Nuclear Chemistry Fission and Fusion

GLE Describe fission and fusion. Describe nuclear waste and sources of nuclear waste. Objective Student will compare nuclear fission and fusion, comment on their potentials as sources of energy, describe methods in nuclear power plants to produce and control fission, and explain the issues involved in storage, containment, and disposal of nuclear waste.

Nuclear Power Handout

Fission When the nuclei of certain isotopes are bombarded with neutrons, they undergo fission, the splitting of a nucleus into smaller fragments. Isotopes – What is the difference between U – 238 and U – 235? An example of U – 235 fission

Fission Activity Modeling Controlled Fission Prior to Enrichment Each table gets two dice and cannot move them Is a sustained “fission” possible and for how long? After being Enriched to Approximately 3 – 4 % Class contribute to setting up different arrangements with the 91 dominoes Is this controlled or uncontrolled? Modeling Controlled Fission Ideas? Let’s give your ideas a try.

Two Steps Involved in a Nuclear Reactor Step 1 – Neutron Moderation Neutrons produced from fission move so fast they will pass right through a nucleus without being absorbed. Water and carbon (graphite) are good moderators because they slow the neutrons (close to elastic collisions) so the chain reaction can be sustained.

Two Steps Involved in a Nuclear Reactor Step 2 – Neutron Absorption To prevent the reaction from going too fast some of the slowed neutrons must be trapped before they hit fissionable atoms. Carried out by control rods made of materials such as Cadmium. Some unintended absorbers are created by the fission process and impact reactor operation (Xenon).

Nuclear Explosion Despite other dangers, a nuclear reactor cannot produce a nuclear explosion. The fuel elements are widely separated and cannot physically connect to produce the critical mass required. Once a nuclear reactor is started, however, it remains highly radioactive for many generations (nuclear waste discussion today, half- life discussion on Friday).

Fusion Fusion occurs when nuclei combine to produce a nucleus of greater mass. In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei. An example, shows that the reaction also requires two beta particles. What is a beta particle?

Fusion versus Fission Fusion reactions release more energy than fission reactions but require extremely high temperatures (in excess of 40,000,000 oC). At the very high temperatures involved, matter exists as a plasma, a high-energy state in which ions exist in a gas-like form. No known structural material can withstand the hot, corrosive plasma. Scientists are experimenting with magnetic fields to contain plasma.

Nuclear Waste Sources Spent Fuel Rods Corrosion products that are made radioactive as they pass through the nuclear core. Gas products from fission that get into the coolant or radioactive gasses from complex chemical reactions in the coolant that build up in the nuclear reactor pressure vessel.

Nuclear Waste Spent Fuel Rods Classified as high-level nuclear waste Contain the remainder of the fissionable isotope along with the fission products Some have half-lives of hundreds or thousands of years Kept on site in pools of water Keeps the fuel rods cooled Shields the fuel rods to reduce radiation levels in the “people tank”

Nuclear Unit Syllabus Go over the syllabus There will be homework, any questions? Let’s build a rubric for the presentations of the pros/cons of nuclear power and the debates (need to be working on the end product a little each day)

Rubric for Pros/Cons of Nuclear Power Presentation Nuclear Unit Syllabus What is a rubric? The rubric contains the expectations for the end product – what areas will be included and a scoring range for each area Rubric for Pros/Cons of Nuclear Power Presentation Needs Improvement Minimal Expectation Exceeds Expectations Time Less than 5 min Less than 10 min At 10 min Research No outside research 1 additional source 2 additional sources Material No equations Equations from lecture Equations from lecture and outside sources Pros/Cons Polarized opinions only Pros/Cons but not balanced Balanced with final viewpoint and one additional question.

Rubric for Team Debates Nuclear Unit Syllabus What is a rubric? The rubric contains the expectations for the end product – what areas will be included and a scoring range for each area Rubric for Team Debates Needs Improvement Minimal Expectation Exceeds Expectations Time Research Material Debate/ Counter Polarized opinions/arguments only Good arguments but not able to counter other team Good balanced arguments with well thought out counter to other team

Homework 1. – Three key ideas from reading on handout. 2. – Page 856, #’s 12 and 13. 3. – Provide your input for the final versions of both rubrics, I will combine them and get the final version back to you by Friday’s class, 2 November.