Page 1 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Status of Safety Analyses for the ESS Target R.Moormann, R.Bongartz, W.Kühnlein, J.Marx, H.Schaal, K.Verfondern (FZJ) P.Berkvens (ESRF), P.Wright (RAL)

Page 2 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Artist‘s view of the ESS Facility

Page 3 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Main parameters

Page 4 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Scheme of ESS target and of mercury circuit (15 t Hg, max. operation temperature: 250°C, max. temperature increase by decay heat: 35 °C) yellow =target block, red = mercury Proton beam

Page 5 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ -The target is the only component in Spallation Sources, which requires detailed accident analyses: accidents, harming the public, are imaginable only for the target due to its substantial radiotoxic and chemical toxic inventory. Other components (accelerators etc.) need safety considerations for normal operation/- abnormal events only. The preliminary safety analysis report (PSAR including updates) for the SNS target is under review with respect to its applicability for ESS

Page 6 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Short description of PSAR Procedure of PSAR (preliminary safety analysis report) : -screening of possible events -rough estimation of consequences and frequencies (limited credit on safety measures = ‘unmitigated’ estimations) -identification of relevant accidents by ‘risk binning’; (risk = dose * frequency) -cut off criteria: low frequencies (< 1.e-6/a) and low consequences (< 1 mSv)

Page 7 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ -more detailed estimation of source term and consequences for relevant accidents (‘unmitigated’ estimations) -in case of transgression of dose limits: repetition of source term/consequence/- frequency estimations assuming additional ‘mitigating’ safety measures -stepwise increase of accuracy, until dose limits are met (advantage: reduction of effort, identification of really important safety measures)

Page 8 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Relevant accidents identified: Fire within the target building Hydrogen/moderator explosion with and without subsequent fire Loss of confinement (Leak in the target circuit) –[Loss of mercury flow] –[Loss of heat sink] [Target hull heat-up by misadjusted proton beam] Earthquake followed by explosion with and without following fire Crane drop accident

Page 9 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Safety work at ESS Main results of PSAR/SNS review are: - PSAR/SNS is a valuable basis for ESS safety work - Additional accident to be considered in case of a Be-reflector: Be-reflector fire - European conditions require a more detailed safety analysis than performed within PSAR/SNS for the following reasons:

Page 10 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ larger ESS radioactive inventory smaller distance ESS – receptor conservative consequence model for ESS required, not a realistic one as for SNS consideration of ingestion pathway for ESS accidents required (contrast to SNS) lower dba dose limits in EU: effective dose/dba: 50 mSv in D 250 mSv for SNS

Page 11 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Safety relevant nuclides in mercury target:

Page 12 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Note: Long lived actinides are not found in spallation sources Comparison of activities in LWR and ESS

Page 13 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Conclusion on comparison of inventories: Determination of spallation yield for long-lived nuclides (Hg-194, Gd-148) is of particular relevance: ESS will perform evaluation of Hg irradiation experiments of ORNL, performed at SINQ Even for individual short lived nuclides the spallation yield is fairly uncertain (which is compensated by the large number of nuclides). Accordingly, short term Hg irradiation experiments are advisable

Page 14 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Comparison of radiotoxicity and chemical toxicity of mercury Comparison is problematic, because only incorporation effects are comparable Comparison for toxicity by inhalation between the total inactive Hg-inventory and the inventory of one individual nuclide (Hg-197) reveals, that the chemical toxicity is about a factor of higher than the radiotoxicity of Hg-197

Page 15 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Nevertheless, due to strong ground shine (Hg-194) and due to the large number of other radiotoxic nuclides, we expect, that radiotoxicity dominates the overall toxicity. Chemical toxicity may however not be neglected.

Page 16 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Loss of confinement accidents 1.Probabilistic and system studies Relevant ESS dba A = anticipated within ESS lifetime U = unlikely

Page 17 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ 2. Deterministic examinations Hg/H-3 thermochemistry has to be examined JSNS work indicated, that mercury iodides (lower volatility than I 2 ) may be formed: - PSAR/SNS assumes a pronounced iodine release in loss of confinement accidents, because the chemical status of iodine is considered as elemental (high volatile). Resulting emissions are too high for ESS conditions. - Thermochemical calculations (using ORNL-code SOLGASMIX-PV) at ESS quantified the chemical composition. Validation will be performed.

Page 18 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Equilibrium composition of an Hg/I and of an Hg/I/Fe system Results of SOLGASMIX-PV

Page 19 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ Additional target and moderator safety work Other accident classes in examination for ESS (probabilistic, system, source term and dose studies) are: External events (earthquake, fire, airplane crash..) Internal explosions

Page 20 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ CFD (CFX-Code): calculations on distribution of moderator within target cell/- building in accidents (burnable gas mixtures etc.): Leak in H 2 -pipe with spontaneous evaporation 1.5 kg of H 2 released in 30 s Air ingress with 0.15 kg/s at 288 K CFD-calculations on particle (Hg-droplets) transport in case of accidents Examinations on moderator explosions

Page 21 SAFERIB I - CERN/Geneva Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ General ESS safety work Decommissioning, final waste disposal Activity transport with ground water flow Consequence estimations for accidents using COSYMA model (planned) Selected design work for safety systems Shielding philosophy and design