05000390/LER-2003-005
| Watts Bar Nuclear Plant | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| 3902003005R00 - NRC Website | |
I. PLANT CONDITIONS
On October 3, 2003, Watts Bar Nuclear Plant Unit 1 was in Mode 6 during a refueling outage with core re-load in progress.
II. DESCRIPTION OF EVENT
A. Event
On October 3, 2003, Watts Bar Nuclear Plant Unit 1 was in Mode 6 during a refueling outage with core re-load in progress. At this time, Train B plant equipment, including Auxiliary Building Gas Treatment System (ABGTS) Train B [Energy Industry Identification (EDS) Code BH], was being protected while various Train A equipment was inoperable due to maintenance or testing status, including Train A Emergency Diesel Generator, 2A-A [EMS Code EK]. With the 2A-A diesel unavailable, the A Train ABGTS was technically inoperable and tracked accordingly in WBN Technical Specification (TS) 3.7.12, "ABGTS", although it was functionally capable of performing its safety function using preferred offsite power [EllS Code EB], which was available. During movement of irradiated fuel, WBN TS 3.7.12 requires two trains of ABGTS to be OPERABLE in order to mitigate the consequences of a potential fuel handling accident (FHA). An inoperable ABGTS train must either be restored within seven days or the operable train placed in service. If these conditions are not met, TS 3.7.12 requires immediate suspension of fuel handling activities.
WBN Operations personnel were in the process of performing equipment alignments for an upcoming surveillance test for the the 1B-B Diesel Generator, 0-SI-82-4, "18 Month Loss of Offsite Power With Safety Injection.
Preparations for these equipment alignments had begun on October 1 at approximately 0300 hrs. Because extensive prerequisite setups and alignments are required in preparation for the test, these activities are typically initiated in advance of the actual test performance, provided any specified precautions/restrictions are satisfied.
Section 4.4.1 (Pre-test Evolutions) of 0-S1-82-4, directs equipment alignments to be performed in accordance with checklists contained in 0.S1-82-4, including a requirement to open the B-Train ABGTS exhaust fan breaker (2-BKR- 30-157) [El IS Code BKR] prior to beginning test performance to prevent its operation during the test. Section 1.3 (Frequency and Conditions) of the procedure addresses Tech Spec considerations for affected equipment based on existing plant Mode, including LCO 3.7.12. Further, Section 3.0.R states that the test instruction is not to be performed while either diesel generator 1A-A or 2A-A is inoperable. However, as a result of inattention and inadequate communications by a licensed test director, at approximately 1324 hours0.0153 days <br />0.368 hours <br />0.00219 weeks <br />5.03782e-4 months <br />, an assistant unit operator (AUO) opened 2-BKR-30-157 which rendered B-Train ABGTS inoperable. As a result of this inappropriate action, both trains of ABGTS were inadvertently and unknowingly rendered inoperable for approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and hence the required action to terminate fuel movement activities was not initiated.
At 1516 hours0.0175 days <br />0.421 hours <br />0.00251 weeks <br />5.76838e-4 months <br />, main control room (MCR) personnel became aware of the open breaker status upon notification by the performers (AUOs) that a portion of the checklist had been completed, including opening of the breaker. An Senior Reactor Operator (SRO) immediately realized the breaker condition as improper and directed the breaker to be re-closed. An operator was immediately dispatched and the breaker was closed at 1521 hours0.0176 days <br />0.423 hours <br />0.00251 weeks <br />5.787405e-4 months <br /> restoring ABGTS Train B to OPERABLE status.
Problem Evaluation Report (PER) 03-016948-000 was initiated to document this event in the TVA Corrective Action Program.
II. Description of Events (continued) B. Inoperable Structures, Components, or Systems that Contributed to the Event 1) Emergency Diesel Generator 2A-A - Diesel generator inoperable but not required to be Operable in accordance with TS 3.8.2, since both B-Train Diesels were Operable.
2) ABGTS Exhaust Fan A-A - Inoperable due to EDG 2A-A unavailability but capable of performing intended function from normal power supplies, assuming no loss of offsite power.
3) ABGTS Exhast Fan B-B - Required to be Operable and protected for the current plant condition. it was rendered inoperable once its associated exhaust fan breaker was opened.
4) A-Train Unit 1 Elevation 737 Penetration Room Cooler [EDS Code Bl] which provides required cooling for A-Train ABGTS and penetration room equipment was unavailable due to maintenance on its essential raw cooling water supply. However, the redundant B-Train Unit 1 Elevation 737 Penetration Room Cooler was available and also provides cooling for Train A ABGTS, C. Dates and Approximate Times of Major Occurrences Date Time Event 9-07-03 1802 WBN plant shut down to begin refueling outage.
