More work and more materials and higher prices for both have pumped up the cost of upgrading Grand Gulf Nuclear Station to $874 million, according to Entergy Corp.’s quarterly financial report filed this week.

The utility increased its forecast for the project’s price tag “considering … additional information from the project’s engineering, procurement and construction contractor, the costs required to install instrumentation in the steam dryer in response to evolving guidance from the Nuclear Regulatory Commission staff and delays in obtaining NRC approval,” read part of the company’s financial breakdown for the first quarter of 2012 filed Wednesday with the Securities and Exchange Commission.

It represents a 34 percent jump in cost estimates from the start of the year. The estimates represent cost shares for Entergy Nuclear and South Mississippi Electric Power Association, which owns 10 percent of Grand Gulf and receives 10 percent of energy the plant generates. In its annual report for 2011, System Energy Resources Inc., the Entergy subsidiary that oversees the plant, did not rule out higher costs as it follows guidelines from the NRC.

Entergy’s share has grown to $787 million, though work done so far “will extend the life of the plant far into the license renewal period,” said Entergy Nuclear spokesman Michael Bowling. The plant’s current license expires in 2024. An application to extend it another 20 years is expected to be considered by NRC by September 2013.

The Claiborne County plant shut down Feb. 19 to refuel the boiling-water reactor and increase its generating capacity by 13 percent. Today makes 83 days at zero capacity, or about eight days beyond what plant officials estimated last year. The unprecedented upgrade will result in the nation’s most powerful single reactor. Work is expected to last at least through June. In the report, the utility says work should be complete “during the summer of 2012.”

“We don’t generally discuss exact outage duration projections for business reasons, but what we are doing here is monumental in scope,” Bowling said.

More than 5,000 workers from 76 companies and 15 subcontractors nationwide have worked on the project. Ordinarily, the plant employs about 700 people, many of whom live in Vicksburg and Warren County.

System Energy purchased $152.2 million in nuclear fuel and construction materials related to the project during the first quarter, bringing investment activities to $218.6 million for the quarter, or 47.2 percent higher than the same time in 2011, the report said.

Entergy Corp. reported $1.106 billion in net revenues for the quarter, less than the $1.148 billion during the same period in 2011. The utility cited a blend of milder weather and rate increases in Louisiana and Texas for the variance.