nuclear reactors accidents safety & radiological impact
DESCRIPTION
Nuclear Reactors Accidents Safety & Radiological impact. William D’haeseleer. NPP : Boiling Water Reactor. NPP : Pressurized Water Reactor. Nuclear Fission + Products. Fission fragments mostly “unstable”. Fission products / fragments. Relative difference factor 600. Around A ≈ 95. - PowerPoint PPT PresentationTRANSCRIPT
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Nuclear Reactors AccidentsNuclear Reactors Accidents
Safety & Radiological impactSafety & Radiological impact
William D’haeseleer
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NPP: Boiling Water Reactor
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NPP: Pressurized Water Reactor
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Nuclear Fission + Products
Fission fragments mostly “unstable”
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Fission products / fragments
[Ref. Krane]
Around A ≈ 95
Around A ≈ 140
Relative difference factor 600
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Fission products / fragments
N=Z line
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Heat generation due to radioactive decay after shutdown
Ref Wikipedia “decay heat”
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Heat generation due to radioactive decay after shutdown
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Spent Fuel Assembly
Ref: CLEFS CEA Nr 53
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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
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Composition of spent fuel
• Typical for LWR:
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Fission ProductsRef: CLEFS CEA Nr 53
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Actinide Buildup
U-235 and Pu evolution
Ref:
Chopin, Liljenzin & Rydnerg, “Radiochemistry and Nuclear Chemistry”, 3-rd Ed, Butterword-Heinemann, 2002
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Actinide BuildupRef: CLEFS CEA Nr 53
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Biological Effects of Radiation
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Ionizing particles
• Directly ionizing particlesalpha (He-4++) & beta (e-/e+)
• Indirectly ionizing particlesGamma or X rays/photons & neutrons
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Ionizations
Energetic ionizing particles move around in sea of electrons, ions & nuclei
Leads to ionizationsi.e., creation of i/e pairs
Excitations in atoms and nuclei
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Ionizations
Ref: Shapiro
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19Kernenergie 2010-2011William D’haeseleer
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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 020y)
~ 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
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20Kernenergie 2010-2011William D’haeseleer
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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 020y)
~ 1 à 2 1018 ionizations over one’s whole life
= one billion times one billion !
How come we don’t all die like flies???
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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…Natural radioactivity in this room…
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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
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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
4019K T1/2 = 1.26 109 y
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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]
4019K T1/2 = 1.26 109 y
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Potassium-40
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β-
EC
γ
40K
40Ar 40Ca
1.46 MeV
Ee,max 1,3 MeV
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Dangers of Ionizing Radiation
1. Distinction External Irradiation versus Contamination
2. Concepts Dose & Units
3. Biological Effects of Ionizing Radiation
4. Natural, Medical & Industrial Exposure in Belgium
5. Permissible Doses
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External Irradiation / Contamination
Fundamental difference between
External (ir)radiation
and
Contamination
Radioactive source Radioactive source outsideoutside body body
Radioactive source Radioactive source insideinside body body
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External Irradiation / Contamination
• External (ir)radiation
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External Irradiation / Contamination
• External (ir)radiation
- depends on type of radiation α β γ n
- shielding* natural: air / water / soil
* engineered: concrete, Pb
- distance
- irradiation time
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External Irradiation / Contamination
• ContaminationEspecially for α & β sources !When inside the body, no possible to shield
α can cause considerable damageβ relatively dangerous
Contamination of the skin: “whipe” / “scrub” clean
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External Irradiation / Contamination
• ContaminationNow also biological T1/2
time to remove half of radioisotope from body urine, stools, sweating, exhaling,…, vomiting,…
Effective T1/2 λeff = λph + λbio 1/Teff = 1/Tph + 1/Tbio
Smallest T1/2 dominates Teff
eff
dNN
dt
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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)
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Units & Radiation Concepts
• Recall Activity [=] Bq
Source characteristic
# disintegrations/sec
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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
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Units & Radiation Concepts
• Absorbed Dose [=] J/kg or Gy
Receiver characteristic
Energy/mass
Joule/kg
Old unit rad; 1 Gy = 100 rad
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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
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Units & Radiation Concepts
• Dose Equivalent [=] Sv
Receiver characteristic in man
Biological damage ~ locally deposited energy
LET: Linear Energy Transfer
~ stopping power
~ keV/μm
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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
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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
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Biologic effects of radiation
1) Somatic effects (own-body related)a) Early effects due to acute high doses
= “deterministic effects”
b) Stochastic effects due to low doses
~ cancer development
2) Genetic effects (offspring-related)Stochastic in nature
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Biologic effects of radiation
1) Somatic effects (own-body related)a) Early effects due to acute high doses
= “deterministic effects”
b) Stochastic effects due to low doses
~ cancer development
2) Genetic effects (offspring-related)Stochastic in nature
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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
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Deterministic effects
• Major characteristics of deterministic effects:
