Accidents in nuclear-powered submarines and their effect on environmental marine pollution

Since 1953, hundreds of nuclear-powered submarines (NPS) have been produced all over the world. Nowadays, about 160 nuclear submarines are in operation. In particular, USSR (then Russia) built 248 NPS between in the last 50 years. Most of them are now not operating anymore and have been dismantled only partially. Nowadays, Russia and USA have 75 and 52 operating NPS, while UK has 16, France has 10, and China has 6. Naval reactors have been in most cases pressurised water types, which differ from commercial reactors producing electricity (PWR) in that: - they deliver a lot of power from a very small volume and therefore run on highly-enriched uranium (>20% U-235, originally 93% but apparently now 20-25% in western vessels, and up to 45% in later Russian ones). This nuclear material has also proliferation problems. - the fuel is not UO2 but a U-Zr or U-Al alloy or a metal-ceramic. - they have long core lives, so that refuelling is needed only after 10 or more years, and new cores are designed to last 50 years in carriers and 30-40 years in submarines Decommissioning nuclear-powered submarines has become a major task for US and Russian navies. After defuelling, normal practice is to cut the reactor section from the vessel for disposal in shallow land burial as low-level waste. In Russia the whole vessels, or the sealed reactor sections, sometimes remain stored afloat indefinitely. Environmental consequences of such procedures may be very dangerous. Incidents and emergencies in atomic submarine fleet of USSR / RUSSIA have been many during their 50 years operational period of NPS: twelve nuclear and more 100 radiation emergencies have taken place. A nuclear emergency is such kind of emergency that concerns with the damage of fuel elements exceeding the established limits of safe operation, and/or irradiation of staff exceeding the permissible level for normal operation, caused by violation of control and managing of a chain nuclear reaction of fission in the reactor core, creation of a critical mass during reload, transportation and storage of fuel elements, or violation of heat elimination from fuel elements. Most of the emergencies were accompanied by serious radiological and ecological consequences. A relatively frequent event is the release of radioactive pollutants to the marine environment. In the Mediterranean sea, the effects of environmental marine pollution due to the presence of nuclear submarines has been recently studied. In particular, the most recent studies originated from the accident to the nuclear submarine "Hartford" that took place in 2003 close to the "La Maddalena" submarines base in Sardinia island (Italy). However it is not demonstrated that environmental release took place during the accident, findings about the presence of plutonium traces in certain types of algae close to the site have put into evidence the presence of artificial radioactive pollutants in that marine environment, a natural area of great ecological importance, designated by the Italian government as a natural marine park.