LONDON, July 6 (Reuters) -
* Britain’s nuclear regulator said it had approved a request from EDF Energy to increase the operating temperature limit inside its Hartlepool and Heysham 1 nuclear reactors.
* EDF Energy asked the Office for Nuclear Regulation to raise the operating limit for the upper surface of hot box domes inside the reactor to 390 degrees Celsius from 380 degrees.
* The hot box domes are steel structures inside the reactors which form a boundary between different pressures of gas. They have a maximum operating temperature to prevent loss of strength and damage over time.
* Heysham 1 and Hartlepool nuclear plants were taken offline in 2014 for some months after cracks on a boiler spine were found at one of them, caused by high operating temperatures. (Reporting by Nina Chestney, editing by David Evans)