1. There is a threshold of dose below which the effects will not be observed.
2. Above this threshold, the magnitude of the effect (= “severity”) increases with dose.
3. The effect is clearly associated with the radiation exposure.
Ref: Stabin, 2008
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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
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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”
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Deterministic effects
Ref: Stabin Fig 6.5
Below 1 Gy mostly no effects
3-D plot: Dose, Severity, Time after exposure
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Biologic effects of radiation
1) Somatic effects (own-body related)a) Early effects due to acute high doses
= “deterministic effects”
b) Stochastic effects due to low doses
~ cancer development
2) Genetic effects (offspring-related)Stochastic in nature
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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
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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
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Stochastic Somatic effects
Careful! Curves for individual
Probability to get malignant/lethal cancer = f (dose equivalent)
LNT hypothesis
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Stochastic Somatic effects
• Over-linear: rejected• Existence “adaptive response” & “hormesis”
recognized, but insufficient exact justification to form basis for norms & standards
• For low doses, also dose rate is important: correction factor
DDREF: Dose and Dose Rate Effectiveness Factor
• For norms & standards, for time being, linear extrapolation is used (perhaps too conservative)
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Stochastic Somatic effects
Slope of LNT line:
~ 5 % per Sv
~ 5 x 10-5 per mSv
or
105 people with 1 mSv 5 radiation induced cancers
Ref: Bodansky
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Stochastic Somatic effects
Ref: BEIR VII
2006
Illustration of downward extrapolation of malignant effects
Taken from Stabin
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Ref: Original BEIR VII 2006 document
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Stochastic Somatic effects
BEIR VII 2007
Number of cases or deaths per 100,000 exposed persons
5 - 7 x 10-5 per mSv fatal cancers (solid & leukemia) DDREF= 1.5
deaths
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Stochastic Somatic effects
• LNT disputed…by some authoritative scientists…• Considered to be an overestimate
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Biologic effects of radiation
1) Somatic effects (own-body related)a) Early effects due to acute high doses
= “deterministic effects”
b) Stochastic effects due to low doses
~ cancer development
2) Genetic effects (offspring-related)Stochastic in nature
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Stochastic Genetic effects• Causes of mutations:
– Heat – Chemicals– Spontaneous mutations– Radiation
• NOT possible to distinguish between the causes!
• Effects: probability genetic disease (also LNT) - first-generation progeny
~ 0.3-0.5% / Sv or 3-5 x 10-6 / mSv - all later generations ~ 1% / Sv
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Dangers of Ionizing Radiation
1. Distinction External Irradiation versus Contamination
2. Concepts Dose & Units
3. Biological Effects of Ionizing Radiation
4. Natural, Medical & Industrial Exposure in Belgium
5. Permissible Doses
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Background radiation• Due to natural, medical & industrial
exposure• In Belgium, total annual equivalent dose:
3.6 à 5 mSv3.6 à 5 mSv• Until ~ 2000, used value was 3.6 mSv/a
– Natural: 2.6 mSv/a• Body + Cosmic + Soil/Buildings = 1.0 mSv/a• Radon = 1.6 mSv/a (average for B)
– Man made: 1.0 mSv/a• Medical = 0.95 mSv/a• Industrial (all) = 0.05 mSv/a
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Background radiation• Due to natural, medical & industrial
exposure• In Belgium, total annual equivalent dose:
3.6 3.6 à 5 mSvà 5 mSv• Until ~ 2000, used value was 3.6 mSv/a
– Natural: 2.6 mSv/a• Body + Cosmic + Soil/Buildings = 1.0 mSv/a• Radon = 1.6 mSv/a (average for B)
– Man made: 1.0 mSv/a• Medical = 0.95 mSv/a• Industrial (all) = 0.05 mSv/a
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Background radiation
• In Belgium, total annual equivalent dose: 3.6 à3.6 à 5 mSv 5 mSv
• Currently, value is 5 mSv/a !!– Natural: 2.6 mSv/a
• Body + Cosmic + Soil/Buildings = 1.0 mSv/a• Radon = 1.6 mSv/a (average for B)
– Man made: 2.4 mSv/a• Medical = 2.352.35 mSv/a• Industrial (all) = 0.05 mSv/a
Overconsumption with CT scans etc…
only for diagnostics; no therapy
Ref. H. Vanmarcke (SCK)
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Background radiation
• In Belgium, total annual equivalent dose: 3.6 à 5 mSv3.6 à 5 mSv
• Radon = 1.6 mSv/a (average for B)– But for Vl ~ 0.5 – 1 mSv/a– And for Wall ~ 2 – 4 mSv/a– Difference of Vl & Wall ~ same order as
average natural background!– Average concentration in B: 50 Bq/m3
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Background radiation
Radon:
Daughter product of Ra-226
Actually Polonium problem!
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Background radiation
• In Belgium, total annual equivalent dose: 3.6 à 55 mSv mSv
• According to LNT estimate:• ~ 5 x 10-5 per mSv• 107 Belgians ~ 2500 fatal cancers per year• Due to natural & medical causes!
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Background radiation
• Typical examples:– Air travel at 11 km
• LA – Paris (11h x 2 roundtrip) ~ 2 x 0.05 mSv• NY – London (5h x 2 roundtrip) ~ 2 x 0.02 mSv
– High radiation regions• Near Ramsar Iran ~ up to 260 mSv/a
– Population too small to draw epidemiological conclusions– But no statistical significant aberrations in blood cells
• Regions in Brazil, India, China
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Background radiation
• In a lifetime (take 60 years):5 mSv/a x 60 = 300 mSv
• 300 mSv at 5%/Sv LNTH 0.015
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Dangers of Ionizing Radiation
1. Distinction External Irradiation versus Contamination
2. Concepts Dose & Units
3. Biological Effects of Ionizing Radiation
4. Natural, Medical & Industrial Exposure in Belgium
5. Permissible Doses
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Current safety standards
• General population:
Max extra artificial dose eq (excl med)
= 1 mSv/a1 mSv/a
• Employees in nuclear sector (Belgian law)
Max extra artificial dose eq (excl med)
= 20 mSv/a20 mSv/aIn normal / routine circumstances
EU directive specifies 100 mSv/5a
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Current safety standards
• Employees in nuclear sector Max intervention dose recommended
= 250 mSv/a250 mSv/a
Max dose for “life saving” intervention= 500 mSv/a500 mSv/a
In exceptional / accidental circumstances (in Belgium)
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Permissible Doses for Astronouts
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References
• Some basic examples (a.o.)