ML19347C533
| ML19347C533 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 12/13/1973 |
| From: | Chipman G, Schemel R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19347C532 | List: |
| References | |
| NUDOCS 8011200208 | |
| Download: ML19347C533 (4) | |
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UNITED STATES ATOMIC ENERGY C0FDiISSION SAFETY EVALUATION BY THE DIRECTORATE OF LICENSING YANKEE ATOMIC ELECTRIC COMPANY DOCVET NO. 50-29 RUPTURE OF HIGH ENERGY LINES OUTSIDE OF CONTAINMILNT INTRODUCTION
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On December 18, 1972, the Atomic Energy Commission's Regulatory staff sent a letter to Yankee Atomic Electric Company requesting a detailed evaluation to substantiate that the Yankee Nuclear Atomic Power Station can withstand the effects 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 wcs further requested that if the results of the evaluation indicated changes to the facility were necessary to assure safe plant shutdown, informatica on the design changes and plant modifications would be required.
Criteria for performing this evaluation were included in the December 18, 1972 letter and in a January 17, 1973 letter containing errata to the criteria. A meeting was held with the licensee on January 31, 1973, to discuss postulated pipe ruptures and the criteria, and to assess those areas where additional detailed information was required.
In response to our letters, a report containing information concerning postulated high energy line failures outside containment was filed by Yankee Atomic Electric Company on July 2, 1973, with additional information filed on September 12, 1973. This Safety Evaluation presents the results of our review of the licensee's submittals concerning high energy line failures.
DISCUSSION The criteria and requirements used by the licensee and the staff are sum-
=arized as follows:
1.
Protection of equipment and structures necessary to shut down the reactor and =aintain it in a safe shutdown condition, assuming a concurrent and unrelated single active failure of essential equip-ment, 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 temperature and service pressure conditions of the fluid exceed 200*F and 275 psig.
80 n200 208
4 Breaks should be assumed to occur in those locations specified in the " pipe whip criteria".
The rupture effects to be considered include pipe whip, structural (including the effects of jet impinge-ment), and environmental.
2.
In addition, protaction 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 failure of essen-tial equipment, should be provided from the environmental and struc-tural effects (including the effects of jet impingement) resulting from a single open crack at the most adverse location in pipes nor-mally carrying high energy fluid routed in the vicinity of this equipment.
The postulated size of the cracks was either 1/2 the pipe diameter in length and 1/2 the wall thickness in width (cri-tical crack size) or equivalent pipe flow cross section in area.
Yankee Nuclear Generating Station is a single unit pressurized water reactor that utilizes a steel sphere containment elevated 30 feet above the ground which contains the entire reactor cooling system, including the steam gen-erators.
The licensee evaluated the following piping systems that contain high energy fluids and are outside containment:
Main Steam, Main Steam Turbine Bypass, Steam to No.1 Feedwater Heater, Steam to Air Ejectors, Steam to Primary Jets, Steam to Building Heating, Auxiliary Steam, Extraction Steam, Feedwater Lines, Heater Drain System, Steam Generator Blowdown System Heater Vents, Feedwater Heater Drain Line, Charging System, Turbine Oil System, Moisture Separator Inlet and Outlet Lines, and Waste Disposal from Evaporator to Evaporator Condenser.
Specifically, the evaluation of these systems was conducted by postulating pipe ruptures and cracks at any and all locations of circumferential welds on fittings.
Our review of the shutdown and cooldown systems indicated that the control room, switchgear room, and cable conduits to the containment are vulnerable to steam or feedwater line failures and the Aicensee has identified those modifications necessary to insure their integrity and operability.
Integrity of the control room will be assured by removal and blockage of vulnerable windows and the addition of weather stripping and quick closure devices in control room doors.
Modifications to protect the switchgear room include:
reinforcement of the floor and walls, the addition of jet impingement plates, installation of pipe restraints on the feedwater system, and the addition of switchgear room interior ventilation dampers.
Jet impinge =ent plates are being installed to protect vital cable conduits. Although not necessary for safe shutdown and cooldown of the plant, modifications are being made to the primary auxiliary building to minimize the restricted access to this area following a high energy line failure in the building.
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. Installation of these =odifications is in progress and will be completed i
no later than the next scheduled refueling shutdown (by July 1974). An interin visual inspection program was initiated by the licensee in April 1973 to mini ize the chances of failures until such time as the noted modi-fications can be made.
This inspection program is considered adequate during the short time remaining before completion of the modifications.
Assuming completion of these modifications, our review shows that compart-ment overpressurization is not possible in those areas housing equipment necessary to initiate and maintain a safe shutdown of the plant due to-the type of construction e= ployed.
Also control room habitability is assured at all times for any steam and feedwater piping failure and no radiation or toxic chemical hazard would exist.
Safe shutdown of the plant is accomplished by insertion of the 24 magnetic jack-type control rods and subsequent boration during cooldown through either the Safety Injection System or the Charging System.
Core cooling may be by:
steam to condenser, shutdown cooling, Low Pressure Surge Tank cooling pump and heat exchanger, secondary feed and bleed, and Primary Feed and Bleed.
Assuming completion of the necessary modifications, our tzview of the reactivity control systems indicates that the control rods and the capability to inject boron are not vulnerable to any pipe break outside containment.
However, loss of power to the control rod system would cause full insertion.
Safe shutdown of the reactor is not precluded by any postulated high energy line break.
In the event of loss of offsite power coincident with a high energy line break, emergency power is available for safe shutdown and cooldown from three independent diesels and electric diesel start systems.
Review of the feedwater system indicates that all three feedwater pumps could be incapacitated by a single failure of a high energy feedwater discharge line. A backup source of cooling water is available from the Safety Injection Tank utilizing the Charging Pumps.
The high pressure and -
l low pressure safety injection systems will also be available for cooling water.
Our review of the main steam system indicates that a steam line rupture could sever two main feedwater lines.
The remaining two feedwater lines are not affected and could be used for core cooling. No single main steam line failure can be postulated that would result in the loss of all core cooling methods.
A failure of the main steam bypass system could prevent normal shutdown due to loss of the main condenser but the other modes of cooling are not affected and therefore would be available.
Failures in all other high energy lines result in fewer restrictions on plant shutdown than those discussed for the feedwater and main oteam line failures.
. CONCLUSION Based upon our review of high energy line breaks for the Yankee Nuclear Generating Station, 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 always be adequate to remove core decay heat.
3.
Emergency diesel-generator power would be available for decay heat re= oval under all accident conditions considered herein.
4.
Compartment overpressurization is not possible and cannot affect any equip =ent necessary for safe shutdown of the plant.
Control room habitability is assured under all accident conditions considered herein.
Therefore, we conclude that upon completion of necessary plant modifications Yankee Nuclear Generating Station can withstand the consequences of a rupture in any high energy fluid piping outside containment without loss of the capa-bility to Laitiate and maintain the plant in a safe shutdown condition.
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l G. L. Chipman Operating Reactors Branch #1 Directorate of Licensing Ongnal signed by Bobert J.Schemel Robert J. Schemel, Chief Operating Reactors Branch #1 Directorate of Licensing DEC 13 1973 r
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