Palo Verde (USA)

Map of Palo Verde

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3 * 1300 MW PWR unit; constructed byCE; grid connection in 1985-87

Facilities in Palo Verde

plantreactor typconstruction startoperation startshut down
Palo Verde-1PWR19761985
Palo Verde-2PWR19761986
Palo Verde-3PWR19761987
1996-04-01

Damaged fuel assembly stuck in core of Palo Verde-2
Arizona Public Service Co. (APS) this week asked the NRC for the go-ahead to use special equipment in its attempt to dislodge a damaged 16X16 fuel assembly that has been stuck in the core of Palo Verde-2 since late last month. If any of the seven fuel pins protruding from the bottom of the assembly break during the move, radioactive gas would be released within the unit's containment.
According to the NRC, APS believes that the lower six inches of the assembly might be structurally damaged. It now is the only assembly left in Palo Verde-2. The root cause of the problem has not yet been determined.
The assembly weights about 675 kg and measures 200 mm square and 4 m high. It contains 236 fuel rods.
The procedure Arizona Service Co. (APS) took weeks to develop for removing a stuck assembly from the core of Palo Verde-2 took only a few minutes to implement early this week as an APS crew lifted the assembly out of the core and into the spent fuel pool.

1995-12-10

Palo Verde-1 tripped from 40% power late last week when a large, wild animal climbed onto transformer bus work in the switch-yard and grounded itself.

1995-12-01

Arizona Public Service Co. (AP) recently discovered that under a very unlikely scenario the auxiliary feedwater system at Palo Verde would not automatically supply water to the steam generators for a full 30 minutes, as calles for in the plant's safety analysis report (SAR).
As postulated, a steam line break under certain conditions could lead to one of the two steam generators in a Palo Verde unit boiling dry. Steam from the second generator, however, is expected to be sufficient to remove the heat from the core.
Officials were quick to point out that the likelihood of such an event is very slim. Calculations put the chances at one in 250-billion years.
NRC regulations require that APS essentially change the design. Two valves supplying steam to the turbine feedwater pump will be redesigned so that both open in the event of a steam break: now only one opens.

1995-12-01

Crews at Palo Verde-3 may have saved Arizona Public Service Co. (APS) about $ 11.5-million last week by wrapping up the unit's refueling outage in 47 days, Breaking all refueling records at the largest U.S. nuclear generating station.
The outage was originally planned to take 70 days. The previous record for the 3,921-MW station was set earlier this year when unit 2 was refueled in 54 days. In the spring, the outage at unit 1 was completed in 56 days. Prior to this year, the station record was 68 days.

1994-09-07

A distracted control room operator overfilled a volume control tank.(900 l more than needed); -> (non significant) change of core reactivity at 100% power. high level alarm aletted the operators to late.

1993-03-14

Tube rupture: hundreds of liters of contaminated water gushed from a ruptured SG tube: leak rate > 950 lit/min. Operators did not isolate the leaking SG for about 3 hours, until the primary and secondary pressures were equalized, to keep atmospheric releases routed through steam jet ejectors, which are filtered. If operators had had to use just one SG and dump steam through its safety relief valves, releases could have been unfiltered and higher ( release of noble gases is estimated by the company at 110 GBq).

1992-05-04

REACTOR POWER DECREASED TO 70%. ELECTRICAL SHORT CIRCUIT DURING CONTINUITY CHECK OF ALARM SYSTEM CAUSED PARTIAL LOSS OF THE NON-SAFETY RELATED ANNUNCIATOR SYSTEM. 1 of the 2 computer systems, that went down in the crash, was the core operating supervisory system that provides information on critcal tolerance limits. the control room lost most of its 2,000 alarms when the anunciator went down.

1991-11-15

Wind blown crane knockes out one of the power lines and initiated a series of events that led to the unit's being cooled by natural circulation for almost half an hour. miscommunication caused the unit-3 operators to disconnect the non-faulted remaining connection to the electrical grid. this caused the reactor coolant pumps to lose power. Coolant temperature was about 295 °C (delta-T across the core 30°)

1990-05-21

Ultimate heat sink: material misapplication could have degraded the ability to provide long term cooling following a LOCA; the keys that connect the valve stem and torque tube of essential spray pond valves were made of carbon steel and experienced corrosion failure.

1990-05-21

Ultimate heat sink: material misapplication could have degraded the ability to provide long term cooling following a LOCA; the keys that connect the valve stem and torque tube of essential spray pond valves were made of carbon steel and experienced corrosion failure.

1990-05-21

Ultimate heat sink: material misapplication could have degraded the ability to provide long term cooling following a LOCA; The keys that connect the valve stem and torque tube of essential spray pond valves were made of carbon steel and experienced corrosion failure.

1989-09-06

Inproperly set ring settings on steam safety valves were discovered.

1989-03-05

Reactor scram on low DNBR signal due to a failure of a control element assembly calculator; loss of a 13.8kV bus due to a fire related to its feeder breaker trip coil.

1989-03-03

A grid disturbance resulted in the main generator breaker opening, several equipment failures followed the load reject: failure of fast transfer to RCP. Failure of ADVS to open on loss of condenser, failure of several drain valves and leakage in RCP seat (AIT to site : main concern was that the steam dump valves which control steam levels in the main steam system failed to operate. The valves which are in separate rooms had o be manipulated by hand - in one room in the dark because the emergency lights did not go.)

1989-02-16

FW regulating valve stuck open -> scram EFW actuation, the SG overfed. Cause: failure of FW controllers resulted in rapid fluctuations in SG level and an apparent overcooling of the RCS.

1988-07-29

18 motor driven relay failures in ESFAS and RPS, have been identified. Corrosion occurs on internals.

1988-07-29

18 MDR relay failures in ESFAS and RPS, have been identified. Corrosion occurs on internals.

1988-07-29

18 MDR relay failures in ESFAS and RPS have been identified, contaminants plate out and /or corrosion occurs on internals

1988-07-06

Auxiliary transformer exploded and caught fire -> deenergizing RCP´s causing scram on low DNBR.