Update 4 May

HFR reparation proceeds according to plan

The welding phase

HFR reparation proceeds according to plan

The repairs to the High Flux Reactor are proceeding well and according to plan. There have been no safety incidents during the period and the radiation dose levels for internal and external employees have remained well below the planned limits.
The removal of concrete by core drilling was completed on April 23rd and the drilling rigs have been removed from the sub-pile room. In total 384 meters drill cores were removed and no contamination was measured in the concrete or drill water. During the drilling a reducer flange was hit after which the drilling scheme was adjusted. The original repair scheme provided in the replacement of both reducer flanges. Careful inspection showed that the removed flange part was in good condition.
NRG continuously strives for minimizing radiation exposure for both our internal and external employees. Within that scope additional measures have been discussed in consultation with the Dutch Competent Authorities to minimize the radiation exposure of employees who remove the concrete between the drill holes. The partial refill of the reactor vessel with water when radiation levels increase, is a protective measure that we have agreed upon.
The manual removal of the concrete between the drill holes started on April 26th. The aluminium cooling pipes, which are going to be repaired, are now visible. First, preliminary assessments indicate that the corrosion mechanism and the condition of the corroded parts of the cooling pipes are as expected. A snapped water tube caused flooding in the reactor basement on May 2nd, resulting in a temporarily suspension of the repair. The tube was part of the cooling system of the drills that were used removing the concrete. On Tuesday, May 4th the repair was continued. In accordance with NRG policy, the leakage has been reported to the Authorities. For the time being, there is no reason for adjusting the project plan. The planned date of the restart remains fixed for the second half of August.
NRG issues a progress update every month. A special page has been added to the NRG website that contains background information, images and a video of the repair project: www.nrg.eu/hfr-repair. Updates 1, 2 and 3 are also available on the website.

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The welding phase

After the concrete removal the repair project now proceeds to the welding phase. Mechanical Engineering Sub Project Manager, Mr. John Verbruggen clarifies the work: “First we take parts of the jacket pipe of the reducer for microscopic investigation to assess whether the material is weldable. We earlier performed some welding tests on the aluminium cooling pipes. A röntgenographic showed good weldability of the material.” Preliminary assessments of the reducers’ corroded parts have indicated that the corrosion mechanism and the condition of the corroded parts are as expected. “Next week we will further assess the situation in full detail and decide, in consultation with the authorities, which of the planned, and extensively trained, repair options will be executed”, says Mr. Verbruggen. The reducer will be cleaned and thickness of the reducer walls will then be measured using ultrasonic equipment. The Dutch company Welldone will perform the welding activities. Because high levels of humidity may develop hydrogen bubbles in the welds, it is crucial to execute the welding activities in a dry environment. “We use air dryers to lower the humidity to less than sixty percent”, explains Mr. Verbruggen. The welds are applied in five layers. Mr. Verbruggen: “Every weld will be inspected a hundred procent by using röntgen graphics. Not until the authorities will have approved the quality of one weld, the next weld can be applied.” After the welding activities a corrosion resistant layer will be applied by coldspray technique, where zinc powder is sprayed on the aluminium with high-speed. Because of this high-speed the zinc particles melt together, forming a layer of zinc around the reducers. Mr. Verbruggen: “The thickness of this layer will be checked by ultrasonic testing. Afterwards we will apply a protective layer of PE-tape around the reducers. After that we will be able to seal the jacket pipe with a concrete cuff. By using concrete instead of the original material of the flange connection, galvanic corrosion in the future will be prevented. Finally we will repair all the smaller drainpipes so the repair project can proceed to the next phase: the applying of the new heavy concrete.”

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