<< Chapter < Page Chapter >> Page >
  • Define nuclear fission.
  • Discuss how fission fuel reacts and describe what it produces.
  • Describe controlled and uncontrolled chain reactions.

Nuclear fission is a reaction in which a nucleus is split (or fissured ). Controlled fission is a reality, whereas controlled fusion is a hope for the future. Hundreds of nuclear fission power plants around the world attest to the fact that controlled fission is practical and, at least in the short term, economical, as seen in [link] . Whereas nuclear power was of little interest for decades following TMI and Chernobyl (and now Fukushima Daiichi), growing concerns over global warming has brought nuclear power back on the table as a viable energy alternative. By the end of 2009, there were 442 reactors operating in 30 countries, providing 15% of the world’s electricity. France provides over 75% of its electricity with nuclear power, while the US has 104 operating reactors providing 20% of its electricity. Australia and New Zealand have none. China is building nuclear power plants at the rate of one start every month.

The image shows people living in their homes located near a nuclear power plant.
The people living near this nuclear power plant have no measurable exposure to radiation that is traceable to the plant. About 16% of the world’s electrical power is generated by controlled nuclear fission in such plants. The cooling towers are the most prominent features but are not unique to nuclear power. The reactor is in the small domed building to the left of the towers. (credit: Kalmthouts)

Fission is the opposite of fusion and releases energy only when heavy nuclei are split. As noted in "Fusion", energy is released if the products of a nuclear reaction have a greater binding energy per nucleon ( BE / A size 12{"BE"/A} {} ) than the parent nuclei. [link] shows that BE / A size 12{"BE"/A} {} is greater for medium-mass nuclei than heavy nuclei, implying that when a heavy nucleus is split, the products have less mass per nucleon, so that mass is destroyed and energy is released in the reaction. The amount of energy per fission reaction can be large, even by nuclear standards. The graph in [link] shows BE / A size 12{"BE"/A} {} to be about 7.6 MeV/nucleon for the heaviest nuclei ( A size 12{A} {} about 240), while BE / A size 12{"BE"/A} {} is about 8.6 MeV/nucleon for nuclei having A size 12{A} {} about 120. Thus, if a heavy nucleus splits in half, then about 1 MeV per nucleon, or approximately 240 MeV per fission, is released. This is about 10 times the energy per fusion reaction, and about 100 times the energy of the average α size 12{α} {} , β size 12{β} {} , or γ size 12{γ} {} decay.

Calculating energy released by fission

Calculate the energy released in the following spontaneous fission reaction:

238 U 95 Sr + 140 Xe + 3 n

given the atomic masses to be m ( 238 U ) = 238.050784 u , m ( 95 Sr ) = 94.919388 u , m ( 140 Xe ) = 139.921610 u , and m ( n ) = 1.008665 u .

Strategy

As always, the energy released is equal to the mass destroyed times c 2 size 12{c rSup { size 8{2} } } {} , so we must find the difference in mass between the parent 238 U size 12{ {} rSup { size 8{"238"} } U} {} and the fission products.

Solution

The products have a total mass of

m products = 94.919388 u + 139.921610 u + 3 1.008665 u = 237.866993 u.

The mass lost is the mass of 238 U size 12{ {} rSup { size 8{"238"} } U} {} minus m products size 12{m rSub { size 8{"products"} } } {} , or

Δ m = 238.050784 u 237.8669933 u = 0.183791 u ,

so the energy released is

E = Δ m c 2 = 0.183791 u 931.5 Me V/ c 2 u c 2 = 171.2 MeV. alignl { stack { size 12{E= left (Δm right )c rSup { size 8{2} } } {} #" "= left (0 "." "183791"`u right ) { {"931" "." 5`"MeV/"c rSup { size 8{2} } } over {u} } c rSup { size 8{2} } ="171"`"MeV" "." {} } } {}

Discussion

A number of important things arise in this example. The 171-MeV energy released is large, but a little less than the earlier estimated 240 MeV. This is because this fission reaction produces neutrons and does not split the nucleus into two equal parts. Fission of a given nuclide, such as 238 U size 12{ {} rSup { size 8{"238"} } U} {} , does not always produce the same products. Fission is a statistical process in which an entire range of products are produced with various probabilities. Most fission produces neutrons, although the number varies with each fission. This is an extremely important aspect of fission, because neutrons can induce more fission , enabling self-sustaining chain reactions.

Questions & Answers

I'm interested in biological psychology and cognitive psychology
Tanya Reply
what does preconceived mean
sammie Reply
physiological Psychology
Nwosu Reply
How can I develope my cognitive domain
Amanyire Reply
why is communication effective
Dakolo Reply
Communication is effective because it allows individuals to share ideas, thoughts, and information with others.
effective communication can lead to improved outcomes in various settings, including personal relationships, business environments, and educational settings. By communicating effectively, individuals can negotiate effectively, solve problems collaboratively, and work towards common goals.
it starts up serve and return practice/assessments.it helps find voice talking therapy also assessments through relaxed conversation.
miss
Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment
Wekolamo Reply
please i need answer
Wekolamo
because it helps many people around the world to understand how to interact with other people and understand them well, for example at work (job).
Manix Reply
Agreed 👍 There are many parts of our brains and behaviors, we really need to get to know. Blessings for everyone and happy Sunday!
ARC
A child is a member of community not society elucidate ?
JESSY Reply
Isn't practices worldwide, be it psychology, be it science. isn't much just a false belief of control over something the mind cannot truly comprehend?
Simon Reply
compare and contrast skinner's perspective on personality development on freud
namakula Reply
Skinner skipped the whole unconscious phenomenon and rather emphasized on classical conditioning
war
explain how nature and nurture affect the development and later the productivity of an individual.
Amesalu Reply
nature is an hereditary factor while nurture is an environmental factor which constitute an individual personality. so if an individual's parent has a deviant behavior and was also brought up in an deviant environment, observation of the behavior and the inborn trait we make the individual deviant.
Samuel
I am taking this course because I am hoping that I could somehow learn more about my chosen field of interest and due to the fact that being a PsyD really ignites my passion as an individual the more I hope to learn about developing and literally explore the complexity of my critical thinking skills
Zyryn Reply
good👍
Jonathan
and having a good philosophy of the world is like a sandwich and a peanut butter 👍
Jonathan
generally amnesi how long yrs memory loss
Kelu Reply
interpersonal relationships
Abdulfatai Reply
What would be the best educational aid(s) for gifted kids/savants?
Heidi Reply
treat them normal, if they want help then give them. that will make everyone happy
Saurabh
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
Practice Key Terms 9

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Concepts of physics. OpenStax CNX. Aug 25, 2015 Download for free at https://legacy.cnx.org/content/col11738/1.5
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Concepts of physics' conversation and receive update notifications?

Ask