ML20207M963
| ML20207M963 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 01/08/1987 |
| From: | Kober R ROCHESTER GAS & ELECTRIC CORP. |
| To: | Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| IEB-86-003, IEB-86-3, NUDOCS 8701130358 | |
| Download: ML20207M963 (7) | |
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ROCHESTER GAS AND ELECTRIC CORPORATION e 89 EAST AVENUE, ROCHESTER, N.Y. 14649-0001
' ftOGER W KOt4ER Y t LEPetDNE WE mE!M NT mara coot vis 546 2700 etecTw; paooucTkm January 8, 1987 U.S.
Nuclear Regulatory Commission Document Control Desk Washington, D.C.
20555 Attn: Dr. Thomas E. Murley, Regional ' Administra tor t
Region-I
Subject:
.IE Compliance Bulletin 86-03 Potential Failure of Multiple ECCS Pumps Due to Single Failure of Air Operated Valve in Minimum Flow Recirculation Line R. E. Ginna Nuclear Power Plant Docket No. 50-244 Reference (a): Letter from R.W.
Kober (RG&E), to T.E. Murley (NRC);
Subject:
IE Compliance Bulletin 86-03, same subject, dated November 5, 1986
Dear Dr. Murley:
Rochester Gas and Electric provided the 30 day response to IE Bulletin 86-03 by reference (a).
The bulletin identified a design deficiency in the Emergency. Core Cooling System in certain plants whereby a potential failure of the Safety Injection pumps could occur as a result of loss of minimum flow to the pumps.
Rochester Gas and Electric previously identified that this problem existed at the R.E. Ginna Nuclear Plant.
Short term corrective action was taken and involved installation of
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mechanical blocking devices in the recirculation valves to preclude inadvertent closure and insure a minimum flow path.
Review and approval was completed and the installation implemented on August 7, 1986.
The short term corrective action has been reviewed and insures continued safe operation as further described in Attachment A.
For the long term corrective action for this postulated single failure event, Rochester Gas & Electric currently plans to replace the minimum flow line valves AOV-897 and AOV-898 with electrically powered motor operated valves.
These valves would be powered f rom separate electrical trains and would be designed to fail-as-is upon loss of electrical power.
The normal position of b
8701130358 870108 P
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. both valves will be open.
Thus, in the event of a single failure or loss of electrical power to one of the valves, the minimum flow line valves will still perform their intended function during the safety injection phase, cold leg recirculation phase, and during periodic testing.
Rochester Gas and Electric is currently preparing the conceptual design for internal review.
Completion of the detailed design followed by procurement and receipt of the new valves is scheduled by the end of 1988.
Installation and testing is scheduled to be performed during the Spring 1989 Refueling Outage.
V truly yours, Of Roger W.
Kober Attachments Subscribed and sworn to me
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on this 8th day of January 1987.
//lA /
d/26 b/
7 LYNN I. HAUCK Nntary Pubhc m tlw State el New York MONROECOUNTY xc:
U.S.
Nuclear Regulatory Commission Dr. Thomas E. Murley, Regional Administrator Region I 631 Park Avenue King of Prussia, PA 19406
N y,_
ATTACHMENT A The Ginna. plant's satety injection system has a minimum flow line dedicated for'each of the three (3) pumps.
The minimum. flow lines merge' into a single line that is equipped with two-(2)
~ Copes-Vulcan air. operated valves in series.
These valves are designed to: fail' closed upon loss of instrument; air or electrical control power.- The valves were designed with a fail closed feature to prevent inadvertent pumping of. reactor coolant f rom the containment-sump-following a loss-of-coolant accident (LOCA)1back to.the refueling water storage' tank (RWST) during'the sump recirculation phase.
The minimum flow lines connected to-the discharge piping of the safety injection pumps merge with the test line-used for-periodic testing _as required by General Design Criteria (GDC) 37 (10CFR50 Appendix A).
This test.line emanates from the safety injection and accumulator piping inside containment and is
. directed back to the RWST via the air operated valves AOV-897 and AOV-898, which provide the primary isolation between the RWST and safety injection pump discharge.
Refer to attached Figure 1.
The valves are normally open.
In the event of a safety injection signal, they remain open and provide a minimum flow through the pumps.
At the Ginna plant, the safety injection pumps-are ' designed for a maximum total developed head of 3500 feet (1510 psig) at shutoff (zero discharge flow).
In a postulated large break LOCA, defined in the FSAR as a ruppure with a cross-sectional area greater than 1.0 ft reactor coolant system depressurization occurs more rapidly than for small break LOCAs.
The maximum break size in the primary system for which the normal makeup system can sustain pressurizer pressure ' of 2250 psia through use'of the charging pumps is a 3/8" diameter-hole.
