Entergy does this over and over again?
January 19, 2017
Findings Introduction.
The inspectors reviewed a self-revealing finding of preliminary low to
moderate safety significance (White) and an associated apparent violation of
Unit 2 Technical Specification 6.4.1.a for the failure to provide adequate
lubrication to the inboard generator bearing so that the Unit 2 emergency
diesel generator A would provide emergency power to safety equipment. Specifically, two separate maintenance
activities introduced errors that led to having inadequate oil to lubricate the
bearing, and the bearing failed on September 16, 2016, during a 24-hour
surveillance.
Description. On
September 16, 2016, 14 hours into a 24-hour surveillance at full load, the
inboard generator bearing for the Unit 2 emergency diesel generator A failed,
as evidenced by load swings, overheating, and sparking. Operators secured the diesel, declared it
inoperable, documented the failure in Condition Report CR-ANO-2-2016-03307, and
complied with Unit 2 Technical Specification 3.8.1.1, “A.C. Sources,” Action
B. Maintenance personnel discovered
significant damage to the bearing indicative of a lack of oil lubrication. On September 28, 2016, the licensee shut Unit
2 down prior to the expiration of the technical specification action
statement. The licensee completed
repairs and successfully tested the diesel on October 22, 2016, and restarted
Unit 2 on October 27, 2016.
During a causal investigation for the lack of lubrication,
the licensee identified that the oil level scribe mark on the sight glass was
below the minimum level necessary to provide proper oil lubrication to the
bearing. The licensee concluded that on
November 11,2014, while performing Work Order 356569, maintenance personnel had
removed and inadvertently inverted the sight glass, which caused the scribe
mark to be below the bottom of the bearing rollers (see diagram below). With the sight glass inverted, the scribe
mark was 3/8-inch lower than if it was in the correct orientation. Post-failure measurements identified that the
scribe mark was 5/8-inch below the correct position. The licensee concluded that adequate oil was
initially provided following the sight glass reinstallation. Evidence to support this included multiple
successful surveillance tests with no increase in vibrations, including a
24-hour surveillance on January 12, 2015, and having an oil sample from the
bearing on June 22, 2016, with no indications of abnormal wear. On June 22, 2016, maintenance personnel
changed the oil in the inboard generator bearing after taking an oil sample in
accordance with Work Order 52656389.
Maintenance personnel documented leaving the oil level within the
procedural limits relative to the scribe mark.
Vibrations and system performance were normal during the
post-maintenance runs and surveillance tests on June 26, 2016. The licensee determined that the inboard
generator bearing had not been leaking oil between the oil change on June 22,
2016, and the September 16, 2016, surveillance failure.
The licensee concluded that the oil in the inboard generator
bearing heated up slowly during the 24-hour surveillance. After 14 hours, enough oil had vaporized
within the bearing casing that the liquid oil level became inadequate to
lubricate the bearing, resulting in bearing failure. Therefore, the inspectors concluded that the
emergency diesel generator could have failed approximately 14 hours after the
start of a postulated event between June 26, 2016, and September 16, 2016. The inspectors concluded that multiple causes
led to the lack of oil lubrication. The
licensee failed to incorporate vendor manual instructions to properly set and
verify the correct oil sight glass scribe mark into Work Order 356569 for
maintenance performed in 2014. The
licensee failed to train maintenance personnel to adequately identify and
control critical parameters during maintenance, specifically the effects of
sight glass installation and maintenance on bearing lubrication. The inspectors also noted that work
instructions in Work Order 52656389 did not specify the correct amount of oil
to add when replacing the oil, or else measure the amount of oil removed and
ensure that a like amount of new oil was added to the bearing. On October 11, 2016, following bearing
reassembly, a system engineer checked the level of the new sight glass and
identified that the scribe mark was too low again. The licensee found that the new oil level had
been marked on the bearing housing prior to assembly, but that the oil level
was below the vendor-recommended level.
In response, the licensee planned and executed a work order to set the
oil level in relation to the generator shaft centerline in accordance with the
vendor recommendations. The inspectors
noted that the licensee had not yet implemented corrective actions to prevent
recurrence of the problem in that licensee’s work plans failed to include
verification of the oil level relative to the generator shaft centerline after
reassembling the bearing. The licensee
subsequently corrected the sight glass position and developed training and
improved work instructions to ensure that the bearing oil level would be
correctly established. After the diesel
bearing failure, the licensee verified through walk downs that all sight glass
marks and bearing oil levels were adequate for other safety-related rotating
equipment. The inspectors also
independently reviewed bearing oil levels.
January 20, 2017
Description. On
August 12, 2016, operations personnel noted elevated chilled water outlet
temperatures on essential chiller B.
Specifically, chilled water outlet temperatures reached between 45 and
46 degrees Fahrenheit, compared to the 42 degrees Fahrenheit maximum allowed
temperature. Due to the elevated
temperatures, at 5:04 p.m., operations personnel declared essential chiller B
inoperable. Because essential chiller A
was already inoperable due to a previous component failure, and there was no
applicable technical specification action statement, the licensee entered
Technical Specification 3.0.3, which required the licensee to begin shutting down
the reactor within 1 hour.
The licensee placed essential chiller AB into service in
place of essential chiller B, and at 6:02 p.m., declared essential chiller AB
operable, which provided the plant with one operable train of chilled
water. This, in turn, allowed the
licensee to exit Technical Specification 3.0.3.
The licensee remained in Technical Specification 3.7.12 and the
associated 72-hour shutdown action statement until maintenance was completed on
essential chiller A and it was declared operable at 11:00 p.m., providing the
plant with two independent, operable trains of chilled water.
Following inspector questions, the licensee performed a
calculation showing that adequate cooling capacity could be provided by the
essential chillers with an outlet temperature of 46 degrees Fahrenheit.
In troubleshooting the event, the licensee found that the
guide vane arm and actuator linkage for essential chiller B was assembled
inappropriately. The guide vane actuator
was previously replaced during an essential chiller B outage on April 11, 2016;
however, post-maintenance testing, an activity affecting quality to ensure that
the safety-related chiller would perform satisfactorily in-service, did not
discover the inappropriately assembled components.
Following the April 11, 2016, outage, the chiller was found
repeatedly tripping on low refrigerant pressure. However, the licensee mistakenly believed the
failures were due to a faulty capacity control module. The licensee replaced the capacity control
module and returned essential chiller B to service on April 22, 2016. Again, post-maintenance testing did not
discover the inappropriate guide vane arm and actuator linkage. The inappropriate guide vane and actuator arm
linkage assembly went undetected until a large load from switchgear ventilation
was placed on the chiller on August 12, 2016, resulting in its inoperability.
During extensive troubleshooting following the August 12,
2016, failure, the licensee inspected the guide vanes and found them
inappropriately aligned. The licensee
corrected the guide vanes, restarted essential chiller, and declared it operable
on September 3, 2016.
The guide vane and actuator arm assembly work is normally
performed by a mechanical maintenance technician, but during the April 11,
2016, maintenance outage, the work was performed by an electrical technician. The work was not verified by anyone from
mechanical maintenance.
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