Troubled reactor to restart

THE troubled reactor at the Daya Bay nuclear plant is likely to be restarted for the summer peak demand without all its problems being solved, Hong Kong Nuclear Investment Co (HKNIC) admitted yesterday.

Anti-nuclear groups said the temporary move was very worrying, because the main safety mechanism would still be flawed.

But experts working on the problems have pledged that safety would not be compromised.

'We are trying to restart as fast as possible. That's what the client wants,' said Marie Carole de Groc, a representative from equipment supplier Framatome at its Paris headquarters.

The Legislative Council's environmental affairs panel will hear today from HKNIC's managing director, Lee Yui-bor, and chairman Ross Sayers, who is also managing director of parent company China Light and Power.

HKNIC senior technical adviser Jacques Pretti said yesterday that the main option being considered was to add eight more control rods to the 53 in the reactor, while also reducing the flow rate of the coolant water through the core and the power output to reduce pressure on the falling rods.

Tests and the required work could mean the reactor would restart in June.

But the reason why seven rods were falling too slowly was thought to be the design of their guide tubes, which could only be solved with a year or more's work at Framatome, said Ms de Groc.

The metal control rods drop into the reactor to slow down or stop the nuclear reaction in an emergency. If they fail, the plant must rely on the reactor building to contain the fallout.

After the replacement of spent fuel, the rods failed an international speed drop test in February. A new set of rods failed the same test at the end of March. Unit two is also shut down for refuelling.

Mr Pretti said the reactor had slots for eight more rods around the outside of the core, which could compensate for the slow falling speed of seven rods further into the core. Only 52 rods had to fall within 2.15 seconds, he said.

'If you have 61 rods and seven of them are not dropping in the required time then you still have 54 rods which do,' he said.

He said computer analysis would be performed to ensure that safety criteria were met even if all the seven rogue rods stuck.

After the board had considered the options, the French and Chinese nuclear safety watchdogs would have the final say on whether the reactor could restart, he said.

But anti-nuclear campaigner and legislator the Reverend Fung Chi-wood said more rods might fail if the root cause was not found. 'This time seven, maybe next time 14. I think it's more responsible and safer to find the real cause,' he said.

Up to three Daya Bay plant workers received a radiation dose on one day of almost the limit allowed for the public for a whole year, figures released by HKNIC yesterday show.

The maximum daily individual dose in January - at the height of the refuelling of the older reactor - was 4.34 milliSieverts compared with an annual limit of 5mSv for the public. The limit for nuclear workers is 50mSv Mr Pretti said that the high individual doses were recorded by three workers who were putting plugs into pipes that carry radioactive coolant water during refuelling.

Their exposure was still within international guidelines and the overall plant figures were good, he said.