Surface contamination HLW casks

Nuclear Monitor Issue: 
#735
6183
21/10/2011
WISE Amsterdam
Article

Concerns are being raised in Japan about the raised radiation levels – above legal limits - discovered on the surface of some of the canisters of vitrified High Level Waste (HLW) shipped recently from Sellafield, UK. In May 1998 a contamination affaire resulted in a ban on reprocessing transports in large parts of Europe.

In August, some 40 tons of HLW, contained in 76 canisters were shipped from Barrow docks onboard the Pacific Grebe, the newest ship in the nuclear fleet operated by Pacific Nuclear Transport Ltd (PNTL). Routed via the Panama Canal, the Pacific Grebe completed its maiden commercial voyage at the Mutsu-Ogawara port in Japan’s Aomori prefecture on September 15. As reported in Japan’s Mainichi newspaper mid-October, the Kyushu Electric utility that owns the HLW has confirmed that, from a batch of 28 canisters being safety tested during transfer to the storage facility at Rokkasho-Mura, 3 had been found to have surface levels of beta and gamma radiation that breached acceptance levels of 4 Bequerels (Bq) per square centimeter – in one case almost 50 times over the limit. Kyushu Electric, also confirmed that surface radiation levels were within the limits before leaving the UK. Japan Nuclear Fuel Ltd (JNFL) which operates the Rokkasho storage facility is carrying out an investigation into the breaches of acceptance levels.

Under the contracts covering Sellafield’s reprocessing of Japanese spent fuel, around 1000 canisters of HLW are destined to be returned to Japan over the next ten years. The latest shipment of 76 HLW canisters was only the second to have been made from Sellafield to Japan. The first, undertaken in January 2010, was itself mired in controversy when, on arrival in Japan, it was discovered that the HLW within the transport flask did not fully tally with the official paperwork – a number of canisters being ‘out of position’ within the holding channels of the transport flask.

Could these high surface contamination levels be the start of an affaire similar to the one that started in May 1998. Then, on May 6,1998, following the discovery of illegal levels of radioactive contamination on the external surfaces of a number of flasks and railway wagons, the French railway company SNCF banned any further movements of flasks from Germany and Swiss nuclear power stations to the reprocessing plant at La Hague. In the following days excessive levels of Caesium 137 and Cobalt 60 was measured on the surface of other casks and the Swiss,  German, Belgian and Dutch governments banned transports to Sellafield and La Hague too. The German environmental Minister (Angela Merkel by the way!) confirmed levels of radioactivity 3000 times greater than the levels allowed (4 Bq/cm2). The French regulatory authority discovered that a quarter of the flasks and 35% of the rail wagons that arrived at Valognes rail terminal in 1997 were contaminated beyond the safety limit. These numbers were known by the nuclear industry but not reported to the authorities. Official explanation is that the contamination was caused because the flasks 'sweat' in transit. While they are loaded at the reprocessing plant, the paint and metal on their outsides absorb radioactivity that is difficult to remove.

The transport ban was lifted in most countries late December the same year.

Sources: CORE Press release, 16 October 2011 / CORE Briefing, 21 May 1998 / New Scientist, 13 June 1998 / Volkskrant (Nl), 9 December 1998
Contact: Cumbrians Opposed to a Radioactive Environment (CORE). Dry Hall, Broughton Mills, Broughton-In-Furness, Cumbria LA20 6AZ, UK
Tel: +44 1229 716523
Email: info[at]corecumbria.co.uk
Web: www.corecumbria.co.uk

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