9-30-03 0415 Emergency diesel generator 2A-A inoperable due to cross training Train A essential raw cooling water (ERCW) with Train B. This action was performed in preparation for Train A ERCW outage.
9-30-03 1643 WBN began reloading core and entered Mode 6.
9-30-03 1643 Entered TS 3.7.12 Condition A for Train A ABGTS inoperable due to 2A-A Diesel Inoperable.
10-01-03 0300 Preparations began for preliminary equipment alignments for 0-51-82-4.
10-03-03 1324 AU0 inappropriately opened breaker for Train-B ABGTS exhaust fan, 2-BKR-30-157.
10-03-03 1324 Both trains ABGTS technically inoperable (Not realized).
10-03-03 1516 MCR personnel became aware of mis-positioned breaker and entered LCO 3.7.12, Condition D for both trains inoperable.
10-03-03 1521 2-BKR-30-157 closed; Train B ABGTS restored to Operable status.
D. Other Systems or Secondary Functions Affected
There were no other systems affected.
E. Method of Discovery
MCR personnel became aware of the open breaker status upon notification by the performers (AU0s) that a portion of the checklist had been completed, including opening of the breaker. An SRO immediately realized the breaker condition as improper and directed the breaker to be re-closed.
F. Operator Actions
Operations personnel responded by immediately dispatching an operator to close the B Train ABGTS breaker, 2-BKR-30-157. Refer to Section III. Cause of the Event, for circumstances related to human performance.
Description of Events (continued)
G. Safety System Responses
Plant safety systems operated as designed. However, as described above, ABGTS Train A was technically inoperable at the time of the event but capable of performing its intended function, assuming no loss of offsite power. For the actual plant conditions, both trains of preferred offsite power circuits were available and capable of supplying ABGTS Train A power requirements.
III. CAUSE OF THE EVENT
A. Immediate Cause
The immediate cause of the event was inattention by a shift test director who was not aware the A-Train ABGTS was inoperable when directing personnel to perform equipment alignments for an upcoming test, which included opening the subject breaker for B-Train ABGTS. The test director did not meet management expectations for consulting the Technical Specifications tracking log to assess the impact of plant manipulations on other equipment that was out of service.
B. Root Cause
The root cause of this event was inattention and inadequate communication by a shift test director responsible for directing alignment activities associated with test prerequisites. The test director realized a "protected" component (B-Train ABGTS exhaust fan breaker) would be de-energized and requested notification from the performers following equipment alignments. However, the specifics of this evolution were not adequately discussed with the performers and other MCR personnel to ensure sufficient awareness and focus on the activity. As a result, the MCR did not become aware of the open breaker status until completion of the checklist, about two hours after the breaker was opened.
C. Contributing Factors
A contributing factor was inadequate work planning/scheduling for the test, 0-S1-82-4, in that the preliminary equipment alignments were not addressed separately in the Outage Schedule.
IV. ANALYSIS OF THE EVENT
The ABGTS consists of two independent and redundant trains which filter airborne radioactive particulates from the area of the spent fuel pool following an FHA and from the area of active Unit 1 Emergency Core Cooling Components and Unit 1 penetration rooms following a loss of coolant accident (LOCA). The ABGTS is a standby system, not used during normal plant operations. The ABGTS design basis is established by the consequences of the limiting FHA. The analysis of the FHA assumes that all fuel rods in an assembly are damaged. The design basis accident analysis of the FHA assumes that only one train of the ABGTS is functional due to a single failure that disables the other train. The accident analysis accounts for the reduction in airborne radioactive material provided by the one remaining train of this filtration system. The amount of fission products available for release from the Auxiliary Building Secondary Containment Enclosure is determined for an FHA and for a LOCA. Since the plant was in Mode 6, the LOCA mitigation function of the ABGTS was not required.
