ML20214J524

SER on Util 860131 & 0512 Proposed Equipment Mods & Procedures to Maintain Water in RCIC Sys Above 65 F. Commitments Acceptable

ML20214J524
Person / Time
Site:	Grand Gulf
Issue date:	11/21/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20214J512	List: ML20214J508 ML20214J524
References
TAC-60652, NUDOCS 8612010338
Download: ML20214J524 (3)

Text

_ - _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _

t Enclosure SAFETY EVALUATION REPORT BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO TRAIN B FEEDWATER LINE FLUED HEAD TEMPERATURE FOR GRAND GULF NUCLEAR STATION, UNIT 1 DOCKET NO. 50-416

1.0 INTRODUCTION

l Section 6.2.8, " Fracture Prevention of Containment Pressure Boundary" of the Safety Evaluation Report for Grand Gulf Nuclear Station, Unit 1 (GGNS) issued in September, 1981, identified the licensee's commitment to determine the '

lowest permissible service metal temperature (LSMT) based on the minimum design \

thickness of the feedwater line and main steam line flued heads and to maintain the flued heads at a temperature equal to or greater than their LSMT.

The licensee committed to the above in order to comply with General Design Criterion (GDC)51,"FracturePreventionofContainmentPressureBoundary"of 10 CFR 50, Appendix A. By letter dated July 20, 1983, the licensee stated that only the flued head of Train B feedwater line can be exposed to temperatures lower than its calculated permissible LSMT (65* F). The above situation can arise during reactor core isolation cooling (RCIC) injection from the condensate storage tank (CST) via the above flued head. Extended plant shutdown i.e., assuming no heat inputs to the CST) with minimum ambient temperatures ((i.e., during winter) can result in CST water temperature falling below 65*F resulting in the flued head temperature being less than 65*F. In the above submittal, the licensee, committed to implement the following action:

1. Install temperature sensors on the CST which alarm in the control room when falling temperatures reach 70*F and 66*F;

2. Make provisions to direct water from the condenser hotwell to the CST when the temperature decreases to 70*F or lower and transfer RCIC suction to the suppression pool (SP) at temperatures of 66*F or lower; and

3. Heat trace and insulate the exposed 20" RCIC suction piping from the CST.

gk P

[$$ 6

o . -

l By letter dated January 31, 1986, the ifcensee proposed to revise the above commitment as follows and provided justification for the same:  ;

1. Install a local temperature sensor with local alarm capability on the CST which will be monitored once per shift during cold weather conditions. If the CST temperature decreases to 70*F, procedures will require that the RCIC suction be transferred to the SP or that CST temperature be increased by makeup / reject from the condenser hotwell;

2. Install insulation on the exposed 20" RCIC suction piping from the CST.

The staff requested additional information pertaining to the proposed local temperature sensors, and the correlation between the CST temperature and the flued head exposure temperature. By letter dated May 12, 1986, the licensee provided the requested information.

2.0 EVALUATION Approximately 13 feet of 20" exposed piping connects the CST to approximately 150 feet of 20" piping buried about 7.25 feet below ground. This, in turn, is connected to approximately 300 feet of piping of various sizes inside the auxiliary building which finally ends up at the flued head. The licensee has committed to heat trace the exposed piping to prevent it from falling below 65*F. Water in the auxiliary building piping will not be a concern since the building is normally well above 65'F. Regarding the buried segment of the piping, since it is buried at substantial depth below ground, ambient air temperature variations will not affect it to any significant degree. A more significant influence on the buried pipe water temperature will be due to annual average air temperature in the area (65.94*F) or due to heat conduction from the plant end of the pipe. Therefore, the water temperature will vary only slightly from the annual average air temperature. For the above reasons, it is concluded that both the exposed and buried piping are adequately protected against temperatures less than 65*F and that the flued head will not be exposed to temperatures less than its pennissible LSMT so lona as the CST from where the RCIC normally takes its suction is at 65 F or above. Corrective actions such as transferring RCIC suction from the CST to the much warmer SP (well above 65*F) or increasing the CST temperature by makeup / reject from the condenser hotwell when the CST temperature decreases to 70*F will protect the flued head against its temperature falling below its calculated permissible LSMT.

As noted above, the licensee proposes to monitor the CST temperature once per 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> shift during cold weather conditions in lieu of their originally proposed control room instrumentation for annunciating an alarm in the control room when the CST temperature falls to either 70*F or 66'F. Their calculation showed that any temperature change of the CST due to changing ambient conditions will be very gradual and that, even under the lowest expected temperatures, the CST will fall only by about 1 F per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> when the CST is at 70'F. Based on the above, the staff finds that the local alarm capability and the proposed monitoring frequency provide time to perform corrective actions well before the CST falls to 65'F and is, therefore, acceptable.

. The licensee, stated that two local temperature sencors, one on the CST and the other on the suction line from the CST to the condensate transfer pumps will be installed, and that the temperature indicators will read full scale if any sensor fails. Operational procedures will ensure repair or replacement of the sensor (s) as appropriate should the sensor (s) fail. The licensee has further committed to monitor the CST temperature utilizino portable thermometers in the unlikely event both sensors fail. The staff finds the above approach acceptable.

3.0 CONCLUSION

Based on the above, the staff concludes that the licensee's currently proposed commitments as described in their January 31, and May 12, 1986, submittals for protecting the Train B feedwater line flued head against falling below its calculated permissible LSMT is acceptable. This acceptance is based on the staff's findings that there is a reasonable assurance that the proposed corrective actions will be performed in a timely manner and that they will ensure that the flued head for the above line will not fall below its calculated permissible LSMT. The requirements of GDC 51 are therefore met.

4

_ .