05000260/LER-2014-001
| Browns Ferry Nuclear Plant (Bfn), Unit 2 | |
| Event date: | 03-27-2014 |
|---|---|
| Report date: | 12-23-2014 |
| 2602014001R01 - NRC Website | |
I. Plant Operating Conditions Before the Event
At the time of discovery, Browns Ferry Nuclear Plant (BFN), Unit 2, was in Mode 1 at approximately 100 percent power and BFN, Unit 1, was in Mode 1 at approximately 78 percent power.
II. Description of Events
A. Event:
On March 27, 2014, BFN determined, by performing a past operability evaluation, that the Required Actions of Technical Requirements Manual (TRM) 3.7.6, Electric Board Room Air Conditioning (AC) System, Condition B would allow both BFN, Unit 2, Electric Board Room (EBR) AC subsystems [ACU] to be inoperable for up to 7 days before declaring the Technical Specifications (TS) supported equipment in the EBRs inoperable. The 7 days is based on placement of a temporary method of cooling in service within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The established temporary method of cooling has not been documented to comply with necessary design requirements such as use of safety-related components, reliable power supply, and seismic qualifications. This TRM 3.7.6 Condition B allowance is contrary with the TS definition of "Operable- Operability" with respect to support systems.
At BFN, there are four EBRs shared between Units 1 and 2. Located in each EBR are 4160 volt and 480 volt Shutdown Boards. EBRs A and B receive room cooling (air conditioning) from either of two BFN, Unit 1, EBR Air Handling Units (AHUs).
EBRs C and D receive room cooling from either of two BFN, Unit 2, EBR AHUs. The EBR AHUs are safety-related Since the BFN, Unit 2, EBR AC System could not perform its necessary support function with both BFN, Unit 2, EBR AC 'A' and 'B' subsystems inoperable, the associated electrical power distribution subsystems were inoperable and resulted in a TS loss of safety function. As a result, BFN, Units 1 and 2, should have entered TS 3.8.7, Distribution Systems - Operating, Condition I. Condition I of TS 3.8.7, requires with two or more electrical power distribution subsystems inoperable that result in a loss of function, immediate entry into Limiting Condition for Operation (LCO) 3.0.3 and a required shutdown.
It was determined, for the past three years, from the past operability evaluation that the EBR AC System and, as a result, its TS supported systems on BFN, Unit 2, were inoperable longer than allowed by TS from October 26, 2011, at approximately 2330 hours0.027 days <br />0.647 hours <br />0.00385 weeks <br />8.86565e-4 months <br /> Central Daylight Time (CDT) to October 28, 2011, at approximately 1448 hours0.0168 days <br />0.402 hours <br />0.00239 weeks <br />5.50964e-4 months <br /> CDT and from February 2, 2013, at approximately 0740 hours0.00856 days <br />0.206 hours <br />0.00122 weeks <br />2.8157e-4 months <br /> Central Standard Time (CST) to February 3, 2013, at approximately 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> CST.
B. Status of structures, components, or systems that were inoperable at the start of the event and that contributed to the event:
Voluntary removal of the BFN, Unit 2, EBR AC subsystems from service caused 1 them to be inoperable and contributed to the failure to comply with TS requirements.
C. Dates and Approximate Times of Occurrences:
March 27, 2014 Operating instruction 0-01-31, Control Bay and Off-Gas Treatment Building Air Conditioning System, Revision 4 was issued with a section for implementation of temporary cooling and provide direction to not declare inoperability until the EBR reached 104°F. A 10 CFR 50.59 review was performed for this change to the operating instruction.
TRM 3.7.6 was created. A 10 CFR 50.59 review was performed for the addition of new TRM 3.7.6.
Operations personnel stopped the voluntary entry into TRM 3.7.6 Condition B for preventive maintenance (PM) on BFN, Unit 2, EBR AC System. A past operability evaluation was requested.
Past operability evaluation determined that BFN, Unit 2, operated in a condition prohibited by TS.
May 23, 1989 August 2000 January 27, 2014 1 D. Manufacturer and model number (or other identification) of each component that failed during the event:
There were no components that failed from this identified condition.
E. Other systems or secondary functions affected:
There were other systems affected in the EBR that are supported by the EBR AC System, i.e., 4kV Shutdown Boards [EB], 480V Reactor Motor Operated Valve Boards [ED], 250V Reactor Motor Operated Valve Boards, instrumentation and controls (I&C) Bus Transformers [XFMR], l&C Bus Voltage Regulators [RG].
F. Method of discovery of each component or system failure or procedural error:
The condition was discovered during the performance of a past operability evaluation.
G. The failure mode, mechanism, and effect of each failed component, if known:
There were no components that failed for this identified condition.
