Image caption The mud disposal site in 2018 was located about a mile off the south Wales coast

Plans to dump more mud from alongside a nuclear power site in Somerset into the sea off Cardiff Bay have been revealed.

The initial work, carried out in 2018, caused huge controversy.

Now the environment watchdog Natural Resources Wales (NRW) says it has received another application.

EDF Energy wants to deposit up to 780,000 tonnes of sediment dredged as part of building work for the Hinkley Point C plant.

The developers have submitted a plan to NRW for sampling and testing the mud, which will now be subject to a six-week consultation with specialists and the public.

Image caption A dredger in the distance involved in the mud dumping operation off Cardiff Bay in 2018

NRW's role is to determine whether the material is suitable for disposal at Cardiff Grounds, a licensed dumping ground for dredged sediment around two and a half miles out to sea from the Welsh capital

Michael Evans, the regulator's head of evidence, knowledge and advice said "the first step of a long application process" was to assess the sampling plan, before the developers request a marine licence to carry out the work.

"The disposal activity in 2018 caused great public concern, so we intend to inform and engage with people about these plans over the next few months," he explained.

"We will only grant the licence if the company can demonstrate it complies with legal requirements and we're confident the proposed activity will not harm people or the environment."

Image copyright PA Media Image caption The base for the first reactor at Hinkley Point C power station being constructed

As well as a marine licence from NRW to deposit the mud in Welsh waters, EDF Energy will also need another from England's Marine Management Organisation in order to dredge off the Somerset coast.

They hope to start carrying out the work in early 2021.

Why is the mud dumping so controversial?

The seabed alongside Hinkley Point C - which is being built near Bridgwater - is being dredged so that the £21.5-22.5bn power station's water cooling system can be installed.

EDF Energy says this will be a "significant piece of infrastructure", involving tunnelling more than 3km into the Bristol Channel.

But anti-nuclear campaigners have raised fears the process could be churning up contamination from the old Hinkley A and B reactors, which used to be on the site.

Tim Deere-Jones, of the Stop the Dump campaign, said he had urged the Welsh Government to carry out radioactivity measurements along the Welsh shoreline before and after the initial dumping of Hinkley mud in 2018.

But he said their refusal had "left coastal communities in a position of complete ignorance about the impacts of the dump".

A public outcry over the original mud dumping led to protests and a petition signed by over 7,000 people - which swelled to six figures online - triggering a full Senedd debate.

BBC Wales has been told it involved 120,000 tonnes of mud, although permission was granted for 300,000.

Though the Welsh Government rejected calls to suspend the marine licence issued to EDF Energy for the work, claiming it would set a dangerous precedent, it instructed NRW to do more to communicate with the public about the process and explain the issues involved in future.

EDF Energy insists all tests on the mud were completed to international standards, and claims it could be toxic are alarmist and wrong.

They say they are proposing to do more in-depth sampling ahead of their latest dredging application, in order to provide further reassurance.

Image caption Laboratory testing of mud samples

How did scientists work out the risk - and what did they find?

EDF have already presented evidence that levels in the mud are so low as to be not classed as radioactive under UK law. This is how scientists carried out their tests.

They "conservatively" assumed a person spent about four hours a day, every day, on the shore near the Cardiff Grounds and ate 50kg of fish and 15kg of crustacean and molluscs a year, all sourced from the Cardiff Grounds

Exposure to the radioactivity in the sediment was also considered from inhaling any sediment that may accumulate on the shore

Assuming a person was to do all of the above, 90% of the radiological dose they would receive would be from naturally occurring radiation

The research found combining natural and artificial levels of radioactivity together, any exposure would be 10,000 times less than an airline pilot's annual dose

It would be 750 times less than the average dose received by a resident of Pembrokeshire due to naturally occurring Radon

It would be equivalent to eating 20 bananas each year - an "infinitesimally small level".

But why off Cardiff Bay and not elsewhere?

Cardiff Grounds is the only site large enough to handle the amount of the type of sediment it wants to dredge, says EDF.

Because it is within a recognised special area of conservation (SAC), any sediment it removes has to be put back in the area "in order to maintain the natural balance" of sediment in the conservation area.

Why is this new dredging being proposed?

Chris Fayers, head of environment at Hinkley Point C, said the second phase of dredging was necessary ahead of drilling six vertical shafts for the cooling water system for the new nuclear power station.

"The mud is typical of sediment found anywhere in the Bristol Channel and no different to sediment already at the Cardiff Grounds site," he said.

"Ahead of the second phase of dredging independent experts will carry out further analysis of the mud and sediment using techniques that are even more stringent than those used in 2017.

"During the first phase of dredging, Natural Resources Wales confirmed that independent analysis showed that the levels were so low as to be not classed as radioactive under UK law. It poses no threat to human health or the environment.

"No dredging will take place until Natural Resources Wales approve a monitoring and dredging plan. The next phase of dredging is not planned to take place until 2021."

Image caption Brian Jones said people in Wales did not want nuclear waste buried in the ground or deposited off the coast

What has been the reaction?

Brian Jones, vice-chairman of CND Cymru, said the process at least appeared to be more transparent and they had a chance to have a say before the award of the licence this time.

"We were expecting it to come," he said. "We've got our chance to have more of our input in the process but in the longer term the nuclear industry tends to get what it wants."

He said they would be campaigning against it and he hoped samples would be taken deeper down into the sediment this time as he fears higher levels of radioactivity could be found.