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NUCLEAR POWER
REACTORS (Reactor Wastes (Solid Wastes
produced from many…
NUCLEAR POWER
REACTORS
Thermal Reactors
Pressurized Water Reactors (PWR)
- cooled by hot high pressure water either D2O or H2O
- the coolant is also used as moderator
VVER (Water-Water Energetic Reactor)
- the fuel elements have a hexagonal cross section and the steam generators are horizontal rather than vertical
- contains more water in the vessel than a typical PWR
Pressurized Heavy Water Reactor (PHWR)
- Advantage: its low thermal neutron capture cross section improves the neutron economy
- the only commercial PHWR type is the CANDU
- the reactor vessel is a horizontal cylindrical tank filled with D2O, through which several hundred horizontal aluminium tube pass.
- each pressure tubes are bundles of zircaloy clad natural UO2 pins.
Boiling Water Reactors
- the coolant is brought to boiling while passing along fuel pins, no separate steam generators and secondary loops exist and the design has less complexity.
- have a negative void coefficient for both fuel and moderator
Advanced Thermal Reactor (ATR)
- Japanese D2O-moderated boiling H2O cooled MOX-fuelled Pu-burner prototype reactor which is now shut down
- has calandria with vertical pressure tubes, cooled with light water
Reactor Bolshoy Moshchnosty Kanalny (RBMK)
- a graphite moderated, boiling H2O cooled, pressure tube reactor of Russian design.
- the use of many pressure tubes (Zr-Nb alloy), each containing two fuel bundles in series
- Boron carbide containing control rods in special channels through the moderator are used to control neutron flux and power distribution
Breed Reactors
- the possibility to breed excess fissile nuclei by consumption of fissile & fertile nuclei increases with increasing fission factor, h.
- Breeding occurs through neutron capture in fertile Th-232 and U-238, with maximum probability between 600 and 700 eV, it is desirable for breeding that the neutron flux not be too low in this region
Thermal Breeder
- U-233 is produced from Th-232
- The reactor may be designed either with a core containing a mixture of 232Th and 233U, or with a central zone (core) of 233U surrounded by an outer layer (blanket) of 232Th.
- it is necessary to minimize parasitic neutron capture in structural materials including monitoring systems, control rods, etc.
Fast Breeder
- consists of a central core of plutonium in which fission occurs, surrounded by an outer blanket of 238U in which neutrons are captured to form new 239Pu. This blanket is surrounded by a reflector, usually of iron.
- The fission yield curve of 239Pu is similar to that of 235U but its heavy mass peak is shifted up by a few atomic mass units.
- The prompt neutron lifetime in a fast reactor is about 1000 times smaller than in a thermal reactor.
Reactor Wastes
Gaseous Wastes
- arise from the ventilation of radioactive or potentially radioactive areas and from process equipment
- The ventilation air generally represents much the greatest volume and the usual method of treatment is high-efficiency filtration (using HEPA filter) and discharge to atmosphere
- In BWR the active gases are transported with the steam to the turbines, where a considerable fraction of the decays occur
- Thus raising the background in this part of the power station to such a level that personnel cannot allowed permanently in the turbine hall during operation
Liquid Wastes
- substantial volumes of radioactive effluents arise from a variety of sources, which could include leakage from plant systems and processes, cooling pond water, and drainage from active areas
- Range of treatment options which may include the following, often in combination: decay storage (for short-lived radioactivity), filtration, and ion-exchange. The purpose of processing by these means is to reduce the level of radioactivity in the effluent to a level acceptable for release into the environment, usually into a river or coastal waters.
Solid Wastes
- produced from many systems and purification circuits of the reactor station
Low Level Waste (LLW)
- LLW has a high radioactivity content but contains limited amounts of long-lived radionuclides
- SOURCES : generated by uranium enrichment processes, reactor operations, isotope production, and medical and research activities
Intermediate Level Waste (ILW)
- ILW contain long-lived radionuclides that will not decay to a level of acceptable activity concentration
- SOURCES : It typically comprises resins, chemical sludges and metal fuel cladding, as well as contaminated materials from reactor decommissioning
High Level Waste (HLW)
- HLW contains the fission products and transuranic elements generated in the reactor core
- SOURCES : Spent fuel from reactors in civilian power generating plants, Obsolete nuclear weapons; the highly concentrated wastes from reprocessing fuel rods; and the solids generated in fuel reprocessing
Exempted Waste (EW)
- EW is a low radioactivity content, which no longer requires controlling by regulatory authority
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