UK GAS-Prices fall as supply risks diminish

LONDON, Sept 17 (Reuters) - British gas prices fell on Tuesday morning, paring the past week's gains as some supply risks diminished, but uncertainty on energy markets kept traders on tenterhooks.

* Day-ahead gas fell 0.25 pence to 30.50 pence/therm by 0850 GMT.

* Within-day gas was down 1.15 pence at 29.85 p/therm.

* Prices dropped after a strong rise in the past week prompted by factors including a requirement for Gazprom to reduce flows via the OPAL pipeline, French nuclear concerns, as well as the oil price jump on Monday after attacks on Saudi Arabia's processing facilities.

* On Tuesday, Brent crude, carbon and coal traded lower, with bearishness spreading to gas markets.

* Russian flows via the OPAL pipeline into Europe were up by 69 GWh/day on Tuesday, compared with Monday, a higher level than expected. Gazprom started to reduce OPAL flows on Saturday.

* "The last few days' upside was again an overreaction and we should see some risk abate," said a source in the UK gas market.

* However, uncertainty remains high as traders await the results of an investigation into French nuclear reactor problems.

* The oil market also remains on high alert to the threat of a military response to attacks on Saudi Arabian crude oil facilities.

* The British gas system was slightly undersupplied on Tuesday, with supply expected at 158.5 million cubic metres (mcm) and demand at 160 mcm, National Grid data showed.

* Wind generation is expected to drop to 2.5 gigawatts (GW)on Wednesday from 5.8 GW on Tuesday, meaning more gas may be needed for power generation, Elexon data showed.

* This has been reflected in a limited drop in the day-ahead contract.

* The working-days-next-week product dropped significantly on Tuesday as Norwegian gas flows are expected to rise next week following maintenance, another bearish factor.

* The UK October gas contract fell by 0.50 pence to 38.80 pence per therm.

* Day-ahead gas at the Dutch TTF hub fell by 0.20 euro to 11.00 euros per megawatt hour (MWh)

* The Dutch month-ahead gas contract fell by 0.38 euro to 14.85 euros/MWh.

* The benchmark Dec-19 EU carbon contract dropped by 0.35 euros to 26.69 euros a tonne (Reporting by Ekaterina Kravtsova; Editing by Pravin Char)