nuclear hazards
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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
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