ML19296D136
| ML19296D136 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 02/22/1980 |
| From: | Pilant J NEBRASKA PUBLIC POWER DISTRICT |
| To: | Ippolito T Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8002290391 | |
| Download: ML19296D136 (10) | |
Text
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LQA8000073
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GLNE R AL OF FICE P O. BO X 499. C OLUM BUS, N E B R ASK A 68601 i
Nebraska Public Power D=str. t i
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February 22, 1980 Director, Nuclear Reactor Regulation Attn:
Mr. Thomas A.
Ippolito, Chief Operating Reactors Branch No. 3 Division of Operating Reactors U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
L.P. Turbine Disc Cracking Potential Cooper Niiclear Station NRC Docket No. 50-298, DPR-46
Dear Mr. Ippolito:
In a meeting with the NRC February 19, 1980, the District was requested to respond in writing to various concerns relating to L.P. turbine disc cracking at Cooper Nuclear Station.
Enclosed please find the District's response to this request.
Attachment A to the enclosed contains proprietary information of Westing-house Electric Corporation and is furnished in confidence.
It is requested that disclosure of this information caly be in accordance with the pro-visions of 10 CFR Part 2.790.
Because of the economic concerns associated with the subject cracking, NPPD will not operate CNS beyond March 1,1980, at which time the unit will be shutdown and both L.P. turbine rotors inspected.
If CMS trips prior to March 1, the plant will remain down unless there are some very unusual power shortages in the area which would necessitate the plant being restarted; however, this event is highly unlikely and startup would only be based upon prior NRC approval.
Because of this accelerated outage schedule, NPPD requests approval prior to March 1, 1980 of our Spiral Fuel Unload / Reload Technical Specification change request of January 14, 1980.
If you have any questions relating to the enclosed information, please Contact me.
Sincerely, M
a Pilant Director of Licensing i
\\
p and Quality Assurance g
JDW/cak Enclosure 8 0 0 2 2 9 0 3ct)
Feb ruary 22, 1980 LQA8000073 NRC Rcouest f or Information_
Cooper Nuclear Station 1.
CRACK FOIENTIAL Provide a description of the L.P. turbine.
A.
Response _
three casing, The turbine unit consists of one tandes compound four flow,2.0 in. HG ABS.
condensing,1800 RPM turbine rated at 970 psia, 541 Each of the two low pressure elements are designated as a Bui Provide crack growth and metallurgical data for all L.P. turbine discs.
B.
Response _
i Since this infor=ation is considered proprietary by Westinghouse Elec A.
Corporation, this data is supplied in Attachment Describe the Turbine Overspeed Protection System.
C.
Resconse turbine overspeed:
There are five circuits which provide protection against There are two circuits protecting the unit which sense the output the turbine from overspeed as breaker positions. These circuits protect the Westinghouse " breaker intercept" They are: (1) the breakers open.
which closes the governor valves, and (2) the NPPD generator protection circuit which trips the " auto-stop" valve which in turn du=ps circuit the DEH control fluid which close all stop, governor, reheat, and inter-
' cept valves and ocen the turbine bypass valves.
In addition to the two circuits described above, there are three over-They are: (1) 103%
speed protection circuits whien cesse turbine speed.
overspeed trip (analog speed sigenl) which close the governor and 106% electrical overspeed trip (digital speed intercept valves, (2) signal) which trips the " auto-stop" valve and dumps the DEH control fluid which close all stop, governor, reheat and intercept valves and ocen the turbine bypass valves, and (3) 108% mechanical overspeed trip which trips the " auto-stop" valve and du=ps the DEH control fluid and causes the valves to act as described above in the 106% trip.
(e.g. trip tests, Describe the history of load rejections and overspeed.
D.
etc.)
Response
CNS with power levels greater than
_We have had four load rejections atof the startup testing program. They 80%.
One was scheduled as a part occurred as follows:
Chart
% Oversoced Cause and/or Cross Elec._
% Power Description Event #
Date 105.5 748 SM 93.5 105.5 12-8-74 Startup Test 666 551 83.2 103.9 1
2-21-76 Stor=
719 MW 89.9 106.7 2
Lightning Strike 96.4 5-31-78 771 MW 3
False Gen. Grd.
1-19-80 4
indicated on any of these trips that receiva a co=puter printout The
- overspeed as determined We did not the turbine reached the 106% overspeed.shows maxitum overspeed was 106 This same from a recorder chartrecords governor valve position while the unitswitches to speed instru=ent the instrumentWestinghouse calculates the unit 1:ed. When the unit trips, as it cakes its change.
