Nuclear fission is when a heavy nucleus (usually Uranium-235 in fuel rods) absorbs a neutron and splits into two smaller nuclei, extra neutrons, and a lot of heat. Those released neutrons can hit other U-235 atoms and cause a chain reaction; control rods absorb neutrons to slow the chain and keep reactions steady. The heat produced boils water (or heats a secondary loop) to make steam that turns a turbine and drives a generator to make electricity. Reactors also use a neutron moderator (like water or graphite) to slow neutrons so fission is more likely. Fission doesn’t emit the air pollutants fossil fuels do, but it produces long-lived radioactive waste (spent fuel) and thermal pollution; risk of core meltdown and contamination is why containment buildings and safety systems are crucial. For AP review, see the Topic 6.6 study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).

Nuclear plants generate electricity by controlled fission of uranium-235 in a reactor core. U-235 fuel is packed in fuel rods; when a neutron hits a U-235 nucleus it splits (fissions), releasing a lot of heat plus more neutrons. Control rods absorb excess neutrons to regulate the chain reaction, and a neutron moderator (water, graphite) slows neutrons so fission stays efficient. The heat boils water to make steam that spins a turbine connected to a generator—that’s how thermal energy becomes electricity (EK ENG-3.G.1). Plants sit inside containment buildings to limit radiation release; spent fuel is radioactive for long times, creating disposal challenges (EK ENG-3.G.3, ENG-3.G.4). For a quick topic review, see the Fiveable Topic 6.6 study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and practice questions (https://library.fiveable.me/practice/ap-environmental-science). This matches what AP expects you to know for ENG-3.G and ENG-3.H.

Uranium-235 is used because it’s one of the few naturally occurring isotopes that’s fissile—one slow neutron can split a U-235 nucleus and release lots of heat plus more neutrons, allowing a controlled chain reaction in fuel rods (EK ENG-3.G.1). That makes it practical for steady heat to make steam and drive turbines. U-238, by contrast, is much less likely to undergo fission with thermal (slow) neutrons, so it won’t sustain the same chain reaction unless converted (bred) into plutonium-239. U-235’s neutron behavior, reasonable natural abundance (after enrichment), and compatibility with moderators and control rods make it the standard fuel. Keep in mind nuclear waste from U-235 remains radioactive for a long time (EK ENG-3.G.3), which is an important environmental concern on the exam. For a focused topic review, see the Fiveable nuclear power study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and try practice problems (https://library.fiveable.me/practice/ap-environmental-science).

Nuclear fission is when a heavy nucleus (like Uranium-235 in fuel rods) splits after being hit by a neutron, releasing heat, more neutrons, and radioactive fragments. That heat makes steam to turn turbines and generate electricity (EK ENG-3.G.1). Fission produces long-lived radioactive waste (spent fuel) and risks like meltdowns (Three Mile Island, Chernobyl, Fukushima) and thermal pollution (EKs ENG-3.G.3–.4, ENG-3.H.1). Nuclear fusion is when two light nuclei (like isotopes of hydrogen) join to form a heavier nucleus, releasing energy. Fusion yields much more energy per reaction and far less long-lived radioactive waste than fission, but it requires extremely high temperatures and pressures and isn’t yet a practical large-scale power source for commercial electricity. For APES, focus on: fission = current commercial reactors (U-235, fuel rods, control rods, moderators, reactor core → steam turbine generator) and environmental effects (radioactive decay, half-life, waste disposal). Review the Topic 6.6 study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq), the Unit 6 overview (https://library.fiveable.me/ap-environmental-science/unit-6), and practice questions (https://library.fiveable.me/practice/ap-environmental-science) to prep for exam-style items.

When a nucleus “loses energy” it’s because it’s unstable and moves to a more stable (lower-energy) state by emitting radiation. That emission can be: - alpha particles (2 protons + 2 neutrons)—changes the element and mass number, - beta particles (an electron or positron)—changes a neutron to a proton (or vice versa), changing the element, - gamma rays (high-energy photons)—no change in identity, just energy loss. Those emissions carry away energy as radiation (and some becomes heat). The rate this happens is described by half-life—the time for half the atoms of a radioactive isotope (like U-235 or Cs-137) to decay. On the AP exam you should connect this idea to nuclear fission (heat from fission powers turbines) and to waste/half-life issues (EK ENG-3.G.2, ENG-3.G.1, ENG-3.H.2). For a focused review, see the Topic 6.6 study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and practice problems (https://library.fiveable.me/practice/ap-environmental-science).

