ML20205B536
| ML20205B536 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 09/06/1985 |
| From: | Carey J DUQUESNE LIGHT CO. |
| To: | Knighton G Office of Nuclear Reactor Regulation |
| References | |
| 2NRC-5-127, NUDOCS 8509120132 | |
| Download: ML20205B536 (7) | |
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'Af Duquesne Lidit 2sggy,27 y..co,,$t2lsI2!$o Nuci ar construction oms on NuYgO'*is2Os September 6, 1985 United States Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Mr. George W. Knighton, Chief Licensing Branch 3 Office of Nuclear Reactor Regulation
SUBJECT:
Beaver Valley Power Station - Unit No. 2 Docket No. 50-412 Response to Auxiliary Systens Branch Question 410.21 Gentlemen:
This letter forwards a revised response for Auxiliary Systens Branch Question 410.21.
The corresponding Final Draf t SER open iten number is 9.
Upon your concurrence, this open iten will be considered closed, and this revised response will be included in a future FSAR amendment.
DUQUESNE LIGHT COMPANY By J.ffCarey VRe President JJS/wjs Attachment cc:
Mr. B. K. Singh, Project Manager (w/a)
Mr. G. Walton, NRC Resident Inspector (w/a)
SUBSCRIBED AND SWOR TO BEFORE ME THIS (ef/ DAY OF u d d o,1985.
02 $b Notary Public ANITA ELAINE REITER, NOTARY PUBLIC ROBINSON TOWNSHIP. ALLEGHENY COUNTY f
8509120132 850906 MY COMMISSION EXPIRES OCTOBER 20,1986 ADOCK 0 % y2 PDR E
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l United States Nuclear Regulatory Conunission Mr. George W. Knighton, Chief 4
Respose to Auxiliary Systems Branch Question 410.21 Page 2 i
COMMONWEALTH OF PENNSYLVANIA )
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COUNTY OF ALLEGHENY
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On this hf/
day of
///I, before me, a f
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Notary Public in and for said Commonwealth and County, personally appeared J. J. Carey, who being duly sworn, deposed and said that (1) he is Vice President of Duquesne Light, (2) he is duly authorized to execute and file the foregoing Submittal on behalf of said Company, and (3) the statenents set I
forth in the Submittal are true and correct to the best of his knowledge.
L Notary Public ANITA ELAINE REITER, NOTARY PUDLIC I
ROBINSON TO'.*'NSHIP, ALLEGHENY COUNTY MY COMM!SSr0N EXPIRES OCTOBER 20,1986 j
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Question 410.21 (Section 9.2.2)
Section 9.2.2.1 states that flow indication will be provided in the main control room in the event of a loss of component cooling water (CCW) to the reactor coolant pumps (RCP).
However, Figures 9.2-10 and 9.2-11 show the flow transmitters and indication and temperature indication to be nonsafety grade.
Further, Figures 9.2-11 and 9.2-12 indicate that the spurious closure of a containment isolation valve could result in the loss of CCW to two of the three RCPs.
Loss of cooling to the RCP bearings may result in i
multiple RCP locked rotors and potentially unacceptable fuel damage.
Therefore, it is our position that compliance with one of the following alternatives be provided:
1.
Demonstrate with test data that RCPs can withstand a complete loss of cooling water for 10 minutes, and that instrumentation, designed in accordance with IEEE Standard 279-1971 which alarms in the control room is provided to detect loss of cooling water to ensure that a period of 10 minutes is available for the operator to initiate manual protection of the plant, 2.
Provide instrumentation designed in accordance with IEEE Standatti 279-1971 to initiate automatic protection of the plant upon loss, of cooling water to an RCP, or 3.
Provide redundant Seismic Category I CCW supply lines to the RCP
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bearings to assure that a single failure does not cause loss of cooling to multiple RCPs.
Response
Component cooling water is provided to the RCP thermal barrier heat exchang-er, as well as to the upper and lower motor bearing oil coolers.
In addi-tion, seal injection flow is supplied to the pumps from the chemical and volume control system (CVCS).
Detailed flow diagrams of the CVCS and the CCW systems are shown in Figures 9.2-23, and 9.2-11 and 9.2-12, respectively.
THERMAL BARRIER SYSTEM The thermal barrier is a welded assembly consisting of a flanged cylindrical shell, a series of concentric stainless steel cans, a heat exchanger coil assenbry, and two-flanged water connections.
The CCW enters the thermal barrier through a flanged connection on the thermal barrier flange.
