Progress Florida nuclear restart seen late March

* Work advances to repair gap in Crystal River wall

* Numerous tests needed before unit can be restarted

By Eileen O'Grady

HOUSTON, Jan 4 (Reuters) - Progress Energy Inc PGN.N will begin to tighten tendons this week in a repaired section of the containment building wall at its Crystal River nuclear plant in Florida as it works to restart the unit by the end of March, a company spokesman said on Tuesday.

The 838-megawatt nuclear unit has been shut since September 2009 to refuel and replace the giant steam generators, work that orginally had been expected to take three months.

However, about one month into the outage, contractors discovered a gap in the 42-inch (107 cm) thick containment building wall which had been opened to allow removal and replacement of the steam generators.

Progress determined that the gap in the wall was caused by initial work to release tension on the structural cables that reinforce the concrete wall.

The repair effort has delayed the unit's return, forcing the utility to buy replacement power to serve its 1.6 million Florida customers.

A spokesman for the U.S. Nuclear Regulatory Commission said the schedule indicates Crystal River could restart in late March.

Progress spokesman Mike Hughes said the work to retighten about 200 tendons in the wall is "highly orchestrated" and will be completed in two steps. First, the tendons will be tightened to about 50 percent; then tightened fully.

"It is a significant undertaking," Hughes said. Tests will be conducted to determine that the containment building meets all safety standards.

Other tests need to be carried out related to the refueling and the new steam generators before the unit can begin to produce power.

Hughes said work remains on schedule to return the unit to service in the first quarter.

Progress initially hoped to restart the unit last October, but officials have delayed the restart twice, most recently for additional computer analysis related to the tendons.

The Florida Public Service Commission is allowing Progress to recover replacement power costs not covered by insurance from customers, beginning this month.

The 3,151-MW Crystal River station, located in Red Level, Florida, about 85 miles (140 km) north of Tampa, includes four coal units and the nuclear reactor.

Progress Energy operates the reactor and has a 90 percent ownership stake. Minority owners include 10 public power agencies.

(Reporting by Eileen O'Grady; Editing by David Gregorio)