STM-D-0948Paper2011Designed, not yet built

Fissile fuel breeding and minor actinide transmutation in the LIFE engine

Sümer Şahin · Mohammad Javed Khan · Rizwan Ahmed

Abstract and summary · read the original at the source · none found

In one page

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.

Why it matters hereChapter 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.

What it claims

01The 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
Designed, not yet built
02Four 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
Designed, not yet built
03The 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
Published and peer-reviewed
04The 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
Designed, not yet built
05The 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
Published and peer-reviewed
06What 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
What to watch

Read it · abstract

Abstract

Progress on The National Ignition Facility (NIF) brings fusion a viable energy source in foreseeable future. Energy multiplication in a fusion–fission (hybrid) reactor could lead earlier market penetration of fusion energy for commercial utilization. Originally, scientists at the Lawrence Livermore National Laboratory (LLNL) have worked out a hybrid reactor design concept; the so-called Laser Inertial Confinement Fusion–Fission Energy (LIFE) engine, which has consisted of a spherical fusion chamber of about 5 m diameter, surrounded by a multi-layered blanket with a beryllium multiplier zone after the first wall.

However, earlier work had indicated extreme power peaks at immediate vicinity of the first wall of a hybrid assembly, if a beryllium multiplier is used. Hence, in the current work, the beryllium multiplier zone has been removed in order to mitigate fission power peaks at the vicinity of the first wall as a result of neutron moderation on beryllium. Furthermore, minor actinides (MA) will cause significant neutron multiplication under fusion neutron irradiation so that an extra beryllium multiplier will not be needed. Present work has made following modifications on the LLNL design of the original (LIFE) engine:

Omission of beryllium multiplier.
TRISO fuel has been suspended as micro-size particles in Flibe coolant in lieu of being dissolved in uranium salt or imbedded carbon matrix in macro-size pebbles.
Carbide fuel is used.
Fissionable fuel charge is kept lower than in the LLNL (LIFE) engine.

The modified (LIFE) engine is kept similar to the LLNL design to a great degree in order to allow mutual feedback between two geographically separated teams towards a more advanced and improved design under consideration of totally independent views. The first wall is made of ODS (2 cm) and followed by a Li17Pb83 zone (2 cm), acting as neutron multiplier, tritium breeding and front coolant zone. It is separated by an ODS layer (2 cm) from the Flibe molten salt zone (50 cm), containing MA as fissionable fuel. A 3rd ODS layer (2 cm) separates the molten salt zone on the right side from the graphite reflector (30 cm).

Calculations have been conducted for a fusion driver power of 500 MWth in S8-P3 approximation using 238-neutron groups. Minor actinides (MA) out of the nuclear waste of LWRs are used as fissile carbide fuel in TRISO particles with volume fractions of 0, 2, 3, 4 and 5% have been dispersed homogenously in the Flibe coolant. For these cases, tritium breeding at startup is calculated as TBR = 1.134, 1.286, 1.387, 1.52 and 1.67, respectively. In the course of plant operation, TBR and fissile neutron multiplication factor decrease gradually. For a self-sustained reactor, TBR greater than 1.05 can be kept for all cases over 8 years. Higher fissionable fuel content in the molten salt leads also to higher blanket energy multiplication, namely M = 3.3, 4.6, 6.15 and 8.1 with 2, 3, 4 and 5% TRISO volume fraction at start up, respectively. For all investigated cases, fissile burn up exceeds 400 000 MW D/MT.

Major damage mechanisms have been calculated as DPA = 50 and He = 176 appm per year. This implies a replacement of the first wall every 3 years.

Sümer Şahin, Atılım University, Ankara; Mohammad Javed Khan and Rizwan Ahmed, Gazi University, Ankara, and the Pakistan Institute of Engineering and Applied Sciences, Islamabad. Fusion Engineering and Design 86, issues 2 to 3, pages 227 to 237 (2011). Abstract as deposited by the publisher; the four design changes are set as a list here and the one inequality is written out in words.

(Abstract only — see the rights note above for why the eleven pages of neutronics, tables and burnup histories are not reproduced here. They are at the source.)

The inertial-fusion neighbours on this site: Jan Badziak’s review of the whole laser route to fusion is at /library/stm-f585d315d5; the National Ignition Facility, the driver this design assumes, is described by its own team at /library/stm-c68b26e4c0; the earlier status of inertial confinement fusion is at /library/stm-b23ae31c98; and inertial fusion turned into a propulsion system is at /library/stm-b87332054a. For the same fusion-plus-fission idea in a completely different machine — NASA Glenn’s lattice confinement fusion driving fast fission — see /library/stm-d32ac233e6 and /library/stm-2053f063ef.

The way in

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

Lattice confinement fusion Plasmoids, charge clusters and the orbs