Future

Fusion technology

In the fusion reaction two lighter atoms fuse together to form new atom of higher atomic number. Total mass of substrates before fusion is higher than mass of final atom. This phenomenon is called "mass defect" and is connected with binding energy of lighter elements in new atom. Additional mass obtained in the reaction means usable radiated energy according to Einstein's formula E=mc2 (c=3*108 m/s - light speed). The highest binding energy can be found in hydrogen and its isotopes. Therefore the most efficient is deuterium and tritium fusion. Deuterium is natural heavy form of hydrogen, occurring in the seawater. Tritium is heavier than deuterium and is not natural isotope. Moreover it is radioactive. However tritium can be easy produced from lithium. With neutrons bombarding lithium readily splits into tritium and helium. Such breeding reaction can be implemented as a part of fusion reactor operation. Neutrons from fusion reaction can react with lithium contained in blanket. Therefore radioactive fuel is not transported and in fact it is not radioactive at all until its placing in the reactor. Fuel demand in the fusion reactor is very low, e.g. 1 GWe fusion power plant is estimated to need 3 tons of lithium and 100 kg deuterium to generate 7 billion kWh. Similar amount of energy fossil power plant produced, burning 1,5 million tons of coal [62]. This also means that to meet electricity demand of the city with one million population for one year, fusion power plant will require only one truck load of fuel. [62]

Under normal conditions lighter atoms are not willingly react to fuse together. Deuterium - lithium fuel have to be heated to temperatures above 100 MēC at low pressure (but allowing to gain the largest amount of net energy). In such temperature fuel gases become plasma and nuclei detach from electrons. Therefore plasma forms ionized gas. Nuclei charged positively normally can not approach each other because of the strong electrostatic forces. Nuclei can overcome repulsion only when they get together at very close range. To provoke fusion conditions temperature has to increase. Then fusion can occur. But additionally it is necessary to limit energy losses to level that fusion energy release is enough to maintain heating process. Then fusion reaction will be self-sustaining and external heating vital to induce reaction will not be necessary. Otherwise, process will not be economical because more energy will be provided from heating devices then fusion will be releasing. Heating switching off will cause temperature decrease and fusion interruption.

Nuclear fusion effectiveness is described by amplification factor Q. Q is a quotient of energy generated during fusion reaction and external energy supplied for heating. Q=1 means, that reactor reaches break even. Energy generated is higher than energy supplied. External energy for heating should minimalized then Q could be possibly high. If heating devices can be switched off, Q will equal infinity. [62]

Ignition in regarding to nuclear fusion describes conditions under that the energy from reaction is high enough to keep constant temperature of plasma without external heating. To obtain fusion ignition and steady state reaction several parameters have to meet Lawson's criterion. Product of density of plasma ions - n, plasma captured time - tE and plasma's temperature must be higher than 50*1020 keV/m3. Values that fulfill the criterion are achievable but only separately. It has not been possible to reach 50*1020 keV/m3 during fusion reaction so far. However, previous attempt for the reaction were successful but with negative energy balance.[61],[64]

Electricity generation will be based on conventional methods. The fusion reaction will provide heat. It will be received from neutrons slowed down in the blanket around the plasma. The coolant will get the energy from the blanket, similarly as the coolant gets the energy from the boiler or the classic reactor. Then normal turbine will allow to produce the electricity.

To provide and keep specific conditions several ideas are proposed:

  • Magnetic containment
  • Inertial containment
  • Hybrid fusion

    • Ref. [60],[61],[62],[63]

  • Copyrights 2011 © Michal Wierzbowski