ML19276H527
| ML19276H527 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 11/16/1979 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Doug Garner Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7911290363 | |
| Download: ML19276H527 (2) | |
Text
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' SMUD SACRAMENTO MUNICIPAL UTILITY DISTRICT C 6201 S Street Box 15830, Sacramento California 95813; (916) 452-3211 Novembe r 16, 1979 Mr. Dan Garner Nuclear Reactor Regulation Operating Reactors Branch #4 Washington, D. C. 20545 Re:
Docket No. 50-312 Power Operation with Decay Heat-Reactor Building Isolation Valves Open
Dear Sir:
This letter is submitted in response to an Inservice Testing (IST) team request of October 4,1979 to provide you with information re garding the consequences of power operation at Rancho Seco with the Decay Heat System Motor Operated Reactor Building Isolation Valves (SFV-26005 and SFV-26006) open.
This request was made in regard to postulated Inter-System LOCA (High Pressure Reactor Coolant System to Low Fressure Decay Heat System) and subsequent loss of reactor coolant outside the Reactor Building.
The Decay Heat System Injection lines enter the Reactor Building through Penetrations 27 and 28.
Penetration isolation is provided by motor operated gate valves (SFV-26005 "A" Loop and SFV-26006 "B" Loop) outside the Reactor Building and stop check valves (DHS-015 "A" Loop and DHS-016 "B" Loop) inside the Reactor Building.
Further isolation of Decay Heat System Injection from the Reactor Coolant System is provided by check valves (RCS-001 "A" Loop and RCS-002 "B" Loop) downstream of the Reactor Building isolation stop check valves.
During normal operation, the motor operated gate valves are " closed" and the stop check valves are "open", but the check function prevents high pressure reactor coolant f rom overpressurizing the Decay Heat System return lines.
Small 3/4 inch lines are connected to each return line upstream of the stop check valves. These lines bypass the stop check valves and are routed to each Core Flood Tank discharge line. Each bypass line is provided with a stop check valve (DHS-017 "A" Loop and DHS-018 "B" Loop), a pressure breakdown orifice (F0-26033 "A" Loop and FO-26034 "B" Loop) and a simple check valve (DHS-067 "A" Loop and DHS-068 "B" Loop). The bypass lines prevent overpressurization of the Decay Heat System Injection lines upstream of the Decay Heat System Injection line stop check valves (DHS-015 and DHS-016) by directing any back leakage from the Decay Heat System Injection check valves (RCS-001 and RCS-002) and the Decay Heat System injection stop check valves (DHS-015 and DHS-016) to the Core Flood Tanks.
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Mr. Dan Garner Page Two Novembe r 13, 1979 Leakage into the Core Flood Tanks will cr a changes in both Core Flood Tank pressure and level. Any changes in either of these parameters will be noted during daily surveillance of selected plant instrumentation required by SP 200.02, Instrumentation Surveillance Performed Each Day.
In addition, Core Flood Tank level and pressure are both indicated and annunciated in the control room.
Reactor Coolant System leakage is estimated from various tank level changes which are recorded by SP 200.02.
If the estimated leakage exceeds 1.0 gpm, SP 207.04B, Weekly RCS Leakage Test, is performed with further action based on Technical Specification requirements.
Because:
(1) A system is in place which bypasses RCS isolation valve leakage to Core Flooding Tanks and prevents penetration overpressurization, and (2) Core Flood Tank level and pressure changes are monitored daily and annunciated in the control room, and (3)
Reactor Coolant System leakage is estimated daily and precisely calculated weekly, and (4) Opening Decay Heat Removal Injection Reactor Building Isolation Valves (SFV-26005 and SFV-26006) exposes low pressure piping and components to possible overpressuri-zation with Reactor Coolant System pressure; we will continue power operation with these valves closed.
Ope rability of the stop check valves (DHS-017 and DHS-018) and simple check valves (DHS-067 and DHS-068) in the bypass lines will be verified by full stroke testing on a cold shutdown frequency. These valves will be added to the Pump and Valve Testing Program as Categcry C Valves, and a request for relief will be submitted to allow full stroke testing on a cold shutdown fre-quency rather than quarterly due to accessability to verify stroking.
Please contact Mr. Ron Colombo with any questions or comments.
Respectfully,
. !&Q 6. J. >bttimoe Assistant General : tanager and Chief Engineer JJM:WBG:sc 1421 207