Office for Nuclear Regulation

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Flood risks at Sellafield

Date released
1 February 2016
Request number
Release of information under
Freedom of Information Act 2000

Information requested

I am writing to request all unpublished information or correspondence held by the ONR regarding the risk of flooding at the Sellafield nuclear site or the low-level nuclear waste site at Drigg, Cumbria since October 2015 up to Jan 4 2016.

It would be helpful if you were to provide any brief notes which might be necessary to understand the context of the information provided, although I recognise that you are not obliged to do this. If you are not the appropriate authority for this request, or for part of it, please let me know as soon as is convenient.

If the information requested contains sections of confidential information, please blank out or remove these sections, and mark clearly that they have been removed.

Information released

I attach the following documents which contain the information held by ONR relevant to your request:

  1. “Context for documentation provided in response to Freedom of Information Request dated 4th January 2016”
  2. email correspondence between ONR and DECC - “DECC201512115 - Flood defences Sellafield and Dounreay”.
  3. “Cumbria flooding”
  4. email between correspondence between ONR and DECC- “Providing reassurance ahead of and during severe weather events
  5. email correspondence between ONR and Sellafield Limited - “No Flood Barrier”.
  6. email - internal ONR correspondence “Recent bad weather in Cumbria”.

Please note that some information has been redacted in the above because it is personal data, and so has been withheld using the exemption under Section 40 of the Freedom of Information Act 2000.  This is an absolute exemption so does not require a public interest test.

In addition I would like to provide some further background information to set the above in context.

As I know you are aware, the recent severe weather has affected the region around the Sellafield and Low Level Waste Repository (LLWR) sites in Cumbria. (LLWR is now the name of the site formerly known as Drigg).  This has included significantly higher than average rainfall for the time of year. The effect on the sites and their operations has however been minimal: There have been no reported incidents of flooding on the sites and at no time has nuclear safety or nuclear security been challenged. We are aware of one example of an access road onto the Sellafield site that became flooded and unusable for a short period, but alternative access roads remained operational, and at no time was access to the site restricted in any material way.

As might be expected, the severe weather prompted some exchanges of information between Sellafield Ltd and ONR; where this was by email, this has been enclosed for your information. The dialogue was however rather limited since ONR has high confidence in the flood protection arrangements at these sites.  This is in part because of the work that the sites undertook following the Fukushima event in March 2011.  That event led to considerable work being undertaken by UK nuclear sites (including at Sellafield and LLWR) to confirm, and where necessary improve, the resilience of their flood protection arrangements.  A summary of this work can be found on the Fukushima pages of ONR’s website:

The ONR 2012 report is a detailed summary of the short term progress made by the sites following the post-Fukushima reviews, while the 2014 report is the latest statement by ONR on the state of progress against the Fukushima recommendations. You will see from both reports that in terms of flood-related recommendations relevant to your enquiry, ONR is content that satisfactory progress is being made.

More generally, UK law requires nuclear site licensees to demonstrate that flood risks at their sites (along with risks for other types of hazard) are kept as low as reasonably practicable.   The sites demonstrate this by preparing safety case(s) - a legal requirement of the nuclear site licence. Natural hazards such as flooding attract a number of regulatory expectations. Principal among these is the requirement to provide flood defences that will conservatively withstand a one in 10,000 year flood event (i.e. an event with 0.01% per year probability of exceedance) from all sources of flooding.  This is referred to as the “design basis event”. To place the present situation in context, the recent weather events in Cumbria are relatively minor in comparison to this type of extreme design basis event.  Further, ONR requires that there is margin (in flood barrier height for example) beyond this design basis level to mitigate against the potential for a sudden increase in nuclear consequences for even more extreme flood events (so-called cliff-edge effects).   Additional mitigation measures are then required for beyond-design-basis events that involve external challenges or multiple failures beyond the design basis.

As such, standards of protection against flooding at UK sites are very high and we would not expect Sellafield or LLWR to have any difficulties in maintaining their very high levels of nuclear safety and security, even when presented with the sorts of weather challenges seen in recent months. 

Exemptions applied

S40 - Personal information

PIT (Public Interest Test) if applicable