Millstone Point (USA)

Map of Millstone Point

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1 BWR and 2 * PWR units;
unit-1: 660 MW BWR constructed by General Electric; grid connection in 1970, shut down in 1998.
unit-2 with 870 MW PWR constructed by CE; grid connection in 1975.
unit-3 with 1200 MW PWR constructed by Westinghouse; grid connection in 1986.

Facilities in Millstone Point

plantreactor typconstruction startoperation startshut down
Millstone Point-1BWR196619701998
Millstone Point-2PWR19691975
Millstone Point-3PWR19741986

Northeast Utilities, the former operator of the Millstone plant, told the NRC (Nuclear Regulatory Commission) in November 2000 that two fuel rods from the facility's unit 1 reactor were unaccounted for when the company conducted an inventory of rods in the plant's storage pool.
The company said that the fuel rods had most likely been cut into segments and sent to a low-level radioactive waste facility along with other irradiated reactor hardware sometime between March 1985 and December 1992.
The NRC agreed with the company's conclusions, but still levied a fine on the plant's new owners -- Dominion Resources' subsidiary Dominion Nuclear Connecticut.
The agency said it found no evidence that the rods were stolen. "The very high radiation level of the material would have made theft difficult, dangerous and highly unlikely," NRC said.
"Notwithstanding the fact that there was no realistic threat, past or present to the public health and safety, the loss of highly radioactive fuel rods is unprecedented and is a very significant violation," NRC said in a letter Dominion.


Operators of Northeast Utilities(NU) Millstone-3 cleared the last hurdle to restart and took the plant critical at June 30 for the first time in 27 months. But the unit was working only 45 minutes due to failure of a monitor.
Millstone-3´s long-awaited return to service will substantially cut NU´s replacement power costs, which made up the bulk of the more than $500-million NU spent on the 27-month Millstone-3 outage.
In all, NU spent in excess of $1.3-billion on the three-units.
Millstone-1´s will probably never return to service,
NU is awaiting the outcome of an economic analysis of unit 1, due in July.


First time fire protection was considered as a restart issue was in June at unit-3.

NRC staff has conducted extensive investigations of fire barriers and penetration seals across the industry in recent years. Resulting studies documented widespread problems of both improper test documentation supporting penetration seals and improper installation, inadequate cure time for the silicone foam mixture, and voids and gaps in the materials.

For example, before Maine Yankee permanently closed, plant operators had found about 90% of its 2,600 fire barrier penetration seals were inoperable" and that fully 1,600 would have to be replaced. The issue was never resolved because the unit was shut.

At Vermont Yankee, improperly installed penetration seals went undiscovered for 13 years - until 1993. NRC cited the deficiency as a violation and imposed no penalty.

In 1994, WNP-2 declared more than 1,000 seals inoperable and Diablo Canyon reached the same conclusion about "basically all" of its seals, but in neither case was the problem considered a restart issue.


Verifying the design basis documentation for Northeast Nuclear Energy Co.'s Millstone-1 will keep the unit down through early April.
The unit, which went down in mid-November and was scheduled to return to service December 24, got into trouble with the NRC after whistleblowers challenged its unanalyzed refueling practice of routinely off-loading the full core.
Bauchamp said, the design basis verification project would be "extremely in-depth". The Utility is checking its operating basis all the way back to its original Final Safety Analysis Report or FSAR.
Beauchamp said she could not estimate how much the job and the outage delay would cost Northeast. Replacement power alone runs about $240.000 a day, she said.


Company started bringing back the unit to service following a nine-month outage on July 31. Only a week later unit was forced to shut after a 200 mm pipe in the heater drain tank recirculation line ruptured. ( 380 mm longitudinal break). Utility says the unit had reached 80% power when operators noriced leakage past the selas in the heater drain tank pumps. Pipe break was caused by erosion wear.
12 hours after the trip the plant was controlling pressure by modulating the atmospheric steam dump valves, when one of these went from 25% open to full open because an instrument controller card failed. such a failure could contribute to accelerated cooldown.


