ML20133C525
| ML20133C525 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 12/27/1974 |
| From: | US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML20133C497 | List: |
| References | |
| NUDOCS 8510070391 | |
| Download: ML20133C525 (7) | |
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SUPPLEMEhT TO THE SAFETY EVALUATION BY THE DIRECTORATE OF LICENSING U. S. ATOKIC ENERGY COMMISSION DOCKET NO. 50-213
, CONNECTICUT YANKEE ATOMIC PO'w'ER COMPANY HADDAM NECK PLANT I
l DEC 27 574 l
8510070391 851004 PDR ADOCK 05000213 P PDR
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5-1 5.0 HICH ENERGY LINE BREAK OUTSIDE OF CONTAITNENT 5.1 General On December 18, 1972, the Atomic Energy Commission's Regulatory
- staff sent a letter to Connecticut Yankee Power Company requesting a detailed evaluation of the consequences of a postulated rupture of any high energy fluid piping outside the primary containment, including the double-ended rupture of the largest line in the main steam or feedwater system. It was further requested that if the results of the evaluation indicated changes to the facility were necessary to assure safe plant shutdown, information on the design changes and plant modifications would be required.
The licensee responded on June 28, 1973, with additional information filed on October 26, 1973 and February 14, 1974. This Safety Evaluation '
presents the results of the staff's review of the licensee's submittals concerning high energy line failures.
5.2 Discussion i The criteria and requirements used by the licensee and the staff are j summarized as follows:
- 1. Protection of equipment and structures necessary to shut down the reactor and maintain it in a safe shutdown condition, assuming a concurrent and unrelated single active f ailure of essential equipment, should be provided from all effects of ruptures in pipes carrying high energy fluid, up to and including a double-ended rupture of such pipes, where the service temper- ,
ature and service pressure conditions of the fluid exceed i 200*F and 275 psig. Breaks should be assumed to occur i=
those locations specified in the " pipe whip criteria." Ine rupture effects to be considered include pipe whip, structural (including the effects of jet impingement), and environmental.
- 2. In addition, protection of equipment and structures necessary to shut down the reactor and min min it in a safe shutdown condition, ass"-d"g a concu rent and unrelated single active i
failure of esse =tial equipment, should be providec from the enviremental and s:ructural effects (including the effects of jet iz:pingemen ) resulting fro = a single open crack at the most adverse location in pipes nor ally carrying high energy fluid routed in the vici=ity of this equipment. Tne postulated size of the cracks was either 1/2 the pipe diameter in length and 1/2 the vall thickness in vidth (critical crack size) or equivalent pipe flow cross section in area.
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5-2 The Connecticut Yankee Plant is a single unit pressurized water reactor that utilizes a reinforced concrete containment which contains the entire reactor cooling system, including the steam generators. The licensee evaluated the following piping systems
- that contain high energy fluids and are outside containment:
Main Steam to Turbine Reheaters, and Steam Bypass, Auxiliary Steam in Turbine Building, Auxiliary Steam in Auxiliary Feedwater Pump Enclosure, Feedwater, Auxiliary Feedwater in Auxiliary Feedwater Pump Enclosure, Condensate, Turbine Extraction Steam, Feedwater Heater Drains, Turbine Moisture Separator Drains, Turbine Reheater Drains, Auxiliary Steam Header in Primary Auxiliary Building, Charging Lines in Primary Auxiliary Building, Bleed (Letdown) Lines in Primary Auxiliary Building, Steam Generator Blowdown Lines in Primary Auxiliary Building, and '
Safety Injection Lines in Primary Auxiliary Building.'
The Licensee's evaluation postulated breaks at all locations specified
) by the AEC criteria for piping break locations. The licensee considered effects of pipe whip, jet impingement, and environmental consequences as required by AEC criteria.
It was found that a main steam line break inside the turbine building could result in loss of the switchgear room and control room from steam envire =t or fro = impact of a whipping pipe. The protection of the control room and switchgear room from postulated breaks by pipe restraints and barriers is "mracticable. Physically, present plant layout of main stea= piping within the turbine building prohibits installation of pipe whip restraints due to both space N. liciations and the inability of non-seie-ic structures to withsand the postulated blowdown loads. The licensee chose to accept the loss of the turbine building, including switchgear roon, control roo=, and main feed pumps and to perform shutdown by alternate methods. As an additional measure of protection against loss of the control roc =
and switchgear roo=, the staff determined that for certain postulated stea= line break locations in the turbine building an augnented inservice inspection progra= should be established in order to provide further assurance of line integriry du-ing the operating life of the facility. Technical Specifications were added to the existing Technical Specifications for the Connecticut Yankee Plant for this purpose.
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5-3 Environmental ef f ects could cause the loss of the switchgear room and control room from certain other line breaks within the turbine building; namely, the feedwater system, extraction steam system, and possibly the three drain systems within the turbine building. Just as with the steam line breaks in this location alternate methods must se relied upon to provide safe shutdown and cooldown in the event that the lines f ail.
The heating steam system was also analyzed for possible safety related consequences in event of pipe failure. Three possible problem
'* areas in the bu11 sing were identified and the following corrective modi-fications were performed which removed the potential problems:
- l. A heating steam line in the reactor containment cable penetration vault which could cause loss of several safety related controls upon failure was removed.
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- 2. Impingement shielding was provided for cable trays near the west end wall of the Primary Auxiliary Building, and also for cable trays over the service building roof. In both locations stea= line failure could have effected critical cables before the shielding was installed.