H. Operator Actions:
There were no Operator actions for this identified condition.
I. Automatically and manually initiated safety system responses:
There were no safety system responses for this identified condition.
Ill. Cause of the Event A. The cause of each component or system failure or personnel error, if known:
Direct Cause Failure of BFN personnel to recognize that the inability to independently isolate the BFN, Unit 2, EBR Air Handling Units (AHUs) requires shutdown of both trains and entry into LCO 3.0.3 by Units 1 and 2 for performance of maintenance.
Root Cause
BFN personnel failed to fully understand the difference between the Technical Requirements Manual (TRM) and Technical Specifications (TS) with respect to operability. When the TS and TRM were implemented, BFN personnel failed to realize the intent of the TRM and believed it was at the same level of the TS.
B. The cause(s) and circumstances for each human performance related root cause:
There was a demonstrated weakness in the ability of BFN personnel to recognize the relationship of the TRM and TS with regard to how to apply the TS definition of Operable-Operability.
IV. Analysis of the Event
The Tennessee Valley Authority (WA) is submitting this report in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.73(a)(2)(i)(B), any operation or condition which was prohibited by the plant's TS.
It was determined that the use of temporary cooling which was not safety-related began long before the TRM was issued. The following explains the progression that led to the incorporation of the use of temporary cooling into the TRM.
During the preparations for recovery of BFN, Unit 2, from the BFN, Units 1, 2, and 3, shutdown in 1985, the need to incorporate Environmental Qualification (EQ) requirements into the restart efforts was recognized. On May 15, 1987, an Engineering Change Notice (ECN) was issued to provide a permanent fix to address redundancy, load shed, and electrical separation issues previously discovered on the EBR AC Systems.
When the ECN was implemented prior to BFN, Unit 2, restart in 1991, it was not recognized that there were no provisions for performing maintenance activities on one subsystem of cooling without affecting the other subsystem.
On May 23, 1989, operating instruction 0-01-31 Revision 4 was issued to provide guidance to declare EBR ventilation inoperable if room ambient temperature exceeds 104°F. Operating instruction 0-01-31 Revision 4 was issued with a section for implementation of temporary cooling and direction to declare inoperability of the components in the EBR when the room reached 104°F. At the time the revision was issued, this appeared to be appropriate because all BFN Units were in an extended shutdown. At the time of the revision, it was not recognized that for BFN, Unit 2, restart that the TS definition of "Operable-Operability" would need to be applied.
The definition of "Operable-Operability" states:
A system, subsystem, division, component, or device shall be Operable or have Operability when it is capable of performing its specified safety function(s) and when all necessary attendant instrumentation, controls, normal or emergency electrical power, cooling and seal water, lubrication, and other auxiliary equipment that are required for the system, subsystem, division, component, or device to perform its specified safety function(s) are also capable of performing their related support function(s).
It was incorrectly believed that maintaining the room below 104°F would satisfy Operability requirements and non-qualified temporary cooling would satisfy that requirement.
The issue with operating instruction 0-01-31 Revision 4 was that qualified temporary cooling was needed to support the safety-related components located in the EBR with the normal safety-related EBR AC Systems out of service to meet the same safety- related qualification requirements. Use of the non-qualified temporary cooling equipment did not satisfy the TS definition of "Operable-Operability" with respect to support systems. The error has been carried forward into the latest revision of operating instruction 0-01-31. Additionally, it was determined operating instruction 0-01-31 is in error because it has inoperability declared only when the room temperature reaches 104°F. With both BFN, Units 1 and 2, shutdown, this position would be appropriate.
However, with either unit in operation, the safety-related EBR AC System is required to
IV
be Operable to maintain the Operability of safety-related components in the EBR in the event of a design basis accident with a loss of offsite power. Therefore, the Operability of the components in the EBR, when either unit is in operation, is based on EBR AC System Operability and maintaining temperature less than or equal to 104°F.
All revisions of operating instruction 0-01-31 were reviewed from Revision 4 to current which affected the temporary configuration. During the reviews, it was identified that the 10 CFR 50.59 screenings for each of the revisions was marked "NO" in relation to impact to TS. The 10 CFR 50.59 process should have been a barrier to prevent the inoperability of TS components from going un-recognized. It was identified that the qualified 10 CFR 50.59 screeners also did not recognize or challenge the use of the non-qualified temporary cooling to support safety-related TS component Operability.
The requirements for 10 CFR 50.59 qualification were reviewed and it was identified that the process relies on experience gained through years of progression through an individual's career and does not include specific requirements for a plant specific knowledge of BFN TS and FSAR.
On May 24,1991, BFN, Unit 2, was returned to operation following an extended shutdown. This is the point at which the errors in operating instruction 0-01-31 become significant.
