05000440/LER-1993-001, :on 930109,RWCU Isolation Occurred as Result of High Differential Flow.Caused by Design Deficiency Associated W/Sys Voiding Phenomenon.Operators Currently Being Retrained & TS Change Request Submitted
| ML20128F093 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 02/05/1993 |
| From: | Conran D, Stratman R CENTERIOR ENERGY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LER-93-001, LER-93-1, PY-CEI-NRR-1604, NUDOCS 9302110242 | |
| Download: ML20128F093 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 4401993001R00 - NRC Website | |
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Y PERRY NUCLEAR POWER PLANT.
Mail Address.
l P O. B OX 97 Robert A. Stretman pg$N 0
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U.S. Nuclear Regulatory Commission Document Control Desk Vashington, D.C.
20555 Perry Nuclear Power Plant Docket No. 50-440
- - t LER 93-001 Dear Sirt Enclosed is Licensee Event Report 93-001 for the Perry Nuclear Power Plant.-
i Sincerely, i
. Robert A. Stratman-N frtw%_
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Enclosuret LER 93-001 cci -NRC Project Manager NRC Resident Inspector
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Perry Nucicar Pcuer Plant, Unit 1 05000 440 1 O' 4 M PkCU Isolation on High Delta Flow While Operating in the Pgdocyl Feedwater_ Tcgvgat, ire ftv3,of,Qzrzdon 9
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ABSTRACT (Limit to 1400 spaces, e o.. approximately 15 single spaced typewimen knes) (16)
On January 9, 1993 at 1759, an Reactor Vater Cleanup (RVCU) isolation occurred as a result of high differential flov.
Immediate corrective action was taken to verify that no actual system leakage had occurred.
The RVCU system was secured and subsequently returned to service.
The event is attributed to a design deficiency associated with system voiding phenomenon which occurs during cooldown of the RVCU system.
This system voiding ultimately caused an isolation on high differential flov.
A contributing cause to this RVCU system isolation is inadequate training to a previous procedure change initiated by LER 92-004.
Following receipt of the Emergency Response Information System (ERIS) varning message, control room operators did not attempt to isolate the system until they received the _45 second dif ferential flow timer initiation.
All licensed operators are currently being retrained to System Operating Instruction (S01-G33), " Reactor Vster Cleanup System (Unit 1), emphasizing the requirement for expeditious shutdown of the RVCU system upon receipt of_the ERIS varning message.
This training is expected to be complete prior to completion of the current outage.
Because the Technical Specification Change Request to increase the delta-flov timer setpoint is expected to be approved in the near-term, no further corrective actions I
are considered necessary.
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1. Introduction
On January 9, 1993 at 1759, an Reactor Vater Cleanup 'RVCU) isolation occurred as a result of high differential flov.
At the time of the event, the plant was in Operational Condition 3 (Hot Shutdown) at 0 percent power with the Reactor Pressure Vessel [RpV) at 425 psi. The NRC Operations Center was informed of the event via the Emergency Notification System at 2145 hours0.0248 days <br />0.596 hours <br />0.00355 weeks <br />8.161725e-4 months <br /> in accordance with notification requirements identified in 10CFR50.72(b)(2)(ii). This event is being reported under the requirements of 10CFR50.73(a)(2)(iv).
II. Event Description
on January 9, 1993, control room operators vere in the process of shutting dovn-the unit to begin a maintenance outage.
Operators on a previous shift had placed the RVCU system in the Reduced Temperature Control for Feedvater Temperature mode of operation in accordance with System Operating Instruction (501-G33), " Reactor Vater Cleanup System (Unit 1)."
At 1744, control room operators received an Emergency Response Information System (ERIS) message, which stated "RVCU RilX Vold Formation." operators reviewed applicable portions of 501-G33, which instructed them to shutdovu the RVCU system by performing Section 6.4, Rapid Manual Shutdovn. Operators received the 45 second differential flov signal at 1759 and initiated manual closure of the containment isolation valves.
The containment isolation valves were in the process of closing when a differential flow isolation signal was received.
