NUCLEAR HAZARDS

SOURCE, EFFECT AND CONTROL

DEFINITION

Risk or danger to human health or the

environment posed by radiation emanating from

the atomic nuclei of a given substance, or the

possibility of an uncontrolled explosion originating

from a fusion or fission reaction of atomic nuclei.

FUSION

A nuclear reaction in which atomic nuclei of low

atomic number fuse to form a heavier nucleus with

the release of energy.

FISSION

A nuclear reaction in which a heavy nucleus splits

spontaneously or on impact with another particle,

with the release of energy.

NUCLEAR HAZARDS

Nuclear power is being used world wide for the generations of electricity.

17% of electricity energy consumed comes from nuclear power.

NUCLEAR HAZARDS

Radioactive substance are present in nature .

They undergo natural radioactive decay in which unstable isotopes spontaneously

give out.

Fast moving particles, high energy radiation or both, at a fixed rate until a new

stable isotope is formed.

The isotopes released either in the form of

Gamma rays (High energy Electromagnetic radiation).

Alpha and Beta particles ( Ionization particles).

ALPHA PARTICLES : fast moving positively charged particles.

BETA PARTICLES : fast moving negatively charged electrons.

These ionization radiations have variable penetration power.

NUCLEAR HAZARDS

SOURCE OF NUCLEAR RADIATION

NATURAL SOURCES : Cosmic rays from outer space

Radioactive radon-222

Soil, rocks, air, water and food

ANTHROPOGENIC SOURCES : Nuclear power plants

Nuclear accidents

X-rays

Diagnostic kits

Test laboratories

Pathways Of Exposure To Man From Release of Radioactive Materials

Natural sources (81%) include radon (55%), external

(cosmic, terrestrial), and internal (K-40, C-14, etc.)

Man-made sources (19%) include medical (diagnostic

x-rays- 11%, nuclear medicine- 4%), consumer products, and

other (fallout, power plants, air travel, occupational, etc.)

SOURCE OF NUCLEAR RADIATION The main source of radiation is nuclear power plant and particularly from the core

and coolant of the reactor. The fission products produced during normal operation

of nuclear plant, remain with in the fuel elements and also in the nuclear wastes.

The real problems are about the storing and disposal of radio active wastes and

possibility of accidents.

Radiation is also emitted from radio active materials such as uranium and radon

gas that occurs naturally in the earth’s crust.

The radio-active contaminants decay by beta emission.

The contamination occurs due to leakage from the reactor. Contamination can also

place due to coolant leak and causes emission of radioactive gases.

Radiation hazards may also occur at the time of overhaul of reactor.

Research reactors also pose special health problems during conducting

experiments nuclear installations and tests contribute to 4% the total radiation.

No observable effect (< .25 Gy)- .25 Gy is nearly 70 times average annual radiation exposure!White blood cell count drops (.25 to 1 Gy) Mild radiation sickness (1 to 2 Gy absorbed dose)• Nausea and vomiting within 24 to 48 hours• Headache• Fatigue• WeaknessModerate radiation sickness (2 to 3.5 Gy)• Nausea and vomiting within 12 to 24 hours• Fever• Hair loss• Vomiting blood, bloody stool• Poor wound healing• Any of the mild radiation sickness symptoms• Can be fatal to sensitive individuals

PHYSIOLOGICAL EFFECTS

Severe radiation sickness (3.5 to 5.5 Gy)• Nausea and vomiting less than 1 hour after exposure• Diarrhea• High fever• Any symptoms of a lower dose exposure• About 50% fatality

Very severe radiation sickness (5.5 to 8 Gy)• Nausea and vomiting less than 30 minutes after exposure• Dizziness• Disorientation • Low blood pressure• Any symptoms of a lower dose exposure• > 50% fatality

Longer term or chronic radiation effects include genetic mutations, tumors/cancer, birth defects, cataracts, etc.

EFFECT OF RADIO ACTIVE POLLUTION

Nuclear warfare poses a continuous threat to the existence of man kind. Exposure to low levels of radiation by large public, increase the risk of cancer and

other disorders. Radioactive emissions can penetrate biological tissue and cause damage and

prevent cell division. radio-active emission is measured in “rem”. One Roentgen is defined as the quantity of radiation which produces 1.6 × 1012 pairs of ions in 1 gm of air.

Radioactive emission is used to destroy cancerous tumour. However, if the whole body is exposed to such levels of radiation over 100 rem, a generalized blockage of cell division occurs and prevents the normal replacement or repair of blood, skin and other tissues and leads to “radiation sickness” and finally may causes death. Very high doses of radiation may totally destroy cells, causing immediate death.

