UK GAS-Prices rise on undersupplied network

* Within-day gas price up 0.3 pence, at 46 pence

* Gas network undersupplied by 17 mcm

May 7 (Reuters) - British prompt gas prices rose on Thursday due to an undersupplied network and reduced nuclear power plant availability boosting demand.

Prices for within day delivery were 46 pence per therm at 0747 GMT, up 0.30 pence since their last settlement.

Prices for delivery on Friday were up 0.65 pence at 45.75 pence per therm.

With supply flows at about 189.5 million cubic metres (mcm) per day on Thursday and demand expected to be about 206.5 mcm, the system was 17 mcm undersupplied, National Grid (LSE: NG.L - news) data showed.

A drop in supply through Shell (LSE: RDSB.L - news) 's Bacton Seal terminal, down to just over 5 mcm from nearly 14 mcm overnight, helped drive the market into deficit.

Flows from Norway via the main Langeled pipeline also fell to 23 mcm from highs of nearly 35 mcm overnight.

Analysts at Thomson Reuters Point Carbon expected Langeled flows to average around 25 mcm/day until May 19.

Three of Britain's 16 nuclear reactors are currently offline. EDF Energy's 550-megawatt (MW) Dungeness B-21 nuclear unit is also expected to go off line on Thursday, taking the capacity of offline nuclear plants to 2.3 gigawatts (GW).

Further along the curve, gas for delivery in June was up 0.30 pence at 42.80 pence per therm.

In the Netherlands, the day-ahead gas price at the TTF hub was 0.15 euros lower at 21.77 euros per megawatt-hour (MWh).

The benchmark European Union carbon price was down 0.04 cents to 7.53 euros. (Reporting by Oleg Vukmanovic in Milan; editing by Jason Neely)