The cooling water flows through the inside of the coiled stainless steel tubing in the heat exchanter and exits through another flanged connection on the thermal barrier flange.
During normal i
operation, the thermal barrier limits the heat transfer from the reactor coolant to the pump internals.
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i UPPER MOTOR BEARING ASSEMBLY / UPPER MOTOR BEARING OIL COOLER The upper bearing assembly contains an oil-cooled, pivoted-pad radial guide bearing (upper guide bearing), as well as a double-acting, oil-cooled Kingsbury-type thrust bearing.
The thrust-bearing shoes are positioned above and below a common runner to accommodate thrust in both directions.
The shoes are mounted on equalizing pads, which distribute the thrust load equally to all the shoes. The oil is circulated through an external oil-to-water shell and tube heat exchanger (oil cooler) to which CCW is supplied.
LOWER GUIDE BEARING / LOWER MOTOR BEARING OIL COOLER The lower guide bearing is a pivoted pad radial bearing, similar to the upper guide bearing.
The entire lower guide bearing assembly is located in the lower oil reservoir, which contains an integral oil-to-water coil type heat exchanger. Component cooling water is supplied to this heat exchanger.
SEAL INJECTION SYSTEM Seal injection flow, at a slightly higher pressure and at a lower tempera-ture than the reactor coolant system, enters the pump through a pipe connection on the thermal barrier flange and is directed to a point between the pump radial bearing and thermal barrier heat exchanger.
Here the flow splits with a portion flowing down through the thermal barrier labyrinth (where it acts as a buffer to prevent reactor coolant from entering the
- radial bearing and seal section of the pump) and into the reactor coolant system. The remainder of the seal injection water flows up through the pump radial bearing and the shaf t seals and is discharged via the seal leakoffs.
LOSS OF CCW TO PUMP THERMAL BARRIER Loss of CCW to the pump thermal barrier heat exchanger is of no operational concern.
The pump internals are capable of operating indefinitely with a loss of CCW to the pump heat exchanger, since seal injection flow is suffi-cient to prevent damage to the pump seals (Reference 1).
LOSS OF CCW TO MOTOR BEARING OIL COOLERS Loss of CCW to the motor bearing oil coolers will result in an increase in 4
oil temperature and a corresponding rise in motor bearing metal temperature.
It has been demonstrated by a combination of tests and analysis as discussed below that the RCPs will incur no damage as a result of the CCW flow inter-ruption of 20 minutes.
Two RCP motors have been tested with interrupted CCW flow; these tests were conducted at the Westinghouse Electro Mechanical Division.
In both cases, the RCPs were operated to achieve " hot" (2230 psia, 552*F) equilibrium i
conditions.
After the bearing temperature stabilized, the cooling water flow to the upper and lower motor bearing oil coolers was terminated and bearing (upper thrust, lower thrust, upper guide and lower guide) tempera-tures were monitored.
A bearing metal temperature of 185*F was established as the maximum test temperature.
When that temperature was reached, the cooling water flow was restored.
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In both tests, the upper thrust bearing exhibited limiting temperature, which was reached in approximately 10 minutes. The maximum test temperature of 185*F is also the suggested alarm set point temperature, and the suggest-ed trip temperature is 195*F.
It should be noted that the melting point of the babbitt bearing metal exceeds 400*F.
Westinghouse Electro Mechanical Division also performed an analysis using a computer model which simulated the operating characteristics of a RCP motor during loss of CCW.
A full flow test was performed on a typical RCP motor with CCW interrupted for various time periods.
The computer model was compared to and extrapolated from test data.
It was concluded from this analysis that the BV-2 RCP motors will successfully operate without CCW flow to the bearings for 20 minutes (Reference 1).
LOSS OF SEAL INJECTION Should a loss of seal injection to the RCPs occur, the pump radial bearing and seals are lubricated by reactor coolant flowing up through the pump.
Under these conditions, the CCW system continues to provide flow to the thermal barrier heat exchanger functioning in its backup capacity, cools the reactor coolant before it enters the pump radial bearing and shaft seel a rer..
The loss of seal injection flow may result in a temperature increase ir. the pump bearing area, a temperature increase in the seal area, and a resultant increase in the number one seal leak rate; however, pump operation can be continued (for up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />), provided these parameters remain within the allowable limits.
SPURICUS CLOSURE OF CCW CONTAINMENT ISOLATION VALVE As shown in the referenced figures, the BV-2 CCW piping is arranged with "A" and "B"
supply and return headers.