The RUCU system was successfully unisolated and returned to service at approximately 1947 on January 9, 1993.
III. Cause Analysis The primary cause of this event is considered to be a design deficiency associated with system voiding phenomenon which occurs during cooldown of the RVCU system. When operating in the Reduced Temperature contrnl for Feedvater Tcnperature mode of operation, process flow is reduced to decrease RVCU return temperature. This is performed to minimize thermal stresses in the feedvater piping. As the Regenerative llent Exchanger (RilX) return flow and reactor pressure decreased, vater on the shell side of the RilX flashed to steam causing a void. Approximately fifteen minutes later the system cooled down enough to allow the void to collapse, and return flow refilled the RilX instead of returning to the RPV via the feedvater injection line. Collapse of this void caused initiation of the 45 second differential flov isolation timer. When this flov timer timed out prior to stabilization of system flov, an isolation on high differential flow occurred.
A contributing cause to this RVCU system isolation is considered to be inadequate training to a previous procedure change initiated by LER 92-004 A
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...m.s... mm o f3 corrective action for this previous event installed an ERIS computer message, "RVCU RHX Void Formation," which provided control room operators varning of a pending system isolation.
Additionally, 501-G33 had been revised to instruct operators to utilize the Rapid Manual Shutdown portion of this procedure _vhen they receive the ERIS varning message. The intent of this previous procedure change vas to expeditiously isolate the system when the ERIS varning message was received.
However, there is no time statement associated with action requirements in the Rapid Manual Shutdown portion of S01-G33.
Control room operators had not yet attempted to isolate the system when they received the 45 second differential flov timer initiation.
During event investigation, control room personnel on several operatirig crevs did not indicate that expeditious isolation of the system following receipt of the ERIS varning message was required.
IV. Safety Analysis
The Leak Detection System compares RVCU inlet flov to return flows (return flow to the reactor vessel through the feedvater line and blovdown flows to the main condenser and radvaste).
All three flovs are summed to generate a total flow value.
A RVCU high differential flov 11gnal is generated from the Leak Detection System when RVCU inlet flov exceeds return flov by 68 gpm.
If this-differential flov signal continues for 43 seconds, a RVCU system containment isolation vill occur. This could occur as the result of a line break in the RVCU system.
The 45 second time delay is intended to allow for system flov transients when operational configurations change.
During this event, although no actual leak existed, it is believed that a KVCU high differential flov did exist due to the apparent formation and subsequent collapse of a void in system.
The Leak Detection system responded as designed to indicate high differential flov and initiated a containment isolation.
All other plant systems responded as designed. Therefore, this event is not considered to be safety significant.
Following a RVCU containment isolation, the loss of the RVCU system may cause reactor coolant conductivity to slowly increase until the system is returned to service.
In this event, the system was returned to service prior to a significant increase in conductivity.
Other RVCU containment isolations have been reported in LERs88-039, 89-025,90-008, 90-022,91-006, 91-011,92-003, and 92-004. Corrective actions previously completed as a result of these events are described in their respective LERs.
Previous corrective.netions taken specific to this voiding l-phenomena includes evaluation of alternate means to re-pressurize /varm-up the systems initiation of a design modification to climinate minor heat exchanger drain valve leakage; installation of an ERIS varning message upon void-j formation; and submittal of a Technical Specification change to increase the l
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en e w as o n RVCU delta-flov timer setpoint.
Implementation of this Technical Specification change is expected to preclude occurrence of a similar isolation in the future.
Additionally, as previously reported in LER 91-011, Supplement 1 a vendor analysis determined that no long-term deleterious effects had resulted or vould result from occasional RVCU system transients involving flashing or voiding.
V. Corrective Action
All licensed operators are currently being retrained to S07.-G33, emphasizing the requirement for expeditious shutdown of the RVCU system upon receipt of the ERIS varning message.
This training is expected to be complete prior to completion of the current outage.
Because the Technical Specification Change Request to increase the delta-flov timer setpoint is expected to be approved in the near-term, no further corrective actions are considered necessary.
Energy Industry Identification System Codes are identified in the text as [XX).
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