ENVIRONMENTAL activists on Thursday demanded Eskom halt proposals to build new nuclear reactors until it has studied using alternatives sources of power. The Johannesburg branch of Earthlife Africa and a Cape Town based group affiliated to the Government By The People Green Party held separate protests on Wednesday specifically against the Pebble Bed Modular Reactor Programme. The PBMR combines helium coolant, a graphite moderator and ceramic fuel pellets which reportedly allow the reactor to operate at very high temperatures, increasing the amount of energy it can convert to electricity.