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Nuclear Event – Automatic Reactor Trip: Watts Bar Nuclear Plant, Unit 2


North America – USA | State of Tennessee, Rhea County, Spring City, Watts Bar Nuclear Plant
Location: 35°36’10.0″N 84°47’22.0″W
Site Operational Age: ~31 years

Watts Bar Nuclear Plant (WBN)

Watts Bar Nuclear Plant (WBN), a Tennessee Valley Authority nuclear power plant located in Spring City, Tennessee. Image:

Nuclear Event in USA on Sunday, 05 June, 2016 at 12:27 [EDT].


“On June 5, 2016 at 1227 Eastern Daylight Time (EDT), Watts Bar Nuclear Plant (WBN) Unit 2 was in MODE 1 at approximately 12.5% power when a safety injection actuation occurred, followed by an automatic reactor protection system (RPS) trip. Preliminary data suggests that the #1 high pressure turbine governor valve failed open causing a steam header pressure rate of decrease safety injection [SI] actuation signal. As designed, the safety injection actuation caused both trains of the shared Emergency Gas Treatment System (EGTS) to align to Unit 2, requiring WBN Unit 1 to enter Technical Specification (TS) LCO 3.0.3 at 1227 [EDT]. Also as designed, Unit 1 annulus pressure momentarily increased, causing operation personnel to enter LCO 3.6.15 Condition B at 1240 [EDT]. At 1242 [EDT], after annulus pressure normalized, operations personnel exited LCO 3.6.15. At 1245 [EDT], Operations personnel secured safety injection and Unit 2 was stabilized in MODE 3 at normal operating pressure and temperature. By 1349 [EDT], Unit 1 Operations personnel had restored both trains of EGTS to standby readiness, and exited TS 3.0.3. No primary safety barriers (RCS, containment and fuel clad) were challenged and no primary or secondary safety or relief valves actuated during the event. The Unit 2 plant trip was uncomplicated and safety equipment operated as expected.

“Unit 2 is stable in Mode 3 at normal operating temperature and pressure, in normal shutdown power alignment. Unit 1 is stable in Mode 1 at 100% power.

“The Senior Resident Inspector has been notified of this event.”

The MSIVs are shut with the steam generators (SG) discharging steam using the atmospheric dump valves. There is no primary to secondary leakage. Motor driven AFW pumps are running to maintain SG levels. RCS pressure remained above ECCS (Emergency Core Cooling System) discharge pressure.

Source: NRC  Event Number: 51982


Previous Events

Nuclear Event in USA on Tuesday, 22 March, 2016 at 11:31 [EDT]. WATTS BAR AUTOMATIC REACTOR TRIP UNIT 1 [due to the actuation of the Over Temperature Delta Temperature bistables.]

Nuclear Event in USA on Thursday, 17 March, 2016 at 01:15 [EDT]. LOSS OF EMERGENCY AND AUXILIARY GAS TREATMENT SYSTEMS – UNIT 1

Nuclear Event in USA on Wednesday, 09 March, 2016 at 03:42 [EST]. UNUSUAL EVENT DECLARED DUE TO A FIRE GREATER THAN 15 MINUTES – UNIT 2

See Also

Grid connection for Watts Bar 2

June 6. 2016
World Nuclear News

Tennessee Valley Authority’s (TVA’s) Watts Bar unit 2 has supplied its first electricity to the power grid. The 1165 MWe (net) pressurized water reactor was synchronized to the grid on 3 June.

The unit will now undergo test runs of generation equipment, followed by full-plant testing of systems and controls at increasing reactor power levels up to 100% as it prepares for full power operation.

Watts Bar 2, near Spring City, Tennessee, reached first criticality on 23 May, over 40 years after construction of the unit first began in 1972. Work on the unit was suspended in 1985 when it was about 55% complete, but TVA decided to resume work in 2007, awarding an engineering, procurement and construction contract to Bechtel.

Upgrades in response to the Fukushima Daiichi accident of 2011 required by the Nuclear Regulatory Commission of all US nuclear power plants have been incorporated into Watts Bar 2, with orders related to post-Fukushima regulatory requirements and cyber security issues adding $125 million to TVA’s original $4.5 billion estimate to complete the project. A total estimated project cost of $4.7 billion was approved by TVA’s board in February.

“This is another major step in fully integrating Watts Bar unit 2 as the seventh operating unit in TVA’s nuclear fleet,” TVA chief nuclear operator Joe Grimes said.

The unit is expected to begin commercial operation later this summer.

Researched and written
by World Nuclear News

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