ML20198H777
| ML20198H777 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 01/06/1998 |
| From: | Graesser K COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BYRON-98-0005, BYRON-98-5, NUDOCS 9801130392 | |
| Download: ML20198H777 (3) | |
Text
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It)ron, ll 610ln9794 Tel Hi 42,4 4 54 il January 6,1998 IIR: IlYRON 98 0005 FilJ1: 2.01.0301 U. S. Nuclear Regulatory Commission Atrention: Document Control Desk Washington D.C. 20555 0001
Subject:
Additional Informatien Related to Emergency Core Cooling System Venting I!yron Nuclear Power Station, Units 1 & 2 Facility Operating licenses NPF-37 and NPF-66 NRC Docket Nos. 50-454 and 50-455 13raidwood Nuclear Power Station, Units 1 & 2 Facility Operating Ijcenses NPF-72 and NPF-77 NRC Dockedes. 50-456 and 50-451
Reference:
K.1. Graesser (Comed) letter to USNRC, Requesting a Technica! Specification Amendment Pertaining to Emergency Core Cooling System Venting, dated September 8, 1997.
In the referenced letter, Commonwealth Edison (Comed) requested an amendment for flyron Units 1 and 2 and liraidwood Units 1 and 2. The proposed change affects Technical Specification 4.5.2.b and associated bases with respect to venting of Emergency Core Cooling System (ECCS) pump casings and discharge piping high points outside of containment. The proposed change brings the Ilyron and j
liraidwood Unit I requirements in conformance with the 13yron and 13raidwood Unit 2 requirements.
During the review of this submittal, NRC raised a concem with potential gas intrusion into the ECCS crossover piping between the Residual IIcat Removal (RH) heat exchanger and ti t Safety Injection (SI) pumps. This piping forms a local high point that is not supplied with a vent valve. The folicnving discussion indicates bw Comed has evaluated the potential for gas intrusion into the crossover piping and the plans for ensuring any gas intrusion into the piping is detected.
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llYRON;98-0005 Page 2 U. S. Nuclear Regulatory Commission January 6,1998 IMtralial Sources of Gu The primary sources of gas intmsion into this section of piping would be limited to leaks from the Reactor Coolant System (RCS) via the R1I to Chemical Volume and Control System (CVCS letdown cross-tie or through back-leakage on t.. pressure isolation valves (S18818s or SI8819s). The RCS in-leakage would be wates that has some concentration of dissolved hydrogen from the Volume Control Tank (VC1) cover gas. The dissolved hydrogen entered solution at approximately 20 psig (VCT cover gas pressure). Therefore, since the crossover piping is maintained at pressures greater than 20 psig by the static head of the Refueling Water Storage Tank, the release of the hydrogen from solution is not credible.
The second potential source ofgas is water from the SI accumulators. The accumulator contents have some concentration of nitrogen from the accumulator cover gas that entered solution at approximately 600 psig (accu..ulator cover gas pressure). If the accumulator water enters the crossover piping due to back-leakage through the pressure isolation valves, the release of nitrogen gas is likely due to the lower pressure in the crossover piping.
Finally,it is unlikely that gas could migrate to these locations from the Ril pumps or suction side of the RII system. The system is vented every 31 days through several vent valves on both the suction and discharge sides of the Ril pumps, thus preventing accumulation of significant quantities of gas. These vents have rarely shown acy accumulation ofgas in the RII system piping. The cross-over piping that contains the local high points only has flow through it during and after an accident. Without fkwv through the piping, there is no means for the gas to make its way through the system to the local high points. Furthermore, the Ril IIcat Exchanger tubes extend to an elevation of about 383'-0", which is higher than the local high points' elevation of 377'. The tubes act as a loop seal to prevent the movement ofgas past the heat exchanger.
Comed lhafor ensuringeas intrusion is detected:
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1.
The current venting and ultrasonic testing (U'l) surveillances performed at a 31 day interval will continue as require:1 by Technical Specification 4.5.2.b for Units I and 2 and the proposed changes for Unit 1.
2.
If the 31 day venting surveillance identifies gas present at either Ril injection to cold legisolation valve (S18809A/B) vent valve (S1058A/B), then UT of the three gas traps associated with the crossover piping will be performed to verify no presence of gas.
1 Through shiftly monitoring of SI accumulator level, significant loss of accumulator water wouki be identified and the potential for gas pockets in the ECCS system evaluated. Leakage from the accumulators would pass through the SI8809A/B valves first, preferentially releasing the gas from solution at that point. Therefore, testing for potential gas pocket formation would involve a venting check at the S18809A/B valves. Ifgas is identified at these valves then UT of the.
three crossover piping gas traps will be performed to verify no presence of gas.
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IWRON;98 0005 Page 3 U. S. Nuclear Regulatory Commission January 6,1998 =
4 Through shiftly monitoring of Rif discharge header pressure, check valve leakage without significant water loss would be identified as an elevated sptem pressure. Although this co.idition would not result in a gas pocket since the gas in solution is still under pressure, the potential for gas pocket formation folicnving changes in plant condition (oc., venting, ulve re-alignment, etc.) does exist. Since the location of gas pocket formation cannot be predicted, UT of the three crossover piping gas traps will be performed to verify no presence of gas.
The above actions will be incorporated into the applicabic plant procedures to provide the necessary guidance and actions to take if unacceptab!c indications are observed.
Please direct any questions to Marcia lesniak, Nuclear Licensing Administrator, at (630) 663-6484, Sincerely C
'.. ftm K.1. Graesser Site Vice President flyron Nuclear Power Station KLG/12/rp cc:
Regional Adminis.rator Rill Senior Resident inspectc,r - 13yron Senior Resident inspector - Braidwood llyron/Ilraidwood Pro!ect Manager - NRR Office of Nuclear Safety - IDNS 4\\98byltr \\980005. doc) l