From January 7, 1994, to February 3, 2013, an EQ PM was performed on the BFN, Unit 2, EBR AC 'A' and 'B' subsystems using electrical preventive instruction (EPI)-2-031-CHR001, Inspection and Maintenance of the Electric Board Room 2A/2B Air Handling Units, multiple times. This required Operations personnel to remove both EBR AC 'A' and 'B' subsystems from service and result in the implementation of the non-qualified temporary cooling using operating instruction 0-01-31. During each of these evolutions, it was not recognized that the TS supported equipment, i.e., electrical power distribution subsystems, were inoperable.
In August 2000, a calculation was issued to support the use of temporary duct fans if room ambient conditions exceed 94°F. The calculation supported a TRM change that added a new TRM section for each BFN unit to enhance the controls and emphasis placed on Operability of the EBR AC System. The new sections provided guidance on installation of fans and ductwork. However, it was not recognized that, with the EBR AC System inoperable while using non-qualified temporary cooling equipment, that the supported TS components, i.e., electric distribution systems, were also inoperable. The TRM change package indicated that the TS were not impacted. It was identified that the 10 CFR 50.59 reviews for the TRM revision was marked "NO" in relation to impact to TS.
It was determined that the qualified 10 CFR 50.59 screeners also did not recognize or challenge the use of the non-qualified temporary cooling to support the Operability of TS safety-related components.
On May 22, 2007, BFN, Unit 1, returned to operation following an extended shutdown.
Since BFN, Unit 1, restarted, the EQ PM was performed on the BFN, Unit 1, EBR AC 'A' and 'B' subsystems using EPI-1-031-CHR001, Inspection and Maintenance of the Electric Board Room 1A/1B Air Handling Units, multiple times. With the return to operation of BFN, Unit 1, performance of the EQ PM on BFN, Unit 2, should have required both Units 1 and 2, to be shutdown for performance of the PM due to impact of EBR AC System inoperability and TS supported systems Operability. However, the associated TS supported systems were not declared inoperable.
On January 27, 2014, the EQ PM was scheduled to be performed on the BFN, Unit 2, EBR AC System using EPI-2-031-CHR001. The Senior Reactor Operator that was contacted did not allow voluntary entry into TRM 3.7.6 Condition B and stopped the planned maintenance activity. Voluntary entry into TRM 3.7.6, Condition B would allow two BFN, Unit 2, EBR AC subsystems to be made inoperable. This would have been contrary to TRM 3.7.6, Required Action B.1 which states: Initiate action to restore one EBR AC subsystem to Operable status Immediately. It was identified that the EQ PM had been performed previously using voluntary entry into TRM 3.7.6 Condition B and reliance on TRM 3.7.6 Required Actions B.2 and B.3 to allow maintenance to be performed without declaring the associated TS supported systems inoperable. Upon review of the TRM requirements, a past operability evaluation was requested to assess any previous voluntary entries into TRM 3.7.6 Condition B.
On March 27, 2014, the past operability evaluation was approved by Operations personnel. The past operability evaluation concluded that the BFN, Unit 2, EBR AC System was inoperable on two occasions within the past three years when both subsystems were removed from service greater than 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br />. It was determined that the EBR AC System and its supported systems on BFN, Unit 2, were inoperable longer than allowed by TS from October 26, 2011, at approximately 2330 hours0.027 days <br />0.647 hours <br />0.00385 weeks <br />8.86565e-4 months <br /> CDT to October 28, 2011, at approximately 1448 hours0.0168 days <br />0.402 hours <br />0.00239 weeks <br />5.50964e-4 months <br /> CDT and from February 2, 2013, at approximately 0740 hours0.00856 days <br />0.206 hours <br />0.00122 weeks <br />2.8157e-4 months <br /> CST to February 3, 2013, at approximately 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> CST.
Based on the results of the root cause analysis, the cause analysis team determined that the BFN 10 CFR 50.59 screeners and evaluators did not recognize that the changes being evaluated had potential TS impacts. Investigation identified, at the time of the changes, the screeners and evaluators were not experienced with the use of the TRM and it was unclear as to the hierarchy of the TRM and TS. This unclear hierarchy or relationship led the screeners and evaluators to inappropriately approve a change in the TRM that should have been made in the TS and receive NRC approval. Proper understanding of the hierarchy or relationship of the TS and TRM would have led the screeners to answer the question, "Is a change to the T/S required for conducting or implementing the change (design or procedure), test, or experiment", as yes.
The cause analysis team saw elements of confusion of the hierarchy of design basis documents (TS and TRM) and lack of program guidance as to the use of the TRM with regard to the changes being evaluated. Further complicating this misunderstanding is the fact the TRM uses the terms of "operability" and " operable", which is the same terminology as that in the TS.
