* EU's Barroso adds political weight to nuclear safety push
* Barroso: reactors must be tested for resilience to attack
* Former regulator warns of "lack of safety culture"
(Adds quotes, details)
BRUSSELS, May 11 Europe's nuclear safety tests should be strengthened to include the impact of man-made events, such as terrorist attacks or aeroplane crashes, European Commission President Jose Manuel Barroso said on Wednesday.
Barroso lent his political weight to the push for tighter nuclear safety as a letter emerged from the former head of Bulgaria's nuclear authority warning that regulators were too close to industry and "demonstrated a lack of safety culture."
European leaders agreed in March to subject Europe's 143 reactors to "stress tests", to prepare for disasters such as the March 11 earthquake and tsunami which battered Japan's Fukushima plant.
Since then, a dispute has broken out between those, such as EU energy commissioner Guenther Oettinger, who want the tests as wide-ranging as possible, and others, such as the French regulator, who oppose the inclusion of terrorist scenarios.
Barroso threw his weight behind Oettinger on Wednesday, aiming to put an end to the dispute ahead of a meeting of the European Nuclear Safety Regulators Group (ENSREG) on Thursday, which will aim to agree methodology for the tests.
"These tests should be comprehensive and include the widest range of scenarios, natural and man-made, focusing on their possible impact on the plants' functioning systems," Barroso said in a statement. "I hope this can be agreed tomorrow."
The former head of Bulgaria's Nuclear Safety Authority warned the Commission that Europe's regulators are too close to industry to police reactors properly.
"Experience shows us numerous cases where nuclear operators and regulators demonstrated a lack of competence," Georgi Kastchiev wrote in the letter seen by Reuters on Wednesday.
Kastchiev's four-page letter cited a number of previous nuclear accidents around the world, including the 1986 Chernobyl disaster.
"Regulators revealed insufficient independence and all parties demonstrated a lack of safety culture," added Kastchiev, who headed the Bulgarian authority from 1997 to 2001.
Barroso said he would also push for tougher international standards, in particular the Nuclear Safety Convention and the Convention on Early Notification of a Nuclear Accident.
The Commission confirmed it had received the letter and EU officials defended the credibility of regulators without wanting to be quoted directly.
Several countries oppose the moves.
"I am not aware that an air plane crashed on Fukushima," said Vaclav Bartuska, a Czech envoy on energy issues.
Those who oppose testing nuclear plants for their resilience to terrorist attack also say the test might reveal weaknesses that terrorists would be quick to exploit. But Oettinger's spokeswoman said there was room for confidentiality.
"It is important that citizens know what we're doing and what the results of our stress tests are, but clearly...there's some information in this area which cannot be published, and the Commissioner said he was willing to compromise on that issue," Marlene Holzner told reporters.
Kastchiev said Europe should agree firm criteria for the closure of plants, such as the lack of containment structures for reactors or fuel pools, or seismic threats.
That should point to the closure of Britain's gas-cooled Magnox reactors, Russian-made units in Slovakia, Hungary and the Czech Republic, and old boiling water reactors in Germany, Spain, Sweden and Finland.
"The stress test is in any case voluntary," Commission spokeswoman Holzner told reporters. "The European Commission, although it has a mandate to develop the stress tests, it does not have a mandate to force a member state to do the stress tests or to shut down a nuclear power plant."
EU officials, however, say that any plant that fails will be difficult to defend in the face of mounting public concern. (Additional reporting by Ilona Wissenbach and Barbara Lewis; editing by Keiron Henderson)
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