Historical research guide · 0948 · 2011

Fissile fuel breeding and minor actinide transmutation in the LIFE engine

Sümer Şahin · Mohammad Javed Khan · Rizwan Ahmed

In one minute

Fusion has a chicken-and-egg problem: the machines that would sell it commercially are the ones nobody has built yet. Sümer Şahin, Mohammad Javed Khan and Rizwan Ahmed take the shortcut the field calls a hybrid. Put a laser fusion chamber at the centre, wrap it in a blanket loaded with the leftover minor actinides from ordinary power-station waste, and let the fusion neutrons do two jobs at once — fission that waste for energy, and breed the tritium the fusion side needs. Their design is a modification of Livermore’s own LIFE engine. They delete its beryllium neutron multiplier, because it drove fission power to a spike right behind the first wall and because the actinides multiply neutrons well enough on their own, and they suspend the fuel as microscopic TRISO particles in the molten-salt coolant instead of embedding it in pebbles. The result, on their neutronics: several times more energy out of the blanket than the fusion driver puts in, and enough tritium to keep itself running.

Connection

Chapter 12 treats fusion as the energy substrate everything else runs on, and this is the engineering answer to the question of what you do while the pure-fusion machine is still being built — a design in which the neutron that comes out of the implosion is worth several times its own energy and burns nuclear waste on the way. Chapter 9 gets the driver end of it: a five-metre chamber whose whole job is to hold a laser-compressed plasma and let its neutrons out.

From the source

The starting point is Livermore’s own design. Scientists at the Lawrence Livermore National Laboratory worked out a hybrid reactor concept, the Laser Inertial Confinement Fusion–Fission Energy engine, consisting of a spherical fusion chamber about five metres in diameter surrounded by a multi-layered blanket with a beryllium multiplier zone behind the first wall.Abstract, third sentence
Four changes are made to that design, and the authors list them. The beryllium multiplier is omitted. TRISO fuel is suspended as micro-size particles in Flibe coolant, rather than dissolved in a uranium salt or embedded in a carbon matrix in macro-size pebbles. Carbide fuel is used. The fissionable fuel charge is kept lower than in the Livermore engine.Abstract, the four bulleted modifications
The reason for deleting the beryllium is a hot spot. Earlier work had shown extreme power peaks immediately behind the first wall of a hybrid assembly when a beryllium multiplier is used, because the beryllium moderates the neutrons there; and minor actinides multiply neutrons strongly enough under fusion neutron irradiation that an extra beryllium multiplier is not needed.Abstract, fourth and fifth sentences
The blanket is specified layer by layer. A first wall of oxide-dispersion-strengthened steel two centimetres thick, then a two-centimetre lithium-lead zone at 17 to 83 composition doing three jobs at once — neutron multiplication, tritium breeding and front coolant — then a two-centimetre steel layer, then fifty centimetres of Flibe molten salt carrying the minor actinides as fissionable fuel, then a further two-centimetre steel layer and a thirty-centimetre graphite reflector.Abstract, the blanket description
The numbers come out of a transport calculation for a 500 megawatt thermal fusion driver, in the S8-P3 approximation with 238 neutron groups. With minor actinides from light-water-reactor waste dispersed homogeneously through the Flibe as carbide TRISO particles at volume fractions of zero, two, three, four and five per cent, the tritium breeding ratio at start-up is 1.134, 1.286, 1.387, 1.52 and 1.67; a self-sustaining reactor needs a ratio above 1.05, and every case holds above that for eight years. Blanket energy multiplication at start-up runs 3.3, 4.6, 6.15 and 8.1 for the two to five per cent loadings, and fissile burnup exceeds 400,000 megawatt-days per tonne in every case.Abstract, the calculational paragraph
What to watch is the wall, not the physics. The calculated damage rates are 50 displacements per atom and 176 atomic parts per million of helium per year, which implies replacing the first wall every three years — so the number that decides whether this design is an engine or a study is a materials number, and it is already written down for the next experiment to beat.Abstract, final two sentences

The way in

https://doi.org/10.1016/j.fusengdes.2011.01.002

Historical source-access record. This guide links to the original; it does not reproduce the paper text.

WHAT THIS IS. Fusion Engineering and Design volume 86, issues 2 to 3, pages 227 to 237 (2011). The LIFE engine of the title is the Laser Inertial Fusion Energy concept worked out at the Lawrence Livermore National Laboratory — in the authors’ own expansion, the Laser Inertial Confinement Fusion–Fission Energy engine. TITLE. Crossref and the library registry both carry the title with a lower-case ‘life engine’, which loses the acronym; it is restored here as LIFE, which is how the paper itself and the Livermore programme write it. AFFILIATIONS as carried by the publisher record: Sümer Şahin, Atılım University, Faculty of Engineering, İncek, Gölbaşı, Ankara; Mohammad Javed Khan and Rizwan Ahmed, Faculty of Technology, Gazi University, Ankara, and the Pakistan Institute of Engineering and Applied Sciences, Islamabad. LICENCE. Crossref carries only Elsevier’s text-and-data-mining licence for this DOI; Unpaywall and OpenAlex both report the article closed, and the only repository record found is the closed bibliographic entry in Gazi University’s AVESIS system — so no text of the paper is reproduced here beyond the author’s own abstract. WHAT WAS READ. The abstract below is the one Elsevier deposited, retrieved in full on 2026-09-08 from the OpenAIRE publications API for this DOI. It is unusually complete — it carries the blanket layout, the calculational method and every headline number — and each claim below is located against the sentence of it that carries the figure. The four design changes are set as a list here; the wording is the authors’ own. Nothing beyond that abstract is asserted on this page.

How to cite it

Sümer Şahin, Mohammad Javed Khan, Rizwan Ahmed (2011) Fissile fuel breeding and minor actinide transmutation in the LIFE engine doi:10.1016/j.fusengdes.2011.01.002

Where it sits in the curriculum

Fusion machines: pinches, focus devices and inertial drivers