THE month-long shutdown of one of Daya Bay's two reactors because of an electricity generator leak has thrown the nuclear plant's refuelling plan into disarray. Technical adviser Dr Jacques Pretti said yesterday that the date for the refuelling of one reactor had now been put back a month until the end of December. The shutdown - which ended on Monday - means less uranium fuel had been used than expected. The 13-week shutdown for refuelling of the first reactor, unit one, has to be finished by March because the same job has to start on unit two by the end of that month, when the second reactor's fuel runs out. Dr Pretti said overlap of the two was ''impossible'' because the organisation would be too complex and there would not be enough staff. ''We need special organisation. Preparation is well advanced,'' he said. Hong Kong's power supply should not be affected because China Light and Power will use its reserve capacity to fill the gap. Planning for the refuelling, which would need up to 500 people working on 3,000 duties, had begun last year and interviews with Chinese contracting firms had started as early as 1991, said former station manager Rene Vella. French contractor Framex would be in charge of the removal of the fuel rods, which was the trickiest job, said Dr Pretti. The 30 fuel handlers had to be tested and approved by the plant manager because breakage of a rod could lead to release of radioactive gases and particles into the site. The spent fuel rods, comprising one third of the total, would be replaced with high-uranium content rods. The other two-thirds, of medium and high uranium content, would be reshuffled and replaced in the reactor. The reshuffling was critical because a batch of high-enrichment rods together would create a hot spot in the reactor, which could make the temperature rise too high when power was increased, said Dr Pretti. ''We know that this can be a very big problem, so we work out the reshuffling by computer,'' he said. Organising the refuelling would be ''very good experience'' for deputy plant manager Fan Heming, who was expected to be the plant's first local chief in two or three years' time, said Mr Vella. But he was worried by Mr Fan's comments about the French management style because they showed that he was critical of the strict procedures used in the nuclear plant, he said. ''It was very hard at the beginning, when [conventional power plant staff] did not understand why there were so many requirements. They say 'we can do that for important work', but it's all important work,'' he said.