Office for Nuclear Regulation

Dounreay Diesel Backup Generators

Date released
19 March 2021
Request number
Release of information under
Freedom of Information Act 2000

Information requested

You answered an FOI about replacement of back up generators at Dounreay in recent years.  Saying you had no records after the May 1998 failure incident (one month after the Good Friday Agreement was signed)

I am asking you to verify that. I think there were two further incidents before Iain GREY (Scottish Energy Minister) called for me to report expanding on an email I sent.  Then Iain GREY contacted Nuclear Police who, as I understand it, reported to Head of Civil Nuclear Security at DTI.

I am asking you to verify that after 1998 you have no further records for failure incidents or concerns to take into account when Dounreay invested in new backup generators.

Information released

I confirm that under Section 1 of the FOIA we do not hold the information you requested.

Following a search of our paper and electronic records, we have been unable to identify any record of further failure incidents or concerns after 1998 and have verified with Dounreay that they have no records of any such notifications to the nuclear regulator. In addition, there are no operational records prior to the most recent loss of grid incident on site that ONR would have been required to take into account in considering Dounreay’s intent to invest in an additional back-up diesel generator.

Turning to the other matters raised in your emails of 19, 23 and 26 February 2021, our Safety Assessment Principles (SAPs) and associated technical guidance to our inspectors are periodically updated to reflect operating experience and evolving nuclear safety standards such as those published by the International Atomic Energy Agency (IAEA). These reflect relevant good practice from across the nuclear industry worldwide.

As we explained in our email to you of 26 February 2021, we have published all of the reports relating to the Fukushima 2011 nuclear incident from the then HM Chief Inspector of Nuclear Installations, Dr Weightman, on our website at: “Fukushima and the UK Nuclear Industry.” As stated, we do not hold any report with the title "post Japanese tsunami review of UK nuclear security and resilience".

The accident on 11 March 2011 at Fukushima Daiichi led to consideration being given even to those highly unlikely but high consequence events which were not previously required to be considered within the nuclear safety and security assessments. However, the situation at Dounreay in relation to back-up power supplies from a diesel generator is very different than that of an operating nuclear power plant. From a nuclear safety perspective, the consequences of losing electrical power at the Dounreay site are very minor and the need to restore power supplies is over long timescales as there is little or no heat generating material that requires forced cooling. Our Technical Assessment Guide covering Emergency Power Generation (issued February 2019) provides more detail. Our requirements are that the safety case is implemented and the Security risks are included in Dounreay Site Restoration Limited’s (DSRL) plans. 

From these assessments Dounreay has not identified the need to provide a back-up Diesel Generator supply for Nuclear Safety purposes. The current back-up Diesel Generator supports the diverse power supply requirement for security systems as identified from the stress testing undertaken by Dounreay as a requirement from the Chief Nuclear Inspector’s Report following the Fukushima accident, “Japanese earthquake and tsunami: Implications for the UK nuclear industry” (dated September 2011). In addition, all systems necessary to provide a radiological safety or nuclear security requirement have their own dedicated back-up power supplies to protect against a Loss of Grid event. Consequently, we have not placed a requirement on Dounreay to provide an additional back-up Diesel Generator. Dounreay’s current intent to proceed with the installation of an additional replacement back-up Diesel Generator is for its own re-assurance purposes to improve redundancy and to provide additional lines of defence not claimed by the safety case and security justifications.

Exemptions applied


PIT (Public Interest Test) if applicable