Zion (USA)

2 * 1100 MW PWR; constructed by Westinghouse; operation since 1973

Facilities in Zion

plantreactor typconstruction startoperation startshut down

Amoco Power Ressources Corp. announced last week an interest in installing gas turbines at ComEd´s Zion plant site and has launched a $250.000 feasibility study that is expected to take a year to complete.
ComEd officials announced in mid-January the decision to prematurely shut Zion after determining it would not be able to compete in an open electricity market.
Last month ComEd cut the plant´s work force from 800 to about 740 workers and has plans to reduce employees to about 150 by the beginning of 1999. Around 2001, the staff is expeted to shrink to an even smaller number of workers who will maintain the plant in a secured state until 2014, when decommissioning is scheduled to begin.
Early estimates for transforming the ComEd site are about $300-million. The natural-gas powered generator expected to be installed would be about 1,000 MW.
While there has never been a nuclear plant totally transformed into a natural gas or fossil-fired plant, two partially completed PWRs - Midland and Zimmer - were converted into, respectively, natural gas and coal-fired plants. In the case of Midland, neither the reactor nor turbines were used. Proposals to co-locate gas turbines on the same site as an operating nuclear station in Britain were abandoned because natural gas is considered too potentially dangerous to operate next to a nuclear plant.


NRC fined ComEd for violations of specifications and poor human performance with 50.000 $:
Fundamental errors during EDG tests: operator adjusted the wrong control causing the EDG to shut down, In another test operators failed to make shure that all auxiliary equipment was available and ran the EDG for 20 minutes without cooling water flow.
Another operator error occured when a tank inside the plant overflowed, spilling about 2000 liters contaminated water on the floor.
A fourth incident occured when timing system aof one ECCS train was out taken out of service for maintenace when second train's timing system was also in maintenance.


Zion is allowed to continue operation despite new indications of SG tube cracks. This is result of the completed reevaluation of 1993 SG tube inspection data. SG tubes at Zion were indspected during the fall outage in 1993, that outage was extended through April 1993 to perform major service water work at both units. the 154 (of 13.500 SG tubes) will be repaired in September 1994.
<10% of unit-1's and <5% of unit-2's SG tubes are plugged.


Power reduction to 50 %, when it was detected that flux suppression inserts were missing in the core. The 8 hafnium inserts are designed to reduce neutron fluence at the vessel weld.


Fire in the insulation on electrical cables due to excessive currents -> shutdown. - during heat wave.


Fire in main generator during restart of the plant after an extended outage.The fire was extinguished with carbon dioxide after 3 hours.


Auxiliary FW PUMP AND A auxiliary FW FLOWPATH SIMULTANEOUSLY INOPERABLE. Equipment debris was found in the line . It was believed that the parts were from an earlier auxiliary FW failure in July, 92, but a review showed that the parts are from a repaired pump.


Loss of offsite power, due to fire protection deluge actuation. -> auxiliary transformer trip -> loss of main FW pump, power reduced. Two EDGs started; similar incident occured at unit in November 1990 except that FW pump was operating on a different transformer.


After repairs on a RHR valve unit was being brought back to operation, when a RCS pump failed. Inspection revealed that the graphite pump bearings were just worn away. It was the first bearing failure of a Westinghouse RCP. Unit shut down to replace the failed pump with a new one (cost $2,5 million); luckily a replacement pump was available. Next utility will have to wait up to 3 years to get a replacement RCP. A Westinghouse RCP failed at Byron in 1984.


Shutdown because of a 30 lit/min leak into the containment through a RHR system valve.


Surface and subsurface crack indication found by ultrasonic testing of the transition cone upper girth weld of the SG