ML20024G827
| ML20024G827 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 07/29/1974 |
| From: | Snell J US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML20024G826 | List: |
| References | |
| NUDOCS 9104300454 | |
| Download: ML20024G827 (6) | |
Text
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a UNITED STATES AT0!!IC ENERGY C0!D11SSIO!!
SATETY EVALUATION BY Tl!E DIRECTORATE OT LICENSI!!G DOCEET No. 50-263 110NTICELLO NUCLEAR GENERATING PIANT ANALYSIS OF Ti1E CONSEOUDiCES OF llIGH ENERGY PIPING FAILURES OUTSIDE CONTAI!O!ENT INTRODUCTION On December 18, 1972, and January 16, 1973, the Atomic Energy Cortnission's Regulatory staf f sent letters to Northern States Power Company requesting a detailcd design evaluation to substantiate that the design of the Monticello Mu lear Generating Plant is adequate to withstand the effects of a postulat ed rupture in cny high energy fluid piping system outside t he primacy centainuent, including the doubic-cnded rupture of the a rg u line in the main stor, ano feedvater system.
It was further requested thet si tne rerelts of the eunluetion indieeted ther chanP,ea in the design were necessary to asr.ure safe plant shutdown, information on these design changes and plant modifications would be required.
Criteria for conducting this evaluation were included in the letters.
A meeting was held on February 5,1973, to discuss the information aircady availabic on the Monticello Plant design concerning postulated pipe ruptures, to discuss the criteria, and to assess those areas where additional inf ornation was required.
In response to our letters, a report concerninr postulated high energy pipe ruptures outside containment vcs filed by Northern States Power Company uith Ictter dated September 7, 1973. A subsequent letter from Northern States Power Company dated
!! arch 8,1974, answered additional questions in a letter from the staf f dated January IS, 1974.
EVALUATION Criteria A sumrary of the criteria and requirements included in our 1ctter of December 18, 1972, is set forth belcm 9104300454 740729 PDR ADOCK 05000263 p
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protection of equipment and structures necesr.ary to shutdown the reactor and maintain it in a safe shutdown condition, l
and unrelated single active failure of assuming n concurrent should be provided from all ef fects resulting prot ec t ed equipment,
f rom ruptures in pipes carrying high energy fluid, where the temperature and pressure conditions of the fluid exceed 200'r and 275 psic, rerpectively, up to and including a double-ended rupture of such pipes.
Breaks should be assumed to occur in those locations specified in the " pipe whip criteria".
The rupture of fects to be considered include pipe whip, structural (including l
the ef f ects of jet impingement), and environmental.
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In addition, protection of equipment and structures necessary to shutdown the reactor and naintain it in a safe shutdown condition, assuming a concurrent and unrelated singic active f ailure of protected should be provided f rom the environmental and structural equipnent, ef f cet s (including the ef fects of jet impingement) resulting f rom a ain2.le open crcck at the most adverre location in pipes carryin?
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fluid routed in the vicinity of this equipment. The size of the
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cracht thould be assured to be 1/2 the pipe diameter it leimth ani 1/2 the wall thickness in width.
Hinh Enerry Ssstem Our evaluation included the following piping systems containing High Energy fluids:
Main, Extraction, and Auxiliary Steam Systems Feedvater System Condensate Systen Reactor Core Isolatien Cooling System (RCIC)
High pressure Coolant injection System (HpCI)
Reactor Water Cleanup System (RWCU)
Residual Heat Renaval System (RHR)
Sampic Lines (Environmental Ef fects Only) fyrcan er Systern Af fected by Hich Enercy pipe Breakn An evaluation was conducted of the ef fects of high energy pipe breaks on the f ollouing systens, cotponevic, and structures, which would be y
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neccesary (in various combinations, depending on the effects of the break) to safely shutduen, cooldown, and maintain cold shutdown conditionst j
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General J
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Control Room i
Control and Instrument Cabics and Tunnels 2.
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Elcetrical Distribution System j
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T.mergency de Power Supply (batteries) a 5.
Emergency ac Power Supply (dicscis) j Heating and Ventilation Systems (needed for long-term occupancy i
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to maintain the reactor in safe shutdoen condition)
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Reactor Control Systems opd associated instrumentation 3
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Cooling and Service Uater Systens I
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ECCS componcntr, j
1 Specific Aleno of Concern l.
ell The applicant hac previded the recults of his examination ot' i
postulated safety related high energy line break locations and evaluated We have reviewed all of this information, the break consequences.
including the folle.dng specific areas of concern where the potential might be severe or where specific corrective action would l
consequenced further ase. ore safe cold shutdown of the plant.
1 Prersurication )
a.
Compnrt ro nt I
Large pipe breake, including the double-ended rupture of the largest pipes in a system, and crall leakage cracks up to the l
design basis size have been considered for the main stcan tunnel, i
the turbine building, the ECCS roots, and the valve compartmentr..
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In the condenser compartment, a failure of a main steam line would pressurize the condenser compartmegt to 1.4 psig maximum 1
with a vent area of approximately 500 ' f t'.
The vent area is i
sufficient to prevent damage or loss of safety equipment and to keep the peak pressure well belou the 8.4 psig design.
l In the main steam tunnel, the ef fects of a main steam lita break
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t were considered as the design cases.
