Neste Oil Oyj (NES1V.HE) Tuesday said it is planning a major turnaround at the beleaguered diesel line at Porvoo refinery to address continuing operational and safety problems.

The company said in its capital market day presentation that it will implement a development program and carry out a significant maintenance program in April 2010 to address low utilization and the additional maintenance costs of the line - known as PL4.

"Development plan for the unit includes several investigations and corrective actions and is designed to stabilize operations and optimize performance," Neste Oil said.

Porvoo refinery manager Erkki Ranta said the length of the shutdown remains uncertain, but it could be as long as one and a half months. "It will be totally closed," he said. No details are yet available about exactly what work the company will carry out on the line.

Neste said the line is currently operating normally.

Porvoo refinery is one of the most modern in Europe. The EUR750-million diesel line started in the summer of 2007, but has been hit by numerous glitches and outages during the startup phase. It upgrades heavy fuel oil and has a capacity of around 1 million metric tons of diesel a year.

Company Web site: www.nesteoil.com

-By Elizabeth Adams, Dow Jones Newswires; +44 (0) 20 7842 9386; elizabeth.adams@dowjones.com