05000483/LER-2006-007

LER-2006-007, Inoperability of Train A Containment Coolers Due to Inadequate Testing

Callaway Plant
Event date:	08-07-2006
Report date:	11-17-2006
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
4832006007R01 - NRC Website

A. REPORTABLE EVENT CLASSIFICATION

50.73(a)(2)(i)B — Operation or Condition Prohibited by Technical Specifications.

50.73(a)(2)(v)D — Event or Condition that Could Have Prevented Fulfillment of a Safety Function:

Mitigate the Consequences of an Accident.

B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT

Mode 1, 100% Reactor Power

THE START OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT

No system, structures, or components were Inoperable at the start of this event which contributed to the event.

D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES

During the refueling outage at Callaway Plant in the spring of 2001, new cleanable cooling coils were installed in one of two cooling units in each safety train of the Containment Cooling system. During the refueling outage in the fall of 2002, new cleanable cooling coils were installed in the remaining two cooling units of both safety trains of the Containment Cooling system. Throughout this time period, the primary method for verifying the Containment Cooling system operability had been the Delta Pressure method with secondary methods of Performance testing and Flow Rate testing until January 13, 2003. On January 13, 2003 Callaway Engineering personnel revised the Containment Cooler performance monitoring strategy to add the Periodic Maintenance (clean and inspect) method to the Callaway Heat Exchanger Predictive Performance program. (These testing methods are described in EPRI NP-7552, 'Heat Exchanger Performance Monitoring Guidelines', and ASME OM-S/G-2003 Part 21, 'Inservice Performance Testing of Heat Exchangers In Light-Water Reactor Power Plants', which give guidance on methods to meet Generic Letter 89-13, 'Service Water System Problems Affecting Safety-Related Equipment'.) After the new cooling coils were installed in the 2001 refueling outage, the following testing was performed to assure Containment Cooler Operability. At the end of each refueling outage, a flow balance of the Essential Service Water (ESW) system was performed to achieve acceptable flows for the required loads, with the Containment Coolers being one of the larger loads in this flow balance evolution. When the flow balance was performed, the differential pressure was measured across each Containment Cooler unit at the same time the flow was measured for each respective cooler. After the proper flow balance was established and the ESW system was declared operable, the ESW flow was measured monthly for each train of Containment Coolers. This measured flow value, which had a minimum acceptance criterion, was then trended throughout the fuel cycle.

(Continued) Callaway personnel believed if ESW flow through the Containment Coolers did not degrade, then macrofouling was not increasing unacceptably to make the coolers inoperable. This reasoning was previously substantiated when a clam incursion into the Containment Coolers was experienced at Callaway Plant prior to the cooling coil replacements. The flow values measured monthly decreased during the clam incursion. Once the coolers were forward flushed, acceptable flow was achieved.

In December 2005 while investigating an unrelated issue, an NRC Resident Inspector at Callaway questioned the ability of the Containment Cooling system to remove a greater heat load in containment considering a given accident scenario, which would reduce the overall margin of the system's cooling capacity. Callaway Engineering personnel could not readily determine the value, because the as-found differential pressure readings were not measured and recorded prior to the coil cleaning which was performed in refueling outage RF14. An actual value for heat removal capacity was not calculated. This prompted the NRC Inspector to ask for the amount of the heat removal capacity of the Containment Cooling trains using the Callaway Technical Specification Bases, Figure B 3.6.6-1, which is an operability curve based on cooling water flow and the heat removal capacity of the Containment Coolers with no cooling coil fouling. Callaway Engineering personnel could not readily determine the value due to the methodology used for testing and documenting Containment Cooling system operability.

The NRC Inspector independently performed calculations to determine operability of the Containment Coolers using a method different than that used by Callaway Engineering personnel. The Inspector's calculations resulted in identifying one data point at which the cooling capacity of the Train A Containment Coolers was not within acceptable limits. The calculation included very conservative estimates on predicted fouling of the Containment Coolers. In response to the issue, Callaway Engineering personnel provided the documentation showing Containment Cooler flows and differential pressure measurements, which were taken during the previous cycle and throughout the time period in question (August 16, 2005 through September 17, 2005) to prove system operability. The Inspector did not agree that the documentation proved the Train A Containment Cooling system was operable.

Callaway Plant had entered the refueling outage RF14 on September 17, 2005. The inside of the cooling coils of the A Containment Cooler was cleaned during the refueling outage between September 21, 2005 and October 12, 2005. The cooler flow and as-left differential pressure readings were measured and recorded after the coil cleaning was complete. However, the as-found differential pressure was not measured and recorded prior to cleaning the cooling coils. The as-found differential pressure for the A Containment Cooler was needed to calculate the cooling capacity including the effect of fouling of the cooling coils. Because the as-found differential pressure for the A Containment Cooler was not required to be measured and recorded by procedure or work document instructions prior to cleaning the A Containment Cooler coils, Callaway Engineering personnel could not perform the calculations required to prove the past operability of the Train A Containment Coolers for the time period in question.