Each supply and return header has two motor-operated containment isolation valves.
One RCP is on the "A" header. The other two RCPs are on the "B" header. The RCPs are located inside containment.
Therefore, the NRC's concern regarding loss of CCW to two RCPs due to spurious closure of a single containment isolation valve could occur only on the "B" header.
Should this occur, the following data are available to the operator to indicate loss of CCW to the RCP:
Status lights for containment isolation valve position are provid-ed on the main board.
Safety grade flow indication is provided from the "B" supply header outside containment and from the thermal barrier on each punp.
Two nonsafety grade Rosemount 1151 electronic differential pres-sure flow transmitters are provided on each pump - one each for the upper and lower motor bearing oil coolers. These flow trans-mitters actuate a common trouble alarm on low flow on the main control board.
Although the transmitters are nonsafety grade, they have been seismically tested and are similar in design and manufacture to models which are qualified to IEEE 323-1974 and 3
344-1975.
The Westinghouse process cabinets, which process the signals from the Rosemount transmitters, and the associated main board indicators are identical to equipment purchased as Category I and qualified to IEEE 323-1974 and 344-1975. Although the procurement documents distinguish between the Category I and Category II equipment, the Westinghouse internal manufacturing i
QA procedures do not.
Therefore, although additional documenta-tion is supplied with safety-related equipment, the safety and nonsafety equipment can be considered to be of equivalent quality.
The - safety-related as well as the nonsafety transmitters receive power from safety-related uninterruptible power supplies. The safety grade transmitters for the thermal barriers are fed from vital buses _ which supply safety grade red or white power.
The nonsafety transmitters for the motor bearing oil coolers are fed from buses which supply nonsafety grade black power fed from blue or yellow safety grade buses through an isolating t rans forme r.
The red, white, blue, and yellow buses are fed from the emergency buses via the uninterruptible power supplies.
All of the vital buses are backed by the emergency diesel generators and Class IE batteries.
All cable associated with both the safety and nonsafety transmie ters is seismically supported.
Further, spurious closure of a containment isolation valve would not cause an abnormal containment environment.
Therefore, the transmitters are expected to operate normally.
The motor bearing temperature is monitored, and approximately 7 minutes after loss of CCW flow a high temperature alarm is actuated.
At this time, bearing temperature is about 185'F.
It is assumed that at 10 minutes the oil temperature will reach 200*F, the maximum recommended oil temperature.
This could occur if the RCP was not shut off on actuation of the alarm. However, the operator has sufficient time to trip the p.m.p before this temperature is reached.
In light of the above, the operator can be expected to be well informed of a spurious containment isolation valve closure.
l LOCKED ROTOR EVENT A locked. rotor event is analyzed in FSAR Section 15.3.3.
The. analysis conservatively assumes an instantaneous seizure of an RCP rotor due to an i
impeller rubbing on a stationary member.
The loss of CCW to the RCPs will not result in an instantaneous seizure of the RCP.
The more realistic i
of such an event will be an abbreviated coastdown of ultimate consequence l
the RCP.
If a limiting condition of the babbitt metal of the motor's l
bearings is considered, an increasing coefficient of friction, as well as an l
increasing ; retarding torque, is expected.
However, in view of the large l
rotational inertia of the pump / motor assembly, an instantaneous seizure will not result.
This position is supported by the failure mode of similar RCPs i
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that did not experience seizure despite extensive bearing damage (Reference -1).
CONCLUSION It has been shown that the RCPs can withstand an indefinite loss of CCW to the thermal barrier heat exchanger since seal injection will prevent damage to the pump seals.
As shown by a combination of tests and analysis, the RCPs are capable of running for 20 minutes after a loss of CCW to the RCP motor bearing oil coolers.
Spurious closure of a CCW containment isolation valve will be detected by ample, reliable data.
These data include status lights and various safety and nonsafety grade flow and temperature indication and alarms on the main control board.
The nonsafety instrumentation is of high design quality and seismically installed for reliability. Due to the large rotational inertia.of the pump / motor assembly a mechanical instantaneous seizure of a pump rotor due to loss of CCW to the RCP is not a credible event. This position is supported by failure modes of similar RCPs.
A multiple locked rotor scenario is likewise not considered credible.
References:
1.
Westinghouse " Loss of CCW Study for RCP" transmitted with letter DMW 4845 dated April 10, 1985.
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