1. ITER and Fusion Safety Aspects H.-W. Bartels, ITER Prague, 13.November 2006

2. Fusion and nuclear safety D Tn He-4 + 17.6 MeV ==> nuclear safety related issues: 1) radioactivity of tritium (~5 kg in reactor) 2) activation from 14 MeV neutrons (~1/2 of activity of PWR)

3. Tritium Half-life:12.3 a ß — radiator: = 5.7 keV  range organic matter: 6 µm  Horny layer skin:70 µm Incorporation:  Inhalation, skin absorption,  Ingestion Very Mobile: HTO, HT Biological half-life:~10 days  Hazard/Bq: tritium <1000*Cs137 Tritium in human body: i)fast component t 1/2 ~10 days ii)slow component t 1/2 ~ 30 – 300 d (organically bound tritium)

4. Activation Products Problematic isotopes: steel: 60 Co: t 1/2 ~ 5 years 1.2 MeV  -radiation tungsten: 185W: t 1/2 ~ 75 days 0.4 MeV  -radiation Favorable elements: - Vanadium (V) - Chromium (Cr) - Titanium(Ti) Neutron activation in some elements (5 MW/m2 in 2.5 years)

5. Schematic Fusion Reactor Build-up

6. Normal operational effluents ALARA principle –lower project release limits Tritium 1 g/a Activated dust10 g/a Corrosion products 50 g/a Dose limits: –vary by country: 0.1-5 mSv/a –average natural dose: 2 mSv/a Doses < 1% of natural dose Technical precedence used: –tritium plants –chemical plants (beryllium) –fission reactors (esp. CANDU’s) –tokamak (D_T: JET, TFTR) Analysis for last year ITER shielding blanket operation Initial releases small: –limited use of tritium –low level of activation –time delay permeation of tritium into coolant

7. Accidents: Design guideline atmospheric release Ultimate safety margin: Evacuation threshold for ground level releases: Tritium: < 100 g Tungsten dust:< 4 kg Event CategoryIncidentsAccidents HTO [g/event] 0.15 Dust [g/event] 150

8. Accidents: Energy Sources

9. Schematics of computer model for integrated accident analysis

10. Accidents: Pressurization and decay heat In-vessel decay heat driven temperature transient VV cooled by natural circulation Accident scenario: –multiple FW failure  –all FW cooling pipes in two toroidal rings damaged  –fast pressurization plasma chamber –pressure limited by suppression system –Maximum pressure ITER: 2 bar –no in-vessel cooling

11. Accidents: Hydrogen in ITER Combustion wave propagates ~2000 m/s Pressures from 15 to 20 bar H 2 formation in fusion: chemical reactions with hot plasma facing components, e.g.: Be + H 2 O  BeO + H 2 H 2 + air explosion

12. Accident: Loss of coolant w/o shutdown

13. In case of on-going plasma burn temperature increase in affected components. –failure of in-vessel components at elevated temperatures –ingress of steam into VV –Be/steam chemical reactions –hazard of hydrogen formation –bypass 1. confinement barrier ==> plasma burn will be terminated by fusion shutdown system Ex-vessel LOCA w/o plasma shutdown 20 40 kg-H2

14. Accident analysis margins Large margins maintained because: –limitation of radioactive inventories; –inherent plasma termination processes; –long time for component heat-up; –gross structural melting impossible; –multiple layers and lines of defense to implement radioactive confinement; –design tolerant to safety system failures Maximum doses < 2 mSv (annual natural dose) ITER accident analysis has confirmed safety potential of Fusion Energy.

15. Accident: Wet bypass Hypothetical event: –loss of coolant plus 2 failures in one heating or diagnostic line (“wet bypass”) –Analysis results: plasma chamber pressurizes opening bypass / suppression tank transport radioactivity into room capture tritium, dust in tank, settling of dust by gravity, condensation of HTO in room cleaning of room after 8 hours:  ~15 g tritium released

16. Accidents: Loss of cooling Fusion Reactor

17. Is it true ? V&V: verification & validation –verification correct coding comparison between different codes and performers –validation comparison codes / data

18. Verification thermo-hydraulic codes Two codes used in ITER: –MELCOR (US) –INTRA (EU) benchmark: large loss of cooling accident in ITER vacuum vessel –initially some differences, but both below design pressure 5 bar –differences could be explained by different treatment of mixed flow of steam and water ==> feedback to design: lower pressures for separation of phases, e.g. pressure suppression system on top of vacuum vessel

19. Validation experiments steam  vacuum

20. Validation thermo-hydraulic codes Two codes used for ITER: –MELCOR (US) –INTRA (EU) Comparison of code results with experimental data of water injection into vacuum vessel Problem is scaling: length 1/10 of ITER ==> larger surface/volume

21. 14 MeV n-Source Experiment

22. Fusion Neutron Source (FNS)

23. ITER Decay Heat R&D - 14 MeV n-irradiation at FNS at JAERI - Decay heat measurement: sum of ß,  radiation SS-316, 7 hours irradiation -International code validation effort: - Uncertainties < 15% Cu, 7 hours irradiation

24. JA dust mobilization experiments

25. Russian hydrogen detonation experiments

26. What if it is not true ?

27. ”No-evacuation” limit and cliff-edge effects Release assumptions: ground level, duration 1 h, worst case weather No-evacuation limit (early dose): IAEA, ITER: 50 mSv  ITER “no-evacuation” limit met for tritium release < 90 g, in HTO form  No cliff-edge effect for tritium (For a hypothetical tritium release of 1 kg no-evacuation limit exceeded for < 1 km2) Area [km 2 ]

28. Long term contamination Tritium concentration in soil after contamination

29. Waste volumes fusion reactor Fusion optimized materials: –V-alloys –steel without Ni, Co –impurities need careful attention (Nb, Ag, Co, U) Significant part (~30%) of activated material can be cleared Volume ~1-2 x larger than fission waste (not counting U- mining~1.5 Mm 3 ) large fractions could be recycled

30. No burden to future generations

31. Conclusion Normal operation –dose < 1% of natural background Accidents –source term ~ 1000 times smaller compared to fission –if properly designed: no destruction due to internal accidents –large reactions times –tritium and dust largest hazard >> allowable releases Waste –volumes comparable (~2 * larger) compared to fission –toxicity 1000 times smaller compared to fission –recycling might be feasible Safety and environmental features dependent on design

32. Other fusion reactions (1a) D + D  3He + n + 3.3 MeV (1b) D+D  T + p + 4.0 MeV (2a) D + 3He  4He + p+ 18.4 MeV (2b) D + T  4He + n+ 17.6 MeV (3) p + 11B  3 * 4He+ 8.7 MeV (4) p + 6Li  3He + 4He+ 3.9 MeV Equations (1a) – (2b) can be summarized as 3D  4He + p + n+ 21.6 MeV D in water ~3.3*e-5  energy content 1 liter water ~ 350 l gasoline

33. Advantages of fusion No radioactive raw material No chain reactions (small amount of fuel ~1 g in plasma) Moderate decay heat (large surfaces) Low biological toxicity and half-life time of activation products Generates no greenhouse gases (no SO 2, NO x )