LIFE, short for Laser Inertial Fusion Energy, was a fusion energy effort run at Lawrence Livermore National Laboratory between 2008 and 2013. LIFE aimed to develop the technologies necessary to convert the laser-driven inertial confinement fusion concept being developed in the National Ignition Facility (NIF) into a practical commercial power plant, a concept known generally as inertial fusion energy (IFE). LIFE used the same basic concepts as NIF, but aimed to lower costs using mass-produced fuel elements, simplified maintenance, and diode lasers with higher electrical efficiency.
Two designs were considered, operated as either a pure fusion or hybrid fusion-fission system. In the former, the energy generated by the fusion reactions is used directly. In the latter, the neutrons given off by the fusion reactions are used to cause fission reactions in a surrounding blanket of uranium or other nuclear fuel, and those fission events are responsible for most of the energy release. In both cases, conventional steam turbine systems are used to extract the heat and produce electricity.
Construction on NIF completed in 2009 and it began a lengthy series of run-up tests to bring it to full power. Through 2011 and into 2012, NIF ran the "national ignition campaign" to reach the point at which the fusion reaction becomes self-sustaining, a key goal that is a basic requirement of any practical IFE system. NIF failed in this goal, with fusion performance that was well below ignition levels and differing considerably from predictions. With the problem of ignition unsolved, the LIFE project was canceled in 2013.
The LIFE program was criticized through its development for being based on physics that had not yet been demonstrated. In one pointed assessment, Robert McCrory, director of the Laboratory for Laser Energetics, stated: "In my opinion, the overpromising and overselling of LIFE did a disservice to Lawrence Livermore Laboratory."
Background Lawrence Livermore National Laboratory (LLNL) has been a leader in laser-driven inertial confinement fusion (ICF) since the initial concept was developed by LLNL employee John Nuckols in the late 1950s. The basic idea was to use a driver to compress a small pellet known as the target that contains the fusion fuel, a mix of deuterium (D) and tritium (T). If the compression reaches high enough values, fusion reactions begin to take place, releasing alpha particles and neutrons. The alphas may impact atoms in the surrounding fuel, heating them to the point where they undergo fusion as well. If the rate of alpha heating is higher than heat losses to the environment, the result is a self-sustaining chain reaction known as ignition.
Comparing the driver energy input to the fusion energy output produces a number known as fusion energy gain factor, labelled Q. A Q value of at least 1 is required for the system to produce net energy. Since some energy is needed to run the reactor, in order for there to be net electrical output, Q has to be at least 3. For commercial operation, Q values much higher than this are needed. For ICF, Qs on the order of 25 to 50 are needed to recoup both the electrical generation losses and the large amount of power used to power the driver. In the fall of 1960, theoretical work carried out at LLNL suggested that gains of the required order would be possible with drivers on the order of 1 MJ.
At the time, a number of different drivers were considered, but the introduction of the laser later that year provided the first obvious solution with the right combination of features. The desired energies were well beyond the state of the art in laser design, so LLNL began a development program in the mid-1960s to reach these levels. Each increase in energy led to new and unexpected optical phenomena that had to be overcome, but these were largely solved by the mid-1970s. Working in parallel with the laser teams, physicists studying the expected reaction using computer simulations adapted from thermonuclear bomb work developed a program known as LASNEX that suggested Q of 1 could be produced at much lower energy levels, in the kilojoule range, levels that the laser team were now able to deliver.
From the late-1970s, LLNL developed a series of machines to reach the conditions being predicted by LASNEX and other simulations. With each iteration, the experimental results demonstrated that the simulations were incorrect. The first machine, the Shiva laser of the late 1970s, produced compression on the order of 50 to 100 times, but did not produce fusion reactions anywhere near the expected levels. The problem was traced to the issue of the infrared laser light heating electrons and mixing them in the fuel, and it was suggested that using ultraviolet light would solve the problem. This was addressed on the Nova laser of the 1980s, which was designed with the specific intent of producing ignition. Nova did produce large quantities of fusion, with shots producing as much as neutrons, but failed to reach ignition. This was traced to the growth of Rayleigh–Taylor instabilities, which greatly increased the required driver power.
Ultimately all of these problems were considered to be well understood, and a much larger design emerged, NIF. NIF was designed to provide about twice the required driver energy, allowing some margin of error. NIF's design was finalized in 1994, with construction to be completed by 2002. Construction began in 1997 but took over a decade to complete, with major construction being declared complete in 2009.
