By Vera Eckert and Karolin Schaps

FRANKFURT/PARIS (Reuters) - Germany, Europe's largest electricity market, has coped well with a surge in demand due to a cold snap, traders said, in what was the market's first real resilience test following the abrupt shutdown of its oldest nuclear plants last year.

But traders said the market balance could tighten next week as the weather is expected to turn even colder and German renewable energy output is set to drop, while demand for German imports from neighbouring markets will rise proportionally.

German and French spot power prices leapt higher for spot and week-ahead positions this week as the markets sought to cover a surge in electricity demand without being able to rely on the nearly 9,000 megawatts (MW) of stable Germany nuclear capacity closed for good last summer.

"Right now, there is no particular tight feel but if there is no wind power next week, it could become more serious, especially if France is not a net exporter," one trader said.

The two countries account for two-thirds of western Europe's power usage in a converging market, which has been tight since Germany shut eight reactors in the wake of the Fukushima disaster.

In the wholesale market, German week-ahead peakload power rose 2 euros a megawatt hour (MWh) on the day to 70 euros respectively but gained as much as 20 euros in France to 105 euros per MWh.

"The system is coping for now but we are using expensive fuels to generate, so we're coping at a price," said one European energy trader at a bank.

"Let's see if it copes throughout the cold snap."

Aggregated border flow data provided by European grid operators showed Germany was exporting over 6,000 MW to its European neighbours, Austria, Switzerland and Denmark, on Wednesday, while receiving 566 MW from France.

France was exporting a total of around 5,000 MW while receiving 3,000 MW power from Spain and via Belgium.

As France is vulnerable to cold weather with much of its heating infrastructure power-based, France could assume a net importer role if below-average temperatures of zero to -10 degrees Celcius are sustained beyond the weekend.

French grid operator RTE said it was not concerned about the power supply situation in France or imports from Germany, but said it could revert to domestic supply restriction programmes in Britanny and the south.

Germany can cope better with a forecast -2 to -22 degrees at night time as its heating infrastrucutre is based on amply stored oil and gas.

Germany's maximum winter power demand is 82 gigawatts (GW)and top load is 86.5 GW, the environment ministry says.

Trade data on Wednesday showed forecast consumption of 76 GW for Thursday, which is a tight match with necessary production, as power cannot be stored.

"Right now, thermal power (from fossil-fuels based plants) alone could meet demand plus you have all the renewable add-on capacity," another trader said.

Energy exchange EEX, which collects aggregated German and Austrian plant data, forecast mainly thermal power supply at 77 GW for the coming days.

Germany has a big buffer of spare capacity on top of this with up to 50 GW of wind and solar power capacity available, but output from these facilities could be zero on a calm evening when there is no sunshine.

France is set to exceed its previous record demand high from late 2010 by 2.3 percent on Feb. 7 at 98.9 gigawatts (GW), with temperatures forecast to drop as low as -16 degrees Celcius in the Alpine region.

A new high pf 97 GW is also expected this Friday, albeit lower than peak-time consumption forecast for Tuesday.

(Reporting by Vera Eckert and Karolin Schaps. editing by William Hardy)