5 MW.
may overspeed to 107.5P. with a design load of 83 some overshoot CNS have always been 103%,
The intended overspeed trip setpoints atFollowing are the dates of overspee 106%, and 108%.
rpn.
108%
106%
1031 Date 1932 1908 184o 1945 5-75 1921 1850 1922 11-75 1905 1844 1928 5-76 1901 1845 1926 9-76 1905 1847 1936 4-77 1900 1848 1928 9-77 1908 1846 10-77 1908 1928 1846 1927 5-78 1908 1846 1928 4-79 1853 9-79 the unit tripped at or In all cases with exception of the 9-79 test, the unit did not trip During the 9-79 test, to below the propar setting.106% because the progratted setting had been The 110% was the It has since been returned to the 106T. setting.
at setting originally recenmended by Westinghouse.
110%.
power lir.taticas due to er.d-of-cycle coast devn.
E.
Discuss the present Resconse_
and the reactor is into the end-of-cycle All control rods are full outThe maximus reactor power level attainable i Power level will be dropping approximately h% per day.
down.
coast 21-80.
2.
It'RSINE DISC CONTAINMENT _
of the turbine discs within the turbine casing, Relating to the containment certain discs would be contained and A.
discuss the FSAR determination thatdiscuss the confirmation o completed for disc 11.
Resocnse 14 to the FSAR, we provided responses to staff questions 11.2 In our response to question 11.2, we stated that disc #6 could In Anendment and 12.49.
3-penetrate 22.1 inches of concrete and disc #4 could penetrate 26.1 inches disc #4 In our response to question 12.49, we stated that of concrete.
We is the more critical disc due to its anticipated ejection energy.
0 ft. lb s.
disc #4 had a calculated ejection energy of 8x10 stated that a velocity We also stated in the same response that disc #4 would exit at of 2865 lbs., and had an of 424 ft./sec., had a disc quadrant weight i= pact area of 3.1 sq. ft.
Since disc 94 was considered the worst case, This analysis was based on 1207, overspeed.
it was used for the analysis.
at that time, it Because of the various calculations (see Attachment B) was considered that only disc #4 and #6 could be ajected through the as missiles. Westinghouse currently recalculated turbine casing to act potential energies from a break-up of #1 disc and the new calculationsdesign overs show that in the event the disc were to burst at or below, all of the disc fragments will be contained within the turbine outer cylinder.
3.
TUR3INE MISSILES A.
Provide a turbine missile analysis including a review of all applicable non-safety syste=s.
Specifically, include discussions of spent fuel pool, reactor building ventilation system, and high pre asure coolant inj ection systems.
Response
We have reviewed the missile analysis submitted in FSAR Amendment No. 14 as our response to FSAR Question No. 11.2.
In this response, we discus-sed the consequences of missiles generated from possible turbine disc b reakup. We analyzed the worst case condition which was a quarter sized fragment from disc #6.
Due to the presence of the 36 inch thick shield walls located frem elevation 932'6" to elevation 952'6", east and west of the turbine shaft, the generated missiles are limited to a vertical exit envelope of approximately 100. With this limitation, a disc fragment cannot make a direct hit to any wall in the reactor building or any other building. The worst case for potential damage would result if the missile left the turbine in a near vertical condician.
In this case, the missile on its return fall has an impact velocity practically the same as the exit velocity if there is not obstructions. Thus, the analysis assu=ed that the worst case missile could penetrate 26.1 inches of concrete.
It should be realized, however, that before a missile can cause da= age to any system or building outside of the turbine building, it must first penetrate the turbine generator building roof steel, roof decking, and enter through another roof structure. Resistance thrcugh these roofs as well as resistance through the atmosphere were neglected in that response.
We have again reviewed this matter and find that our earlier evaluation is still appropriate and conservative for disc 41.
We conclude that a turbine missile can have =inimum af fect on safety related systems.
We have also looked at the affect of a missile on non-safety systems.
We have concluded that a missile could net prevent safe shutdown of the plant. We generally conclude that the breaking of secondary containment is of most concern; however, we conclude that safe shutdown can be reached and maintained without any significant release of contamination to the environs. We also believe that temporary repair of secondary containment breaching from the missile can be completed within about 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
The following is a general description of our recent review:
Electrical Power Systems The station electrical power systems consist of the nor=al main and startup A-C pcwer systems, the ere*gency A-C pcwer system, 125 and 230 volt D-C power system, 24 volt D-c power system and the 113/230 volt uninterruptible A-C power system. The prcbability of the damage and the effect of a missile hitting each part of the above system is discussed as follcws:
The normal station service transfor=er will, of course, be inoperable because of a unit trip. Thus, a missile impact on this transformer
. will have no effect on the plant. Power would nor= ally be supplied by the startup transformer.
