* Commission cannot force states to apply recommendations
* Says expects to propose new safety law next year
* Nuclear stress tests should not be a "one-off" (Adds reaction)
BRUSSELS, Oct 4 (Reuters) - Regulators and operators should act now to improve safety at nuclear power plants, the EU energy commissioner said on Thursday, following inspections across the European Union.
The stress tests, carried out in the aftermath of the Fukushima disaster, found safety improvements costing between 10 billion ($12.90 billion) and 25 billion euros were necessary in European plants, a draft seen by Reuters showed this week.
"Nearly everywhere there is major potential for improvement," Energy Commission Guenther Oettinger told reporters.
"We therefore think that we should talk together with operators and regulatory authorities to act rapidly so that the highest possible standards can be guaranteed very soon."
One of the lessons of Fukushima was that two natural disasters could strike at the same time and knock out the electrical supply system of a plant completely, so it could not be cooled down.
The stress tests sought to avert any repeat of that series of events by establishing whether nuclear plants can withstand natural disasters, aircraft crashes and management failures, as well as whether adequate systems are in place to deal with power disruptions.
Among the findings were that on-site seismic instruments should be installed or improved in 121 reactors.
In addition, 24 reactors did not have a back-up emergency room in case the main control room became uninhabitable.
LIMITS OF EU POWER
Because EU authorities do not have power to determine the energy mix of member states, the stress tests were voluntary, but Oettinger said they would not just be "put in a drawer".
"We are at the beginning of a new European safety dynamic," he said.
He confirmed the Commission would follow up with legislative proposals early next year to enhance safety.
The proposals would include insurance and liability, but Oettinger said it was not yet clear what that might mean for electricity bills.
Austria, which banned nuclear plants in 1974, said the stress tests were "good, but not good enough".
"Our demand is very clear: retrofit nuclear plants or shut them down," Austrian Environment Minister Niki Berlakovich told reporters in Vienna, referring to the possibility of adding safety measures.
Rebecca Harms, a Green member of the European Parliament, told Reuters Television the stress tests report had dodged the tough questions, but said they had still served to highlight the problems.
"Mr Oettinger has done the debate on lacking security standards a great favour," she said.
She added that the tests had "produced a handsome list of deficiencies, showing that there is a large deficit of security standards in every country that runs nuclear power plants".
ASN, the nuclear regulator in France, which relies on atomic energy for about 75 percent of its power, was highly critical of the report, saying "some important recommendations had been ignored".
It has already said France needs to invest billions of euros.
The chief inspector of Britain's nuclear plants, Mike Weightman, who also made recommendations for improvements after Fukushima, said: The stress test process was a valuable exercise, reinforcing the conclusions we had reached here in the UK".
($1 = 0.7751 euros) (Additional reporting by Oliver Denzer; Michael Shields in Vienna; Marion Douet in Paris; editing by William Hardy and Jason Neely)