For the subject event, an operator inappropriately opened breaker 2-BKR-30-157 for the protected B-Train ABGTS Exhaust Fan rendering its filtration train inoperable. As a result, both trains of ABGTS were unknowingly rendered inoperable for approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> until the mis-positioned breaker was discovered and restored. In this condition, WBN TS require immediate suspension of the movement of irradiated fuel to eliminate the possibility for the occurrence of an FHA concurrent with an inoperable ABGTS system. Although the need to suspend fuel movement was not realized, it is very likely that at least one train of ABGTS would have been available to perform its required safety function in the event of a design basis FHA. For the FHA, site emergency procedures require the operator to promptly assure ABGTS is in operation. ABGTS status indication is provided in the MCR and breaker restoration can be quickly performed in the adjacent 480V board room of the Auxiliary Building. In addition, with off site power available, the A Train ABGTS train would have immediately responded to an event and begun to perform its filtration function while the otherwise operable B train was manually restored. Although Unit 1 737 Train A Penetration Room Cooling was unavailable, Train B Penetration Room cooling was available to ensure cooling for A Train ABGTS.
The following evaluation considered the consequences of an FHA in the Auxiliary Building with no ABGTS safety function. For the subject event, plant shut down occurred at 1802 hours0.0209 days <br />0.501 hours <br />0.00298 weeks <br />6.85661e-4 months <br /> on September 7. 2003. Consequently, the fuel had decayed approximately 619 hours0.00716 days <br />0.172 hours <br />0.00102 weeks <br />2.355295e-4 months <br /> when this event occurred.
Results:
The control room doses are as follows (rem):
Spent Fuel Pit/Auxiliary Building FHA, 20.6 seconds MCR isolation Standard Core ARCON96 Gamma 2.804E-02 Beta 4.097E-01 Thyroid (ICRP-30) 21.50E+00 The offsite doses were determined to be (rem):
Spent Fuel Pit/Auxiliary Building FHA Standard Core 2-hr EAB 30-day LPZ Gamma 3.107E-02 7.218E-03 Beta 1.316E-01 3.058E-02 Thyroid (ICRP-30) 24.21E+00 5.623+00 Based on this evaluation, the MCR operator doses resulting from a FHA with 619 hours0.00716 days <br />0.172 hours <br />0.00102 weeks <br />2.355295e-4 months <br /> decay time and no ABETS are less than the 10 CFR 50, Appendix A, GDC 19 limits of 5 rem gamma, 30 rem beta. 30 rem thyroid. The 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> Site Boundary (SByExclusion Area Boundary (EAB) and 30 day Low Population Zone (LPZ) doses from a FHA are less than 25 percent of the 10 CFR 100 limits of 25 rem gamma, 300 rem beta, and 300 rem thyroid (= 6.25 rem gamma, 75 rem beta, 75 rem thyroid).
V, ASSESSMENT OF SAFETY CONSEQUENCES Based on the discussion in Section IV above, there was no safety significance to this event.
VI, CORRECTIVE ACTIONS
A. Immediate Corrective Actions
The immediate corrective action was to close Train B ABGTS breaker which restored the system to operable status and exit the LCD. In additional, stand downs with both night shift and day shift were conducted reemphasizing refueling outage technical specification requirements. The independent work of the individual was also restricted until management determined that standards and expectations were understood and were being implemented.
B. Corrective Actions to Prevent Recurrence: (TVA does not consider these items to constitute regulatory commitments, TVA's corrective action program tracks completion of these actions.) 1. The test director was counseled on maintaining attention to detail and adequate communication with MCR personnel during test activities.
2. The test director will be retrained on Management expectations for maintaining an awareness of plant conditions and protected equipment, including use of the TS Tracking log.
3. A separate item will be added to future refueling outage schedules to address the performance of prerequisites for all 18 Month Loss of Power (blackout) testing procedures.
4, � Coached the responsible Unit SRO on the need for maintaining proper communication with test personnel during testing activities.
5. As an enhancement, the diesel generator Blackout testing procedures will be revised to add additional procedural controls to prevent removing both trains of ABGTS from service.
6. Add Blackout testing to the Operations "Just in Time" refueling outage training matrix.
VII. ADDITIONAL INFORMATION
A. Failed Components
There were no failed components that contributed to this event. Once the subject breaker was closed, ABGTS Train B was capable of performing its function. In addition, Train A ABGTS remained capable of performing its required function using preferred offsite power.
B. Previous LERs on Similar Events A review of previous WBN LERs indicated there have been several events involving redundant safety systems being concurrently inoperable but none have resulted from inappropriate component manipulations in support of planned testing.
VII. ADDITIONAL INFORMATION (continued) C. Additional information None.
D. Safety System Functional Failure Consideration
This event is considered a safety system functional failure for ABGTS in accordance with Nuclear Energy Institute (NEI) 99-02, Revision 0, since the system was rendered incapable of automatically performing its safety function as designed.
E. Loss of Normal Heat Removal Consideration This event did not result in a scram and did not involve a loss of heat removal.
WU, COMMITMENTS
None.