For a-4" diameter break, which would be classified as a small break
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LOCA, it would take approximately 22 seconds for the. reactor coolant system to be depressurized to the point where high head safety injection flow would occur.
If a safety injection signal was initiated by low pressurizer pressure of 1723 psig coincident with loss of offsite power, the normal sequencing would start two safety injection pumps in 15 seconds, the third pump 2' seconds la te r.
Since the reactor coolant system pressure would decrease to 1723 psig in about 6-7 seconds according to the transient analysis, the total time of about 21 to 22 seconds would elapse before the first two pumps would be actuated.
Hence, in this particular scenario, the pumps would be actuated at approximately the same time that the system pressure would permit flow into it.
If offsite power is not lost, pump actuation would occur 5 seconds f rom generation of the SI signal resulting in an elapsed time of 11 to 12 seconds.
Therefore, in this scenario the pumps would be required to run for about 10 seconds at shutoff with only minimum recirculation flow before system depressurization would permit safety injection pump discharge flow.
Since the pumps are
9 designed to operate continuously at minimum flow, this condition would become a safety concern only if closure of one or both of these valves occurred concurrently with the small break LOCA.
But the pumps can operate for some period of time, on the order of a few minutes without recirculation flow, before the water temperature within the pump would put the pumps at risk.
- Hence, the 4" diameter break would not be expected to pose a serious safety problem insofar as risk of pump failure.
For breaks between the 4" diameter and the 3/8" diameter bounds, the elapsed time for actuation of the safety injection pumps would be less than the time expected for reactor coolant system depressurization to be]ow the pumps shutoff head to occur.
In these cases, the pumps would operate deadheaded with only flow through the minimum flow lines resulting for longer periods of time than in the 4" break scenario.
Assuming that the probability of valve failure or loss of instrument air increases with time, operation of the pumps at minimum flow during the postulated break between 3/8" and 4" diameter would have a greater probability of putting pumps at risk than larger breaks.
Failure of either of the air-operated valves AOV-897 and AOV-898 in the minimum flow line due to loss of instrument air or electrical control power would cause closure of these fail closed valves, causing ultimate pump failure if allowed to continue in this mode.
Failure of multiple ECCS pumps due to a single failure violates the single failure criteria of General Design Criteria (GDC) 35.
To correct this deficiency on an interim basis, mechanical blocking devices have been installed in valves AOV-897 and AOV-898 to prevent them from closing in the event of loss of instrument air or electric control power.
During the cold leg recirculation phase of emergency core cooling, the residual heat removal (RHR) pumps take suction f rom the containment sump and discharge to the reactor vessel as well as the safety injection pumps' suction when additional flow from the high head safety injection pumps is required.
Refer to a ttached Figure 2.
The mechanically blocked open valves AOV-897 and AOV-898 are procedurally required to be closed prior to opening RHR pumps to SI pump suction valves (MOV-857A, B and C) and prior to starting the SI pumps by procedure ES-1.3, TRANSFER TO COLD LEG RECIRCULATION.
If the blocking devices cannot be removed, manual valves upstream of AOV-897 and AOV-898 in each minimum flow line would be closed (V-1820A, V-1820B and V-1820C).
There is also an interlock between minimum flow line valves AOV-897 and AOV-898 and the RHR pumps to SI pumps suction valves MOV-857A (Train A) and MOV-857B and C (Train B).
If the RHR suction valves from containment sump, MOV-850A and B, are open, then MOV-857A, B and C cannot be opened if the minimum flow line valves AOV-897 and AOV-898 are both open and MOV-896A and MOV-896B are both open.
MOV-896A and B are series motor opera ted RWST inlet valves which must be closed prior to the cold leg recirculation phase.
Refer to attached Figure 2.
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The switchover to the recirculation phase from the injection phase would commence on low RWST level of 28%, and would be completed with RWST level a t 15%.
1 For large breaks, primary system depressurization would occur rapidly below the safety injection pump shutoff head.
For small breaks, the depletion of inventory of the RWST due to high head safety injection flow would be relatively slow.
Plant cooldown and depressurization to below safety injection pump and RHR pump shutof f head would be accomplished prior to initiation of the cold leg recirculation phase.
Hence, for all size breaks, closing the minimum flow valves AOV-897 and AOV-898 will not endanger the safety injection pumps, since primary system pressure would be low enough to permit discharge flow from the safety injection pumps.
Installation of the mechanical blocking devices therefore insures continued safe opera tion of the safety injection system in the event of small or large break LOCAs concurrent with loss of instrument air to the minimum flow line valves.
It also provides for proper transfer to the cold leg recirculation phase.
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