What are the transport safety measures?

All the equipment used for the transportation of the returned residues is designed in accordance with relevant regulations, which take into account possible accident scenarios.

Transport vessel safety features

The ships used for the safe transportation of vitrified residues have routinely transported spent fuel from Japan to France and the United Kingdom for more than 20 years with no radiological incident. These ships meet the international standards and regulations of the International Maritime Organisation (IMO). They also comply with the Japanese Ministry Of Transport (JMOT) regulation KAISA no 520.

In particular, the ship is equipped with:

• a double bottom and double hull structure for minimising damage and for safety in case of accident,
• duplicated navigation, communication, electrical and cooling systems,
• a cask cooling system installed inside each hold,
• a comprehensive fire fighting system maintained in case of emergency,
• emergency sources of electrical power,
• satellite navigation and tracking systems.

All sea transport operations are carried out according to applicable international regulations. A full worldwide emergency response system is operated, including a 24-hour standby team and salvage cover.

Transport cask safety features

The TN 28 VT transport cask, as a Type B package, complies with a series of technical criteria, established in order to cover both normal operations and extreme situations.

A list of very stringent tests must be performed to check the resistance and safety of the package. The IAEA accident conditions tests include two kinds of drop tests: a 9 metre drop onto a totally unyielding surface and a one metre drop onto a steel spike. The cask, with any damage sustained in the drop tests, is then subjected to an engulfing fire test for 30 minutes at 800 degrees Celsius, followed by an immersion test. After these tests the cask must still be leaktight and retain enough of its shielding to ensure radiation doses are within internationally agreed limits.

A complete safety evaluation, including regulatory tests of the TN 28 VT cask, has been performed showing that the safety criteria related to structural integrity, thermal performance, containment level, shielding capability and maintenance of sub-criticality are all satisfied. This ensures the safety of the transportation cask under normal and extreme situations.

Safety in depth

A series of barriers are used in order to protect nuclear cargo during every phase of the transport process: this system of protection is called "safety in depth". From the vitrified stable glass in a stainless steel canister to the 100 tonne transport cask, fixed in the hold of the ship and protected by its double hull, a scenario of the glass becoming directly exposed to the sea water is incredible.

Even in the highly extraordinary assumption of the successive ruptures of the hold, the cask and the canister, leading the solid glass block itself to be exposed, the leach rate of this special material is very low.

The results of an environmental impact assessment performed by the Japanese Science and Technology Agency (1995) show that the effect of such a scenario would be negligible, an exposure rate to the most affected person of less than one thousandth of the naturally occurring radioactivity they receive annually.

Main tests for Type B packages

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