ML19274C860
| ML19274C860 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 11/14/1978 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19274C857 | List: |
| References | |
| NUDOCS 7811280083 | |
| Download: ML19274C860 (4) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION y*
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WASHINGTON, D. C. 20555 z
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 52 FACILITY OPERATING LICENSE NO. DPR-3 YANKEE ATOMIC ELECTRIC COMPANY YANKEE NUCLEAR POWER STATION (YANKEE-ROWE)
DOCKET N0. 50-29 Introduction By application dated June 6,1978 (Proposed Change No.160) as supplemented by letter dated August 22, 1978, Yankee Atomic Electric Comoany (the licensee) requested an amendment to Facility Operating License No. DPR-3 for the Yankee Nuclear Power Station (Yankee-Rowe). The amendment would change the provisions of the Technical Specifications to permit operation with a modified Emergency Core Cooling System (ECCS) recirculation subsystem.
Discussion Yankee-Rowe is a four-loop Pressurized Water Reactor (PWR). The long-term core decay heat removal capability needed following a LOCA is provided by an ECCS recirculation subsystem.
Presently, this subsystem includes the two purification pumps, and two fixed speei reciprocating charging pumps.
Immediately after initiation of the recirculation cooling phase following a LOCA, the purification pumps draw the spilled reactor cooling system water from the containment sump arid pumo it through the reactor cooling system cold legs into the reactor vessel. As the coolant flows through the reactor core and spills out of the pipe break back into the contain-ment sump, decay heat is removed from the core. After about 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> of recirculation through the cold legs, part of the flow from the purification pumps is diverted to the suction side of the charging pumps which deliver it to the hot leg of the reactor cooling system loop No. 4.
We have previously concluded that the flows provided by these pumps are adequate for long-term decay heat removal following a LOCA and for preventing boric acid precipitating during the recirculation phase with hot leg injection.
7811280o33,
. In the June 6,1978 application the licensee proposed modifications to the ECCS recirculation subsystem to improve the long-term cooling capability of the ECCS. The modifications involve the use of the existing ECCS Low Pressure and High Pressure Safety Injection (LPSI and HPSI) pumps for coolant recirculation in lieu of the purification pumps presently used for this function.
New piping, valves and associated instrumentation, and controls would be installed. The licensee's proposed technical specifi-cations would allow facility operation with the modified ECCS recirculation subsystem.
The modifications are scheduled to be completed during the present Core 14 refueling and maintenance outage.
Evaluation The licensee would install the following components for use of the existing LPSI and HPSI pumps in the proposed modified ECCS recirculation subsystem:
- 1) A 6 in. line from the sump to the section header of the LPSI pumps with two isolation valves in parallel and one check valve.
- 2) A 2 in, line from the discharge side of the HPSI pumps to the hot leg charging line with two isolation valves in parallel, a throttling valve, a check valve and a flow meter.
- 3) A motor operated gate valve and a check valve in the line connecting the safety injection tank to the suction header of the LPSI pumps.
In the modified ECCS recirculation subsystem the LPSI pumps would draw cooling water from the containment sump through the newly installed pipe-line. The flow would then be diverted to the suction side of the HPSI pumps which would deliver it to the reactor through the cold and hot legs.
The cold leg injection would be accomplished through the high pressure safety injection header. The hot leg injection flow would be provided through the newly installed line connecting the HPSI pumps to the presently existing hot leg charging line. Because of the much larger flow rate from the LPSI and the HPSI pumps compared with flow rate from the purification pumps, there would be greater assurance that the core will remain covered, decay heat will be removed, and that boron precipitation will not occur during the recirculation cooling phase following a LOCA.
We have evaluated the suitability of the existing LPSI and HPSI pumps for the proposed use in the modified subsystem.
