Update number 10 – September 2010

HFR back to service

The repairworks

HFR back to service

On Thursday 9th September 2010 NRG succesfully returned the High Flux Reactor (HFR) back to service following the repair of the primary cooling water system. The reactor reached full nominal power (45 MW) at 15.50 hours. With the succesfull restart of the HFR; NRG has completed the repair work on the reactor. Over the last months many NRG employees and external parties have worked hard to replace the corroded parts of the reducers to return the reactor to service. The repair of the HFR proceeded well and went according to plan. NRG’s top priority during this work was the safety and health of all the employees working on the repair and in the surrounding area. There were no safety incidents during the repair period and the radiation dose levels for internal and external employees remained well below the planned limits.


Restart
With the restart of the HFR on the 9th September 2010, NRG will again supply medical isotopes for the treatment of patients worldwide and will make important contributions to nuclear technology research. The HFR is an indispensible facility for the production of radioisotopes for medical imaging and therapy and normally produces around 60% of the European annual demand. In addition, the HFR plays a key role in international energy research projects for fuel and materials testing and for nuclear waste reduction and environmental issues.

Updates
This is the last of the monthly updates on the progress of the project NRG has issued during the repairworks. 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. Previous Updates are also available on the website.

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The repairworks

A routine in-service-inspection in August 2008 detected a jet of gas bubbles in one of the reducers, a part of the primary cooling water system. It was already known that the pipes had some deformations and that this was probably due to local galvanic corrosion. The bubble jet of tiny bubbles was the result of this corrosion. Althought there was no external water leakage, NRG decided not to restart the reactor before conducting a more detailed evaluation of the bubbles and the extent, cause and possible consequences of the deformations in the reducers and assessing the prospects for carrying out a repair.
As part of an HFR return-to-services programme NRG generated a plan to restart the HFR and in parallel, prepared for a full final repair of the cooling water system. On the 16th February 2009 the reactor was restarted under a special license, the reactor final repair started on the 19th February 2010.
During the repair, a specifically designed densimet radiation shield system was installed to protect the workers against the residual radiation emanating from the reactor core area, because the radiation level would increase when the pool was drained. After draining the pool, the reducers which were located in the concrete floor of the reactor, were revealed from underneath. The concrete was removed using core drilling techniques. Following detailed inspection and measurement and in agreement with the Dutch competant authorities NRG decided to execute local repairs to the reducers. The coroded parts of the reducers were removed and new aluminium plates were welded in place. The welding phase was succesfully completed on 30th June. The repair of the reactor floor with heavy concrete proceeded according to plan and the pool was refilled allowing the removal of the densimet shielding material.

The reactor then had to be fully reconstructed and tested. Prior to the restart, NRG carried out extensive safety tests, including a five-day containment test to verify the leak tightness of the HFR dome. The inspection team also took a ‘Zero Time Point’ measurement of the repaired pipe sections. The results of this measurement will be used as the reference point for future in-service-inspections.

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