By Nikki Junewicz

KEWAUNEE, Wis. (WBAY/CNN) - After nearly 40 years of service, a nuclear power plant outside of Green Bay, Wis. has begun a permanent shutdown.

The move comes after its owner, Virginia-based Dominion, failed to find a buyer for the Kewaunee Power Station.

Company leaders blame a changing electricity market, but the plant means more than just business for those who work there.

After being shut down, white steam billows out of the Kewaunee Power Station's reactor, a sign of the beginning of the end.

"The reactor operates at 600 degrees, and so we need to cool it down sufficiently so we're able to do the fuel move out of the reactor and into the spent-fuel pool," said Daniel Stoddard, vice president of nuclear operations, Dominion.

They knew this day was coming for months now, but with 600 jobs and livelihoods at stake, time hasn't made the plant's closure any easier.

Stoddard talked about what the mood was like amongst employees as they helped shut down a place they've called home for decades.

"Very much a tone of focus and professionalism. You know, obviously a touch of sadness for the people, for the relationships that they have for each other and people who'd be leaving, for their relationship with the power station. I mean, this is more than a place, it's almost like a person," he said.

The shutdown is expected to cost around $900 million and take as many as 60 years to complete.

It leaves the state of Wisconsin with just one operating commercial nuclear power plant.