The Bulletin of the Atomic Scientists has published a detailed critique of fusion power written by Dr Daniel Jassby, a former principal research physicist at the Princeton Plasma Physics Lab with 25 years experience working in areas of plasma physics and neutron production related to fusion energy.1
Here is a summary of his main arguments.
"[U]nlike what happens in solar fusion ‒ which uses ordinary hydrogen ‒ Earth-bound fusion reactors that burn neutron-rich isotopes have byproducts that are anything but harmless: Energetic neutron streams comprise 80 percent of the fusion energy output of deuterium-tritium reactions and 35 percent of deuterium-deuterium reactions.
"Now, an energy source consisting of 80 percent energetic neutron streams may be the perfect neutron source, but it's truly bizarre that it would ever be hailed as the ideal electrical energy source. In fact, these neutron streams lead directly to four regrettable problems with nuclear energy: radiation damage to structures; radioactive waste; the need for biological shielding; and the potential for the production of weapons-grade plutonium 239 ‒ thus adding to the threat of nuclear weapons proliferation, not lessening it, as fusion proponents would have it.
"In addition, if fusion reactors are indeed feasible ‒ as assumed here ‒ they would share some of the other serious problems that plague fission reactors, including tritium release, daunting coolant demands, and high operating costs. There will also be additional drawbacks that are unique to fusion devices: the use of fuel (tritium) that is not found in nature and must be replenished by the reactor itself; and unavoidable on-site power drains that drastically reduce the electric power available for sale."
All of these problems are endemic to any type of magnetic confinement fusion or inertial confinement fusion reactor that is fueled with deuterium-tritium or deuterium alone. The deuterium-tritium reaction is favored by fusion developers. Jassby notes that tritium consumed in fusion can theoretically be fully regenerated in order to sustain the nuclear reactions, by using a lithium blanket, but full regeneration is not possible in practice for reasons explained in his article.
Jassby writes: "To make up for the inevitable shortfalls in recovering unburned tritium for use as fuel in a fusion reactor, fission reactors must continue to be used to produce sufficient supplies of tritium ‒ a situation which implies a perpetual dependence on fission reactors, with all their safety and nuclear proliferation problems. Because external tritium production is enormously expensive, it is likely instead that only fusion reactors fueled solely with deuterium can ever be practical from the viewpoint of fuel supply. This circumstance aggravates the problem of nuclear proliferation ..."
Fusion reactors could be used to produce plutonium-239 for weapons "simply by placing natural or depleted uranium oxide at any location where neutrons of any energy are flying about" in the reactor interior or appendages to the reaction vessel.
Tritium breeding is not required in systems based on deuterium-deuterium reactions, so all the fusion neutrons are available for any use including the production of plutonium-239 for weapons ‒ hence Jassby's comment about deuterium-deuterium systems posing greater proliferation risks than deuterium-tritium systems. He writes: "In effect, the reactor transforms electrical input power into "free-agent" neutrons and tritium, so that a fusion reactor fueled with deuterium-only can be a singularly dangerous tool for nuclear proliferation."
Further, tritium itself is a proliferation risk ‒ it is used to enhance the efficiency and yield of fission bombs and the fission stages of hydrogen bombs in a process known as "boosting", and tritium is also used in the external neutron initiators for such weapons. "A reactor fueled with deuterium-tritium or deuterium-only will have an inventory of many kilograms of tritium, providing opportunities for diversion for use in nuclear weapons," Jassby writes.
It isn't mentioned in Jassby's article, but fusion has already contributed to proliferation problems even though it has yet to generate a single Watt of useful electricity. According to Khidhir Hamza, a senior nuclear scientist involved in Iraq's weapons program in the 1980s: "Iraq took full advantage of the IAEA's recommendation in the mid 1980s to start a plasma physics program for "peaceful" fusion research. We thought that buying a plasma focus device ... would provide an excellent cover for buying and learning about fast electronics technology, which could be used to trigger atomic bombs."2
Another problem is the "huge" parasitic power consumption of fusion systems ‒ "they consume a good chunk of the very power that they produce ... on a scale unknown to any other source of electrical power." There are two classes of parasitic power drain ‒ a host of essential auxiliary systems that must be maintained continuously even when the fusion plasma is dormant (of the order of 75‒100 MW), and power needed to control the fusion plasma in magnetic confinement fusion systems or to ignite fuel capsules in pulsed inertial confinement fusion systems (at least 6% of the fusion power generated). Thus a 300 MWt / 120 MWe system barely supplies on-site needs and thus fusion reactors would need to be much larger to overcome this problem of parasitic power consumption.
