Chemistry · Ch 13 — Nuclear Chemistry and Radioactivity
Electrical Energy from Nuclear Fission (the Nuclear Reactor)
Electrical Energy from Nuclear Fission (the Nuclear Reactor)
Nuclear fission offers a genuine alternative energy source to burning fossil fuels. Traditionally, the steam that drives a power-plant turbine comes from boilers fuelled by oil, gas or coal -- all of which are depleting, non-renewable resources with rising extraction costs -- which is a large part of the practical case for relying instead on nuclear fission for electricity generation.
A nuclear reactor is a device that harnesses the energy released by fission in a CONTROLLED manner for peaceful purposes such as electricity generation. Inside the reactor core, a fissionable material -- typically uranium-235 or plutonium-239 -- is stacked together with a moderator, either heavy water (D2O) or graphite. Neutrons released by fission events pass through this moderator and lose part of their kinetic energy (they are 'slowed down'); these now-slow neutrons are then efficiently captured by further fissile nuclei, initiating new fission events and sustaining the chain reaction. Cadmium control rods, which readily absorb neutrons, are inserted into or withdrawn from the moderator to speed up, slow down, or hold steady the overall rate of the chain reaction -- this is what makes the process CONTROLLED rather than an uncontrolled explosive chain reaction.
The energy released by fission appears as heat, which is removed from the reactor core by circulating a coolant liquid. That heated coolant is then passed through a heat exchanger (steam generator) to produce high-pressure steam, which drives a turbine to generate electricity, after which the spent steam is condensed back to liquid water (using, for example, cooling river water) and returned to the loop. …
What this figure shows. A schematic of the core of a nuclear reactor: uranium fuel rods immersed in a moderator (heavy water or graphite), with control rods (typically cadmium, which readily absorbs neutrons) that can be inserted or withdrawn to speed up or slow down the fission chain reaction, and a neutron source to start the reaction. A radiation shield surrounds the whole assembly. Neutrons released in fission pass through the moderator and lose kinetic energy (are 'slowed down'), after which the slowed neutrons are efficiently captured by other 235U nuclei to sustain further fission, at a rate held steady by the control rods. FIDELITY NOTE: this is the third use of the figure label 'Fig. 13.4' in the same chapter (after Fig. 13.4 for the activity-vers …
What this figure shows. A larger schematic showing the full power-generation loop built around the reactor core of Fig. 13.4(a): high-pressure liquid water is heated by the fission reaction and carries that heat to a steam generator; the steam generator produces high-pressure steam, which is piped to drive a turbine (generating electricity); the spent steam then passes to a condenser, where it is cooled back to liquid water using river water flowing at roughly 80 degF in and 100 degF out, and a pump returns the condensed water to the reactor loop to be reheated, completing the cycle. A cooling tower is …
Worked out. The Bhabha Atomic Research Centre (BARC), Mumbai, has set up irradiation plants for preserving agricultural produce such as mangoes, onions and potatoes, located at Vashi (Navi Mumbai) and Lasalgaon (Nashik) -- a real-world, peaceful, non-power application of controlled nuclear/radiation technology, distinct from electricity generation. …