The startup transformer is separated from the e=ergency transformer.
If one of the transfor ers is damaged from a =1ssile, the other transformer would be used.
If both transfor=ers were damaged, two independent and separated diesel generator units contained in concrete structures are available to supply safe shutdown pcwer.
Only one unit is needed.
The electrical buses and switchgear for the normal and startup station service are not protected from missile damage. However, they are not needed as the buses and switchgear for the emergency transformer and the diesel generator are contained in the control building which can withstand a missile. The two critical switchgear roces are also separated such that damage in one room should not create problems in another room.
All D-C power syste=s are in lower levels of the control building and the reactor building such that they cannot sustain damage from a missile.
Emergencv Cenerators The two diesel generators providing backup pcwer to the critical system in the plant are protected in a concrete structure that will withstand the turbine =issile i= pact. The fuel to the diesels is contained in two underground tanks that can also withstand a missi.'e impact.
Service Water The service water pu=ps are contained in a room in the _ntake structure building. The roca has an 13" reinforced concrete slab roof. With the energy that is expanded in the missile leaving the roof of the turbine building and entering the roof of the intake structure building, it is doubtful that the missile vill penetrate the 18" reinforced concrete roof; however, if it did penetrate the roof, multiple damage is limited due to the physical separation and spacing between the various pu=ps, strainers and associated piping. Since the largest missile section is postulated to be approximately 2 feet in diameter, potential da= age is limited to one compenent.
In addition, the piping is supported such that it will withstand an impact of at least 3G.
HPCI, RCIC, ADS, LPCI, RER These systems are all contained in lower levels of the reactor building and cannot be damaged from a missile from the turbine building.
A disc missile cannot directly impact the walls of the reactor building because of the turbine building shield wall. A lobbed missile could not penetrate through floors above these systems.
S tandby Liquid Contol System The standby liquid control system is located in the 976' level of the reactor building.
It is protected by a reinforced concrete floor above the rocm that ranges frem 12" to 18" thick. There are redundant pu=ps but only one tank and a co= mon header.
It =ay or may not survive a
=issile impace..
The stancby liquid control system is a backup for the shutdown provided by "he control rods.
Its loss will not affect safe shutdown of the plan
- Standby Cas Treatment System The standby gas treatment units are protected from a turbine missile by a reinforced concrete floor above the room ranging f rom 12" to 18" thick. The rwo units are separated approximately 10 feet. Thus, simultaneous damage of both units is highly unlikely.
Scent Fuel Pool A missile could be lobbed through the reactor building roof and into the fuel pool. Although some fuel and rack damage may occur, it is not expected that any significant structural damage would occur.
The pool would definitely retain its capacity to contain water.
CRD System All components of the control rod drive system are contained in the lower levels of the reactor building and cannot be danaged from a turbine missile.
Primarv and Secondarv Containment A turbine missile cculd penetrate the roof of the reactor building and thus, destroy the ability to maintain 1/4" of water negative pressure in this building.
Even though secondary containment could not be assured, the ventilation system would most probably continue air ficw into the hole rather than out the hole.
A turbine missile could not penetrate primary containment. Two layers of concrete shield plugs each 36 inches thick protect primary contain-ment from above the reactor. The reactor building walls protect primary containment from the side.
Reactor Bu11 dine Ventilation The upper portien of the reactor building ventilation could be damaged by a turbine missile; hewever, this would not have an affect on safe shutdcwn.
The standby gas treatment system would still be available.
Turbine Buildinz Ventilation The turbine building ventilation is vulnerable to a turbine missile; however, activity within the building is low and ventilation loss would not create a significant problem. The turbine building venti-lation is not needed for safe shutdcun.
Condensate and Feedwater The cutside condensate storage tank is vulnerable to missile damage; however, it does not provide an essential or necessary function in an emergency. We have two emergency condensate storage tanks in the basement of the control building. These tanks provide a supply for HPCI and RCIC.
The condensate boostar and feedwater pumps are protected frca a turbine missile. They are not needed for safe shutdcwn but do provide a water
9
. backup source in the event other emergency sources are not available.