(Continued) Callaway Plant received NRC report "Callaway Plant - NRC Integrated Inspection Report 05000483/2006003" on August 7, 2006. The report stated the performance data for the Train A Containment Coolers did not demonstrate the Containment Coolers were capable of performing their required design bases function during the time period between August 16, 2005 and September 17, 2005 due to fouling. The report further indicated the evaluation performed by Callaway Plant prior to returning the containment cooler to service was inadequate. Callaway Licensing and Engineering personnel met with the NRC Resident Inspector on October 23, 2006 to discuss this issue and review the bases and calculations used to reach the Inspector's conclusions. The Inspector discussed his analysis of the performance and trending data for Cycle 14 associated with the Containment Coolers and his independent calculations performed to verify operability of the Containment Coolers. Callaway Engineering personnel later determined the Train A Containment Coolers to be inoperable during the time period between August 16, 2005 and September 17, 2005.

ERROR

Callaway Plant received NRC report "Callaway Plant - NRC Integrated Inspection Report 05000483/2006003" on August 7, 2006. The report stated the performance data for the Train A Containment Cooler did not demonstrate the containment cooler was capable of performing the required design bases function during the time period between August 16, 2005 and September 17, 2005 because of fouling. The report further indicated the evaluation, performed prior to returning the containment cooler to service, was inadequate.

A. SAFETY SYSTEMS THAT RESPONDED

No safety system actuations occurred in this event.

B. DURATION OF SAFETY SYSTEM INOPERABILITY

The time period of the inoperability of the Train A Containment Coolers is from August 16, 2005 at 00:00 through September 17, 2005 at 19:50 when the plant entered mode 5 for refueling outage RF14.

The duration of the inoperability was 31 days, 19 hours2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br />, and 50 minutes. Because it was not recognized that the Train A Containment Coolers were inoperable during this period of time, entry into the applicable Technical Specification actions for the following conditions was not performed:

3.6.6.0 One Containment Cooling train inoperable in MODES 1, 2, 3, or 4.

Restore Containment Cooling train to OPERABLE status within 7 days and 10 days from discovery of failure to meet the LCO.

3.6.6.D Required Action and associated Completion Time of Condition C not met in MODE 1, 2, 3, or 4.

Be in MODE 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Be in MODE 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

(Continued) A review of Control Room Logs was performed to determine the operability of the Train B Containment Cooling System from August 16, 2005 at 00:00 through September 17, 2005 at 19:50. The Train B Containment Cooling System was found to be inoperable during the following time periods:

September 1, 2005 from 12:19 to 12:26 Train B Load Shed Emergency Load Sequencing inoperable due to surveillance testing.

September 6, 2005 from 00:15 to 00:38 Train B Essential Service Water inoperable due to surveillance testing.

September 7, 2005 from 02:27 to 02:51 Train B Essential Service Water inoperable due to surveillance testing.

September 8, 2005 from 08:43 to 09:27 Train B Emergency Diesel Generator inoperable due to maintenance work.

September 8, 2005 from 12:43 to 13:03 Train B Emergency Diesel Generator inoperable due to maintenance work.

September 13, 2005 from 14:10 to 15:13 Train B Essential Service Water inoperable due to surveillance testing.

Because both trains of the Containment Cooling System were inoperable during these time periods, entry into the applicable Technical Specification action for the following condition was also missed:

3.6.6.E Two Containment Cooling trains inoperable in MODES 1, 2, 3, or 4.

Be in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Be in Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT.

The degradation of the Train A Containment Coolers would not have had a significant impact on nuclear safety. Callaway Engineering personnel has determined the fouling of the Train A Coolers would have resulted in a heat removal capacity of no less than 120 MBTU/hr under accident conditions. The analysis of record at the time of the degradation credited a minimum heat removal capacity of 141.4 MBTU/hr under accident conditions. At the time of the degradation of the Train A Containment Coolers, the plant was in the original steam generator (OSG) configuration.

In order to determine the implications of the degradation, the OSG containment response to a Loss of Coolant Accident and Main Steam Line Break accident were re-run crediting a heat removal capacity of 100 MBTU/hr. The value of 100 MBTU/hr per train of coolers was selected to conservatively bound the 120 MBTU/hr worst case degradation discussed in this LER.

(Continued) The results of these sensitivity cases indicate that peak post-accident pressure would not be jeopardized by the degradation of Train A Containment Cooling system. The peak post-accident containment pressure of 48.1 psig reported in Callaway's FSAR would remain bounding.

Additionally, post-peak temperatures would not have had an adverse impact on the EQ envelope.

The degradation of the Train A Containment Coolers had the potential to challenge General Design Criteria 16 and 38:

Criterion 16—Containment design. Reactor containment and associated systems shall be provided to establish an essentially leak-tight barrier against the uncontrolled release of radioactivity to the environment and to assure that the containment design conditions important to safety are not exceeded for as long as postulated accident conditions require.

