Office for Nuclear Regulation

Criticality detector at Sellafield

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

Information requested

Can Sellafield Ltd confirm or otherwise, that a criticality detector, or detectors was recently discovered in the main reprocessing plant at Sellafield, which was found to be shrouded in lead, potentially rendering the criticality detector, or detectors, useless, thereby putting the Sellafield workforce at increased risk, and potentially putting personnel in danger of receiving a fatal dose of radiation in the event of a criticality?

New Information: 8 May 2021

In the light of new information received, can the ONR confirm, or otherwise, that the criticality detector in question has been essentially inoperative since 1989, some 32 years, having been wrapped in lead, and encased in concrete?

Information released

We aim to be as open as possible when answering requests for information. However, we consider your request a general enquiry, and not a request for information we hold under the FOIA. We have therefore processed your request as a general enquiry.

This is because Section 84 of the FOIA defines information as “information recorded in any form”. Nevertheless, to be as helpful as possible and in accordance with our duty to provide advice and assistance under section 16 of the FOIA, we have answered your question below.

We are aware of this issue and are satisfied with the programme of work being undertaken by Sellafield Ltd to address the issue. We are continuing to engage with Sellafield Ltd and are content that appropriate measures are currently in place to protect the public and workforce.

We will be conducting preliminary enquiries to determine the facts of how this issue arose and whether any formal regulatory action is required and therefore it would be inappropriate to comment further on this issue at this time.

Exemptions applied


PIT (Public Interest Test) if applicable