The water supply for these pumps, the condenser hot well, may be lost during a turbine incident; however, the water will be contained in the turbine building lower level.
Fire Protection Ihree fire pumps are contained in a room in the intake structure that has an 18" reinforced concrete roof. The pu=ps are separated such that missile penetration should not damage all pumps. A branch line of the fire protection system in the turbine building or an auxiliary building may be destroyed; however, this line can be isolated and adequate spare hoses are available to provide fire protection to any area of the plant.
MC Sets The motor generator sets are located in the reactor building and are protected by the 12" to 18" reinforced concrete floor from above. They are also separated by distance such that it is highly unlikely that both units would be da= aged if the missile penetrated the floor area. These units are not needed for safe shutdown of the plant.
Air System Instrument and service air are not essential for safe shutdown of the reactor; however, they are useful for continued plant shutdown. The air compressors are in the control building basement and are protected from a turbine missile. A branch air line in the turbine building, shop, and water plant could be broken by a missile; however, this broken line could be quickly isolated.
Radwaste Building and Augmented Radwaste Building In many areas, these buildings will withstand a missile impact from above; however, there are areas where the missile may penetrate a roof. There is no equipment in either building that is required for safe shutdown of the plant.
There may be some minor release of contanination as a result of loss of building integrity and venti-lation integrity.
RBCCW or REC Svstem The reactor building equipment cooling system is mostly protected frem a turbine missile; however, the system does have a surge tank that is located in the fourth floor of the reactor building and is protected only by a 12" to 18" thick floor above.
The capability of introducing service water into the critical headers will assure cooling capability for the system, and loss of the tank will not affect safe shutdown.
Control Room The control room is protected with a 24" slab of reinforced concrete as - roof.
Although our worst case analysis ind.cated a fragment from disc 14 wo ld penetrate 26.1 inches of concrete, we also stated that a fragment from disc 16 could penetrate only 22..I inches of concrete. A
=issile from disc #1 vould have even less energy.
Thus, we have con-
cluded that disc ill could not damage the control room or its contents such that a safe shutdown could not be made and maintained.
Reactor Protection, Neutron Monitorint, and Radiation Process Monitoring Svstems These systems are located in the Control Room and lower floors of the reactor and control buildings.
A =issile would not damage these systems.
Area Radiation Monitoring This system is located throughout the plant.
Some sensors for this system could be damaged by the missile, however, this system is not required for safe shutdown of the plant.
Cire Water and Screen Wash Svstems The cire water rtmps and the screen wash pumps are in the intake struc-ture in a part of the building that could be penetrated by a turbine missile. Mcwever, these pumps are separated such that no more than one or two pumps should be damaged by one missile. The cire water pumps are not needed during plant shutdown. One of the 4 sparger or screen wash pumps would be adequate for service water pump screen cleaning. The water for service water pumps could also be routed through a cire water bay and screen wash may not be required.
Heatinz Boilers Two oil-fired heating boilers provide auxiliary steam and heat to the plant. They are separated such that a missile should not destroy both units; however, in event both units were destroyed, steam would not be needed for an extended period of time.
A portable auxiliary boiler could be brought to the station.
B.
Discuss procedure for responding to =issile damage to the reactor building roof.
Resconse A special instruction letter was issued describing the methods of repairing a hole in the reactor building roof if a missile from the turbine were to penetrate the roof.
Calculations indicate that less than one curie of fission gas, primarily Krypton-85, would escape frem each damaged bundle. We esti= ate that up to 25 fuel bundles could be damaged by the missile. The 25 curies of Kr-85 released would produce a maximum concentration of ab;ut 3x10-6 ue/=1 on the refueling floor.
This gas would be dispensed quickly through the ventilation system.
The release of the 25 curies of Kr poses an insignificant risk to public health and safety.
C.
Discuss the status of the CNS Emergency Plan and the Nebt aka State Emergency Response Plan as they relate to present NRC req, :ements.
Resoonse NPPD submitted a revised CNS Emergency Plan January 11, 1980 which confor:s to the recc==endations of Regulatory Guide 1.101 and which incorporates the NRC Action Level Guidelines, NUREG-0610.
CNS recently had a visit by the NRC Emergency Planning Review Team and no significant defects in planning were discovered.
CNS successfully exercised the Emergency Plan December 4, 1979 in a
=ulti-state drill which was observed by FEMA and NRC observers with no significant defects noted.
The Nebraska State Emergency Response Plan is presently concurred in for another nuclear facility in the state and NRC concurrence for CNS is expected.