The neutron radiation damage in the solid vessel wall of a fusion reactor is expected to be worse than in fission reactors because of the higher neutron energies, potentially putting the integrity of the reaction vessel in peril.
Fusion fuel assemblies will be transformed into tons of radioactive waste to be removed annually from each reactor. Structural components would need to be replaced periodically thus generating "huge masses of highly radioactive material that must eventually be transported offsite for burial", and non-structural components inside the reaction vessel and in the blanket will also become highly radioactive by neutron activation.
Molten lithium presents a fire and explosion hazard, introducing a drawback common to liquid-metal cooled fission reactors.
Tritium leakage is another problem. Jassby writes: "Corrosion in the heat exchange system, or a breach in the reactor vacuum ducts could result in the release of radioactive tritium into the atmosphere or local water resources. Tritium exchanges with hydrogen to produce tritiated water, which is biologically hazardous. Most fission reactors contain trivial amounts of tritium (less than 1 gram) compared with the kilograms in putative fusion reactors. But the release of even tiny amounts of radioactive tritium from fission reactors into groundwater causes public consternation. Thwarting tritium permeation through certain classes of solids remains an unsolved problem."
Water consumption is another problem. Jassby writes: "In addition, there are the problems of coolant demands and poor water efficiency. A fusion reactor is a thermal power plant that would place immense demands on water resources for the secondary cooling loop that generates steam as well as for removing heat from other reactor subsystems such as cryogenic refrigerators and pumps. ... In fact, a fusion reactor would have the lowest water efficiency of any type of thermal power plant, whether fossil or nuclear. With drought conditions intensifying in sundry regions of the world, many countries could not physically sustain large fusion reactors."
Due to all of the aforementioned problems, and others, "any fusion reactor will face outsized operating costs." Whereas fission reactors typically require around 500 employees, fusion reactors would require closer to 1,000 employees. Jassby states that it "is inconceivable that the total operating costs of a fusion reactor will be less than that of a fission reactor".
"To sum up, fusion reactors face some unique problems: a lack of natural fuel supply (tritium), and large and irreducible electrical energy drains to offset. Because 80 percent of the energy in any reactor fueled by deuterium and tritium appears in the form of neutron streams, it is inescapable that such reactors share many of the drawbacks of fission reactors ‒ including the production of large masses of radioactive waste and serious radiation damage to reactor components. ...
"If reactors can be made to operate using only deuterium fuel, then the tritium replenishment issue vanishes and neutron radiation damage is alleviated. But the other drawbacks remain—and reactors requiring only deuterium fueling will have greatly enhanced nuclear weapons proliferation potential."
"These impediments ‒ together with colossal capital outlay and several additional disadvantages shared with fission reactors ‒ will make fusion reactors more demanding to construct and operate, or reach economic practicality, than any other type of electrical energy generator.
"The harsh realities of fusion belie the claims of its proponents of "unlimited, clean, safe and cheap energy." Terrestrial fusion energy is not the ideal energy source extolled by its boosters, but to the contrary: It's something to be shunned."
1. Daniel Jassby, 19 April 2017, 'Fusion reactors: Not what they're cracked up to be', Bulletin of the Atomic Scientists, http://thebulletin.org/fusion-reactors-not-what-they%E2%80%99re-cracked-...
2. Khidhir Hamza, Sep/Oct 1998, 'Inside Saddam's Secret Nuclear Program', Bulletin of the Atomic Scientists, Vol. 54, No. 5, www.iraqwatch.org/perspectives/bas-hamza-iraqnuke-10-98.htm