UK GAS-Prompt price up on tight supply, October dips on EDF relief

LONDON, Sept 18 (Reuters) - British gas contracts were mixed on Wednesday, with prompt prices rising on tight supply and the month-ahead price falling after French utility EDF said there is no need to close any of its nuclear reactors despite some technical problems.

* Within-day gas rose 0.9 pence to 26 pence per therm at 0745 GMT.

* Day-ahead gas was flat at 26 pence per therm.

* The system was slightly undersupplied, with demand forecast at 181.5 million cubic metres (mcm) and supply seen at 178.1 mcm, National Grid data showed.

* Temperature forecasts were reduced by almost 1 degree Celsius to 11.8 degrees, with the chilly weather possibly prompting some households to switch on gas heating.

* An unplanned outage at Aasgard in Norway has reduced output by 9.7 mcm, according to a regulatory notice, while the Langeled pipeline remains shut for maintenance.

* Sendout from liquefied natural gas (LNG) terminals was down by 6 mcm, though an additional tanker declared for Britain on Wednesday, bringing the total to four LNG tankers due in Britain by Oct. 1.

* Russian flows via the OPAL pipeline into Europe were 57 gigawatt hours per day (GWh/d) lower on Wednesday than the previous day, but that fluctuates by the hour, Refinitiv data showed.

* Gazprom started to reduce OPAL flows on Saturday after a top EU court curtailed the Russian gas giant's access to the pipeline based on antitrust regulations.

* Further along the curve, both British and Dutch gas prices for October delivery fell after EDF said it was not planning any reactor shutdown in the short term. Issues with welding at its French nuclear power stations had emerged last week, its French nuclear power stations emerged last week, causing a near-20% price spike in both contracts.

* The UK October gas contract fell 1.95 pence to 33.2 pence per therm.

* The Dutch month-ahead contract fell 0.82 euros to 12.88 euros per megawatt hour.

* Day-ahead gas at the Dutch TTF hub was down 0.27 euros at 9.43 euros per megawatt hour.

* The benchmark Dec-19 EU carbon contract fell 0.60 euros to 25.59 euros a tonne. (Reporting by Sabina Zawadzki Editing by David Goodman)