ML20092F028
| ML20092F028 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 02/13/1992 |
| From: | William Cahill TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 1-SR-90-002-01, 1-SR-90-2-1, TXX-92070, NUDOCS 9202190055 | |
| Download: ML20092F028 (3) | |
Text
_
m F E Log # TXX-92 70 t
,--1
. File # 10250
=
=
. 905.4 1UELECTRIC R # 1UC'R50' 0(')(5i February 13,-1992 Wllilani J. Cahill. Jr.
Gwup Vke besident U. S. Nuclear Regulatory Commission Att _n: Document Control Desk i
-D.
C.
20555
SUBJECT:
COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)
DOCKET NO. 50-445 AUTOMATIC OPERATION OF PRESSURIZER PORV IN RESPONSE-TO AN LTO' SIGNAL SPECIAL REPORT NO 1-SR-90-002-01 Gentlemen:
Enclosed is a supplement ~ to Special Report-1-SR-90-002 submitted in accordar :e with CPSES Unit 1 Technical Specification 3.4.8.3, " Reactor Coolant System Overpressure Protection Systems".
This supplement provides a revision to Section 4-of;the.Specia_1 Report by eliminating the statement instructing the use-of decay heat f_or-establishing a pressurizer bubble.
A reevaluation was performed, based'on-plant experience, to determine the-feasibility for establishing _a pressurizer bubble.using_ decay _ heat and:
pressurizer heaters-pri_or to starting the Reactor Coolant Pumps.
It was-
-concluded that the system design'is not conducive =to utilizing decay; heat for-uniform Reactor Coolant System heatup.
. Sincerely, s
el -
_ William J. Cahill -Jr.
. JET /fds
-Enclosure-c R. D. Martin,: Region-IV-Resident: Inspectors,~CPSES (2)
T._At-Bergman,..NRR L
480064 3
_- gDR - ADOCK 05000445-P.o Box :002 > oien noie. Texas 760451002 -
gg' g
-9202190055-920213 I
- PDR
Enclosure TXX-92070 Page 1 of 2 TU Electric Comanche Peak Steam Electric Station, Unit 1 Docket No. 50 445 Automatic Operation of Pressurizer Power Operated Relief Valve in Response to a Low Temperature Overpressure Protection Signal Special Report No.1-SR-90-002-01 1.0 REPORT REQUIREMENT On February 21,1990, a Reactor Coolant System (RCS) pressure transient resulted in the automatic actuation of a Pressurizer Power Operated Relief Valve (PORV). This Special Report is being submitted in accordance with Comanche Peak Steam Electric Station Unit 1 Technical Specification 3.4.8.3. REACTOR COOLANT SYSTEM OVERPRESSURE PROTECTION SYSTEMS LIMITING CONDITION FOR OPERATION. Specification 3.4.8.3 requires that a Special Report be submitted to the Nuclear Regulatory Commission pursuant to Specification 6.9.2 describing any event in which a Pressurizer PORV, or the Residual Heat Removal suction relief valves, or the RCS vents are used to mitigate a RCS pressure transient.
2.0 EVENT DESCRIPTION On February 21,1990, at approximately 1317 CST, with the plant in cold shutdown and RCS temperature at 140 degrees F, a Pressurizer PORV automatically opened in response to a Low Temperature Overpressure Protectior (LTOP) signal. Just prior to the event the RCS fill and vent procedure had been completed up to the vent of the RCS following the fourth Reactor Coolant Pump (RCP) one minute run.. At the time of the event, the RCS was in a water solid condition and was being pressurized to 325 psig in preparation for the RCP ten minute runs. Letdown flow had been reduced to a flowrate less than the charging flowrate, resulting in an increasing RCS pressure. The solid plant pressure response to the reduced letdown Dowrate was quicker than anticipated by the Reactor Operator (RO) and resulted in RCS pressure exceeding the target value.
The RCS reached a maximum pressure of 436 psig. "Ihe system functioned as designed, causing a Pressurizer PORV to'open for approximately 4 seconds, preventing the RCS pressure from exceeding the applicable limits. The RO reduced charging flow and; increased letdown flow, stabilizing RCS pressure at 260 psig within two minutes. A I
review of recorded data subsequent to the event verified that the open PORV resulted in a drop in RCS pressure to 350 psig and a-f corresponding rise in the Pressurizer Relief Tank level.
s
Enclo:ure TXX-92070 Page 2 of 2 3.0 CAUSE OF EVENT The following have been identified as causes for the event:
ne procedure for Illling and venting the.RCS requires that the operator perform an iterative process, but does not consider the variation in plant response to identical instructions in going from a system containing air to a water solid system. The procedure does not adequately caution the RO of the change in expected plant response.
Re process for pressurizing the RCS following a vent had been to completely isolate letdown flow resulting in a loss-of-le+down-flow alarm for the failed fuel monitor. The alarm, which should have alerted the RO to insufficient letdown flow, had become an expected alarm.
4.0 CORRECTIVE ACTION The pressure transient was discussed with the RO. and the need for increased board awareness during solid plant operations was reinforced.
A Lessons Learned summary was reviewed by all crews, and increased sensitivity of the plant to changes in letdown and charging was discussed.
The operating procedure will be revised as follows to incorporate lessons learned from this event:
Eliminate repetitive _ steps for which differing plant responses are expected.
Instruct the operator to avoid completely securing letdown flow, ensuring normal operation of the failed fuel monitor, and adequate operator response to a loss-of-flow alarm.
Cauuons will be added to alert the operator of expected plant responses in transitioning from a system with air to a water solid system.
l
{
I