Outage began Oct.1., has been extended by at least 4 month because of worker errors (e.g. service water leak into the switchgear room due opening of a hydrogen line which was not depressurized). and erosion corrosion problems in the service water systems (worse than expected) - uses sea water.


A recurrent valve leak in chemical and volume control system was repaired by injecting more and more sealant to plug it up - 30 times from June to August. On August 5, one of the 4 closure studs failed and a leak of lit/min developed -> shutdown.


RCS leak caused by failure of a letdown isolation valve.


Modification of the reference legs of water level monitoring devices will keep dissolved gasses from getting trapped to eliminate the problem of inaccurate water level readings during rapid depressurization. (During rapid depressurization reactor operators might not know how much water is covering the core.)


Design errrors in the mounting area coolers could allow a loss of CCW during a seismic event, -> could result in inoperability of the feedwater injection pumps.


Manual scram after rupture of a moisture seperator reheater drain line, filling the turbine building with steam. The pipe break was attributed to errosion/corrosion. MISVs were closed and the leak isolated. Reactor was cooled down via SG atmospheric dump valves and auxiliary FW cooling.


Shutdown after analysis of the 2 SG found that a main steam line pipe break could lead to containment pressures 50% above design specifications. Unit was restarted after an employee was qualified to monitor containment pressure indicators and close a motor operated block valve manually if necessary. This temporary fix will remain in place until the SG will be replaced.


Shutdown, because 8 of 20 operators and managers failed their annual license examen.


8 control rods exhibited delays in scram insertion times. Cause: slow pilot solenoid valves.


Mussels fouled the engine jacket water cooling heat exchanger of 1 o the EDGS, repeat of earlier occurrences.


Failure of a MFW pipe could result in a loss of both emergency generators and a loss of all AC power.


design errors in the PRZ level indicating system could result in inaccurate readings during accident, cond. existed since initial operation.


Rupture of high pressure condensat piping from corrosion/errrosion (power:86%); pipe was 50 mm thick, diameter:150 mm. 87.000 liters of scalding water dumped on the turbine building floor. Incident induced transient on the unit. (Rupture occured, because plant officials omitted the drain lines from the pipe inspection program)


All 4 main condenser vacuum trip setpoints for RPS were found to be calibrated non-conservatively, due to setpoint drift.


A service water cross-tie valve was found open, which would have allowed a single failure to cause a loss of service water. Failure existed about 2 weeks.


A pipe hanger in the service water system was found to not meeting the seismic requirements. Failure of this could affect both service water headers. Condition existed for an indetermined period.


LPCI heat exchanger flow rates required by emergency operating procedures exceed their design limits. Flow rates need to be decreased by approx. a factor of 2 to prevent flow vibrations, which could lead to tube failures- design error.


containment recirculation spray was inoperable due to fouling of the area cooler heat exchangers. the fouling caused severe erosion of a drain hole in the heat exchanger divider plate


House heating steam lines passing through vital areas ,in case of seismic event, could cause multiple failures, resulting in loss of multiple trains of safety equipment (failure of 1973 analyses).


Various vital areas of the plant with vital equipment were found to be susceptible to harsh environments caused by a rupture of auxiliary steam piping, included the control room ventilation and the diesel areas.


Low voltage emegency power system, as well as the control room were determined to be at risk of degradation from the house heating system (failure of analyses performed in 1973).


Leak at a PRZ safety valve: the threads on the nozzle ring set screw were eaten away due to boric acid corrosion, resulting in the set screw backing out, the seal breaking, and the leakage: Temperature of the discharge piping was rising 180°C to 100 °C combined with a slight increase in the containment radiation levels., leak rate < 40 liters /min.


Loss of all onsite AC power due to a single failure -> scram.


Scram, both circulation pumps tripped causing low condenser vacuum causing turbine trip, Subsequent reactor system leaks.


Boric acid crystals found above reactor vessel and in containment air coolers.


Pressure transient (cold overpressure protection inoperable due to human errors, failed to respond.