UK GAS-Prices rise on French nuclear worries, Opal flows cut

LONDON, Sept 12 (Reuters) - British wholesale gas prices mostly rose on Thursday as uncertainty over the impact of a cut in flows through the Opal pipeline and French nuclear plant issues dominated the market.

* The day-ahead contract was up 0.60 pence at 28.00 p/therm by 0833 GMT.

* The within-day gas contract was up 0.45 p at 27.00 p/therm.

* "There's oversupply but noone is sure what's going on with the nukes and Gazprom," a gas trader said.

* German regulator Bundesnetzagentur said on Wednesday flows through the Opal pipeline would need to be halved immediately following a European Union court ruling.

* Oliver Sanderson, head of European gas market analysis at Refinitiv, said this could curb European winter gas supply by around 30-40 million cubic metres (mcm) a day, but that could be replaced by other sources such as liquefied natural gas (LNG) imports.

* French nuclear power producer EDF was also informed this week of anomalies in welds on some steam generators and components used in its reactors and.

* French nuclear regulator ASN said in newspaper Le Figaro at least 5 reactors were affected although it is still unclear whether they will need to close for repairs.

* Any nuclear closure could increase demand for electricity from Europe’s gas-fired power plants.

* Britain's gas system was oversupplied by 17.2 mcm, with demand forecast at 152.6 mcm and flows at 169.8 mcm/day, National Grid data showed.

* October contract up 0.90 p at 38.20 p/therm.

* Q4 2019 contract up 2.10 p at 46.20 p/therm

* Day-ahead gas price at the Dutch TTF hub up 0.62 euro at 10.85 euros per megawatt hour.

* Benchmark Dec-19 EU carbon contract up 0.37 euro at 26.64 euros per tonne. (Reporting by Susanna Twidale; editing by Nina Chestney)