Short answer: nuclear waste stays radioactive from decades to hundreds of thousands of years, depending on the isotope. Some common numbers: cesium-137 has a half-life ≈ 30 years (so it takes ~30 years to drop to half its radioactivity), while plutonium-239’s half-life is ~24,100 years—meaning some waste remains hazardous for many thousands of years. Why disposal’s hard: spent fuel contains many isotopes with different half-lives and emits heat and radiation, so it needs secure cooling, shielding, and long-term isolation from people and groundwater. You can’t safely rely on short-term storage; engineers prefer deep geological repositories, vitrification, or reprocessing, but each is expensive, politically controversial, and must guarantee containment for timeframes far beyond human institutions. For AP review, know fission, radioactive decay/half-life calculations, and waste solutions (vitrification, reprocessing, deep geological storage). See the Topic 6.6 study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and more unit review (https://library.fiveable.me/ap-environmental-science/unit-6). Practice problems: https://library.fiveable.me/practice/ap-environmental-science.

In 1986 a reactor core at Chernobyl experienced a meltdown and explosion that released large amounts of radioactive isotopes (notably iodine-131 and cesium-137) into the air. I-131 (half-life ≈ 8 days) caused high short-term thyroid exposure, increasing thyroid cancer and acute radiation sickness in people nearby. Cesium-137 (half-life ≈ 30 years) contaminated soils, forests, and agricultural lands for decades, moving through food chains (bioaccumulation in plants, fungi, and animals) and forcing long-term exclusion zones and bans on local food production. Ecosystem effects included tree die-off patches, altered species distributions, and slower ecosystem recovery where contamination persisted. For the APES exam, Chernobyl is a key example of reactor core meltdown and long-term radioactive contamination (ENG-3.H). For a focused review, check the APES Topic 6.6 study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq), the Unit 6 overview (https://library.fiveable.me/ap-environmental-science/unit-6), and extra practice problems (https://library.fiveable.me/practice/ap-environmental-science).

Half-life is the time it takes for half of the atoms in a sample of a radioactive isotope to decay (emit radiation and change into something else). Think of it like a countdown where every half-life the amount left drops to 50%: after one half-life you have 1/2, after two you have 1/4, after three you have 1/8, and so on. For APES (EK ENG-3.H.2), you’ll use half-life to calculate how radioactive a sample is at different times (like cesium-137’s ~30-year half-life after Chernobyl). It’s exponential decay, so you can plug time and half-life into N = N0(1/2)^(t/half-life) to get remaining activity—a common exam calculation. For more review on nuclear power and practice problems, check the Topic 6.6 study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and extra practice questions (https://library.fiveable.me/practice/ap-environmental-science).

Nuclear power is called a "clean" energy source mainly because, during normal operation, it produces virtually no air pollutants or greenhouse gases—unlike coal or natural gas plants—so it doesn’t drive smog or most CO2 emissions (CED: EK ENG-3.G.4). That said, it does create hazardous solid radioactive waste (spent fuel) that stays radioactive for a long time (EK ENG-3.G.3). The trade-off is: pollution is concentrated and (ideally) contained rather than emitted to the atmosphere. Strict engineering (containment buildings, vitrification, reprocessing options) and regulated long-term storage reduce environmental release risk, though accidents (Three Mile Island, Chernobyl, Fukushima) show containment can fail (EK ENG-3.H.1). For AP exam focus: be ready to describe fission → heat → steam → turbine (ENG-3.G) and compare clean-air benefits vs. thermal pollution and hazardous waste disposal challenges (ENG-3.G.4, ENG-3.H). Review the topic study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and unit overview (https://library.fiveable.me/ap-environmental-science/unit-6) for practice.

Three Mile Island (1979)—Partial meltdown of the reactor core released only small amounts of radioisotopes; no confirmed deaths but big public distrust, stricter regulation, and local evacuation/cleanup. Environmental contamination was limited and mostly short-term; long-lived waste and thermal pollution remained issues. Chernobyl (1986)—Explosive core meltdown released large amounts of iodine-131 and cesium-137 (Cs-137 half-life ≈ 30 years), causing acute radiation, long-term soil and ecosystem contamination, a large exclusion zone, bioaccumulation in food webs, and increased thyroid cancers in exposed populations. Impacts persist decades later. Fukushima Daiichi (2011)—Tsunami-induced loss of cooling led to core meltdowns and releases to air and the Pacific. Result: coastal water and soil contamination (notably Cs-137), fisheries closures, large volumes of radioactive water to manage, long-term decontamination and radioactive waste storage, plus thermal and habitat impacts. For the AP exam, focus on how reactor core meltdowns release radioisotopes, short vs. long-term impacts, bioaccumulation, and using half-life to predict decay (see the Topic 6.6 study guide: https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq). For more practice, try Fiveable’s unit resources (https://library.fiveable.me/ap-environmental-science/unit-6) and practice problems (https://library.fiveable.me/practice/ap-environmental-science).

