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Status of Safety Analyses for the ESS Target

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). Artist‘s view of the ESS Facility. Main parameters. Proton beam.

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Status of Safety Analyses for the ESS Target

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  1. 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) Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  2. Artist‘s view of the ESS Facility Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  3. Main parameters Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  4. Proton beam 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 Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  5. 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 Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  6. 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) Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  7. 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) Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  8. 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 Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  9. 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: Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  10. 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 Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  11. Safety relevant nuclides in mercury target: Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  12. Comparison of activities in LWR and ESS Note: Long lived actinides are not found in spallation sources Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  13. 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 Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  14. 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 10 - 30 higher than the radiotoxicity of Hg-197 Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  15. 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. Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  16. Loss of confinement accidents • Probabilistic and system studies Relevant ESS dbaA = anticipated within ESS lifetimeU = unlikely Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  17. 2. Deterministic examinations • Hg/H-3 thermochemistry has to be examined • JSNS work indicated, that mercury iodides (lower volatility than I2) 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. Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  18. Results of SOLGASMIX-PV Equilibrium composition of an Hg/I and of an Hg/I/Fe system Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  19. 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 Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  20. Examinations on moderator explosions • CFD (CFX-Code): calculations on distribution of moderator within target cell/- building in accidents (burnable gas mixtures etc.): • Leak in H2-pipe with spontaneous evaporation • 1.5 kg of H2 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 Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

  21. 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 Status of safety analyses for the ESS targetRainer Moormann, PES-FZJ

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