Maine Yankee (USA)

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PWR 820 MW constructed by CE; operation since 1972, shut down in 1997

Facilities in Maine Yankee

plantreactor typconstruction startoperation startshut down
Maine YankeePWR196819721997

Stone & Webster Engineering Corp., the original engineer for the Maine Yankee plant, will head a turnkey project for $ 250-million decommissioning and decontamination of the NPP.
The contract would be the first fixed-priced contract. Stone & Webster - assumes the financial risk for executing the project safely and on time.
The contract includes an option for Stone & Webster to reconstruct the plant as a gas-fired plant. In this case Maine Yankee would get money that would reduce total decommissioning costs. The earliest possible operation of a gas-fired plant would be in 2002, Stone & Webster said.
Stone & Webster expects to employ about 175 workers on average on the project, and up to 400 during peak periods.
The contract cost doesn't include maintenance of the spent fuel, which is currently stored in a pool.


Engineers discovered potential design defects in the ECCS instrumentation system. An attempt to restart the plant in late August was aborted when officials discovered that a wire had been removed from the circuit that would automatically start pumps in the ECCS. NRC investigates allegations enginieers improperly manipulated computer testing of ECCS in the 1980s. New tests are planned using different computer models.


Maine Yankee does not meet post-TMI requirements, NRC says:
Maine Yankee Atomic Power Corp.'s Maine Yankee is operating out of compliance with post-Three Mile Island regulations on small break loss-of-coolant accidents (SBLOCAs), but the NRC´s top safety regulator says the licensee meets "the intent" of the regulations and that other acceptable accident analyses provide sufficient safety margin to let the plant operate, albeit at reduced power.


16 workers were exposed to radioactive gas; 2 of them received minor contaminations.


Maine Yankee will be restricted to the 90% power level until it can supply a safety analysis for a small break loss-of-coolant accident that does not rely on the Yankee Atomic Electric Co.'s (YAEC) Relap5-YA computer code, or that can account for oscillations in the coolant system predicted by the code. There are some minor questions about the plant's containment analysis as well that must be satisfied before ascending to the higher power level.
Maine Yankee is returning from a year-long outage during which it had Westinghouse sleeve some 17.000 steam generator tubes that had circumferential cracking at the top of the tubesheet.


An anonymous allegation that Maine Yankee Atomic Power Co. and Yankee Atomic Electric Co. falsified key plant safety documents in the 1980s could pose a threat to the scheduled restart of Maine Yankee later this month.
The allegations - which were delivered anonymously to the Union of Concerned Scientists (UCS) and passed by UCS to Maine state regulators December 4 - claim that officials from both Maine Yankee and Yankee Atomic falsified computer calculations to obscure inadequacies in the plant cooling system'ability to handle a loss-of-coolant accident (LOCA).
Maine Yankee has been shut since January for sleeving about 17,000 or nearly all the tubes in the unit's three steam generators. A special state panel analyzed the sleeving job and on November 30 gave its approval for restart to Maine Governor Angus King. The unit is scheduled to be reconnected to the grid by December 31.
According to a copy of the allegation provided by UCS, the alleger claims that Yankee Atomic Electric's "management knew that the emergency core cooling system (ECCS) and the containment system of Maine Yankee did not meet the licensing requirements even for the pre-1989 power rating of 2,630 MW thermal.
The alleger claims that small-break LOCA analyses with computer codes showed that the plant's ECCS is "grossly inadequate" after calculations produced peak clad temperatures of 1200°C.


After discovering of substantial cracking in SG tubes, that had not been identified in previous inspection, the plant decided to repair all tubes in the 3 SG: sleeving all 17 000 tubes - (placing smaller tubes inside cracked or faulty tubes). Cost US$ 40 million.


Trip from full power because of a ground in the main generator; Officials decided to keep the unit off line and go directly into refueling outage.
24 of the 303 plugged tubes did not meet the NRC requirements for tube integrity; during the outage a 100% inspection of all 3 SG hot legs is planned. Cracking problems have been found mostly in the hot leg side; if more circumferential cracks are found Maine Yankee will do additional in-situ pressure tests.


Shutdown because of increased primary to secondary side leakage (200 liters/day). 4 tube cracks had eaten through more than 90% of the tube walls. More than 300 circumferential cracks of various depth were found. (might have been overlooked by last years inspection); 305 tubes were plugged in the 3 SG. The number of plugged tubes is still only 3,3%. Reanalysis of previous inspection data for the leaking tubes indicated that circumferential crack indications were present in these tubes since at least 1990. Similar cracking near the top of the tubesheet has been noticed at Ark.Nuclear One-2 and at some Westinghouse SG. During eddy current inspection in March 1995 mor GS tubes with significant circumferential cracks have been found.


Rupture of a 50 mm elbow on one of the four MSR vent pipes. -> steam leak . Cause: erosion corrosion. PIPE WAS REPLACED. Examination of some 100 additional carbon steel pipes on secondary side. 21 pipes and elbows in the MSR system were to be replaced due to erosion corrosion.


Design error in EDG output breakers could cause lockout of the EDGS if they are synchronized to their bus leading to a loss of power.


Explosion caused by a ruptured hydrogen line caused scram and fire at the steam turbine. Fire was extinguished after 4 hours. Fire damaged the main generator.


Failure of control element assembly: end caps cracked and dislogged; 9 of 23 original CEAS suffered from irradiation assisted stress corrosion cracking, 3 were missing components. 1 would not insert below 675 mm.


Two neutron flux cable assemblies failed pressure tests and developed leaks in the cable assembly. Potential consequence was loss of flux indication during accident.