Lower doses may damage DNA, the genetic substance in side the cell. Cells with damaged DNA may begin dividing and growing out of central forming malignant tumours and leukaemia (disease in which too many white blood cells are produced causing finally death).

It also weakens immune system, causes mental retardation and development of cataracts. All the above health hazards and adverse effects are directly related to the level of exposure. Generally, the doses in the range of 10 – 15 rem result in the increased risk of cancer.

CONTROL OF RADIO-ACTIVE POLLUTION

The control of radioactive pollution from natural sources is difficult, but efforts can

be made to reduce the level of pollution from man made sources.

Protection against radiation exposure : The three factors that influence radiation

protection are :

DISTANCE FROM THE SOURCE

The exposure decrease with the square of distance from the source.

TIME OF EXPOSURE

The time of exposure should be kept as low as possible to complete a particular

task.

SHIELDING

A shield made up of dense attenuating material may be placed between source

and the surrounding.

CONTROL OF RADIO-ACTIVE POLLUTION

CONTROL OF RADIO-ACTIVE POLLUTION

The radioactive particles are particularly hazardous if inhaled causing

irradiation. this can be minimized by using laboratory hoods, air filters, and

exhaust systems, eliminating dry sweeping, wearing protective clothing and

radiation indicators which show the total amount of radiation to which a

person is exposed.

Use of respirators, prohibition of smoking and eating where radio active

materials are used.

The accessibility to areas which are susceptible for radiation exposure

should be controlled by placing appropriate sign boards like “ Restricted

area” or “Radiation zone”. Radiation resistant enclosures or barriers are to

be placed for screening workers from radioactive materials

NUCLEAR REACTOR DISASTERS

Chernobyl1986

Chernobyl Worst accident ever in the history of Nuclear power

Released more than 100 times the radiation produced by the atom bombs of Hiroshima and Nagasaki

Affected Western Soviet Union, Eastern, Central and Northern Europe, and Eastern and Northern America

336,000 people evacuated and resettled elsewhere

Where is the Chernobyl Plant?

Ukraine

18km northwest of Chernobyl town

110km north of Kiev

Power Plant 4 reactors of type – RBMK-1: now obsolete class of graphite

moderated nuclear reactor

Reactor capacity – 1Gigawatt (total plant capacity: 4 Gigawatt)

Provided 10% of Ukraine’s electricity at time of accident

2 additional reactors under construction at time of accident

Series of events in Reactor 4 resulting in:

Catastrophic “Steam Explosion”

Nuclear meltdown

Graphite fire

April 25th 1986 11pm: Control rods were lowered to reduce reactor output for planned turbine

test) BUT too quickly - almost complete shut down

1am: control rods raised to increase reactor activity for the test (12%)

1:23am: Reactor overheats; water coolant turns to steam

6 control rods left; minimum safe number = 30

Emergency shut down button pressed

Control rods re-inserted BUT fault causes power surge in reactor; Out put:100 times normal

Fuel pellets explode; roof blown off; air sucked in causing fire

Immediate Aftermath Area evacuated, but quite slowly - “exclusion zone”

Tragedy made worse by poor preparation, equipment and assessments

Radiation estimated at 20,000 Rontgen/hr (lethal dose = 100 R/hr)

True radiation unknown

Fire burned until helicopters extinguished it by dropping water, sand, lead and boron

Radioactive cloud observed

Ecological Effects Radioactive cloud floated in easterly direction

Radiation travelled as far as Sweden (1100km)

Initial Soviet Union reports: 60% contamination in Belarus

River Pripyat and Dnieper river-reservoir systemcontaminated (reduced after initial period)

Fresh water fish contaminatedto several times the safelimits (reduced afterinitial period)

Pine forest within 4kmradius turnedginger brownand died: Red Forest

“exclusion zone” became wildlife haven

Human Effects 336,000 people evacuated and resettled

237 suffered

from acute

radiation sickness

31 deaths within

3 months

9,000 cancer deaths expected as direct

result of radiation exposure

4,000 thyroid cancer

cases among children by 2002

IMPERFECTION REACTOR DESIGN

High void coefficient: weaken convection currents

Graphite tipped control rods: increase activity for short period

Vertical water channels in core: temperature gradient in core

Partial containment measurements to save costs

Operational for 1 year – stored fission by products

Reactor vessel warped under intense heat, preventing insertion of control rods