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Assessment of shutdown dose rates at ESS target cooling system using SCALE6.2

This presentation discusses the assessment of shutdown dose rates at the European Spallation Source (ESS) target cooling system using the SCALE6.2 software. The study includes modeling hypotheses, methodology, and sensitivity analysis, as well as benchmarking SCALE6.2 against MCNP6. The results provide valuable insights for maintenance and safety considerations.

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Assessment of shutdown dose rates at ESS target cooling system using SCALE6.2

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  1. International Collaboration on Advanced Neutron Sources - ICANS XXIII 13th-18th October, Chattanooga, TN Assessment of shutdown dose rates at ESS target cooling system using SCALE6.2 Amalia Chambon1 Esben Klinkby1 L.Emås2 Bent Lauritzen1 1) Center for Nuclear Technologies, Technical University of Denmark 2) European Spallation Source Operation and Safety

  2. Context and scope Context Design of the ESS targetcooling system • During operation, the tungsten target is eroded. • The released products are filtered in the target • He cooling system. • Scope • Determineshutdowndose rates • Validate non-standard software for ESS Total W mass: 3,1 t Erodedamountduring 5400 h at 5 MW beam power: 0.01 kg Ref : J. Haines, ESS target facility design, 2015 Add Presentation Title in Footer via ”Insert”; ”Header & Footer” 2

  3. Outline of filter system Main Filter Particles > 5 μm Mass flow: 3kg/s Pressure: 1 MPa Inlet temperature: 230 ˚C Outlet temperature: 40 ˚C HEPA filter Getters Ref :ESS-0042995 technicaldocument, rev 2, 2018 Mesh filter Large particles Regularly, getters has to be changed after a minimum cooling time of 24 h 3

  4. Overview of the presentation • SCALE6.2 shutdowndose rate calculations for maintenance of getters • Calculationscheme • Modellinghypotheses • Results and Sensitivitystudy • Benchmarking SCALE6.2 • Methodology and Modellinghypothesesusing MCNP6 • Conclusion - Perspectives 4

  5. 1- SCALE6.2 Shutdown dose rate calculations (1/7) Software SCALE6.2.3(Standardized Computer Analyses for Licensing Evaluation - ORNL) => Modellingand simulation suite for nuclearsafetyanalysis and design (ENDF/B-VII) => Criticality, reactorphysics, radiation shielding, source term characterisation, sensitivity-uncertainty • Methodology • SCALE cancomputedose rate mapsbased on the MAVRIC sequence. MAVRIC Monte-Carlo Dose calculation ORIGEN2 Decay calculation Gamma Source term Ref : SCALE code System, ORNL/TM-2005/39, 2018 D. Peplow, “Monte-Carlo Shielding Analysis Capabilities with MAVRIC”, Nucl. Technol., 174 (2), 289-313, 2011 Add Presentation Title in Footer via ”Insert”; ”Header & Footer” 5 5 PADR

  6. 1- SCALE6.2 Shutdown dose rate calculations (2/7) Activity in He loop, Bq, t=0 ORIGEN2 DecayCalculation for Gamma Source term Criteria: most active gamma emitters 99,8% of the total activity at t=0 is represented Hypotheses: noble gases and 100% of particles < 5 μm caught by getters ORIGEN2 energymesh(for 100% of the source binned) 6

  7. 1- SCALE6.2 Shutdown dose rate calculations (3/7) MAVRIC Calculation and modellinghypotheses XY view Air XZ view Ref : Ambient InlinePurifier, 902 Purifiction Media Specification, SAES Pure Gas Add Presentation Title in Footer via ”Insert”; ”Header & Footer” 7 PADR

  8. 1- SCALE6.2 Shutdown dose rate calculations (4/7) MAVRIC sequence for dose rate mapcalculation MONACO with Automated VarianceReductionusingImportanceCalculation DENOVO Sn adjointfluxcalculation Source : use of data stored in ORIGEN .f71 binary file photon energy mesh using 19 groups – standard mesh MAVRIC Variancereduction parameters Parameter block: perBatch=100000 batches=10000 • collect mesh tally information outside the getter (in air region) MONACO shieldingcode 3D fixed source, MG Monte-Carlo calculation Add Presentation Title in Footer via ”Insert”; ”Header & Footer” 8 PADR

