Wylfa consent to start up Reactor 1

Magnox Ltd, that operates and maintains Wylfa Power Station, has requested ONR consent to restart Reactor 1 at the end of its 2011 periodic shutdown in accordance with Licence Condition 30(3) of Nuclear Site Licence 58A.


Wylfa Power Station consists of two Magnox reactors. During operation the reactors are cooled by high-pressure gas, which is circulated through the reactors and then fed to boilers where the heat boils water, turning it into steam, to drive turbines which then generate electricity.

To continue to operate safely and reliably reactors require examination, inspection, maintenance and testing. Continuous improvement also requires plant upgrades to be implemented. Whilst some of these activities can take place when a reactor is generating electricity, many of them require a reactor to be shut down and at relatively low temperatures. To enable such activities each reactor at Wylfa undergoes a periodic shut down every two years. Following a periodic shutdown the reactor cannot start-up without the permission of ONR.

The current shutdown for Reactor 1 at Wylfa commenced on 17 August 2011.

Assessment and inspection work carried out by ONR in consideration of this request

ONR has undertaken a number of inspections and assessments in relation to this request. The most significant are as follows:

  • a meeting with the licensee on 12 July 2011 to discuss and agree the work to be undertaken during the outage;
  • an inspection visit to assess the station’s radiological protection procedures;
  • an inspection visit to sample the quality and standard of maintenance work on electrical systems;
  • an inspection visit to sample the quality and standard of maintenance work on control and instrumentation;
  • an inspection visit to sample the quality and standard of maintenance work on mechanical systems;
  • an inspection visit to sample the results of structural integrity inspections;
  • an inspection visit to sample the results of graphite sampling and inspections;
  • an assessment of the report written by the licensee’s internal expert (known as the ‘Appointed Examiner’) of the inspection of the civil structures;
  • several visits by the site inspector during the outage to carry out outage related compliance inspections; and
  • a start-up meeting on 24 November 2011 to review outage findings and agree actions to be completed before start-up of the reactor.

Matters arising from ONR’s work

There are no significant findings from the periodic shutdown that would prevent the reactor restarting.


The ONR programme of inspections and assessments gives sufficient confidence to issue Consent to start-up the reactor at Wylfa following its periodic shutdown.


Consent to start up the reactor should be given by issuing Licence Instrument Number 549 to the licensee.

Read the full PAR here.

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