The plight of the Danish vessel MV Parida has been much on Scotland's mind this week after she got into trouble trying to take some nuclear waste from Dounreay back to its country of origin, Belgium.

A fire broke out in one of the funnels after she left the Caithness port of Scrabster. Her engines refused to restart, leaving her at risk of crashing into the Beatrice production platform, which had to be evacuated. But in the end she was safely towed away to the safety of the Cromarty Firth.

The episode has raised many questions about the safety of transporting nuclear material by sea.

But not much has been said about the presence of another vessel in the Pentland Firth last week, the Oceanic Pintail.

Dounreay Site Restoration Ltd, which is charged with the decommissioning of the plant, confirmed that this other vessel was undergoing trials to see if sea transport was a viable option for taking Dounreay's so called "exotics" to Sellafield in Cumbria.

These represent 26 tonnes containing unirradiated highly-enriched uranium; unirradiated plutonium and irradiated fuels. This is not nuclear waste, and is potentially more dangerous than cargo bound for Belgium. It is estimated it will need 60 trips carrying 24 flasks at a time.

Nuclear engineer John Large has said of the "exotics": "We're talking about bomb-grade material that would be a target for terrorists. It is also fuel from an experimental reactor which will have got broken up and will have been in storage in an uncertain condition.

"It will be very difficult to inspect it before it is transported and the only safeguard is based on their assumption that they would not encounter an accident with a big enough impact to break open the flask."

The campaigning group Cumbrians Opposed to a Radioactive Environment (Core) have long had their collective eye on the Oceanic Pintail, which they say is based in Barrow.

Core compares the two nuclear cargo boats thus: "The 5800 tonne Parida, a roll-on roll-off cargo vessel, was built in Turkey in 1999. By comparison, the Oceanic Pintail was built in 1987 and at 27 years of age, has well exceeded the 25-year shelf-life that has historically been enforced on Barrow's fleet of nuclear cargo carriers. "

Core is concerned about the age of the Oceanic Pintail and "its continued use as a dangerous nuclear materials transport vessel" , especially since the Department of Transport's withdrawal of emergency tow coverage for the notoriously difficult waters of the Minches in 2013.

As a result, should the Oceanic Pintail suffer the same fate as the Parida, its rescue would be reliant on the emergency tug based in Orkne,y but often in Shetland.

This, Core argues, would result in an extended rescue time lapse that could seriously jeopardise the safe recovery of the ship and its radioactive cargo...all the more so given the treacherous waters of the Minches, from Cape Wrath in the north to the Mull of Kintyre in the south.

Core says the vessel has an interesting history which includes having been armed at one point, presumably because of the risk from terrorists or pirates:

"The Oceanic Pintail was transferred to Nuclear Decommissioning Authority ownership in 2012. Prior to transfer, the ship was operated by Pacific Nuclear Transport Ltd as the Pacific Pintail and employed almost exclusively on nuclear transports to and from Japan.

"Along with her sister ship Pacific Teal she was fitted with 'physical protection equipment' in the form of three naval canon at Barrow in 1999 in preparation for shipping mixed oxide fuel fuel from Sellafield to Japan the same year with an armed security crew and escorted by the Pacific Teal. For her transfer to the Nuclear Decommissioning Authority, the naval canon were removed."

She may not need to be armed against pirates in the Minches, but Core still has grave concerns about her vulnerability because of age.

But Dounreay Site Restoration says such worries are misplaced. It insists: "The Oceanic Pintail...meets the highest level of the International Maritime Organisation's Code, which regulates shipments by sea of packaged irradiated nuclear fuel, plutonium and high level radioactive wastes. There is no policy or practice to retire ships at 25 years of age."

Whatever the merits of the boat, it serves to underline the problems about decommissioning our nuclear plants. What do you do with their radioactive legacy?

Dounreay was located in the far north of Scotland specifically so it would be far away from centres of population. This was deemed necessary, given the nature of the pioneering nature the fast breeder reactor programme pursued after it was commissioned in 1955.

But now the radioactive material either has to be left where it is or transported to some other nuclear facility, with Sellafield the obvious choice.

The former option would have meant that Dounreay could not be decommissioned in any real sense of the word, so rightly or wrongly was rejected. The latter means a way has to be found to get the stuff to Cumbria, by road, rail or sea. And the first two mean taking it near or through population centres.

After the Parida episode, the Scottish Government has made clear it isn't prepared to leave such matters to the UK Office of Nuclear Regulation.

This is to be welcomed as clearly there has to be some greater public engagement and transparent assessment before Dounreay's exotics take to the high seas.