Safety Aspects

1. Safety Aspects Nuclear Energy

2. Physics Workshop Every Wednesday 3.40pm-4.40pm in O8 Is this time good for most people?

3. Learning Objectives • Describe the range of safety features associated with a nuclear reactor. • Derive the equation relating half life and the decay constant. • Practice calculations on radioactive decay.

4. High Energy Electron Diffraction • Any 6 from:- • A beam of high energy electrons is directed at a thin sheet of an element • and accelerated through a potential difference of about 108 volts (MeV/high energy) • A detector measures the number of electrons diffracted at a number of different angles. • Scattering effects occur due the charge of the nuclei and electron and this causes the count rate of the beam of electrons to decrease as angle increases. • The electrons are also diffracted by the nuclei in the sheet which causes minima and maxima to observed in the final pattern • as long the de Broglie wavelength of the electrons is of the same order as the size of the nucleus, which is about 10-15 m. • The diameter of the nucleus can be calculated using the angle to the first minimum, θmin • and the wavelength of the incoming beam λ using the diffraction equation R sin θmin = 0.61λ.

5. Safety Features The reactor is a thick steel vessel designed to withstand the high pressure and temperature in the core. The core is in a building with very thick concrete walls which absorb the neutrons and gamma radiation Emergency shut down system – designed to insert the control rods fully into the core. Sealed fuel rods are inserted and removed using remote handling devices. Spent rods are more radioactive than before use.

6. How to Remember? C - Concrete building. R - Remote Handling. E - Emergency shut down system. S - Steel vessel for reactor core. S - Spent fuel rods much more radioactive. Spells CRESS, helps us remember?

7. Dangers of Nuclear Power • Chernobyl (1986) • Wanted to see if coolant pumps would keep operating if there was a loss of power. • When they pushed control rods into reactor, caused loss of power and reversed direction of the rods!

8. Aftermath Overheating caused decomposition of water into hydrogen and oxygen which gases collected at the top of the vessel. Ignited and blew the lid off the reactor and turned the vessel on its side. Nine tonnes of caesium-137 floated across Europe along with many other tons of radioactive material. Caesium-137 is water-soluble and extremely toxic in minute amounts (half life 30 years).

9. Okay let’s try it Describe the range of safety features associated with a nuclear reactor (5 marks).