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Conceptual questions

Explain why the fission of heavy nuclei releases energy. Similarly, why is it that energy input is required to fission light nuclei?

Explain, in terms of conservation of momentum and energy, why collisions of neutrons with protons will thermalize neutrons better than collisions with oxygen.

The ruins of the Chernobyl reactor are enclosed in a huge concrete structure built around it after the accident. Some rain penetrates the building in winter, and radioactivity from the building increases. What does this imply is happening inside?

Since the uranium or plutonium nucleus fissions into several fission fragments whose mass distribution covers a wide range of pieces, would you expect more residual radioactivity from fission than fusion? Explain.

The core of a nuclear reactor generates a large amount of thermal energy from the decay of fission products, even when the power-producing fission chain reaction is turned off. Would this residual heat be greatest after the reactor has run for a long time or short time? What if the reactor has been shut down for months?

How can a nuclear reactor contain many critical masses and not go supercritical? What methods are used to control the fission in the reactor?

Why can heavy nuclei with odd numbers of neutrons be induced to fission with thermal neutrons, whereas those with even numbers of neutrons require more energy input to induce fission?

Why is a conventional fission nuclear reactor not able to explode as a bomb?

Problem exercises

(a) Calculate the energy released in the neutron-induced fission (similar to the spontaneous fission in [link] )

n + 238 U 96 Sr + 140 Xe + 3 n,

given m ( 96 Sr ) = 95.921750 u and m ( 140 Xe ) = 139.92164 . (b) This result is about 6 MeV greater than the result for spontaneous fission. Why? (c) Confirm that the total number of nucleons and total charge are conserved in this reaction.

(a) 177.1 MeV

(b) Because the gain of an external neutron yields about 6 MeV, which is the average BE/ A for heavy nuclei.

(c) A = 1 + 238 = 96 + 140 + 1 + 1 + 1, Z = 92 = 38 + 53 , efn = 0 = 0 size 12{A=1+"238"="96"+"140"+1+1+1,`Z="92"="38"+"53",`"efn"=0=0} {}

(a) Calculate the energy released in the neutron-induced fission reaction

n + 235 U 92 Kr + 142 Ba + 2 n,

given m ( 92 Kr ) = 91 . 926269 u and m ( 142 Ba ) = 141 . 916361 u .

(b) Confirm that the total number of nucleons and total charge are conserved in this reaction.

(a) Calculate the energy released in the neutron-induced fission reaction

n + 239 Pu 96 Sr + 140 Ba + 4 n ,

given m ( 96 Sr ) = 95 . 921750 u and m ( 140 Ba ) = 139 . 910581 u size 12{m \( "" lSup { size 8{"140"} } "Ba" \) ="139" "." "910581"`u} {} .

(b) Confirm that the total number of nucleons and total charge are conserved in this reaction.

(a) 180.6 MeV

(b) A = 1 + 239 = 96 + 140 + 1 + 1 + 1 + 1, Z = 94 = 38 + 56 , efn = 0 = 0 size 12{A=1+"239"="96"+"140"+1+1+1+1,`Z="94"="38"+"56",`"efn"=0=0} {}

Confirm that each of the reactions listed for plutonium breeding just following [link] conserves the total number of nucleons, the total charge, and electron family number.

Breeding plutonium produces energy even before any plutonium is fissioned. (The primary purpose of the four nuclear reactors at Chernobyl was breeding plutonium for weapons. Electrical power was a by-product used by the civilian population.) Calculate the energy produced in each of the reactions listed for plutonium breeding just following [link] . The pertinent masses are m ( 239 U ) = 239.054289 u , m ( 239 Np ) = 239.052932 u , and m ( 239 Pu ) = 239.052157 u .

