ML19325E141
| ML19325E141 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 09/28/1972 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| 5377, NUDOCS 8911020075 | |
| Download: ML19325E141 (4) | |
Text
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1 NSID NORTHERN STATES POWER COMPANY
.s M IN N E A PO LIS, MIN N E S OTA 5 5401 Regulatory No Cy.
September 28, 1972 i
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Mr. Donald J Skovbolt V
Assistant Director for Operating Reactors 6
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Directorate of Licensing United States Atomic Energy Commission gg,
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Washington, D C 20545 2
00T 2 1972 e-h REGULA7 dry 3
Dear Mr. Skovholt:
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MONTICELLO NUCLFAR GENERATING PIANT-g c
Docket No. 50-263 License No.. DPR-22
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In response to your inquiry of August 3,1972 relating to the flooding incident at Quad Cities Unit 1, we have investigated the potential for like flooding at Monticello.
In addition, we have evaluated Monticello in accordance with your y
request.
In general, no significant flooding hazard exists in either the reactor build-i l
ing or the turbine building above reactor building grade level, elevation 930' mal. Of primary concern, however, is a potential breach of the circulating water system below grade. The Mmticello circulating water system utilizes -
rubber expansion joints at four locations on each of the two lines. ' Three of i
these joints are in locations potentially vulnerable to flood damage; i.e.,
the circulating veter pump discharge located in the intake structure, and the condenser inlets and outlets located at elevation 911' mal in the turbine tuilding. The probability of failure of one'of these. joints,.via the mechan-ism reported at Quad Cities Unit 1, does not exist, since the Monticello cir-culating water system does not have a flow reversal capability.
If a break in j
a circulating water line should occur, however, there are presently no positive barriers which could localize flooding.
It must be assumed that water.vould f
propagate to d.her areas in the turbine building basement. Some emergency load centers are located on the 911' elevation.
In all cases, however, load centers for
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the redundant systems are provided on elevation 931. There is no possibility of common-mode failure of redund' at systems occurring as a result of flooding from the circulating water system.
The intake structure is connected to the turbine buildinc by a Class I piping tunnel at elevation 916' mal. The RHR Service Water piping extends through a slot cut, at elevation 924', through a Class I barrier near the turbine build-ing end of the pipe tunnel. With a cir" Gating pipe break,-the water level in the turbine building has been conservatively estimated to increase at a rate
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of approximately one foot per minute assuming both circulating water pumps con-tinue in operation. 'Ibe flooding would have to continue unabated for more th
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13 c:.inutes without detection before it would begin to spill into. the intake I
stmeture side of the barrier. At present, the sump in the condenser hot well area is equipped with a level alarm that would prompt immediate operator l
In addition, consideration is being given to upgrading the investigation.
A review of the need for i
capability for gross flood detection in this area.
this capability.is currently in progress.
Some safeguards cooling water equipment is located on the operating floor of.
ne circulating water pumps are the intake structure at elevation 919' mal.
located in a bay (floor elevation 899' ms1) open to the Ismainder of intake As was noted earlier, rubber expansion bellows are located at the st meture.
As the system is currently being operated, if one of these pun:p discharge.
bellows failed, flood levels in the pump bay are limited by the river level When the system is run closed cycle, which is nominally at elevation 910' mal.
however, flood levels due to this type of break are increased but are limited to the maximum vater level in the cooling tower basin, elevation 918' mal.. In addition, since the circulating water pumps will be flooded before other pumps in the intake structure and vill trip, flow vill be gravity forced and the level vill increase slowly. An overflow is provided in the pump. house struc-l ture at elevation 9168 Lines from these Major Class II piping systems are summarized in the FSAR.
systems are located in many areas of the plant includin6 areas housing essen-tial equipment. A review of these systems has been made. In general the lines are isolatable and are not of sufficient capacity to cause more than localized flooding damage; in no case are there situations where common mode failures of redundant systems could reasonably be expected.. Investigations are currently underway to identify means of further reducing the potential l
for adverse interactions with essential equipment. Lines are being treated j
on an individual basis. Of particular interest is the condensate storage and transfer system.
J Class II lines from the condensate storage tanks are extended to all ECCS com-The capacity of the tanks is sufficient to flood any.one of the partments.
Investigations are currently in progress to determine the j
ECCS compartments.
feasibility of reanalyzing the condensate transfer line sections for the forces of a Design Basis Earthquake with the intent of eventually upgrading them to Both MIR rooms are pzesently equipped with high water lev-Class I equivalent.
ele probes which indicate water levels in excess of approximately one foot.
The potential for coincident flood-
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I Annunciation is made in the contzel room.
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L ing is extremely lov vith the layout of the torus cavity and ECCS rooms at I
The ECCS equipment are housed in separate individual rooms and l
Monticello.
are not freely communicated with the torus cavity.
It is our conclusion that common-mode failure of redundant equipment vill not Bis review has identified j
occur as a result of failure of Class II equipment.
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' means of improving protection levels. Plant operators vill be briefed on present flooding procedures.
It is our conclusion that events of this type are of sufficiently low probability to pose no significant hazard to con-tinued operation.
Yours very truly,
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t L 0 M1yer, P.E.
Director of Nuclear Support Services LOM/IWJ/br ec: B H Grier ii-V i
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AEC DISPRIBlfrION FOR PART 50 DOCKET MATERIAL CONTROL NO: 5377.
(TEMPORARY FORM)
FIIz FRON:
DATE OF DOC:
/
Nortis rn States Power Company
.f_g Minneapolis, Minnesota 55401 9 M-72 10-2-72 x
L. O. Hayers To:
D. J. Skovholt I signed 39 SENT LOCAL PDR X
CIAS3:
,hPROPINFO INPUT NO CYS REC'D DOCKET NO:
40,
50 263 DESCRIPTION:
ENCLOSURES:
Ltr re our 8-3-72 itr... furnishing results of investigation regarding potential flood at Monticello.... (re.. Quad-Cities Unit i 1 flooding incident).
NOTE: *PLEASE CIRCUIATE - INSUFFICIENT COPIES RECEIVED FOR FULL DISTRIBUTION.
P-r oxzS geen. Neue.r G.nera**"*
ACKNOWLEDGED 00 NOT REMOVE FOR ACTION /INFORMATION w
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