And you thought your dentist charged a lot.

The cost of getting rid of two cavities at FirstEnergy's Davis-Besse nuclear power plant could approach $300 million.

The Akron utility yesterday announced it will spend between $55 million and $75 million to buy and install an unused reactor vessel head to replace the boric acid-damaged one sitting atop Davis-Besse's reactor. The utility said it bought the potential replacement yesterday and hopes to get it in place sometime in the last three months of the year.

In addition, the company said it may spend as much as $70 million more in maintenance and upgrade projects at Davis-Besse.

That puts the potential price tag for the damage and upgrades as high as $290 million if the plant stays closed through the end of December.

The new figure includes the estimated cost for FirstEnergy to purchase electricity from other sources to make up for the loss of Davis-Besse. The company estimates it will pay as much as $20 million a month for power in July and August, when air-conditioning demand peaks, and as much as $15 million in each of the other months the reactor stays shut down.

Earlier estimates put the cost to repair the damaged vessel head at $120 million.

Davis-Besse, in Oak Harbor east of Toledo along Lake Erie, was shut down in mid-February for refueling and a safety inspection and has remained shut down since the acid damage was found in March.

The replacement vessel head, which is not radioactive, will come from the never-completed Midland Nuclear Plant in Midland, Mich. FirstEnergy initially had wanted to repair the damage at Davis-Besse, but NRC staff said they would prefer the vessel head be replaced, not fixed.

``Based on our analysis, replacing the head is our preferred option for returning Davis-Besse to safe and reliable operation,'' Lew W. Myers, chief operating officer for FirstEnergy Nuclear Operating Co., said in a prepared statement.

``The repair plan now becomes the contingency plan,'' said FirstEnergy spokesman Richard Wilkins.

Installing a replacement head appears to be the better way to go, said David Lochbaum, the nuclear power expert with the Union of Concerned Scientists.

``It seems to be a simpler, safer option than the patch,'' he said.

While Lochbaum said he hasn't seen the technical specifications for the potential replacement head, the part will have to be modified to work with the Davis-Besse reactor.

The NRC will be watching every step of the way, said spokesman Jan Strasma.

``Essentially, we will be looking at how the Midland vessel compares to the Davis-Besse vessel and if it meets all of the requirements,'' he said. ``We have to approve what they want to do.''

The vessel head is a massive piece of machined steel 17 feet in diameter and 7 feet high weighing more than 100 tons. It sits on top of the reactor, covering the radioactive fuel core.

Boric acid, part of the reactor coolant, leaked on top of the Davis-Besse vessel head and created two cavities, one of which went almost entirely through more than six inches of steel. A thin inside lining of stainless steel prevented what is called a ``loss of coolant accident'' that would have released hot, radioactive coolant into the containment chamber that surrounds the reactor.

The stainless steel lining was not designed to hold in the coolant, and nuclear power opponents said the plant by luck avoided the worst nuclear incident in the United States since the partial meltdown at Three Mile Island in 1979.

The type of damage found at Davis-Besse has never been seen in a U.S. reactor, and the NRC says the nation's other nuclear power plants don't appear to be at risk of developing similar cavities.

FirstEnergy will have to cut an opening at the Midland plant to remove the vessel head there, and also cut an opening in the Davis-Besse containment building to install it, Wilkins said. Extra security precautions will be taken during the process, he said.

FirstEnergy will transport the Midland vessel head either by truck, train, barge or a combination of all three, Wilkins said. The damaged vessel head eventually will be cut up and taken to a low-level radioactive waste site, he said.