V. Assessment of Safety Consequences
Two redundant subsystems of the EBR AC System are required to be Operable to ensure that at least one is available, assuming a single failure under design basis accident conditions (i.e., loss of coolant accident with a loss of off-site power) disables the other subsystem. Total system failure could result in the equipment operating temperature exceeding the 104°F Operability limit.
Voluntary entry into TRM 3.7.6, Condition B allowed the BFN, Unit 2, EBR AC System to be made inoperable. This is a contradiction to TRM 3.7.6, Required Action B.1 which states: Initiate action to restore one Electric Board Room AC subsystem to Operable status Immediately. Operations personnel were relying on TRM 3.7.6 Required Actions B.2 which states, "Place an alternate method of cooling in operation in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />," and B.3 which states, "Restore one electric board room AC subsystem to Operable status in 7 days," to allow maintenance to be performed without declaring the associated TS supported systems inoperable.
The past operability evaluation determined that while Operability was not maintained under these conditions, functionality was maintained through the use of non-qualified temporary cooling to ensure temperature in the EBR would not exceed the 104°F Operability limit of the associated safety-related components.
Based on the analysis above, there was no significant effect on safety consequences.
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event:
This condition did not result in any components and/or systems that failed.
B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident:
The reactor was not in shutdown at the time the condition was identified.
C. For failure that rendered a train of a safety system inoperable, an estimate of the elapsed time from the discovery of the failure until the train was returned to service:
It was determined, for the past three years, from the past operability evaluation that the BFN, Unit 2, EBR AC System and, as a result, its supported systems on BFN, Unit 2, were inoperable longer than allowed by TS from October 26, 2011, at approximately 2330 hours0.027 days <br />0.647 hours <br />0.00385 weeks <br />8.86565e-4 months <br /> Central Daylight Time (CDT) to October 28, 2011, at approximately 1448 hours0.0168 days <br />0.402 hours <br />0.00239 weeks <br />5.50964e-4 months <br /> CDT and from February 2, 2013, at approximately 0740 hours0.00856 days <br />0.206 hours <br />0.00122 weeks <br />2.8157e-4 months <br /> Central Standard Time (CST) to February 3, 2013, at approximately 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> CST. In addition, the BFN, Unit 2, EBR AC System was inoperable from March 10, 2012, at approximately 1450 hours0.0168 days <br />0.403 hours <br />0.0024 weeks <br />5.51725e-4 months <br /> CST to March 10, 2012, at approximately 2250 hours0.026 days <br />0.625 hours <br />0.00372 weeks <br />8.56125e-4 months <br /> CST which was within the TS limits.
After further review of the condition, it was determined that BFN, Units 1 and 2, did not experience a SSFF.
VI. Corrective Actions
Corrective Actions are being managed by TVA's corrective action program under Problem Evaluation Report (PER) 846040. In addition to the corrective actions listed below, other corrective actions are being implemented to address the human performance issues associated with this event.
A. Immediate Corrective Actions:
An Operations standing order was issued on the TRM deficiency and will remain in place until the TRM is corrected. The Standing Order requires in the event of two EBR AC subsystems becoming inoperable to immediately declare the supported systems inoperable.
B. Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future.
Revise the TRM to clearly delineate the intent and use with respect to operability.
The revision will consist of an addition to TRM Section 1.0, Use and Application, which clearly delineates the intent and use of the TRM with respect to operability and defines the appropriate use of the TRM versus the TS.
Revise NPG-SPP-3.12, "Technical Specifications/Licenses and amendments", to clearly delineate the role of the TRM and TS.
VII. ADDITIONAL INFORMATION
A. Previous Similar Events:
A search of BFN LERs for Units 1, 2, and 3 for approximately the past five years did not identify any previous similar conditions in LERs.
A search was performed on the BFN corrective action program. The search identified PERs 59167, 211522, and 841629 as being similar to the condition identified in this LER. These PERs would not have prevented this condition.
B. Additional Information:
There is no additional information.
C. Safety System Functional Failure Consideration:
In accordance with NUREG-1022, this condition is not considered a SSFF. The original review determined that there was a SSFF. However, that was predicated on the assumption that multiple TS supported components were inoperable as a result of the both BFN, Unit 1, EBR AC subsystems being inoperable concurrent with other TS equipment being inoperable. Further review and evaluation determined that the BFN, Unit 1, EBR AC System has two 100% redundant trains that are isolable. No occurrences were identified where both Unit 1 EBR AC subsystems were out of service at the same time. Therefore, there were no instances where BFN, Unit 1, EBRs lost room cooling. As a result there was no SSFF associated with this event.
D. Scram With Complications Consideration:
This condition did not include a reactor scram.
VIII. Commitments There are no commitments.