May 11 (Reuters) - U.S. power company Constellation Energy CEG.O beat Wall Street estimates for first-quarter adjusted profit on Monday, helped by rising power demand and contributions from its recently acquired Calpine assets.

Shares of the company rose nearly 5% in premarket trading.

U.S. power consumption, which hit its second consecutive annual record high in 2025, is expected to rise further in 2026 and 2027, according to the Energy Information Administration.

Constellation, the largest U.S. nuclear power operator, has been expanding beyond its nuclear-heavy fleet after completing its Calpine acquisition in January, adding a large gas-fired generation portfolio that gives it more flexibility in high-demand markets such as Texas and California.

Earlier this year, the company said it plans $3.9 billion in capital spending and raised its share buyback authorization to $5 billion, as it prepares to meet growing demand for clean electricity.

Constellation also achieved commercial operation at the Pin Oak Creek Energy Center, a 460-megawatt natural gas power plant in Fairfield, Texas, on April 30.

In March, the company said it would sell a portfolio of PJM generation assets to LS Power for about $5 billion, as part of regulatory commitments linked to its acquisition of Calpine.

Total quarterly operating revenue came in at $11.12 billion, compared to $6.79 billion from a year ago.

The Baltimore, Maryland-based company posted an adjusted profit of $2.74 per share for the three months ended March 31, beating the average of analysts' estimates of $2.57 per share, according to data compiled by LSEG.

Its nuclear fleet produced 44,666 gigawatt-hours (GWh), down from 45,582 GWh a year ago, due to higher planned refueling outage days compared with last year.