Nuclear Reactors Accidents Safety & Radiological impact

1. Nuclear Reactors AccidentsSafety & Radiological impact William D’haeseleer

2. NPP: Boiling Water Reactor

3. NPP: Pressurized Water Reactor

4. Nuclear Fission + Products Fission fragments mostly “unstable”

5. Fission products / fragments Relative difference factor 600 Around A ≈ 95 Around A ≈ 140 [Ref. Krane]

6. Fission products / fragments N=Z line

7. Heat generation due to radioactive decay after shutdown Ref Wikipedia “decay heat”

8. Heat generation due to radioactive decay after shutdown

9. Spent Fuel Assembly Ref: CLEFS CEA Nr 53

10. Composition of spent reactor fuel • Spent reactor fuel assembly consists of • Fission products FP • Left over U (U-238 and U-235) • Newly produced Pu • Transuranics (Minor Actinides MA) • Some transmuted elements

11. Composition of spent fuel • Typical for LWR:

12. Ref: CLEFS CEA Nr 53 Fission Products

13. Actinide Buildup U-235 and Pu evolution Ref: Chopin, Liljenzin & Rydnerg, “Radiochemistry and Nuclear Chemistry”, 3-rd Ed, Butterword-Heinemann, 2002

14. Ref: CLEFS CEA Nr 53 Actinide Buildup

15. Biological Effects of Radiation

16. Ionizing particles • Directly ionizing particles alpha (He-4++) & beta (e-/e+) • Indirectly ionizing particles Gamma or X rays/photons & neutrons

17. Ionizations Energetic ionizing particles move around in sea of electrons, ions & nuclei • Leads to ionizations i.e., creation of i/e pairs Excitations in atoms and nuclei

18. Ionizations Ref: Shapiro

19. Impact ionizing particles Due to natural radiation: number of e/i pairs in person 70 kg ~ 109 = 1 billion per second x 60 years(taking into account weight evolution 020y) ~ 1 à 2 1018 ionizations over one’s whole life = one billion times one billion ! Ref: J.P. Culot, “Ioniserende straling: fysische kenmerken”, in H. Vanmarcke et al., “Ioniserende straling: Effecten van lage dosissen”, NIROND-96-03, NIRAS-ONDRAF, Brussel, 1996, hoofdstuk 1 – pag 31 Kernenergie 2010-2011 William D’haeseleer 19

20. Impact ionizing particles Due to natural radiation: number of e/i pairs in person 70 kg ~ 109 = 1 billion per second x 60 years(taking into account weight evolution 020y) ~ 1 à 2 1018 ionizations over one’s whole life = one billion times one billion ! How come we don’t all die like flies??? Kernenergie 2010-2011 William D’haeseleer 20

21. Some orders of magnitude Natural Radioactivity in oceans: U-238 4-5 1019 Bq (x 14 because progeny) K-40 1.85 1022 Bq Natural Radioactivity in earth crust: Contiguous states US, 1 km deep; about 3-4 1023 Bq Natural Radioactivity body (70kg) About 8000 Bq (~ 55% from K-40, 40% from C-14) Rn-222 Radioactivity in buildings in Belgium About 50 Bq/m3 (Flanders ~20-30; Ardennes ~70-80) Natural radioactivity in this room… 21

22. Cosmogenic isotopes Tritium / pure Beta- decay T1/2 = 12.3 year Carbon 14 / pure Beta- decay T1/2 = 5715 year Phosphor 32 / pure Beta- decay T1/2 = 14.3 days

23. Primordial radionuclides Potassium 40 89% Beta- decay to Ca-40 with Emax=1.3 MeV 11% EC to Ar-40, with Gamma of 1.46 MeV Typically in human body ~ 50 Bq/kg T1/2 = 1.26 109 y 23

24. Primordial radionuclides Potassium 40 Decay products are Ca-40 or Ar-40 (both stable) Present for 2.1% (weight) earth crust and 0.044% sea water K-40 only 0.01117% of natural K (mostly K-39) K present for about 0.15 kg in human body Further info from [Wade Alison, “Radiation and Reason”, 2009, p 51] T1/2 = 1.26 109 y 24

25. Potassium-40 40K EC β- Ee,max 1,3 MeV γ 1.46 MeV 40Ar 40Ca 25

26. Dangers of Ionizing Radiation • Distinction External Irradiation versus Contamination • Concepts Dose & Units • Biological Effects of Ionizing Radiation • Natural, Medical & Industrial Exposure in Belgium • Permissible Doses

27. External Irradiation / Contamination Fundamental difference between External (ir)radiation and Contamination Radioactive source outside body Radioactive source inside body

28. External Irradiation / Contamination • External (ir)radiation

29. External Irradiation / Contamination • External (ir)radiation - depends on type of radiation αβγ n - shielding * natural: air / water / soil * engineered: concrete, Pb - distance - irradiation time

30. External Irradiation / Contamination • Contamination Especially for α & β sources ! When inside the body, no possible to shield α can cause considerable damage β relatively dangerous Contamination of the skin: “whipe” / “scrub” clean

31. External Irradiation / Contamination • Contamination Now also biological T1/2 time to remove half of radioisotope from body urine, stools, sweating, exhaling,…, vomiting,… Effective T1/2λeff= λph + λbio1/Teff = 1/Tph + 1/Tbio Smallest T1/2dominates Teff

