The last reported flight taking high-grade nuclear material from Dounreay in Caithnesss has taken place.
But the movements have again sparked a furious reaction from politicians.
Highland Green MSP John Finnie said: “Given the secrecy surrounding this reckless operation, I fear we will never know for sure what is to happen to the material which presumably was the cargo on the now reportedly cancelled further six flights.
“I’ll be writing the Nuclear Decommissioning Authority about this matter.”
Highlands and Islands regional MSP Rhoda Grant added “The transportation of nuclear waste from Dounreay has always been a concern for me and I always thought that the decommissioning and storage of such high risk waste should have been carried out at Dounreay itself, which I believe would have been a safer option.
“Not only that, but keeping the decommissioning at Dounreay would have protected much needed local jobs and boosted the local economy.
“That said, I am pleased that this final flight was completed safely as any movement of this material is risky.”
Tor Justad, chairman of Highlands Against Nuclear Transport (HANT), said: “HANT has opposed these flights since they were first announced during a Cameron-Obama nuclear summit deal in 2016
“The summit agreed that the UK would transport 700kg of highly enriched uranium to the US from Dounreay while a different form of nuclear material would be moved from America to European Atomic Energy Agency (Euratom) and turned into radio isotopes used to detect and diagnose cancer.
“HANT is fully aware of the security implications of these flights but is also of the view that the public have a right to know the risks involved in transporting this most dangerous of cargoes by air from the UK which would not meet US standards for civil nuclear shipments.
“HANT will again be raising these questions with local MPs and MSPs to get to the truth on these matters.”
A spokeswoman for DSRL (Douneay Site Restoration Ltd) said: “Dounreay is closing down and nuclear materials are being removed from the site ahead of its planned closure.
“Our priority at all times is to comply with regulations governing the safe and secure transportation of nuclear material, both in storage and transit.
“Compliance with these regulations includes protecting information about routes, dates, timings and locations of nuclear materials in any current or future transport.”