LIFE Throughout the development of the ICF concept at LLNL and elsewhere, several small efforts had been made to consider the design of a commercial power plant based on the ICF concept. Examples include SOLASE-H and HYLIFE-II. As NIF was reaching completion in 2008, with the various concerns considered solved, LLNL began a more serious IFE development effort, LIFE.
Fusion–fission hybrid When the LIFE project was first proposed, it focused on the nuclear fusion–fission hybrid concept, which uses the fast neutrons from the fusion reactions to induce fission in fertile nuclear materials. The hybrid concept was designed to generate power from both fertile and fissile nuclear fuel and to burn nuclear waste. The fuel blanket was designed to use TRISO-based fuel cooled by a molten salt made from a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2).
Conventional fission power plants rely on the chain reaction caused when fission events release thermal neutrons that cause further fission events. Each fission event in U-235 releases two or three neutrons with about 2 MeV of kinetic energy. By careful arrangement and the use of various absorber materials, designers can balance the system so one of those neutrons causes another fission event while the other one or two are lost. This balance is known as criticality. Natural uranium is a mix of three isotopes; mainly U-238, with some U-235, and trace amounts of U-234. The neutrons released in the fission of either of the main isotopes will cause fission in U-235, but not in U-238, which requires higher energies around 5 MeV. There is not enough U-235 in natural uranium to reach criticality. Commercial light-water nuclear reactors, the most prevalent power reactors in the world, use nuclear fuel containing uranium enriched to 3 to 5% U-235 while the leftover is U-238.
Each fusion event in the D-T fusion reactor gives off an alpha particle and a fast neutron with around 14 MeV of kinetic energy. This is enough energy to cause fission in U-238, and many other transuranic elements as well. This reaction is used in H-bombs to increase the yield of the fusion section by wrapping it in a layer of depleted uranium, which undergoes rapid fission when hit by the neutrons from the fusion bomb inside. The same basic concept can also be used with a fusion reactor like LIFE, using its neutrons to cause fission in a blanket of fission fuel. Unlike a fission reactor, which burns out its fuel once the U-235 drops below a certain threshold value, these fission–fusion hybrid reactors can continue producing power from the fission fuel as long as the fusion reactor continues to provide neutrons. As the neutrons have high energy, they can potentially cause multiple fission events, leading to the reactor as a whole producing more energy, a concept known as energy multiplication. Even leftover nuclear fuel taken from conventional nuclear reactors will burn in this fashion. This is potentially attractive because this burns off many of the long lived radioisotopes in the process, producing waste that is only mildly radioactive and lacking most long-lived components.
In most fusion energy designs, fusion neutrons react with a blanket of lithium to breed new tritium for fuel. A major issue with the fission–fusion design is that the neutrons causing fission are no longer available for tritium breeding. While the fission reactions release additional neutrons, these do not have enough energy to complete the breeding reaction with Li-7, which makes up more than 92% of natural lithium. These lower energy neutrons will cause breeding in Li-6, which could be concentrated from the natural lithium ore. However, the Li-6 reaction only produces one tritium per neutron captured, and more than one T per neutron is needed to make up for natural decay and other losses. Using Li-6, neutrons from the fission would make up for the losses, but only at the cost of removing them from causing other fission reactions, lowering the reactor power output. The designer has to choose which is more important; burning up the fuel through fusion neutrons, or providing power through self-induced fission events.
The economics of fission–fusion designs have always been questionable. The same basic effect can be created by replacing the central fusion reactor with a specially designed fission reactor, and using the surplus neutrons from the fission to breed fuel in the blanket. These fast breeder reactors have proven uneconomical in practice, and the greater expense of the fusion systems in the fission–fusion hybrid has always suggested they would be uneconomical unless built in very large units.
Pure IFE
The LIFE concept stopped working along fusion-fission lines around 2009. Following consultations with their partners in the utility industry, the project was redirected toward a pure fusion design with a net electrical output around 1 gigawatt.
Inertial confinement fusion is one of two major lines of fusion power development, the other being magnetic confinement fusion (MCF), notably the tokamak concept which is being built in a major experimental system known as ITER. Magnetic confinement is widely considered to be the superior approach, and has seen significantly greater development activity over the decades. However, there are serious concerns that the MCF approach of ITER cannot ever become economically practical.