Nuclear Fission (Part 2) Flashcards
What is the equation for Ф(t), the number of neutrons at time t in a fission reaction?
Ф(t) = Ф(t0)*exp(τ/T)
What does the pressurised water reactor do?
Pressurises water to drive turbine for generator, then condenses the water to be pressurised again back in the generator.
What does a boiling water reactor do?
Similar to PWR, but water at 1/2 pressure, and we can control the power output through the boiling rate.
What does a fast breeder reactor do?
- U converted to Pu by neutron capture
- Core surrounded with U and make more fuel than reactor consumes
- Enriched core generates high heat flux
- Liquid metals used as coolant
What does a high-very high temperature gas reactor do?
- Carbon moderator and He coolant run at very high temperatures
- Increased efficiency due to Carnot cycle
- He can also drive turbines
- At 1200C, can split H20 into 0 and H2, which can be used as fuel
What does a thorium reactor do?
- More Th than U
- Doesn’t lead to Pu production
- Moderated, so not highly enriched core
- Normal coolant e.g. water
What are 2 major nuclear accidents?
Three mile island reactor number 2 and Chernobyl.
Why did the three mile island reactor fail?
- Main feed water pump failed
- Backup water activated but valves were closed
- Water in core overheated so control rods inserted
- Opened to release pressure but did not close again
- beta decay continued, water evaporated so core melted
What kind of reactor was Chernobyl?
Water cooled with graphite moderator, LWR
What are 5 things which started the Chernobyl disaster?
- safety test so power turned to 50%, but test delayed because they need power for grid
- Xenon builds up slowing in core reducing reaction rate
- Some control roads removed completely to increase power
- Warnings ignored
- Turned off emergency cooling system
Why did Chernobyl explode?
- Drop in heat extraction due to decreased power of turbine
- Caused water to bubble and reaction rate increased, called positive void coefficient
- Began safety test, but energy output was too big
- Control rods inserted to try and stop but bottom part was graphite and deformed overheated core prevents control rods to go further
- Reactor vessel exposed too the air: BOOM
