The temporary closure follows problems identified since the new reactor began operating 11 months ago. ANSTO chief executive Ian Smith said the shutdown would affect silicon customers and cause delays in neutron beam research.

"During the shutdown, equipment which has faults will be thoroughly investigated and, where possible, repaired," he said. This included a dilution problem earlier this year where light water from a reactor pool seeped into the heavy water contained in the reflector vessel around the core. "To solve the dilution problem, further pressure testing is required," Dr Smith said.

"Whilst the dilution issue does not affect safety or operation, if left unrepaired it would ultimately affect the performance of the reactor." Dr Smith said ANSTO also would examine fuel plates that were dislodged this week when fuel assemblies were inserted into the reactor's core during the last monthly fuel change. "ANSTO will be undertaking a series of tests to fully determine the cause of that event," he said.

The supply of nuclear medicines would not be affected by the temporary shutdown as arrangements were in place to import these products, he said.

Web Editor: Less than a year in operation and the complications mount. Dr Smith is not perturbed by these events. It is more than his highly paid job is worth not to pretend that he has everything under control. "…faults will be thoroughly investigated and, where possible, repaired," he said.

And where not possible—what then? Just carry on as usual and hope that he is on holidays if the whole reactor blows up?