Criterion 38--Containment heat removal. A system to remove heat from the reactor containment shall be provided. The system safety function shall be to reduce rapidly, consistent with the functioning of other associated systems, the containment pressure and temperature following any loss-of-coolant accident and maintain them at acceptably low levels.

Since the peak post-accident pressure reported in the FSAR would not have been exceeded as a result of the degraded cooler train, the satisfaction of Criterion 16 regarding the containment design as essentially leak-tight would not have been jeopardized. Furthermore, based on satisfactory results regarding peak pressure, and the lack of adverse impact on the EQ envelope, it can be stated that the heat removal system would still have functioned to maintain post­ accident pressures and temperatures. Therefore, the satisfaction of Criterion 38 would not have been jeopardized by the degradation of the Train A Containment Cooling system.

The safety consequences of the inoperabilty of the Trains A and B Containment Coolers were evaluated within the context of the Callaway PRA model. The Callaway PRA large early release frequency (LERF) model credits the containment coolers for post-accident containment heat removal. However, the basic events representing failures of the containment coolers exist only in very low frequency LERF cutsets (scenarios). These cutsets are truncated from the LERF results during quantification. That is, their frequency of occurrence is below 1E-11 per year.

Consequently, failure of the containment coolers has no appreciable impact on the calculated Callaway LERF. Therefore, the event described herein is of very low risk significance.

III. CAUSE(S) OF THE EVENT AND CORRECTIVE ACTION(S)

A root cause analysis team was formed to perform the following:

• evaluate the applicable data and sequence of events.

• determine the root cause of the inoperabilty of the Train A Containment Coolers.

• and determine the appropriate corrective actions to prevent recurrence.

The root cause analysis team determined the root cause of the inoperability of the Train A Containment Coolers was that the testing was not adequately performed to produce a rigorous calculation, which could represent the current and past performance of the Train A Containment Coolers.

(Continued) Several corrective actions to improve Callaway Plant's heat exchanger testing program were identified, which would collectively prevent recurrence of this event. The corrective actions, listed below, will be incorporated to change the heat exchanger testing from a knowledge-based methodology to a rule-based methodology.

• Obtain industry expert to assist with the review of the heat exchanger program, Callaway's Technical Specifications requirements, and Callaway's commitments to GL 89-13.

• Incorporate other recommendations from the industry expert into the heat exchanger program to ensure compliance with regulatory requirements.

• Revise program to ensure proper documentation of trending required by GL 89-13 and ensure plots are sent to QA file to provide documentation of trending required by GL 89-13.

• Revise EDP-ZZ-01112, Heat Exchanger Predictive Performance Manual, to specify the minimum post-installation and post-modification retest requirements for safety-related heat exchangers.

• Include external operating experience to identify industry best practices for potential incorporation into the revised heat exchanger program at Callaway.

• Project effectiveness to accident conditions, if required, based on Callaway's Technical Specifications and commitments to GL 89-13.

• Determine if T/S Bases 3.6.6.7 and Figure B 3.6.6-1 should be revised or eliminated, based on Callaway's Technical Specifications and commitments to GL 89-13.

• Revise the surveillance procedures associated with T/S Bases 3.6.6.7 and Figure B 3.6.6-1.

• Revise work documents to measure as-found differential pressure prior to cleaning containment coolers each refueling outage.

• Establish requirements and responsibilities of heat exchanger engineer.

Corrective actions, which have been performed or are in progress, include:

• Cleaned the inside of the cooling coils of A Containment Cooler in Refuel 14.

• As-found flow balance values for both Containment Cooler trains were found acceptable during Refuel 14.

• Continuing monthly trending of Containment Cooler flow values.

• Verified Containment Cooler flows did norsubstantially degrade during Cycles 13 and 14.

Other associated corrective actions to be performed include:

• Purchase more accurate differential pressure gauges.

• Send a spare containment cooling coil offsite for testing to verify pressure drop assumptions across A Containment Cooler coil.

• Revise administrative procedure Government Agency Interface Instructions, to require a corrective action document to be generated to track open items or unresolved issues which are identified by a Regulator verbally or in written correspondence.

(Continued) The combination of all the corrective actions will provide the following:

• heat transfer test results,

• clean coil differential pressure measurements,

• the containment cooler heat transfer computer model,

• containment cooler cleaning/inspection cycles established,

• trends of as-found and as-left differential pressures measurements.

• ability to better predict cooler performance with much greater assurance using the above data in Engineering Calculations.

• more robust testing and monitoring program to prevent recurrence of the inoperability for Containment Coolers.

IV. PREVIOUS SIMILAR EVENTS

No previous similar events have been identified.

V. ADDITIONAL INFORMATION

The system and component codes listed below are from the IEEE Standard 805-1984 and IEEE Standard 803A-1984 respectively.

System:�BK Component: CLR The manufacturer of the replacement Containment Cooler coils is Aerofin Corporation.

Manufacturer's Code:�A089