tube sheet area.
was no evidence that the object moved out of the lower vessel head area.
m 1
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- - g 6, : A Unit 2' reactor coolant pump was run for a few seconds to induce
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momentary' motion of the suspected loose object.
The noise sounded similar to a. rolling / sliding object on the lower vessel' head during thelcoastdown (about like~a ball coming to rest on a roulette wheel).
l.
7 Baseline data tapes taken on the loose parts monitoring system during l
_ earlier periods of both Unit I and Unit 2 operation did not Indicate I
this noise.
i
'8.
The level of noise is significantly less than the cold water flow noise and is indicative of low energy contacts.
The noise to background ratio 1s higher during the flow coastdown than during the continuous pump operation, i
9 Other sources of noise in the plant were investigated.
Indication of a' decay heat-system check valve movement and possible secondary plant-related~ noises were detected in addition to noises occurring in the lower vessel head area.
- 10. Sampled steam generator secondary-sides for boron and radio-isotopes.
Nothing abnormal was detected.
Based upon the above investigations /results, the following conclusions have been reached:
1.
Based on Oconee 3 diagnostic tests, we suspect the object may be metallic and of a mass' consistent with a 5/8" diameter sphere.
2.
The data indicate high probability for the object being in the lower vessel head area.
i 3
The object tends'to become fixed in location as the reacter coolant f'ow
(
increases to that of two (or more) reactor coolant pumps.
The following steps have been taken to' determine the source of the loose j-obj ect:
1.
Valves have.been--radiographed.in the high pressure injection and low pressure Injection systems to ensure that valve stems, p1_ugs, and guides are.still in place. No useful information.was obtained due to the thickness of the valve bodies.
2.
Valves have'been cycled-in the high pressure injection and. low pressure-injectionisystems to. verify. the flow' can be stopped and that valves are This work will'be completed before unit startup.
operating properly.
7..
3 lit has been verified that the high pressure injection thermal sleeves '
are In place.
f.
The HPI-flow restriction _ orifices will be. dismantled and inspected t
prior. to unit startup.
L5. _ All control rod; drive mechanisms _were exercised and functioned normally.
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l Safety Evaluation is considere'd to be the I
The objective of 1[his statement is to address whatfrom the postulated loose ii f the worst possible safety-related situation ar s ngThe worst case assu h
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diagnostic testing done to date, is considered to be t eit.could then be assu
.l part.
l boiling of the object within a fuel assembly.
fuel clad failure occurs due to either the departure from nuc eateAs
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l parameter for judging or mechanical wear (fretting).
tisfactory Only localized fuel l
would increase; hence, activity would be a sa i
the status of_ fuel clad integrity during operat on.
l ble geometry.
damage is postulated; therefore, the core would' remain in a coo a h t down for-Coolant. activity will be monitorec and the plant pro j
dd Con-I h
sequently, Duke Power Company _ considers that t e con d safety of the Oconee 2 does not represent. undue risk to the health anC i
l h Babcock & Wilcox Review Committee, the Nuclear Safety Review Committee, t eDuke Steam public.
Company, Oconee fluclear Station management, General O All concur in this evaluation and conclusion.
Monitoring Programs _
following monitoring Conditional to the continued operation of Oconee 2, themption of operatio and surveillance programs will be implemented upon resu d or if These programs will be discontinued if the particle is remove evaluaticn shows that they are no longer necessary.
LOOSE PARTS MONITOR:
A.
t m Sensors will be positioned to optimize both: total nuclear s ea head-surveillance.
supply system and reactor. vessel lower 1.
itor Personnel will listen continuously to the loose p h
s 2.
lly Personnel will listen to the loose parts monitor periodica d period of
'during steady-state' operations and for some designate 3
i
-(Sometimes the time after an alarm on-the loose parts mon tor.
i
) The length telephone horn vibration exceeds the alarm po nt.
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c dure.
of this listening period will~be s'pecified in a station pro e
- 4.. Capability to analyze transport time differences bet i h noise tapes.
will be on-call.the loose _ parts monitor and will be famillary w t CORE PONER DISTRIBUTION:
'T B..
er
- 1. aA core power distribution will be obtained at 40 percent pow
-(non-equilibrium' xenon) with plant conwhich existed w taken prior to
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d
' shutdown. - These results will be compared, an an vre explained before operation at; higher power..
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. The core power distribution test program will be continued at 75 2.
percent power with extra attention to local effects.
C.
NEUTR0ft NOISE:
1.
At 40 percent power, a neutron noise signature will be obtained at plant conditions comparable to those which existed when an earlier signature was taken at 40 percent. The power spect.al densities of these two signatures will be compared, and any differences will be evaluated prior to operation at higher power.
Cross correlations from neutron detectors will be compared within seven days.
At 75 percent power, a signature to the one obtained at 40 percent 2.
power will be taken and cross correlations completed prior to operation above 80 percent power.
D.
REACTOR COOLANT RADIDACTIVITY:
Reactor coolant radioactivity will be closely monitored.
Quantitative limits will be established, and if the reactor coolant activity exceeds these limits, the reactor will be shutdown and the cause of the increase in activity determined.
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