Five years ago the Rainbow Warrior sailed along the Fukushima coast conducting radiation sampling. Now it's back, and has Japan's ex-Prime Minister on board.

Greenpeace Ship Rainbow Warrior Sailing past the destroyed Fukushima Daiichi nuclear plant.

Scotland is over 9,000 km from Japan, but there’s something the two countries have in common. Along the Scottish coastline, buried in riverbeds, and mixed into the Irish Sea, you can find significant radioactive contamination coming from the other side of the world. Yes, radioactive contamination. All the way from Japan.

Since the 1970s, Sellafield, a nuclear-reprocessing plant in northwest England has been contracted to process high level nuclear waste spent fuel from Japanese reactors. More than 4000 tonnes of spent nuclear fuel was shipped from Japan to Sellafield, including waste from Tokyo Electric Power Company (TEPCO), the owner of the Fukushima Daiichi nuclear plant. As result of reprocessing at Sellafield, more than 8 million litres of low level nuclear waste is discharged into the ocean every day. It’s been labelled the “most hazardous place in Europe” - with levels of contamination in the fields, soils and estuaries at a level that can only be described as a nuclear disaster zone. In fact, the Irish Sea is arguably the most radioactively contaminated sea in the world

The Sellafield Nuclear Power Station (2002).

We’re about to approach the five-year anniversary of the Fukushima Daiichi nuclear disaster, and this is a stark reminder that no matter where you are or how far away, nuclear power has a local and global impact.

I remember waking up to the news on March 11, 2011. Though I was at home in Scotland, I’ve never felt so connected to the people of Japan. Having spent decades with Greenpeace actively campaigning against nuclear power in Japan, I knew deep down that a catastrophic accident was only a matter of time. With media requests coming in thick and fast, I recall appearing on BBC World News live. In mid-interview, as I was talking about the specific threat at Fukushima, I was interrupted as the news crossed to Japan where Reactor 3 exploded.

A satellite image shows damage at Fukushima I Nuclear Power Plant that was caused by the offshore earthquake on 11 March 2011.

Greenpeace Japan sent a team to the Fukushima evacuation zone to conduct independent radiation testing; and researchers on the Rainbow Warrior, kitted up in full body chemical suits, pulled floating seaweed from the surrounding area to use as samples. Our results were unfortunately as you would expect – high levels of contamination. Subsequently, we’ve also found radiation is still so widespread that it’s unsafe for people to return across large parts of Fukushima.

Greenpeace radiation monitoring team conduct seaweed testing along the Fukushima coastline.

Nearly five years later and I’m in Japan on-board the Rainbow Warrior - this time with the famously anti-nuclear former Prime Minister of Japan, Mr. Naoto Kan. It’s truly an honour and privilege to hear him describe the first hours and days of the accident in March 2011, as well as show him the research that we are carrying out. As we sailed within 2km of the nuclear plant the feelings are both profound and surreal. From the deck we’ve seen steel tanks holding hundreds of thousands of tons of contaminated water; the four reactors now shielded behind temporary structures in an effort to contain some of the radioactive material from being released into the atmosphere; and inside the reactors themselves lie hundreds of tons of molten reactor fuel for which there are no credible plans to deal with.

The Fukushima Daiichi nuclear plant as seen from Greenpeace ship, Rainbow Warrior.

But there’s another reason the Rainbow Warrior is here. A Greenpeace Japan research vessel is conducting underwater marine radiation surveys within a 20km radius of the Fukushima Daiichi plant, with the Rainbow Warrior acting as campaign ship. As with the radioactive contamination near my home in Scotland, Greenpeace is aiming to further the understanding of the impacts and future threats from nuclear power and in particular the Fukushima Daiichi nuclear accident.

For Mr Naoto Kan, who was Japan's leader when the disaster hit, this voyage is as much personal as it is political. In the years since 2011 he has spoken out publicly against the nuclear industry, standing alongside millions of Japanese people opposed to nuclear power – a far cry from the current “tone-deaf” Abe administration, which is desperately trying to save a nuclear industry in crisis. Opposed by the majority of citizens, and beset by enormous technical, financial and legal obstacles, it's an effort that I believe is doomed to failure.

Naoto Kan, former Prime Minister of Japan on board Rainbow Warrior.

But there’s hope.

Like the many communities across the country that are switching to innovative renewable power projects, Mr Kan knows that nuclear should be buried in the past. Renewables in Japan are rising. In the 2015 fiscal year, solar power capable of generating an estimated 13 TWh was newly installed - more than the two Sendai reactors in southern Japan that were restarted that year can produce.

For Japan to go 100% renewable it must urgently formulate more ambitious targets; stop all planned investments in new coal power plants and finally abandon plans to restart its ageing reactors and remove the institutional and financial obstacles to renewable energy growth.

A nuclear free future is not only possible it is essential. Renewable energy is the only safe and secure energy for the people of Japan and the world. .

Shaun Burnie is a senior nuclear specialist with Greenpeace Germany.