By Thomas Escritt

THE HAGUE (Reuters) - The 58 world leaders gathered in The Hague to discuss nuclear security were asked to explore how they would react to a nuclear attack or accident by taking part in a simulation set in a fictional country called Brinia.

It was a big departure from the formats typically adopted at major multilateral summits, and some of the leaders said on Tuesday they were impressed at the exercise set up by their Dutch hosts.

"It was a new, helpful experience," German Chancellor Angela Merkel said after the exercise, which was held on Monday. She said the exercise had tested leaders' reactions to nuclear incidents and terrorist attacks.

Dutch Prime Minister Mark Rutte, whose background as a human resources manager at Unilever may have given him insight into the challenge of training a disparate group of leaders, said he wanted to bring a fresh, interactive element to the conference.

"On the basis of scenarios, you can have discussions as to what to do in certain situations which are as real as possible," Rutte told Reuters.

"It gave new insight into some of the questions they would face if - and we hope it won't - such a situation would arise."

Educational gaming is increasingly popular in training programs and uses fictional scenarios, role-playing and often elaborate computer-generated graphics to explore how people would react to situations before they arise.

The Technical University of Delft, which researches the technique, has developed "Charlie Papa", a game for training security guards, who must roam a virtual city centre, scanning it for threats while interacting politely with members of the public. Another game was designed to help managers at Dutch railways improve internal communications.

Rutte, who still teaches a few hours a week at a secondary school, refused to say which leaders took part and how they had reacted. "We would never have this type of program again if people felt that what they said or did would be revealed to the press," he said.

(Additional reporting Andreas Rinke and William James in The Hague; Editing by Geert De Clercq and Janet Lawrence)