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A Look at NuclearScience and Technology

Larry Foulke

Radiation and Realism

4.3 Damage to materials and protection from radiation

Background radiation

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Nuclear Engineering Program

REACTOR MATERIALS NEUTRON ENVIRONMENT

Quantification

Knief Problem 3-19: A pressure vessel is fabricated from a materialwhose properties become unacceptable after receiving a fast

fluence of 1021n/cm2. Calculate the expected lifetime in years forsuch a vessel subject to a fast flux (fluence) of 5x1011n/cm2-sec

nvt( )max

= tmax = 1021n / cm2 sotmax =

1021n / cm2

5x1011n / cm2 sec= 2x109 sec

or63.4

yrs

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Nuclear Engineering Program

REACTOR MATERIALS

POTENTIAL CONSEQUENCES

Hardening / Embrittlement

Swelling

Phase Transformations

Decreased Corrosion Resistance

Changes in Mechanical Properties

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Radiation Effects on Materials Lattice

Defects

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Nuclear Engineering Program

How do we optimize radiation exposure to get it as lowas reasonably achievable?

Three basic principles

Restrict proximityT I M E

Dose = Dose Rate Time

Increase the D ISTANCEfrom the source

Point source: 1-over-r-squared reduction

Use SH I E LD I NG material

(r) =S0

4r2

Dose Reduction

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Other subordinate approachesAllow to DECAYaway with time

Provide CONTA I NM ENT Isolate contaminated materials & surfaces

Containment enclosures

Isolate workers

Respirator

Protective clothing (Bunny suits, Anti-Cs)

Monitor (personal dosimetry, area monitors) Provide engineered controls

Procedures, physical controls

Dose Reduction

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Purpose of radiation shielding

Protect personnel and/or equipment behind theshield from radiation exposure

Absorb primary radiation incident on the shield

Reduce primary radiation energy (usually throughscattering) to produce secondary radiation that is lessdamaging / easier to absorb.

Absorb secondary radiation generated within the shieldmaterial.

Radiation Shielding

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Radiation Buildup

Absorption/scattering collisions

Secondary radiations

Secondary Radiation

Scattered gamma rays

Compton scattering

Capture gamma rays

Neutron capture (n, )

Can dominate over primary radiation

Shielding Effects

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Nuclear Engineering Program

Alpha / beta radiation

Short range, small thickness of any material will work.

Requires only simple shielding (Layer of skin / piece of foil).

Gamma / neutron radiation

Extremely penetrating, reaction rates are highly materialdependent (preferred shielding materials).

Shielding

Have to worry about both primary and secondary radiations

Usually requires composite shields containing severaldifferent materials.

Radiation Shielding

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Penetrating Properties of

Radiation

Image Source: See note 2

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Nuclear Engineering Program

Radiation Shield Types

Simple

Lead Nowhazardous (toxic)

Concrete General Purpose

Water Good for stopping neutrons

Composite (for mixed n, radiations)

Optimize gamma & neutron attenuation

Minimize thickness / weight

Specialized shields

Lead Glass for use in shielded hot cells that workers mustsee inside of.

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Nuclear Engineering Program

Composite Shield

Image Source: See Note 1

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Radiation Protection Clearly massive amounts of ionizing radiation

can cause biological damage.

However, cells have advanced repair

mechanisms for this damage and can easilycope with mild to moderate exposure.

How much is too much radiation?

Government sets radiation standards that providedose limits to prevent people from receiving harmfulradiation exposure.

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Nuclear Engineering Program

Intent

Protect health and safety

Workers

Public

Allow efficiency in operations

Basic standards

External radiation sources (excluding background). Derive limits for intake and internal deposition of

radionuclides in body.

Radiation Standards

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Nuclear Engineering Program

Natural background radiationVaries in world with altitude and soil composition.

US Average -- 300 mrem/y + Medical mrem/y[NCRP]

Cosmic 33 mrem/y 0.33 mSv/yr

Terrestrial 21 mrem/y 0.21 mSv/yr

Internal (Food/Water) 28 mrem/y 0.28 mSv/yr

Inhaled (Radon) 228 mrem/y 2.28 mSv/yr

Medical / Etc. 300 mrem/y 3.0 mSv/yr

Background Radiation

Ionizing radiation exposure of the population of the United States, National

Council on Radiation Protection and Measurements, 2009, NCRP 60

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Natural background radiationVaries in the U.S. with altitude and soil

composition.

Background Radiation

Image Source: See Note 3

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Natural background radiation

Varies in world

My personal Average -- 620 mrem/y.

Take a few minutes to fill out your background doseworksheet on

http://www.new.ans.org/pi/resources/dosechart/

What is your average and where is it coming from?

Background Radiation

http://www.new.ans.org/pi/resources/dosechart/http://www.new.ans.org/pi/resources/dosechart/

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Nuclear Engineering Program

Natural occurring background radiation is the mainsource of exposure for most people.

Background Radiation

Image Source: See Note 4

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1. Adapted with permission from the American NuclearSociety. Nuclear Engineering Theory andTechnology of Commercial Nuclear PowerbyRonald Allen Knief, 2nd Edition. Copyright 2008 by

the American Nuclear Society, La Grange Park,Illinois. Figure 3-3 (slide 5) and 3-6 (slide 13).

2. Creative CommonsAttribution 2.5 Generic: User:Stannered:

http://en.wikipedia.org/wiki/File:Alfa_beta_gamma_radiation_penetration.svg

3. U.S. Geological Survey Digital Data Series DDS-9,1993.

4. Reprinted with permission from World NuclearAssociation

Image Source Notes

http://creativecommons.org/licenses/by/2.5/deed.enhttp://en.wikipedia.org/wiki/File:Alfa_beta_gamma_radiation_penetration.svghttp://en.wikipedia.org/wiki/File:Alfa_beta_gamma_radiation_penetration.svghttp://en.wikipedia.org/wiki/File:Alfa_beta_gamma_radiation_penetration.svghttp://en.wikipedia.org/wiki/File:Alfa_beta_gamma_radiation_penetration.svghttp://creativecommons.org/licenses/by/2.5/deed.en