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Dredging mud in the Bristol Channel

What’s happening?

Mud dredging and disposal is required as part of works to install Hinkley Point C’s cooling water intakes in the Bristol Channel. The mud is no different from mud elsewhere in the channel and comprehensive testing has shown that it poses no harm to people or the environment. An independent report commissioned by the Welsh Government found that the mud would be deemed suitable for disposal at sea.

Legal action brought by campaigners attempting to halt the dredging was dismissed by the High Court in March 2022. The campaigners chose not to challenge the ruling in the Court of Appeal.

Further maintenance dredging is now underway, ahead of placement of the heads for the cooling water system. As part of our dredging licence, the mud has to be disposed of within the Severn Area of Conservation (SAC) in order to maintain the balance of sediment and mud in the area. As a result , the mud will be transported to the Portishead licensed disposal site.

Hinkley Point C is one of many companies - over many decades – which has dredged and deposited mud in the Bristol Channel for industrial or construction purposes. Dredging first began in September 2018 when contractors successfully completed the first licensed work to dredge and deposit mud in the Severn Estuary.

The Marine Management Organisation approved licences, along with licence conditions, for dredging and disposal of mud at the Portishead licensed disposal site for the second phase of dredging. We complied with all requirements and fully supported efforts to inform and explain the dredging work to the public.

Key facts

  1. Following the first phase of dredging, the latest testing goes above and beyond internationally recognised best practice with more samples taken, at greater depth and with a greater range of analysis.

  2. The mud in the Bristol Channel has been independently tested by CEFAS in 2009, 2013, 2017 and 2020 as commissioned by Natural Resources Wales and Hinkley Point C.

  3. In all four cases, the studies concluded that the levels of radioactivity in the mud are so low that they equate to ‘not radioactive’ under UK law.

  4. The mud poses no threat to human health or the environment.

  5. The dredged mud must be kept within the Special Area of Conservation (SAC). The Cardiff Grounds and Portishead licensed disposal sites are the most suitable locations within the SAC that are large enough to handle the amount of mud we need to move.

  6. Radioactivity occurs naturally, including in foods we eat and the air we breath. Any sediment in UK coastal waters will contain naturally occurring levels of radiation.

Is the mud and sediment radioactive?

The sediment is typical of sediment found elsewhere in the Bristol Channel, and under UK law it is not radioactive.

Radioactivity occurs naturally, including in foods we eat, and can be artificial/produced by human activities. Any sediment in UK coastal waters will contain naturally occurring levels of radiation, and in areas of industrial activity there may be extremely low levels of artificial radiation present.

In the case of the Bristol Channel, the very low levels of radioactivity identified in the sediment are predominantly naturally occurring, with a small amount of artificial radioactivity, which will have originated from legacy discharges from hospitals, medical isotope manufacturing facilities (including those formerly based in Cardiff) and nuclear facilities. The addition alpha and tritium analysis undertaken on the 2020 samples has confirmed that the levels of artificial radioactivity are very low. Whether the radioactivity is naturally occurring or artificial this has no impact on how it interacts with the human environment.

Who carried out the tests?

The tests were carried out by CEFAS, an executive agency of the UK Government. CEFAS has some of the most advanced radiation testing equipment in the world and also provides services to Natural Resources Wales and the Welsh Government, as well as the Marine Management Organisation.

But what is radiation?

We often hear the word “radiation” but what actually is it?

Radiation is energy emitted from a source such as heat or light from the sun, microwaves from an oven or x-rays from an x-ray tube.

The type of radiation people often refer to in relation to nuclear power is sub-set of this called “ionising radiation”. This is electromagnetic waves or particles with sufficient energy to directly or indirectly knock electrons out from an atom or molecule, producing ions.

The atoms of some elements found in nature or produced artificially are slightly unstable and to achieve greater stability, the emit ionising radiation. These atoms are referred to as radioactive.

At what level is ionising radiation safe?

There are multiple sources of ionising radiation in everyday life:

  • It naturally occurs in food such as brazil nuts, bananas and coffee
  • It can be found in your home in the form of a radioactive gas produced by rocks (radon)
  • It is used in everyday items such as your smoke detector
  • It can even be found in some glasses and ceramics


There is no difference between naturally occurring ionising radiation or ionising radiation produced by artificial activities such as nuclear power.

In order measure exposure to ionising radiation the term “dose” is used, this has the units of a mSv (milli-Sieverts). The graphic below shows a comparison of dose by various activities.