It should be noted that alternate shutdown methods were rvailable
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before any of the modifications resulting from the heati 3 steam system analysis were performed.
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Analyses of a possible steam line break or feedwater pipe break in the main steam non-rariirn valve area showed that loss of the auxiliary feedwater pumps could occur, and this would elirinate a possible cool-down method. However, safe shutdown could still be accomplished by nor=al na-hads and cooldown could be accor.,J aubed by fee,r coclant directly to the reactor coolant syste= dat h the emergency core cooling systa=. The licensee vill TCcii e . additional me hod of
, cooling under this eventuality, boverc., % i.ns =114ng a motor driven anvd 14 =7 feed pu=p. Tne pu=p vill be of the same size as the present stea= turbine driven auxiliary feed pumps, and will be safely located at ground level in an enclosure beside the demineralized water storage tank. T.lectric power supply vill be fro = the diesel genera: ors.
The licensee identified 3 independen; methods of placing the plan:
in a cold shutdown condition which are now avs'1 =hle. Essentially these methods made use of:
- 1. The motor driven feedwater pu=ps and normal power supply.
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- 2. The steam driven auxiliary feedwater pumps and emergency power supply.
- 3. The emergency core cooling system and emergency power supply.
The licensee found that at least one method of safe shutdown /cooldown was avai.lable for every postulated high energy line break, even assuming the unavailability of offsite power. The addition of the motor driven auxiliary feed pump will provide at least two independent methods of safe shutdown /cooldown for every postulated high energy line break assuming the unavailability of offsite power.
The above procedures can be implemented from the control room, or otherwise can be implemented manually if the control room is uninhabit-able, such as might be the case in the event of a failure in the turbine -
room. In order to provide an alternate central control location the licensee will install an emergency shutdown panel, supplementary
' switchgear and batteries in the enclosure for the diesel generators.
This will allow centralized control to accomplish safe shutdown /
cooldown of the plant independent of the control room and switchgear rooms. Critical power and control cables serving the new emergency control panel will be routed around environmentally hazardous areas.
) All essential safe shutdown /cooldown controls will be located on the
, emergency panel. Emergency com=unications will be provided.
The licensee also evaluated pressurization as a consequence of high enerEy line failure as required by the AEC criteria. He identified three buildings containing high energy lines that required analysis to determine if rupture could cause failure of the buildings. lhese structures are:
- 1. Tne turbine building.
- 2. Tne enclosure for the two steam driven a'w414=7 feedwater pumps.
- 3. The primary amrf14 ary building.
Peak pressures in these buildings were calculated and were found to be sufficien-dy low that no structural damage would result except in the case of the turbine building. In no case would the pressurization of the buildings affect the safe shutdown of the plan. 2During the winter the turbine building is equipped with only 700 f t of vent ares, and double ended rupture of the 36 inch steam pipe manifold at 915 psia would produce a maximu= pressure difference of 1.39 psi across its walls.
5-5 The turbine building siding consists of insulated aluminum panels.
Sections as large as 20 ft by 20 ft could .become detached through tearing at the bolt type fastening since this construction could not withstand differential pressure across the wall in excess of
.75 psi. No safety related structure or equipment could be reached or penetrated by detached air-borne turbine building siding panels with the possible exception of the circulation water screen and pump house.
These sections of light aluminum panels would have insufficient energy to penetrate the pump house (150 feet from the turbine building) and cause damage to any of the four (4) service water pumps.
The licensee also considered the consequences of flooding as the result of a postulated high energy line break. The breakage of a high pressure water-carrying pipeline could damage certain vital motors used for shutdown /cooldown. Not more than one of the several available methods could conceivably be eliminated from service at one time through this type of failure, however.
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Modifications have been accomplished to mitigate some of the conse-quences of pipe f ailure. In addition the licensee has co.__itted to the addition of a motor-driven emergency-powered auxiliary feedwater
') , pucp and emergency control panel which would permit centrally-located control to accomplish safe shutdown and cooldown despite the loss of the switchgear room and control room. With these two modifications, two independent means of acco=plishing safe shutdown /cooldowr. vill exist for every postulated high energy line break, even assuming unavailability of offsite electrical power.
5.3 Conclusions .
Co=pletion of these two modifications is scheduled for the next refueling outage presently expected to occur in Spring 1975. The licensee has initiated an augnented inservice inspection progra= which monitors high stress stea= line vs.1ds in -le turbine roon vbose failu e could threate= the control room or switchgear roo=. The requirement for augmented inse_vice inspection has been incorporated into the Technical Specifications.
Eased upon the staff's review of the licensee's submittals of his evaluation of high energy line breaks for the Connecticut Yankee Flant,
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5-6 the following conclusions are made regarding the effects of a potential rupture in any high energy fluid piping system outside the primary containment:
- 1. At least one reactivity control system would always be available for safe shutdown of the reactor.
- 2. Shutdown heat removal capability would be available adequate to remove core decay heat.
- 3. Emergency diesel-generator power would be available for decay heat removal under all accident conditions considered herein.
. 4. Compartment overpressurization cannot affect any equipment necessary for safe shutdown of the plant.
Upon completion of scheduled plant modifications remote central control for safe shutdown and cooldown will be available for all conditions in which dhe control room is not habitable and at least two independent methods of accomplishing cooldown will exist for every postulated high energy line braak.
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Therefore, the staff concludes that upon completion of scheduled plant modifications the Connecticut Yankee Plant can withstand the consequences of a rupture in any high energy fluid piping outside containment without loss of the capability to initiate action and maintain the plant in a safe shutdown condition.
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