05000366/LER-2004-002, Unplanned Group 2 PCIS Isolation from a Water Level Transient Following Manual Reactor Scram
| ML043340255 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 11/23/2004 |
| From: | Sumner H Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-04-2305 LER 04-002-00 | |
| Download: ML043340255 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv), System Actuation |
| 3662004002R00 - NRC Website | |
text
H. L Sumner, Jr.
Vice President Hatch Project Southern Nuclear Operating Company. Inc.
Post Office Box 1295 Birmingham, Alabama 35201 Tel 205.992.7279 November 23, 2004 SOUTHERNAZ COMPANY Energy to Serve Your World'"
NL-04-2305 Docket No.:
50-366 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin 1. Hatch Nuclear Plant - Unit 2 Licensee Event Report Unplanned Group 2 PCIS Isolation Results From a Water Level Transient Following a Manual Reactor Scram Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73(a)(2)(iv)(A), Southern Nuclear Operating Company is submitting the enclosed Licensee Event Report concerning an unplanned Group 2 isolation which resulted from a water level transient following a manual reactor scram.
This letter contains no NRC commitments.
If you have any questions, please advise.
Sin eely,
.ASU471-tA~
H. L. Sumner, Jr.
HLS/OCV/daj Enclosures: LER 2-2004-002 cc:
Southern Nuclear Operating Company Mr. J. T. Gasser, Executive Vice President Mr. G. R. Frederick, General Manager - Plant Hatch RTYPE: CHAO2.004 U. S. Nuclear Regulatory Commission Dr. W. D. Travers, Regional Administrator Mr. C. Gratton, NRR Project Manager-Hatch Mr. D. S. Simpkins, Senior Resident Inspector-Hatch
Abstract
On 9/25/2004 at 0106 EST, Unit 2 was in the Run mode at an approximate power level of 981 CMWT (35 percent rated thermal power). At that time, Operations personnel manually scrammed the reactor per procedure 34GO-OPS-013-2, "Normal Plant Shutdown," for a planned Unit outage for the repair of the "L" Safety Relief Valve (SRV). Following the manual scram, water level decreased due to void collapse from the rapid reduction in power, reaching a minimum of approximately minus 6 inches above instrument zero (about 152 inches above the top of the active fuel). The decrease in water level resulted in receipt of a Group 2 Primary Containment Isolation System (PCIS) isolation signal and closure of the Group 2 Primary Containment Isolation Valves per design. The operating Reactor Feedwater Pumps restored level to its desired value. Personnel reset the Group 2 isolation signal and restored the isolation valves to normal per procedure 34AB-C71-001-2, "Scram Procedure."
The receipt of the unplanned Group 2 PCIS isolation was the result of a vessel water level decrease due to void collapse from the rapid reduction in power following the planned insertion of a manual scram.
Procedure 34GO-OPS-013-2, "Normal Plant Shutdown," failed to inform the operators that the receipt of a Group 2 signal was expected. Upon inserting the scram water level decreased to a point approximately equal to the Group 2 PCIS isolation setpoint. The Normal Plant Shutdown procedure will be revised to provide guidance to preclude reaching the Group 2 Isolation setpoint as well as provide guidance to state when the Group 2 isolation is expected.
NRC FORM 366 (6.2004)
(if more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A)
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT This report is required by 10 CFR 50.73 (a)(2)(iv) because of the unplanned actuation of containment isolation valves in more than one system. Following a manual scram, reactor vessel water level decreased due to void collapse. Level reached a minimum of about minus six inches above instrument zero (about 152 inches above the top of the active fuel). The decrease in water level resulted in automatic Reactor Protection System actuation and Group 2 PCIS isolation on low water level and closure of the Group 2 Primary Containment Isolation Valves per design. The Reactor Protection System and PCIS are Engineered Safety Feature systems.
The operating Reactor Feedwater Pumps automatically restored water to its desired value. Operations personnel verified correct system response and restored the isolation valves to their normal positions.
All systems functioned as expected and per their design given the water level transient. Water level was maintained well above the top of the active fuel throughout the transient and was restored to its desired value without the need for emergency core cooling system actuation. Therefore, it is concluded the event had no adverse impact on nuclear safety. This analysis is applicable to all power levels.
CORRECTIVE ACTIONS
The Normal Plant Shutdown procedure will be revised to provide guidance to preclude reaching the Group 2 Isolation setpoint as well as provide guidance to state when the Group 2 isolation is expected.
ADDITIONAL INFORMATION
Other Systems Affected: No systems other than those already mentioned in this report were affected by this event.
Failed Components Information
No failed components directly caused or resulted from this event.
Commitment Information: This report does not create any permanent licensing commitments.
Previous Similar Events
There has been one previous similar event in the past two years in which a planned manual reactor scram at low power level resulted in unplanned Engineered Safety Feature system actuations.
In this event, reported in Licensee Event Report 50-321/2002-005, dated 12/6/2002, Unit 1 was scrammed manually with power level at approximately 48.5 percent rated thermal power. The resulting water level transient caused the Group 2 Primary Containment Isolation Valves to close on low reactor vessel water level. From this event, procedural instructions were reviewed and revised as required to improve the methodology used for reactor vessel level control during planned shutdowns.
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