Production Nuclear fission product

1 production

1.1 power reactors

1.1.1 nuclear reactor poisons


1.2 nuclear weapons
1.3 application

production

small amounts of fission products naturally formed result of either spontaneous fission of natural uranium, occurs @ low rate, or result of neutrons radioactive decay or reactions cosmic ray particles. microscopic tracks left these fission products in natural minerals (mainly apatite , zircon) used in fission track dating provide cooling (crystallization) ages of natural rocks. technique has effective dating range of 0.1 ma >1.0 ga depending on mineral used , concentration of uranium in mineral.

about 1.5 billion years ago in uranium ore body in africa, natural nuclear fission reactor operated few hundred thousand years , produced approximately 5 tonnes of fission products. these fission products important in providing proof natural reactor had occurred. fission products produced in nuclear weapon explosions, amount depending on type of weapon. largest source of fission products nuclear reactors. in current nuclear power reactors, 3% of uranium in fuel converted fission products by-product of energy generation. of these fission products remain in fuel unless there fuel element failure or nuclear accident, or fuel reprocessed.

power reactors

in nuclear power reactor, main sources of radioactivity fission products, actinides , activation products. fission products largest source of radioactivity first several hundred years, while actinides dominant 10 10 years after fuel use.

fission occurs in nuclear fuel, , fission products retained within fuel close produced. these fission products important operation of reactor because fission products contribute delayed neutrons useful reactor control while others neutron poisons tend inhibit nuclear reaction. buildup of fission product poisons key factor in determining maximum duration given fuel element can kept within reactor. decay of short-lived fission products provide source of heat within fuel continues after reactor has been shut down , fission reactions stopped. decay heat sets requirements cooling of reactor after shutdown.

if fuel cladding around fuel develops holes, fission products can leak primary coolant. depending on fission product chemistry, may settle within reactor core or travel through coolant system. coolant systems include chemistry control systems tend remove such fission products. in well-designed power reactor running under normal conditions, radioactivity of coolant low.

it known isotope responsible majority of gamma exposure in fuel reprocessing plants (and chernobyl site in 2005) cs-137. iodine-129 1 of major radioactive elements released reprocessing plants. in nuclear reactors both cs-137 , strontium-90 found in locations remote fuel. because these isotopes formed beta decay of noble gases (xenon-137 {halflife of 3.8 minutes} , krypton-90 {halflife 32 seconds}) enable these isotopes deposited in locations remote fuel (e.g. on control rods).

nuclear reactor poisons

some fission products decay release of neutron. since there may short delay in time between original fission event (which releases own prompt neutrons immediately) , release of these neutrons, latter termed delayed neutrons . these delayed neutrons important nuclear reactor control.

some of fission products, such xenon-135 , samarium-149, have high neutron absorption cross section. since nuclear reactor depends on balance in neutron production , absorption rates, fission products remove neutrons reaction tend shut reactor down or poison reactor. nuclear fuels , reactors designed address phenomenon through such features burnable poisons , control rods. build-up of xenon-135 during shutdown or low-power operation may poison reactor enough impede restart or interfere normal control of reaction during restart or restoration of full power, possibly causing or contributing accident scenario.

nuclear weapons

nuclear weapons use fission either partial or main energy source. depending on weapon design , exploded, relative importance of fission product radioactivity vary compared activation product radioactivity in total fallout radioactivity.

the immediate fission products nuclear weapon fission same other fission source, depending on particular nuclide fissioning. however, short time scale reaction makes difference in particular mix of isotopes produced atomic bomb.

for example, cs/cs ratio provides easy method of distinguishing between fallout bomb , fission products power reactor. no cs-134 formed nuclear fission (because xenon-134 stable). cs formed neutron activation of stable cs formed decay of isotopes in isobar (a = 133). in momentary criticality time neutron flux becomes 0 little time have passed cs present. while in power reactor plenty of time exists decay of isotopes in isobar form cs, cs formed can activated form cs if time between start , end of criticality long.

according jiri hala s textbook, radioactivity in fission product mixture in atom bomb caused short-lived isotopes such i-131 , ba-140. after 4 months ce-141, zr-95/nb-95, , sr-89 represent largest share of radioactive material. after 2 3 years, ce-144/pr-144, ru-106/rh-106, , promethium-147 bulk of radioactivity. after few years, radiation dominated strontium-90 , caesium-137, whereas in period between 10,000 , million years technetium-99 dominates.

application

some fission products (such cs-137) used in medical , industrial radioactive sources. tco4 ion can react steel surfaces form corrosion resistant layer. in way these metaloxo anions act anodic corrosion inhibitors - renders steel surface passive. formation of tco2 on steel surfaces 1 effect retard release of tc nuclear waste drums , nuclear equipment has become lost prior decontamination (e.g. nuclear submarine reactors have been lost @ sea).

in similar way release of radio-iodine in serious power reactor accident retarded adsorption on metal surfaces within nuclear plant. of other work on iodine chemistry occur during bad accident has been done.