The resultant pressure was i
calculatcc 'e inercase tc 10.2 psig.
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f 2 for the main steam chase is provided
,7hc vent area of 180 ft by ventilation ducts, doorways, and bicuout pancis between the tunnel and above the turbine operating deck.
The vent area is l
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sufficient to hoop the peak pressure beloa the design of 13.4 l
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psig.
1 A failure of the Reactor Core Isolation Cooling System (RCIC) 1 steam line could result in the loss of one emergency service J
I:ven if a single f ailure disabled the redundant water line.
3 line, emergency incasures of manual connection could be accomplished and allow cooling water to required componenta in titte to enable a safe shutdown of the plant.
An llPCI steam line failure in the 11PCI compartment could result i
in discharge of steam until automatic isolation is achieved.
l A maximum pressure occurring in the compartment has been cal-l culated to reach 0.9 psig which is below the structural capabilitics i
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of approximtely 2.0 psig, i
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A postulct ed IEU high encrgy line f ailure in the ciconup r.ystem i
pu:r.p or h a t enchann r compartments results in a single-ended A check valvs in the piping, fcilurc until inlat h is achioved.
i upstream connection into the feedwater piping would prevent extensive
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l bachflow.
Tne calculated pressure resulting from a pipe failure would be 0.6 pr.ig in the heat exchanger room, and 0.2 psig in the 4
The minimum design capacities of these compartraents l
pump compartment.
are 16.0 psi for both the heat exchanger and pump compartments.
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Tine PhQ The reactor and turbine building areas were considered for the ef fect of pipe whip and jet impingement from the taain steam feed-i vater and condensate lince.
The steam tunnel has been dceigned i
vith thich reinf orced concrete capabic of uithstcnding large static and dynamic Joads. The reinforced concrete steam tunnel in which the main steam and feedwater lines are routed from the primary I
contair.mont to the turbine room is s Jbjected only to the loads j
of the piping and a liva load from che floor on toi, of the tunnt:
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roof. A whipping taain steam or fredwater line in the main stean tunnel could cause rupture of thr.IIPCI, RCIC turbine steam inlet j
l lines and the RUCU lino.
Ilowever, loss of these lines would not itapair safe shutdown of the plant.
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l A jet impingement from a broken feedwater line in the area of j
vital motor control centers (!!CC) could cause some loss to redundant i
i safeguarb, (quipment b failure of the mer.rantne floor. The l
addition el c.dditional piping restraints in this area will reduce the forces which impinge on the mezzanine floor and thereby i
l protect the MCC.
Rupture of condensate piping would not cause a hazard to safeguards 3
equipment and would only cause minor flooding. The high energy t
line to the llPCI turbine inlet is routed above the torus, therefore l
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rupture of this line may deform the torus, llowever, the torus l
l would not rupture and would remain functional.
4 Other high energy lines such as the sample lines at.d reactor water i
j cicanup lines are locatett such that their rupture would not cause i
damage to the torus.
A whip of either the RCIC or HPCI steam line outside the torus compartment could damace system isolation i
valves on the HPCI or MCIC lines.
llowever, the resultant damage wE n N h pr.h r G shutdown of the unit.
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The main control roon in physically isolated from all high energy ifnco. Neither the control room equipment nor its ventilation i
system will be affected ty environmental effects caused by a
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rupture of a high energy line, f
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Environmental Tffeets_
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l Componenn and equipt ent were analy cd and checked for possible j
adverse environrental effects which could be caused by the rupture j
of a high ene*gy line. Adverse temperature, pressure,'and humidity vere the parimeters which were ured in the evaluation-of safety j
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related equipment.
We have reviewed the licensee assessment of i
j the consL]uences of environmental effects on safety.related j
j equipment. We find that safety related equipment has.been designed 3
to limito In ca. cess of postulated conditions which could arise trou f
the rupture of a'high energy line.
Modifications _
Modifications to the existing facility are currently being undertaken by Northern States in order to assure that the design will have l
adequate r,afety ticrnine in the event of a high energy line rupture f
outcide the containment. These modifications-are to be complete prior to restart of the plant following the current refueling outore, currently scheduled to end on or about.May 15, 1974.
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Additional piping restraints are being installed in the areas of il or near the MCC where a jet impingement could the mezzanine cause a loss of redundant safeguards equipment. With the addi-i tion of the pipe restraints, the possibility of jet impingement
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and pipe whip hau 'een reduced and provides reasonabic assurance that redundant saf eguards equipment will not be lost.
CONCLUSIONS i
l On the basis of this review of the information submitted to us and on discussioas with Northern States power, we find that their assessment j
of the consequences of high energy line failures outside containment is acceptable. Some modifications are necessary. We have concluded that the potential consequenceo of these postulated high energy pipe i
f ailures, following the modifications, will not prevent the capability to achieve safe cold shutdown conditions consistent with the single f ailure and redundancy requirements as describad in our letter of j
December 18, 1972.
Tne licens;e has stated that the codifications were completed prior to With the icturning to operation from the spring 1974 refueling outagc.
completion of these modifications, there is reasonable assurance that the health and saf ety of the public will not be endangered by continued j
operation.
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James C. Snell s
Operating Reactors Branch #2 j
Directorate of Licensing i
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Dennis L. Zicmann, Chief j
Operating Reactors Branch #2 Directorate of hicensing
' iPs Date:
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