The mud testing process



CEFAS obtained 10 sediment samples at depths up to 4.8m as part of the HPC Planning Application.

Levels of radioactivity in the sediment are found to be so low they equate to ‘not radioactive’ in law. In addition, no artificial radioactivity was observed below 2m.


Natural Resources Wales commissioned an independent analysis by CEFAS to determine the radioactive characteristics of the sediment to assess the licence application. 17 sediment samples were taken in 2013.

Levels of radioactivity in the sediment are found to be so low they equate to ‘not radioactive’ in law.


Hinkley Point C commissioned CEFAS to undertake an analysis as required, and approved, by NRW to support the Licence. 12 sediment samples were taken in May 2017.

Levels of radioactivity in the sediment are found to be so low they equate to ‘not radioactive’ in law.


Hinkley Point C commissioned CEFAS to undertake analysis on further sediment samples following approval of the sampling plan.

35 sample stations, with further contingency built-in. Samples were taken from surface and from depth.

The results are consistent with all previous analysis.  The additional detailed alpha and tritium analysis shows the presence of those radionuclides is insignificant

The 2020 sediment sampling plan was designed to update and build upon previous sampling results. In addition to  satisfying scientific and regulatory requirements, the widened scope for the 2020 sediment sampling goes beyond internationally recognised best practice and includes the collection and analysis of additional samples from depth (until bedrock is reached, or up to 9m maximum depth below chart datum).

When testing the sediments, the type and energy of radiation, along with the composition of the sample being measured effects how easy it is to measure the amount of radioactivity.

Generally, a radioactive atom emits either an alpha or beta particle. This is usually accompanied by a gamma-ray.

Due to this fact, the most common means of measuring radiation is to use a technique called gamma ray spectroscopy. This allows you to detect the majority of alpha, beta and gamma emitting radionuclides, identify the radionuclides present and measure the amount radioactivity.

As some radionuclides only emit alpha or beta particles, with no gamma-ray, there are some cases where additional testing may be needed, however this is usually not required.

In the case of the sampling of the mud at Hinkley Point C, the testing and sampling plan was developed independently by CEFAS (an executive agency of the UK Government), which carries out work to the highest international standards.

The analysis includes the use of high resolution gamma-ray spectroscopy, allowing the identification of a wide range of alpha, beta and gamma emitting radionuclides, and thorough assessment of the level of any radioactivity in the mud.

Additional monitoring, including the use of alpha particle spectroscopy, was undertaken as part of the 2020 sampling campaign to determine the presence of pure alpha emitting radionuclides and tritium. The testing confirmed conclusively that the mud and sediment is safe.

Radiological impacts of the disposal

Taking account of the natural and artificial radioactivity together, and based on the results of previous analysis, the dose received would be:

40 times less than the dose received from a transatlantic flight

Equivalent to eating 20 bananas per year

A fifth of the annual dose from drinking a cup of coffee a day

3,500 times less than having a chest CT scan

This is an infinitesimally small level of exposure to radiation, far below the threshold requiring a more detailed assessment or even close to approaching a radiation dose that could impact human health or the environment.

Location of the disposal site

Cardiff Grounds has been a licensed disposal site since the 1980s, and takes on average 1,500,000m3 of sediment each year. It is important to emphasise that Hinkley Point C is not the only company licensed to use the Cardiff Grounds - the site will have received several million cubic metres of dredged sediment from other parts of the Bristol Channel over several decades.

Cardiff Grounds is the closest site to the location of the offshore dredging operations planned in the Bristol Channel. Disposal within close proximity to the dredged site(s) will result in a lower carbon-footprint due to less distance being travelled by vessels, and therefore lower overall emissions.

How does Wales benefit from Hinkley Point C?

As well as being part of the National Grid network that will benefit from the affordable and reliable low carbon electricity produced by Hinkley Point C, Wales is benefiting during its construction.

Apart from local workers at the Somerset site, the largest group of employees come from Wales – over 1,000 Welsh residents are working on site each day.

More than 200,000 tonnes of Welsh steel are being supplied to the project and valuable contracts have already been awarded to over 200 Welsh companies in areas including steel fabrication, training, engineering, scaffolding, water management, transportation and site services.

Contact us

The best way to contact us about Hinkley Point C is by completing our online enquiry form. You can also call us on 0333 009 7070 (24 hour free phone number).

For EDF's 24/7 media enquiry line call 01452 652233.

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