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1 Nuclear Reactors Nuclear Reactors Accidents Accidents Safety & Radiological Safety & Radiological impact impact William D’haeseleer

Nuclear Reactors Accidents Safety & Radiological impact

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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 Presentation

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Page 1: Nuclear Reactors  Accidents Safety & Radiological impact

1

Nuclear Reactors AccidentsNuclear Reactors Accidents

Safety & Radiological impactSafety & Radiological impact

William D’haeseleer

Page 2: Nuclear Reactors  Accidents Safety & Radiological impact

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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

Page 17: Nuclear Reactors  Accidents Safety & Radiological impact

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

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 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…

Page 22: Nuclear Reactors  Accidents Safety & Radiological impact

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

25

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.)