VIENNA: Changes to the design of Iran's planned Arak research reactor could drastically reduce its output of potential nuclear weapon material, US experts said in a proposal.

How to deal with Arak is one of several issues that must be tackled in negotiations between Iran and six global powers that got under way in February with the aim of reaching a long-term deal on the decade-old nuclear dispute by late July.

Princeton University academics said that annual production of plutonium could be cut to less than a kilogram – well below the roughly eight kg needed for an atomic bomb – if Iran altered the way the plant is fuelled and lowers its power capacity.

“These redesigns would not reduce the usefulness of the reactor for making radioisotopes and conducting research,” wrote Ali Ahmad, Frank von Hippel, Alexander Glaser and Zia Mian – members of Princeton's Programme on Science and Global Security.

“This approach would meet Iran's needs and would address the concerns of the international community,” said their article, due to be published on Wednesday by the on-line journal of the Arms Control Association, a US research and advocacy group.Iran denies Western allegations that it is seeking the capability to make nuclear bombs, saying its programme is aimed at generating electricity and carrying out peaceful research.

Experts from Iran and the United States, Russia, France, Germany, Britain and China are due to meet in Vienna for three days from Thursday to be followed by a third round of political-level talks next week.