Radioactive Waste Management
Nuclear power is characterized by the very large amount of energy available from a very
small amount of fuel. The amount of waste is relatively small, but a lot of it is radioactive and
must be managed as hazardous waste.
1.
There are four kinds of radiation out of which three have to be considered: alpha, beta and
gamma. (The fourth, neutron radiation, generally only occurs inside a nuclear reactor.)
The different types of radiation require different forms of protection:
- Alpha radiation cannot penetrate the skin and can be blocked out by a sheet of paper,
but is dangerous in the lungs.
- Beta radiation can penetrate into the body but can be blocked out by a sheet of
aluminium foil.
- Gamma radiation can go right through the body and can be blocked by several
centimetres of lead or concrete or about a metre of water.
Radioactive wastes are normally classified as low-level, medium-level or high-level wastes,
according to the amount and type of radioactivity in them.
Another factor in managing wastes is the time that they remain hazardous. This depends on
the kinds of radioactive isotopes in them, and particularly the half life characteristic of those
isotopes. The half life is the time it takes for a radioactive isotope to lose half of its
radioactivity.
The rate of decay of an isotope is inversely proportional to its half life; a short half life means
that it decays rapidly.
2.
In the management of radioactive wastes three general principles are employed.
- to concentrate and contain
- to dilute and disperse, and
- to delay and decay
The first two are also used in the management of non-radioactive waste. The waste is either
concentrated and then isolated, or is diluted to acceptable level and then discharged to the
environment. Delay and decay, however, is unique to radioactive waste management; it means
that the waste is stored until its radioactivity considerably decreases naturally.
3.
Low-level waste comes from hospitals, laboratories and industry as well as the nuclear fuel
cycle. (Paper, rags, tools, clothing, filters, etc.) Usually it is buried in shallow landfill sites. It
is often compacted or incinerated to reduce its volume.
Intermediate-level waste typically comprises resins, chemical sludges and reactor
components. It may be solidified in concrete or bitumen for disposal. Short-lived waste is
usually buried, but long-lived waste is disposed of deep underground.
High-level waste is the spent fuel itself or the principal waste from reprocessing this, and it
holds 95% of the radioactivity. It contains the highly radioactive fission products and some
heavy elements with long-lived radioactivity. It generates high amount of heat and requires
cooling as well as special shielding during handling and transport.
4.
Radioactive wastes occur at all stages of the nuclear fuel cycle (mining and milling of
uranium ore, its processing and fabrication into nuclear fuel, its use in the reactor, the
treatment of the spent fuel and disposal of wastes).
At uranium mines, dust is controlled to minimize inhalation of radioactive minerals, while
radon gas concentration is kept to a minimum by ventilation and dispersion in large volumes
of air.
When uranium is used in the reactor, significant quantities of highly radioactive wastes are
created. The spent fuel can be regarded entirely as waste or it can be reprocessed. In both
cases the spent fuel is first stored for several years under water in large cooling ponds at the
reactor site. The concrete ponds and the water in them provide radiation protection and
remove the heat generated during radioactive decay.
5.
The ultimate disposal of wastes requires their isolation from the environment for long periods.
The most favoured method is burial in dry, stable geological formations about 500 metres
deep, for 1,000 years until most of the radioactivity decays.
1. The following subheadings are missing from the above text. Put them in their proper
place:
Types of radioactive waste
Types of radiation
Waste disposal
Wastes from the nuclear fuel cycle
Tasks to be accomplished
2. The names of several materials, chemical elements and compounds are mentioned in
the text. Find and list them:
1.………. 2. ………. 3. ………. 4. ………. 5. ………. 6. ……….. 7. ………. 8.………..
3. Form nouns from the following verbs:
concentrate
radiate
require
decrease
delay
disperse
contain
isolate
manage
penetrate
dilute
bury
decay
decrease
dispose
evaporate
inhale
process
ship
solve
store
treat
3. Fill in the following sentences with the proper forms of some of the verbs above:
Alpha radiation cannot …..1….. the skin.
Radioactive waste is stored and its radioactivity is allowed …..2….. .
Low-level waste …..3….. small amounts of mostly short-lived radioactivity.
Very radioactive materials …..4….. in special containers.
Radioactive isotopes …..5….. into non-radioactive ones.
At the mill radon gas …..6….. and …..7….. to the atmosphere.
High-level wastes need …..8….. from the environment for a long time.
Liquid high-level wastes …..9….. .
Final disposal of high-level waste …..10….. for about 40 years.
Key vocabulary
to compact
concentrate
concrete
to contain
decay
decrease
delay
to dilute
to disperse
to dispose of
to evaporate
fission
half life
to incinerate
to inhale
inversely proportional
to isolate
lead
ore
to penetrate
radiation
to require
resin
to ship
sludge
spent fuel
to treat
összenyom, tömörít
tömörül, tömörít, koncentrátum
beton
tartalmaz
radioaktív bomlás
csökken, csökkent
késleltet, késleltetés
hígít
szétszór, feloszlik, feloszlat
lerak, ártalmatlanít
párolog(tat)
(mag)hasadás
felezési idő
eléget, elhamvaszt
belélegez
fordítottan arányos
elkülönít, elkülönül
ólom
érc
áthatol, behatol
sugárzás
igényel
gyanta
szállít, szállítmányoz
iszap, üledék
elhasznált, fáradt üzemanyag
kezel