Iodine-131 decays to form xenon-131. The half-life of this reaction is 8.07 days. From a 200-g sample of iodine-131 how much of the sample is xenon-131 after 16.14 days?

Updated: 12/14/2022

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How can the fission be controlled or stopped in a nuclear reactor?

The nuclear chain reaction is controlled using neutron absorbing control rods containing boron, and in PWR's by also using soluble boron when necessary. Nuclear engineers use a term called reactivity, which just means the surplus of neutrons from one generation to another, and in steady operation this is zero. During the fission reactions fission products are produced, some of these are neutron absorbers like Xenon131, and their concentration changes with power changes, so that adjustments with the control rods are necessary following such changes. On start-up with new fuel for example it takes some hours before equilibrium xenon is reached, and if power has to be reduced the xenon rises again as a delayed action, so enough control to overcome the increased poisoning has to retained, or the reactor will shut itself down. The reactivity with new fuel loaded is higher than at the end of the fuel life, and this is where boric acid added to the reactor water circuit is useful. The reactor power (neutron flux level) is constantly monitored with instruments so that the control room staff know what is happening and can respond. In addition automatic safety circuits are triggered if there is an increase in flux beyond a certain point which the operators don't react to, and this inserts the control rods fully (scram or trip) which shuts the reactor down and holds it down. So there is no chance of a runaway.

How can the fission be controlled or stopped in a nuclear reactor?

The nuclear chain reaction is controlled using neutron absorbing control rods containing boron, and in PWR's by also using soluble boron when necessary. Nuclear engineers use a term called reactivity, which just means the surplus of neutrons from one generation to another, and in steady operation this is zero. During the fission reactions fission products are produced, some of these are neutron absorbers like Xenon131, and their concentration changes with power changes, so that adjustments with the control rods are necessary following such changes. On start-up with new fuel for example it takes some hours before equilibrium xenon is reached, and if power has to be reduced the xenon rises again as a delayed action, so enough control to overcome the increased poisoning has to retained, or the reactor will shut itself down. The reactivity with new fuel loaded is higher than at the end of the fuel life, and this is where boric acid added to the reactor water circuit is useful. The reactor power (neutron flux level) is constantly monitored with instruments so that the control room staff know what is happening and can respond. In addition automatic safety circuits are triggered if there is an increase in flux beyond a certain point which the operators don't react to, and this inserts the control rods fully (scram or trip) which shuts the reactor down and holds it down. So there is no chance of a runaway.

Iodine-131 decays to form xenon-131. The half-life of this reaction is 8.07 days. From a 200-g sample of iodine-131 how much of the sample is xenon-131 after 16.14 days?

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How can the fission be controlled or stopped in a nuclear reactor?

How can the fission be controlled or stopped in a nuclear reactor?

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