Use the half-life decay formula: N = N0 × (1/2)^(t / t½). - N0 = starting amount, t = elapsed time, t½ = half-life. You can also use the exponential form N = N0 × e^(−λt) with λ = ln(2)/t½. Example (like the Chernobyl cesium-137 problem): N0 = 187 kBq/m², t = 90 yr, t½ = 30 yr. - t / t½ = 90 / 30 = 3, so N = 187 × (1/2)^3 = 187 / 8 = 23.375 kBq/m² → 23.38 kBq/m² (matches the AP multiple-choice result). On the AP exam, show your steps, substitute numbers, and include units. For more review on nuclear power and half-life practice, see the Topic 6.6 study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and practice problems (https://library.fiveable.me/practice/ap-environmental-science).

Nonrenewable. Nuclear power uses fission of a finite fuel (Uranium-235) in fuel rods to release heat, make steam, turn turbines, and generate electricity (CED EK ENG-3.G.1). Because economically recoverable uranium reserves are limited and not continuously replenished on human timescales, nuclear energy is classified as nonrenewable (CED EK ENG-3.G.4). It’s often called “cleaner” than fossil fuels because it emits little air pollution or CO2 during operation, but it produces thermal pollution and highly radioactive solid waste (spent fuel) that remains hazardous for long periods (CED EK ENG-3.G.3; ENG-3.H). For AP exam prep, this topic appears in Unit 6 under ENG-3.G/H—review the nuclear power study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and try practice problems (https://library.fiveable.me/practice/ap-environmental-science) to see how questions connect to the CED.

Thermal pollution from nuclear plants is the release of excess heat—produced by fission of Uranium-235 in the reactor and used to make steam for turbines—into nearby water bodies or the air (even though nuclear plants don’t emit many air pollutants, they do release heat; EK ENG-3.G and ENG-3.G.4). Many plants use once-through cooling: cold water is withdrawn, heated, then discharged warmer. Ecological effects: warmer discharge lowers dissolved oxygen (warmer water holds less O2), which stresses or kills fish and aquatic invertebrates, disrupts reproduction and metabolic rates, and can force species to migrate. Higher temps also favor heat-tolerant or invasive species and can increase algal blooms, changing food webs and ecosystem stability. Cooling towers reduce but don’t eliminate thermal impacts. For AP review, see the Topic 6.6 study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).

Think of the nucleus like a tightly packed cluster of protons and neutrons held together by the strong nuclear force. In fission (the process used in reactors) a U-235 nucleus absorbs a neutron, becomes unstable, and splits into two smaller nuclei plus a few neutrons. That splitting releases a lot of binding energy because the total binding energy per nucleon is higher in the smaller fragments—so some mass is converted to energy (E = mc^2), which shows up as heat. The extra neutrons can hit other U-235 atoms and cause a chain reaction; control rods absorb neutrons to slow or stop the chain, and a moderator (often water) slows neutrons so fission stays efficient. The heat from fission makes steam that turns turbines to produce electricity (EK ENG-3.G.1). For AP review, check the Topic 6.6 study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and practice problems (https://library.fiveable.me/practice/ap-environmental-science).

Short answer: nuclear accidents cause immediate (short-term) harm from released radiation and heat, and long-term harm because radioactive isotopes persist and keep contaminating ecosystems for years to centuries. Why: a reactor meltdown or containment failure releases radioactive isotopes (like iodine-131 and cesium-137) produced during fission of U-235. Short-term effects include acute radiation exposure to people and wildlife, thermal pollution from loss of coolant, and immediate contamination of air, water, and soil. Long-term effects come from radioactive decay and half-lives: some isotopes (cesium-137 ~30-year half-life) remain hazardous for decades, contaminating food chains, reducing biodiversity, and making land unusable for farming. Cleanup is slow and costly (decontamination, long-term monitoring, spent fuel storage). Cases to remember: Three Mile Island, Chernobyl, Fukushima (CED EK ENG-3.H.1; EK ENG-3.G.1–3.H.3). For AP review, see the Topic 6.6 study guide (https://library.fiveable.me/ap-environmental-science/unit-6/nuclear-power/study-guide/6cp8hJAGRndDsFGLiCIq) and practice problems (https://library.fiveable.me/practice/ap-environmental-science).