Verlag des Forschungszentrums Jülich
JUEL-4136
Moormann, Rainer
Safety and Licensing of the European Spallation Source (ESS)
58 S., 2004
As part ofpreparation of the ESS Technical Design Report, substantial effort was spent in
2001-2003 in examination ofsafety features and licensing requirements ofESS. This work is
documented in the report in hand, being a stand-alone version ofthe safety chapter ofthe ESS
Project Volume III Update Report, which is available soon on the internet:
http://neutron.neutron-eu.net/n_documentation/n_reports/n_ess_reports_and_more/106
One main item in ESS safety work was shielding: General guidelinesfor ESS shielding design
were developed. Ongoing work deals with shielding to the bottom, which is mainly
determined by the activation of soil and ground water and migration of activity with the
ground waterfow.
The examinations on the nuclide vector in the ESS target were updated, which led to larger
long-lived activities and radiotoxicities, compared to former ESS-results: Radioactive
inventories and radiotoxicities ofESS with mercury targets are ofsimilar size as in a medium
sized research reactor. Safety relevant advantages of a mercury target are its inert chemical
character, avoiding oxidation problems in accidents and the easy decay heat removal as in
liquid targets. On the other hand, the pronounced radiotoxicity (compared with Ta and W
solid targets, where additionally the crystal lattice acts as barrier for activity release), the
remarkable chemotoxicity, and the high volatility have to be considered as safety drawbacks
of Hg-targets, which however can be overcome by adequate safety measures. Examinations
on ESS decommissioning and disposal revealed, that liquid mercury targets have to be
solidified prior to disposal.
A preliminary safety studyfor ESS was performed on basis of SNS-studies. In comparing dose
regulations and specific site conditions it was found, that tolerable radioactive releases in
design basis accidents are at least 2 orders of magnitude smaller than those, still acceptable
for SNS; one reasonfor this is, that ESS is to be build in an urban area and not like SNS deep
inside a large laboratory. System, reliability and source term studies for ESS came to the
conclusion, that there is sufficient potentialfor the required proof ofreduced source terms. It
seems even to be achievable tofulfil safety goalsfor ESS, which are more stringent than those
used in present nuclear technology. Hg-194 dominates the radiological consequences ofESS
accidents.
For several EU countries regulations for licensing/authorization/disposal of innovative
spallation sources like ESS either do not exist or are incomplete . In order to avoid delays
during the construction phase, the creation of a sufficient basis for ESS
licensing/authorization has to be prepared in detail by potential host countries prior to
making a final proposal for an ESS site. A listing of topics where further safety studies are
crucial can be found in thefinal chapter.
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