32. Special Characteristics • Note the passive nature of radio-isotopes • Do not have “legs”  do not migrate actively • Can only migrate passively  must be transported away by carrier (e.g., dissolved,…) • Because of ionizations • Ionizing radiation (as a rule) well measurable(compared to e.g., chemical / toxic substances)

33. Units & Radiation Concepts • Recall Activity [=] Bq Source characteristic # disintegrations/sec

34. Units & Radiation Concepts • Recall Activity [=] Bq Source characteristic 1 Bq= 1 disintegration/sec 1 Ci = 37 GBq Does not say anything about the nature of the radiation Does not say anything about the energy of the radiation

35. Units & Radiation Concepts • Absorbed Dose [=] J/kg or Gy Receiver characteristic Energy/mass Joule/kg Old unit rad; 1 Gy = 100 rad

36. Units & Radiation Concepts • Dose Equivalent [=] Sv Receiver characteristic in man Energy/mass Weighted for distribution deposited energy & biological damage Old unit rem; 1 Sv = 100 rem

37. Units & Radiation Concepts • Dose Equivalent [=] Sv Receiver characteristic in man Biological damage ~ locally deposited energy LET: Linear Energy Transfer ~ stopping power ~ keV/μm

38. Biological effect of radioactive source • Depends on the emitted particle • Depends on the energy • Depends on external irradiation vs internal contamination (inhalation, ingestion) • For contamination: depends on distribution in body

39. Biological effect of radioactive source Typical examples in body (70kg man): • 40K 4433 Bq  0.18 mSv (whole body) • 14C 3217 Bq  0.011 mSv (whole body) • 226Ra 1.48 Bq  1.4 mSv (bone lining) • 210Po 18.5 Bq  0.12 mSv (gonads) 0.6 mSv (bone) • 90Sr 48.1 Bq (1973)  0.026 mSv (endosteal bone) 0.018 mSv (bone marrow) Ref: Jacob Shapiro, “Radiation Protection”, 4-th Ed., Harvard Univ Press, 2002

40. Biologic effects of radiation • Somatic effects (own-body related) a) Early effects due to acute high doses = “deterministic effects” b) Stochastic effects due to low doses ~ cancer development • Genetic effects (offspring-related) Stochastic in nature

41. Biologic effects of radiation • Somatic effects (own-body related) a) Early effects due to acute high doses = “deterministic effects” b)Stochastic effects due to low doses ~ cancer development • Genetic effects (offspring-related) Stochastic in nature

42. Deterministic effects • Due to acute & high dose radiation • Basically accidental situation • Appears after some hours to some weeks after acute exposure • Because depletion of cells in important organs (death cell / impairing cell division) • Organs such as • bone marrow • digestive track • brains

43. Deterministic effects • Major characteristics of deterministic effects: • There is a threshold of dose below which the effects will not be observed. • Above this threshold, the magnitude of the effect (= “severity”) increases with dose. • The effect is clearly associated with the radiation exposure. Ref: Stabin, 2008

44. Deterministic effects • Dose ~ 1 Gy “radiation sickness” (…vomiting…); ~ after few hours; Due to damage to cells small intestine • Dose < 1.5 Gy probably no early death • Dose >~ 2 Gy ‘could’ lead to death after ~ 2 weeks Not really a strict threshold for fatal outcome Also no real threshold for certain death; but acute doses >~ 8 Gy probably fatal

45. Deterministic effects • 30LD50 ~ 3 Gy for man [following Stabin 3.5 à 4.5] • deadly dose for 50% of exposed people within 30 day • Dose 3 - 10 Gy “infection death” Due to depletion white blood cells (possible medical ‘correction’ perhaps bone-marrow transplant) • Above 10 Gy most likely death after 3 à 5 days Due to depletion cells intestine  bacterial invasion; “death due to gastro-intestinal system” • Still higher doses >~ 20 Gy and more: “CNS death”

46. Deterministic effects 3-D plot: Dose, Severity, Time after exposure Below 1 Gy mostly no effects Ref: Stabin Fig 6.5

47. Biologic effects of radiation • Somatic effects (own-body related) a) Early effects due to acute high doses = “deterministic effects” b) Stochastic effects due to low doses ~ cancer development • Genetic effects (offspring-related) Stochastic in nature

48. Stochastic Somatic effects • After certain weighting period, radiation exposure can lead to cancer (solid cancers / leukemia) • ‘Cancer’ = uncontrolled proliferation of cells in the body; due to damage to the ‘control system’ of a cell (cell nucleus, DNA,…) • Based on observation of • Atom bomb survivors • Radiologists • Radiation therapy patients • Uranium mine workers etc • Based on radiobiological research

49. Stochastic Somatic effects • Actually extrapolation downward from ~ medium & high level doses (300 mSv …1… Sv) • Effects below ~ 100 à 200 mSv limited statistical significance • Difficulty to estimate risk: • Long & variable waiting period (5…30y or more) • Radiation-driven cancers indistinguishable from other cancers • Human tests/experiments not justified • Animal tests/experiments not directly transferable to humans

50. Stochastic Somatic effects LNT hypothesis Careful! Curves for individual Probability to get malignant/lethal cancer = f (dose equivalent)