05000445/LER-2001-003
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4452001003R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
This Licensee Event Report is submitted to report a condition prohibited by the plant's Technical Specification pursuant to the requirements of 10CFR50.73 (a)(2)(i)(B).
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
On March 12, 2001, when this issue was discovered, Comanche Peak Steam Electric Station (CPSES) Unit 1 was coasting down in preparation for its eighth refueling outage, and CPSES Unit 2 was in Mode 1, Power Operations.
C. STATUS OF STRUCTURES, SYSTEM OR COMPONENTS THAT WERE
INOPERABLE AT THE START OF THE EVENT AND THAT CONTRIBUTED TO
THE EVENT
There were no other inoperable structures, systems or components that contributed to event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND
APPROXIMATE TIMES
The turbine overspeed protection system surveillance test procedure cycles the turbine control and stop valves, when the main turbine is not rolling, and provides allowance to open the turbine trip system power supply breakers. The test procedure states that the affected unit may be in Mode 2, 3, 4, or 5, when performing the test.
CPSES Technical Specification 3.3.2, "Engineered Safety Feature Actuation System (ESFAS) Instrumentation" Table 3.3.2-1, Function 8.a identifies that the "Reactor Trip, P-4" ESFAS interlock is required to be operable in Modes 1, 2 and 3. Thus, a turbine trip from a reactor trip, P-4 signal, is required in Modes 1, 2 and 3.
The allowance in the turbine overspeed protection system test procedure to open the turbine trip system breakers in Modes 2, 3, 4 or 5 prevents the reactor trip (P-4) signal from initiating a turbine trip.
On March 12, 2001, a CPSES plant operator (licensed, utility) noted that, if turbine overspeed protection system testing is performed in Modes 2 or 3, the instructions would make both trains of the reactor trip P-4 signal inoperable.
Facility Name (1) LER Number (6) Pagc(3) Year � Sequential � Revision Number � Number 01 � 003 � 00 Docket Enclosure to TXX-01082 On March 13, 2001, reviews of the previously performed tests for the turbine overspeed protection system were performed. It was determined that at least on two instances, during CPSES Unit 2 fifth refueling outage (September 30, 2000) and CPSES Unit 1 seventh refueling outage (September 25, 1999), the tests were conducted in Mode 3. Therefore, it was concluded that CPSES had violated the Technical Specification requirements.
E. METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE OR
PROCEDURAL ERROR
The Technical Specification Bases, which were developed when CPSES converted to the improved Standard Technical Specification, details the requirements associated with P-4 operability (i.e., stating the exact output required of the P-4 signal). On March 12, 2001, during a review of the turbine overspeed protection system test procedure, which included a comparison with the Technical Specification Bases, a CPSES operator (utility, licensed) noted that the procedure was in conflict with the Technical Specification Bases. Operations personnel reviewed the documents and verified that the CPSES Technical Specification requirements for the reactor trip P-4 signal being available to initiate a turbine trip was defeated on at least two instances.
II. ANLYSIS OF THE EVENT
A. SAFETY SYSTEMS THAT RESPONDED
Not applicable — there were no safety system responses associated with this event.
B. DURATION OF SAFETY SYSTEM INOPERABILITY
Not applicable — there were no safety systems rendered inoperable due to this event.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT
The reactor trip signal (P-4) initiates a turbine trip on reactor trip (i.e., reactor trip breaker and bypass breaker open). Although P-4 has several other functions, this is the only function upon which the Technical Specification LCO is based. When the turbine control/stop valves are closed, and the turbine is already tripped (in a safe position), the P-4 function is complete rendering the P-4 technically inactive. When the reactor trip breakers and reactor trip bypass breakers are opened, a P-4 signal would not actuate any end components because those components are already in the "turbine trip" state.
� Enclosure to TXX-01082 In Mode 3, CPSES procedures allow, at most, the withdrawal of the shutdown rods only.
There is only a minimal amount of heat to be removed through the secondary. Thus, most of the transients and accidents considered in FSAR Chapter 15 are not possible in this operational mode or would not have a significant impact on the plant had they occurred.
Although no event actually occurred during the two tests performed in Mode 3 with P-4 defeated, had steam been inadvertently supplied to the turbine through the turbine controllstop valves which were opened for testing, the magnitude of the steam release would have been well below that assumed for the main steam piping break accident presented in FSAR Section 15.1.5. In that analysis, the plant is assumed to be at hot zero power conditions (i.e., Mode 3).
The steam release path to the containment atmosphere through the double-ended rupture of the largest steam pipe is significantly larger than that available through a single turbine stop/control valve steam admission path. Upon exceeding the low steamline pressure setpoint, a Steamline Isolation Signal and a Safety Injection Actuation Signal are generated. The Steamline Isolation Signal initiates the closure of the MSIVs to prevent the complete blowdown of more than a single steam generator, including the effects of a single failure.
Among other functions, the Safety Injection Actuation Signal initiates reactor trip and turbine trip signals. The P-4 signal is not credited for the initiation of the turbine trip and the termination of any steam flow. All relevant event acceptance criteria are shown to be met.
Because no inadvertent steam release occurred, and because the results of any inadvertent steam release would have been bounded by existing analyses present in the FSAR, it was concluded that this event did not adversely impact the safe operation of CPSES or the health and safety of public.
III. CAUSE OF THE EVENT
During 1994, Comanche Peak personnel revising the procedure for testing of the turbine overspeed protection system did not recognize that placing the turbine trip system breakers in the open position would render the reactor trip, P-4 signal inoperable by making it unavailable to initiate a turbine trip.
The cause of the subject reportable event was deemed to be less than adequate procedures.
IV. CORRECTIVE ACTIONS
There were no immediate actions required since both Units were operating and the turbine trip system breakers were closed. The procedures have been revised, and the test was successfully implemented during the eighth refueling outage for Unit 1.
Facility Name ( I) COMANCHE PEAK STEAM ELECTRIC STATION UNIT 1 LER Number (6) Year Sequential � Revision Number � Number 0 1 M 003 1111 00 Docket Pagc(3) Enclosure to TXX-01082
V. PREVIOUS SIMILAR EVENTS
There have been other previous events, which resulted from less than adequate surveillance procedures. However, the causes for the less than adequate surveillance procedures for those events are sufficiently different than subject event such that the corrective actions taken for the previous events would have not prevented this event.
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