Each of the three LPSI pumps is a horizontal four stage impeller pump and each of the three HPSI pumps is a seven stage impeller pump. These pumps are supported by radial and thrust ball bearings with the rotor in between. The licensee has provided data which substantiate ti.at during various modes of operation there will be adequate Net Positive Suction Head (NPSH) available for reliable pump performance. The various modes of operation analyzed assume that reactor coolant pressure is m'inimum thereby maximizing flow rates and NPSH required while minimizing NPSH available.
Debris which may enter the pump internals during the ECCS recirculation phase of operation could be a concern. The licensee has stated that the spherical containment vessel acts like a settling chamber which prevents any debris from entering the pump suction.
In addition the flow rates during recirculation are relatively small and the resultant low velocities coupled with high containment water level above the suction pipe ensure that debris will settle out and vortexing will not occur. We agree with this appraisal.
In addition the operating history of these pumps indicates that except for routine maintenance no major repairs have been required and that the pumps have operated satisfactorily. Nevertheless, periodic testing and inspections of these pumps will be performed in accordance with existing technical specifications and a proposed inservice inspection and testing program presently being reviewed by us.
Based on the above considerations we have concluded that use of the LPSI and HPSI pumps (in three redundant trains) in lieu of the purifintien pumps (in two redundant trains) provides increased operability and relisbility and is acceptable for performing the intended functions.
The licensee has proposed to add a pipe and valves from the LPSI pumps to the existing recirculating piping.
In addition the licensee has proposed to install a new line and valves which would run from the HPSI pump discharge header to the charging pumo discharge piping, for hot leg injection. The recirculation system piping and valving would be designed to Safety Class 2.
All major components will be designed to Codes and Standards that meet at least the original design requirements of the existing ECCS recirculation subsystem.
Components and installation will be in accordance with the requirements in the quality assurance program previously approved by us.
In addition, based on our review of the licensee's single failure modes and effects analysis and our examination of the piping and valve schematics we find from a systen standpoint that the proposed modified ECCS recircu-lation subsystem meets the single failure criterion for active components.
We have therefore concluded that the proposed installation of new piping and valves for the modified ECCS subsystem is acceptable.
The control circuit for each Motor Operated Valve (MOV) in the modified ECCS recirculation subsystem (SI-48, SI-49, SI-516, and SI-517) is equipped with dual motor starters in series and two independent control circuits and switches.
Both interrupting devices must be energized by control switches to change valve position from their nomal operation position. Position indications for 5, s SI-49,51-516, and SI-517 are provided at the recirculation panel. Position indication for M0V SI-48 is provided at the safety injection panel. Both panels are located inside the control This position indication satisfies the NRC staff position in room.
Branch Technical Position, EICSB BTP-18. The electrical power for each of the two redundant MOVs in parallel (SI-516 and SI-517) and for each of the two redundant MOVs in series (SI-48 and SI-49) is supplied from a different power source. We have concluded that the electrical power supply and control for the MOVs in the modified ECCS recirculation subsystem meet the single failure criterion and tim requirements for Class IE systems and are therefore acceptable.
The licensee has proposed technical specifications which establish limiting conditions for operation and surveillance requirements for the modified ECCS recirculation subsystem. The licensee also has proposed to delete certain provisions of the technical specifications for those features which would be replaced by the proposed modifications and will no longer be required to perform a safety related function. We have concluded that the proposed changes to the technical specifications appropriately reflect the changed facility conditions, add necessary provisions for safe operation with the modified ECCS recirculation subsystem, and are therefore acceptable.
Environmental Considerations We have determined that the amendment does nct authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this detemination, we have further concluded that the amendment invalves an action which is insignificant from the standpoint of environmentel impact and, pursuant to 10 CFR 951.5(d)(4), that an environmental. impact statement or negative declaration and environmental impact appraisal neei not be prepared in connection with the issuance of this amendment.
Conclusion We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of accidents previously considered and does not involve a significant decrease in a safety margin, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such acitivities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the comon defense and security or to the health and safety of the public.
Date: November 14, 1978
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