Dominion to consider seeking modification to change Millstone Unit 2 spent fuel storage plans

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American nuclear power plants are overwhelmed by more and more highly radioactive spent nuclear fuel every year which has to be carefully offloaded into already overcrowded spent fuel pools.  The spent-fuel pools in America’s oldest nuclear power plants now hold up to five times more fuel than they were initially designed to handle.  Dominion Nuclear Connecticut is considering seeking a modification in its operating license that would enable it to change the way fuel assemblies are stored in the Unit 2 spent fuel pool, said Neil Sheehan, NRC spokesman.

Used or spent fuel must be stored in a manner that isolates it from the public and the environment because of its high level of radioactivity. Presently, it is stored in a spent fuel pool located near the refueling cavity of each plant. The pool is filled with water, and the fuel assemblies are lowered into storage racks in the pools.

Millstone’s Unit 2 reactor was originally licensed to hold 677 spent fuel assemblies. It now holds 909 assemblies, or 304 metric tons, and is licensed to hold 1,346 assemblies.  The spent fuel assemblies and equipment account for more than 95 percent of the radioactive materials in the reactor building.

Millstone’s Unit 3 reactor was originally licensed to hold 756 assemblies. It now holds 1,040 assemblies, or 449 metric tons of waste, and is licensed to handle up to 1,860 assemblies.

During refueling, the top of the reactor vessel is removed and the large, stainless steel-lined cavity that contains the vessel is flooded with water. A fuel-handling crane above this cavity is used to move the fuel. Each refueling, approximately one-third of the fuel assemblies are removed from the vessel and replaced with fresh assemblies. In addition to refueling the reactor, a large number of maintenance and surveillance jobs are scheduled.

Dominion also stores used nuclear fuel from Millstone Unit 2 in Horizontal Storage Modules developed by Transnuclear. These modules are approximately 20 feet high, 10 feet wide and 20 feet deep, with walls and roof up to 5 feet thick. The modules are located within the Protected Area of the Millstone station.

The fuel is placed in a steel canister that is capable of holding 32 fuel assemblies. Once filled, the lid on the canister is seal-welded in placed to ensure the radioactive material is permanently isolated from the environment. The canisters, which weigh more than 40 tons fully loaded, are then inserted into a Horizontal Storage Module.

In a pre-application meeting last month, NRC raised several questions about the plan. Holt said Dominion hopes to have another pre-application meeting with NRC to answer questions and to submit an application for a license modification by the end of this year. The pre-application meeting would be open to the public.

Spent fuel pools were originally intended to be temporary storage and as a result were not given the same level of protection as reactors. As the volume of spent fuel grew over the years, scientists began warning the pools could be more dangerous than the reactor because they now held more radioactive material. Without a national storage site, plant operators, with the blessing of the Nuclear Regulatory Commission, packed more and more spent fuel rods into the pools.

“Reactors are inside steel vessels surrounded by heavy structures and containment buildings,” says Gordon Thompson, senior scientist at the Institute for Resource and Security Studies. “Spent fuel pools, containing some of the largest concentrations of radioactivity on the planet, can catch fire and are in much more vulnerable buildings.”

Spent fuel pools were never intended to be a long-term storage area for spent nuclear fuel, and as the volume of spent fuel accumulated over the years the space in between assemblies shrank smaller and smaller.  Storage pools are reconfigured to be able to increase the load the spent fuel pool is able to carry by redesigning the location and spacing of the nuclear fuel rods and adding additional materials to suppress the nuclear fission process.

Over the years of operation this has increased the risks posed by a loss of coolant scenarios or extended station blackout events.  A 1997 study by the Brookhaven National Laboratory on Long Island concluded that a pool fire at a plant like Millstone Nuclear Power Station in Waterford, Conn., or Pilgrim Nuclear Generating Station in Plymouth could kill 100 people instantly and another 138,000 people eventually. Some $546 billion in damage would result, the study said, and 2,170 square miles of land could be contaminated.

In a 2002 report, Robert Alvarez, a former top official at the federal Department of Energy and a senior scholar at the Institute for Policy Studies, wrote in the Bulletin of Atomic Scientists that if a fire broke out at the Millstone Reactor Unit 3 spent-fuel pool in Connecticut it would result in a three-fold increase in background exposures [“What About The Spent Fuel?” ]. That would trigger the NRC’s evacuation requirement and could render about 29,000 square miles of land uninhabitable, severely affecting Connecticut, much of Long Island and even New York City.

“On average, spent fuel ponds hold five to 10 times more long-lived radioactivity than a reactor core,” Alvarez wrote in his report.

“Particularly worrisome is the large amount of cesium 137 in fuel ponds, which contain anywhere from 20 to 50 million curies of this dangerous isotope. With a half-life of 30 years, cesium 137 gives off highly penetrating radiation and is absorbed in the food chain as if it were potassium. According to the NRC, as much as 100 percent of a pool’s cesium 137 would be released into the environment in a fire,” Alvarez wrote.

Millstone 2

  • Net Generating Capacity: 870 mwe
  • Cost: $424,400,000
  • Commercial Operation: December, 1975
  • Station Employees: 1,270
  • Reactor Manufacturer: Combustion Engineering Inc.
  • Turbine Generator Manufacturer: General Electric Company
  • Engineer/Constructor: Bechtel Corporation
  • Containment Walls (Thickness): 3.75 ft.
  • Steel Liner Thickness: 1/4 inch
  • Height from base: 176 ft.
  • Material: Reinforced Concrete
  • Reactor Height: 42 ft.
  • Reactor Diameter: 14 ft.
  • Steel Wall Thickness: 4 3/8 – 8 5/8”
  • Number Fuel Assemblies in Reactor: 217
  • Operating Temperature: 572 degrees F
  • Operating Pressure: 2,235 psig
  • Uranium Fuel: 192,000 lbs.
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