238 U + n 239 U + γ 4.81 MeV

239 U 239 Np + β + v e 0.753 MeV

239 Np 239 Pu + β + v e size 12{"" lSup { size 8{"239"} } "Np" rightarrow "" lSup { size 8{"239"} } "Pu"+β rSup { size 8{ - {}} } +v rSub { size 8{e} } } {} 0.211 MeV

The naturally occurring radioactive isotope 232 Th size 12{"" lSup { size 8{"232"} } "Th"} {} does not make good fission fuel, because it has an even number of neutrons; however, it can be bred into a suitable fuel (much as 238 U size 12{"" lSup { size 8{"238"} } U} {} is bred into 239 P size 12{"" lSup { size 8{"239"} } P} {} ).

(a) What are Z size 12{Z} {} and N size 12{N} {} for 232 Th size 12{"" lSup { size 8{"232"} } "Th"} {} ?

(b) Write the reaction equation for neutron captured by 232 Th and identify the nuclide A X produced in n + 232 Th A X + γ .

(c) The product nucleus β size 12{β rSup { size 8{ - {}} } } {} decays, as does its daughter. Write the decay equations for each, and identify the final nucleus.

(d) Confirm that the final nucleus has an odd number of neutrons, making it a better fission fuel.

(e) Look up the half-life of the final nucleus to see if it lives long enough to be a useful fuel.

The electrical power output of a large nuclear reactor facility is 900 MW. It has a 35.0% efficiency in converting nuclear power to electrical.

(a) What is the thermal nuclear power output in megawatts?

(b) How many 235 U size 12{"" lSup { size 8{"235"} } U} {} nuclei fission each second, assuming the average fission produces 200 MeV?

(c) What mass of 235 U size 12{"" lSup { size 8{"235"} } U} {} is fissioned in one year of full-power operation?

(a) 2 . 57 × 10 3 MW size 12{2 "." "57" times "10" rSup { size 8{3} } `"MW"} {}

(b) 8.03 × 10 19 fission/s size 12{8 "." "04" times "10" rSup { size 8{"19"} } `"fission/s"} {}

(c) 991 kg

A large power reactor that has been in operation for some months is turned off, but residual activity in the core still produces 150 MW of power. If the average energy per decay of the fission products is 1.00 MeV, what is the core activity in curies?

Questions & Answers

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Victor Reply
The process plants use to convert sunlight into food (energy).
juanita
Some other organisms use
juanita
types of photosynthesis
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ps1 and ps2
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what is used to determine phylogeny?
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which condition is the basis for a species to be reproductively isolated from other members?
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Why is it so important for scientists to distinguish between homologous and analogous characteristics before building phylogenetic trees?
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(CH2O)n is the stoichiometric formula of
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what are nucleotide
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Methane,ammonia,water and sugar are dissolved to form nuceotide
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Introduction To Biology
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can ringworm be caused by bacterium
fred Reply
Nope
ejikeme
Branches of biology
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no it does not occurs by bacterium
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what is gene in biology?
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it is a heredity unit
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what is DNA
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carrier of genetic information
missy
deoxyribonucleic acid
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it contains genetic information and brings it to one generation to other
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it is of two Types circular DNA and linear DNA
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plasmids are the type of small circular DNA which lies outside the genomic DNA
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And what makes a virus to be difficult to destroy
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Robin Reply
there is respiration from the soak seeds which shows on the walls of the vacuum flask
Israel
what's mammals ?
Istifanus Reply
mammals are vertebrates ,any member group of vertebrates animals in which the young are nourished with milk from special mammary glands of the mother.
yousaf
what are actin and myosin
Praveen Reply
they are muscle filaments
Israel
they make up the microfibrils of the muscle ,relaxing and contracting to cause movement
Israel
Please did anybody know the questions that will come out in the coming practical?
Oladimeji
Why it is importantthat there are different types of protein in plasma membraine for the transport materials into and out of a cell?
Louellie Reply
the nerve cell
Mustapha Reply
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Source:  OpenStax, Physics for the modern world. OpenStax CNX. Sep 16, 2015 Download for free at http://legacy.cnx.org/content/col11865/1.3
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