While accident statistics on seagoing ships are readily available, data collection on marine casualties has been under way in several countries. Many data, however, are being collected for purposes other than the study of accident scenarios, which means that available data had to be sorted and evaluated carefully for their relevance to the CRP. Wherever possible, Member
The primary purpose of this CRP was to provide a co-ordinated international effort to assemble and evaluate relevant data using sound technical judgement concerning the effects that fires, explosions or breaches of the hulls of ships might have on the integrity of radioactive material packages. The probability and expected consequences of such events could thereby be assessed. If it were shown that the proportion of maritime accidents with a severity in excess of the IAEA regulatory requirements was expected to be higher than for land transport, then pertinent proposals could be submitted to the forthcoming Revision Panels to amend the IAEA Regulations for Safe Transport of Radioactive Material and their supporting documents.
At the first RCM, held in Vienna in 1995, five research proposals were presented.
Subsequently, two more participants joined the CRP. This meeting provided a good opportunity to participants to comment on the proposed studies and make sure that all the objectives were covered. It also provided an opportunity to review the scope and terms of reference for the programme, establish a timetable for further efforts, set priorities, and consider the structure and purpose of the final CRP report.
RCM meetings were held in Cologne in 1996, Albuquerque in 1997 and Vienna in 1998.
Four main areas of research were included in the CRP. These consisted in studying the probability of:
· ship accidents,
· fire,
· collision, and
· radiological consequences.
2.1. Type of materials and packaging
The types of material included in the study were high level waste (HLW), irradiated nuclear fuel and mixed oxide fuel (MOX). These materials are all transported in Type B packages.
The study did not consider Type A packages and small Type B packages.
2.2. Types of ships
While this study encompassed marine transport of packaged radioactive material on four different types of ships: container ships, roll-on/roll-off (Ro-Ro) ships, general cargo (break-bulk) ships, or purpose-built ships, ship accident data covering all types of ships were collected and analysed for the 15-year period between 1979 and 1993. The results of the study are applicable to any ship transporting radioactive material that complies with the applicable cargo ship requirements of the International Convention for Safety of Life at Sea (SOLAS), as well as with the specific requirements of the IMDG Code for the radioactive material considered. In addition, for ships that carry shipments of INF code materials, the study takes into consideration special provisions of the three separate classes of ships, depending on the total maximum radioactive quantity that may be carried on board:
· Class INF 1 Ships: ships that are certified to carry INF cargo with an aggregate activity less than 4000 TBq,
· Class INF 2 Ships: ships that are certified to carry irradiated nuclear fuel or high level wastes with an aggregate activity less than 2 × 106 TBq and those certified to carry plutonium with an aggregate activity less than 2 × 105 TBq,
· Class INF 3 Ships: ships that are certified to carry irradiated nuclear fuel or high level wastes and those certified to carry plutonium with no restriction of the maximum aggregate activity of material.
The requirements established are, of course, more stringent for Class INF 3 ships than for Class INF 1 and 2 ships.
2.3. Accident environment
The accident statistics have been taken mainly from the Lloyd’s database and the Marine Accident Investigation Branch (MAIB) of the UK. The Lloyd’s database, originally intended for insurance purposes, covers total losses around the world. The MAIB database covers all accidents for the UK ships for which an accident declaration has been submitted to the authorities.
The accident probabilities determined are based on all accidents, while the analyses do not cover military ships, general cargo and fishing ships.
Even though from the beginning the study was meant to focus on fire accident, accidents such as collision, foundering and sinking were also included.
The accidents probabilities have also been divided in accordance with where the accidents occurred. It was shown that the highest probability of certain kinds (collision, wrecked) of accidents are in ports followed by coastal water. The lowest probability of a ship accident is on the open ocean.
2.4. Effects of accidents
The effects of an accident on the package have also been studied. Several reports in the study cover mechanical effects as well as thermal effects on the packages.
As far as the consequences are concerned, the studies include both release to water and to air.
2.5. Summary of the findings
The principal technical conclusions of this CRP are:
· Ship collisions depend on ship traffic density and thus on the region of the ocean in which a ship is sailing. Traffic density does not affect the frequency of ship fires. However, the chance of a fire during a voyage increases directly with voyage distance or sailing time.
· Ship collisions and ship fires are infrequent events; most ship collisions and ship fires will
chance that a ship collision or a ship fire will subject a RAM transport package to loads that might fail the package is very small.
· If a ship collision subjects a RAM flask to crush forces, the magnitude of these forces will be less than or at most comparable to the inertial forces experienced by the flask during the regulatory certification impact test.
· Ship collisions are unlikely to damage a RAM flask, because collision forces will be relieved by collapse of ship structures, not flask structures.
· Ship fires are not likely to start in the RAM hold. If a fire starts elsewhere on the ship, its spread to the RAM hold is not likely. Even if a fire spreads to the RAM hold, the lack of fuel or air will usually prevent the fire from burning hot enough and long enough in the RAM hold to cause the release of radioactive material from a RAM flask or, given flask failure due to a preceding collision, to significantly increase the release of radioactivity from the failed flask.
· Heat fluxes from small creeping fires which do not engulf the RAM hold are unlikely to exceed the heat fluxes developed by the regulatory test fire for flask certification.
· Most radioactive material released to the interior of a RAM flask as a result of an accident will deposit on interior flask surfaces; therefore, flask retention fractions are large and flask-to-environment release fractions are small.
· Should a ship collision or fire lead to the sinking of a RAM transport ship and thus loss of a RAM flask into the ocean, recovery of the flask is likely if loss occurs on the continental shelf. If this flask is not recovered, the rate of release of radioactive material from the flask into ocean waters will be so slow that the radiation doses received by people who consume marine foods contaminated as a result of the accident will be negligible compared to background doses.
· If a RAM transport ship, while in port or sailing in coastal waters, is involved in a severe collision that initiates a severe fire, the largest amounts of radioactive material that might be released to the atmosphere as a result of the accident would cause individual radiation exposures well below background.
Consequently, since the probabilities of severe ship collisions and severe ship fires are small and since the individual radiation doses that might result in the event of such collisions or fires are smaller than normal background doses, the risks posed by maritime transport of highly radioactive material such as irradiated nuclear fuel, vitrified high level waste and mixed oxide fuel in Type B packages are very small.