The EnergySolutions empire grew Tuesday as it purchased another company for more than a third of a billion dollars, underlining its emergence as a top business in the nuclear services industry.

Salt Lake-based EnergySolutions signed a definitive agreement to acquire Duratek, based in Columbia, Md., for $396 million. The amount includes assumption of Duratek's outstanding debt, according to a Duratek announcement released Tuesday.

"The acquisition will be funded through a combination of debt to be provided by a group of banks led by Citigroup, cash held by Duratek and EnergySolutions, and equity provided by the owners of EnergySolutions," the release said.

Duratek bills itself as a provider of safe, secure disposal services for radioactive material. Its Web site notes that it has permits for disposal at Envirocare in Utah as well as other sites. The company provides services for commercial and government customers.

EnergySolutions is to buy all outstanding shares of Duratek for $22 a share, a premium of 25.7 percent over the stock's price on Monday, according to Duratek.

The deal requires the approval of Duratek's stockholders, but the boards of directors of each company have approved it.

The formation of EnergySolutions itself was announced just last Thursday. The owners of Envirocare of Utah bought the British government radioactive waste cleanup company, BNG America, and merged it with Envirocare and an Envirocare division, Scientech D&D, to create EnergySolutions.

This project has been in the works for three years, according to Steve Creamer, the Utahn who is president and CEO of EnergySolutions.

Until Federal Trade Commission regulators approve the latest acquisition, the Maryland firm will continue working under the name Duratek. The FTC must review the acquisition for compliance with antitrust laws.

After regulators give the OK, expected in three to six months, Duratek too will be operating as EnergySolutions.

"We'll be one of the leading nuclear energy services companies," said Creamer.

Corporate headquarters will be at 423 W. 300 South, a new building at the location of the old Salvation Army building. About 150 to 200 employees will work there, while total employees, counting those of Duratek, will number more than 2,000 nationwide, Creamer said.

With BNG America, the new entity acquired the North American rights to technologies developed by that firm. BNG America belonged to the British government — the initials derived from British Nuclear Group — and Great Britain has been a leader in reprocessing spent nuclear fuel rods.