March 28, 2024
BANGOR DAILY NEWS (BANGOR, MAINE

Maine Yankee will rerack its spent-fuel assemblies later this year

With a federal high-level radioactive waste facility not due to open until 2010, Maine Yankee engineers have initiated a long-term program to store spent fuel at the nuclear power plant in Wiscasset.

Maine Yankee uses for fuel uranium dioxide supplied in a pellet “that is the diameter of your pencil and about half an inch long,” said Bob Jordan, a senior licensing engineer. To ensure their proper spacing, pellets are inserted into grids, with 176 rods per grid.

“This whole apparatus is called a fuel assembly,” Jordan said. “There are 217 fuel assemblies in the reactor core.”

Every 18 months, Maine Yankee “refuels” its reactor by replacing one-third of the fuel assemblies. Removed assemblies are stored 26 feet deep in a spent-fuel pool measuring a perfect 40-foot cube. The water level reaches to 38 feet.

“Fuel that is placed in the pool for storage is high-level waste. That is the only high-level waste we have,” Jordan stated. “Maine Yankee has stored fuel in this manner, as has every other nuclear plant since the inception of nuclear power.”

Maine Yankee, which became operational in 1972, has been licensed to run until 2008. The spent fuel that has been stored on-site for almost 26 years should have been removed in 1998, but will not be.

The federal government has been responsible for disposing of spent fuel “since nuclear plants were inceptualized in the late ’50s and early ’60s,” Jordan said. The Department of Energy examined various underground repository sites before deciding to build one at Yucca Mountain in Nevada.

This repository was supposed to open in two years, but according to Jordan, “DOE has slipped the schedule for the transfer of high-level waste by at least 11 years. The repository is scheduled to open in 2010. This leaves Maine Yankee with a problem: How do we safely store all our spent fuel through the operation of the plant?”

About six years ago, “we realized the seriousness of the DOE delay and knew we would have to take up the slack,” he said. “We decided to rerack the spent-fuel pool.”

Within the pool, the spent-fuel assemblies are stored in racks, each of which contains a single fuel assembly. “Each fuel assembly has its designated spot in the pool,” Jordan said. “The goal of our project is to replace the existing racks to expand the capacity of the pool to accommodate all of Maine Yankee’s spent fuel until 2008.”

Marshall Murphy, Maine Yankee director of public affairs, said the project involved designing and fabricating new racks to Maine Yankee specifications. The company worked with several companies (Stone & Webster Engineering Corp. in Boston; Rust Utility Services in Connecticut; General Dynamics-Electric Boat Division in Quonset Point, R.I.; Yankee Atomic Electric Co. in Bolton, Mass.; AAR Brooks & Perkins of Michigan; and several smaller consulting firms) on the project. It began in January 1992.

The new racks were designed to meet stringent Nuclear Regulatory Commission criteria “regarding the safe storage of spent fuel,” Jordan said. The project was submitted in January 1993 to the NRC, which authorized it in March 1994.

“We initiated a fabrication effort at Quonset Point (Electric Boat),” Jordanm said. “This was the first commercial contract that General Dynamics had ever had.”

He described how Navy officials, worried that “the Maine Yankee product did not interface with any submarine work” (Electric Boat builds nuclear submarines), requested that the Maine Yankee fabrication “take place in an environment independent of any Navy work at the yard. All the processes and materials were developed from scratch. Even the personnel could have no contact with submarine work; the fabrication shop was located away from anything that looked like a submarine part.”

Maine Yankee instituted an on- and off-site quality-assurance program, with some inspectors spending much time at the Electric Boat Division. Rust Utility Service and Electric Boat finished the fabrication in late summer 1995, and the 29 racks were shipped to Maine Yankee for testing.

“Each individual cell was drag-tested to extremely rigid specifications,” Jordan said. “Clearance between the walls of the rack and the walls of the cells is less than a sixteenth of an inch. That’s very close.

“All the rack cells were found to be acceptable,” he said. “In the spring, we will move the racks one at a time to the spent-fuel pool. We will place them in the pool, substituting them for the existing racks.”

As each rack is placed in the pool, spent fuel will be transferred to it from an existing rack. “This process will require us to put racks into the pool and take them out on a very precise schedule,” Jordan said.

According to Murphy, the spent fuel is transferred underwater; because the pool could not hold an additional 29 racks, the new racks will be filled one at a time. The project, involving various Maine Yankee engineers and other company officials, “will be done on an accelerated schedule, 10 hours per day, six days per week,” he said.

“The expected radiation dose to the workers is extremely low,” Murphy said. “The water acts as an excellent barrier against radiation.”

The new racks will be stored closer together, which will enlarge the storage capacity of the spent-fuel pool. “This will ensure Maine Yankee can store its high-level (radioactive) waste through 2008,” Murphy commented.

Jordan anticipates the project will take until late fall to complete. The old racks will be shipped to a federally licensed Tennessee company to be decontaminated and sold for scrap.


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