  9. 1- SCALE6.2 Shutdown dose rate calculations (5/7) Results:Conservative case-withoutpurification, 1 day of cooling time Photondose rate (rem/h) wwp cards wwinp file 1,00E+09 particlessimulated Calculation time 8,4 h (1 proc on laptop) 1 mm from the getter=> red area => 4,42 mSv/h ± 0,01 mSv/h 10 cm from the getter => orange area => 1,50 mSv/h ± 3 μSv/h 9

  10. 1- SCALE6.2 Shutdown dose rate calculations (6/7) Results: 1 year of normal operation, with purification, 1 day of cooling time Photondose rate (rem/h) • 99,97% of particles < 5 μm removed from the gas 1 mm from the getter=> red area => 2,85 mSv/h ± 0,01 mSv/h 10 cm from the getter => orange area => 0,95 mSv/h ± 2 μSv/h 10

  11. 1- SCALE6.2 Shutdown dose rate calculations (7/7) Sensitivity study results After 1 day of cooling time After 6 months of cooling time 11

  12. 2- Benchmarking SCALE6.2 results (1/2) • Benchmark SCALE6.2 against MCNP6.2 • SCALE6.2 offers the capability to select the isotopes of interest • First step: selection of the main isotope of interest 125I is the maincontributor to the total source term activity Ref: J.T Gorley et al., ”Initial MCNP6 Release Overview – MCNP version 6.1”, LA-UR-13-22934, 2013 12

  13. 2- Benchmarking SCALE6.2 results (2/2) For most consitent problem, 125I spectra is discrete in bothcalculations. Main gamma energy = 27 keV 125I spectradescriptionusable in SCALE6.2 XY view 7 cm First results indicates that the order of magnitude of the dose rates is in agreement between the two models. 13

  14. 3- Conclusion and Perspectives • Conclusion • SCALE6.2 welladapted to treatthis kind of dose rate problem • Allows to choose the isotopes of interest for decay calculation This value seems to be acceptable so there is no need of shieldings and robot arms - The regulatory dose limit for a nuclear worker is 20 mSv/year Perspectives • MCNP is the baseline tool for neutronics assessment at ESS, preliminary benchmark results seems to show an agreement considering a pure 125I source. This study may be refined. • The impact of the following uncertainties could also be interesting to evaluate: • tungsten target particles released is an uncertainty. • CINDER90 calculations giving the radioactive inventory also subject to uncertainty. 14

  15. Thank you for your attention ! 15

  16. Target Helium cooling system Fractionscaptured: He filters particulates > 5 μm ≈ 100% (He filtered at least 5 times each min) HEPA filters < 5 μm = 99,97% H, C, O, N, I, S in chemicalgetters= 99,71% (assumption for conservativecalculation) Isotopes catched by HEPA filter

  17. SCALE6.2 Shutdown dose rate calculations Source description in MAVRIC • Takingintoaccount the decayhistory for the source distribution in MAVRIC: have the good • normalizationconstant • New way of describing the decaycalculation with ORIGEN2: • Decay has to bedescribed in different cases to obtain the good source distribution • One case = one time step • Number of case then given to the MAVRIC calculation + corresponding source strength Ref : D. Peplow, T. Miller, C. Celik , ”ShieldingCapabilities in SCALE6.2 (Monaco/Mavric)”, 2017

  18. SCALE6.2 Shutdown dose rate calculations Conservative case,1 day of cooling time Photondose rate absoluteuncertainty (rem/h) Order of magnitude max: 10 μSv/h in the corresponding green area

  19. SCALE6.2 Shutdown dose rate calculations Normal operation case, 1 day of cooling time Photondose rate absoluteuncertainty (rem/h) Order of magnitude max: 10 μSv/h in the corresponding green area

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