Arkansas Nuclear One (USA)

Map of Arkansas Nuclear One

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2 PWR units:
unit-1 840 MW constructed by Babcock&Wilcox, grid connection 1974.
unit-2 860 MW constructed by General Electric, grid connection 1978.

Facilities in Arkansas Nuclear One

plantreactor typconstruction startoperation startshut down
Arkansas Nuclear One-1PWR19681974
Arkansas Nuclear One-2PWR19711978

A recent inspection at Entergy´s Arkansas Nuclear One-1 found the SGs in good condition, but the eight-year-old Combustion Engineering SGs in ANO-2 are rapidly deteriorating.
At ANO-2, the utility is doing all it can to increase the lifespan of the recirculating SGs, which are due to be replaced in September 2000 and will cost an estimated $150-million.
Problems with ANO-2´s SG tubes were first discovered during an outage in March 1992. In November 1996 the unit had to be shutdown because of a leaking SG tube.


Prior to this outage, the unit's SGs had about 900 tubes plugged and 448 sleeved. Most of the tubes sleeved this outage, about two-thirds, were in steam generator A.
After this outage, the unit will be at a total equivalent plugging rate of about 7.3%, while its safety limit is set at 10%. However, the utility is working on an analysis to raise the limit to 15%.
Entergy officials had pitched the idea to NRC of allowing tubes with circumferential cracking indications to remain in service, claiming it could adequately characterize such cracking with advanced non-destructive examination technology . However, NRC shot down the proposal and urged Entergy officials to work through a generic industry program at Electric Power Research Institute.


ANO-2 returned to power following a mid-cycle outage to inspect SG tubes. In all 305 tubes were plugged bringing to 543 , and 417 respectively, the total plugged in both SG ( 7% & 5% of the tubes). More cracks were found than anticipated. Next inspection is scheduled for September 1995.
Since leaking tubes forced an outage in March 1992 utility has inspected the SG tubes fife times.


During inspections more circumferential cracks were found at the top of the tube sheets. Outer diameter stress corrosion cracking is responsible for the circumferential cracks. The concern is that even with the cracked tubes plugged, the circumferential cracks could propagate and leave the splits ends of the tube free to move about and damage other operating tubes.


Increased primary to secondary side leakage in one SG. Circumferential cracks were found at the top of the tube sheets.


Because of a cooling water cross flow path the EDGs could not provide design electrical load under worst case accident conditions. Design fault existed since initial operation.


Design error in the DC electrical system could result in the loss of both safety related buses during accident.


Undersized breaker control power transformers for EDG ventilation exhaust fans had been installed. This could have rendered the EDGs inoperable under certain conditions. Fault existed since initial operation.


Generic fault existed since initial operation: main feedwater line was in proximity to service water return lines. Rupture of the feedwater line could damage the service water line, affecting cooling to ESF components.


Leaking cooling coil containment isolation valve caused by corrosion. Design error was discovered, which could have resulted in failure of the casing drain valves of the HPCI pumps and subsequent radioactive releases. Valves were not designed to withstand maximum system pressure.


Flow restrictors that were just installed, to limit the flow in the event of a break in the HPCI, were removed. Flow restrictors should protect the plant against a small-break LOCA. The flow restrictors had to be removed because of excessive vibrations of the piping, which resulted in about 950 liters of reactor coolant leaking from 2 HPCI series valves into the reactor building cavity. The vibrations caused the valve cap on the vent line to back completely off as well as causing both vent valves (in series) to come off their closed seats by several turns.


Potential degradation of the RCS boundary. Severe boric acid's corrosion, caused 2 of 8 bolts on CRDM to become loose.


Excessive leakage from flange connection of RPV head vent valve: safety injection system check valve, which isolates low pressure SIS from RCS failed to reseat. Potential for overpressurizing the LPCI system and causing an interfacing LOCA. Several attempts to stop backleakage failed.


Multiple complications and RCS boundary check valve leakage. Feedwater block valve failed; SG overfilling; HPI manually started to compensate for overcooling and shrink. Incident began when voltage fluctuations tripped the turbine, various equipment problems followed and allowed reactor coolant to backflow outside containment through a HPCI line. Later it turned out that a postulated break in the HPCI line could result in a small-break LOCA outside of the unit's design basis.


Leak in the make-up system. After a seal weld repair, workers failed to retighten packing in a makeup isolation valve. The 95 liters per minute leak continued for 5 hours, 20 000 liters of reactor coolant collected in the sump.


Loss of 2 trains of RHR system. Wrong fuse removed; RHR cooler outlet valves went closed, which is inconsistent with their design.