Corrosion was detected around the reducers in the cooling system of the Petten nuclear power station during an inspection in 2008. It was concluded that the corrosion would eventually result in leaks. The reducers had to be repaired or replaced to prevent leakage.

Public interest
For significant public interest reasons it was decided to leave the reactor in service (under strict supervision) until mid-February 2010. Petten is one of six nuclear reactors worldwide that produce medical isotopes. Global production of these isotopes is in jeopardy due to unexpected delays in repairing a nuclear reactor in Canada. Every day approximately 24,000 patients all over the world are treated with isotopes originating from the High Flux Reactor in Petten. This equates to about 30% of all treatments worldwide.

Stringent requirements
Strict supervision and extremely stringent requirements were laid down for the repair process because of the nuclear aspects. The Department of Nuclear Safety, Security and Safeguards, the Reactor Safety Commission and the International Atomic Energy Agency brought together specialists to review every step in the process. Nothing is being left to chance and a mock-up was made of the part that will be repaired using identical materials with the same concrete properties and armouring. All repair techniques and procedures are tested and rehearsed.

Structural solution
The reducers are situated on the top side of the concrete reactor floor. Two holes must be made from the basement below the reactor floor to make the reducers accessible. The floor supports the entire weight of the reactor so there are stringent rules for floor deformations. Iv-Consult made EEM calculations to demonstrate that the weakening of the reactor floor caused by the holes will not exceed the permissible tensions and deformations. Assumptions made in the advanced calculation were tested in practice and calibrated. Iv-Consult designed the supporting structure in the basement below the reactor floor. In an emergency this structure will absorb the loads exerted by the reactor.