Technological Hazard – Nuclear Events: Susquehanna Nuclear Power Plant, Pennsylvania
Technological Hazard – Nuclear Event: Reactor Shutdown
North America – USA | State of Pennsylvania, Salem Township, – Susquehanna Nuclear Power Plant
Location: N 41° 5.333, W 76° 8.933
Time: 2015-04-10 at 23:46 [EDT]
Present Operational Age: ~32 years
Damage Level: RPS ACTUATION – CRITICAL
Nuclear Event in USA on Friday, 10 April, 2015 at 23:46 [EDT].
AUTOMATIC REACTOR SCRAM CAUSED BY MAIN TURBINE TRIP DUE TO DEGRADING MAIN CONDENSER VACUUM
“At 2346 EDT on April 10, 2015, Susquehanna Steam Electric Station Unit 2 reactor automatically scrammed due to a main turbine trip caused by loss of turbine steam seals and degrading main condenser vacuum.
“Unit 2 reactor was being shutdown for a refueling outage. At approximately 37 percent power, turbine steam seals were lost resulting in a degrading vacuum. The vacuum degraded quickly, resulting in a main turbine trip before the reactor operator could insert a manual scram. At 37 percent power, the turbine trip caused an automatic scram. This occurred during a transfer from normal steam seal supply to the auxiliary boiler supply. All control rods [fully] inserted. Reactor water level lowered to +2 inches causing Level 3 (+13 inches) isolation. No ECCS actuations occurred. The Operations crew subsequently maintained reactor water level at the normal operating band using RCIC [Reactor Core Isolation Cooling]. No steam relief valves opened. The reactor recirculation pumps tripped on EOC-RPT due to the turbine trip at power.
“The reactor is currently stable in Mode 3. Investigation into the cause of the loss of turbine steam seals is underway.
“The NRC Resident Inspector was notified. A voluntary notification to PEMA [Pennsylvania Emergency Management Agency] and press release will occur.”
Unit 2 is in a normal shutdown electrical lineup. Turbine steam seals were restored to the normal steam supply and condenser vacuum was restored. Decay heat is being removed via the steam bypass valves to the condenser. Unit 2 is proceeding with their cooldown to support the scheduled refueling outage.
Nuclear Event in USA on Saturday, 11 April, 2015 at 00:51 [EDT].
SECONDARY CONTAINMENT INOPERABLE DUE TO FAILURE OF RUNNING FANS
“On April 11, 2015 at 0051 EDT, Secondary Containment became inoperable requiring a Technical Specification 188.8.131.52 entry for failure to meet SR [Surveillance Requirement] 184.108.40.206.1 on Unit 1 and Unit 2, loss of required differential pressure.
“The inoperability was caused by a loss of normal Zone 2 differential pressure due to loss of running fans and failure to start of standby fans. The cause is being investigated.
“Engineering and maintenance personnel implemented a Temporary Engineering Change, which allowed restoration of one set of fans and dampers. Normal secondary containment differential pressure was restored. Technical Specification 220.127.116.11 was exited at 0320 EDT.
“This event is being reported under 10 CFR 50.72(b)(3)(v)(c) and per the guidance of NUREG 1022 Rev 3 section 3.2.7 as a loss of a Safety Function. There is no redundant Susquehanna Secondary Containment system.
“The NRC Resident Inspector was notified.”
Temporary Engineering Change consisted of removing air to a previously running fan discharge damper so it would close and allow standby fans to start.
Nuclear Event in USA on Saturday, 11 April, 2015 at 09:58 [EDT].
DRYWELL LEAKAGE POINT IDENTIFIED
“On 4/11/15, Unit 2 drywell entry was performed during a planned Unit 2 refueling inspection outage. At 0958 EDT, the licensee identified leakage from a weld on the 3/4 inch seal vent piping connected to the 2A reactor recirculation pump seal area. The location is within the reactor recirculation loop isolation valves, therefore it is isolable from the reactor vessel. The piping is ASME Class 2 and is a reactor coolant pressure boundary. The reactor was in mode 3 at the time of discovery.
“This event is being reported as a degraded condition pursuant to 10CFR50.72(b)(3)(ii)(A).”
The licensee notified the NRC Resident Inspector.