Conceptual design for a LIFE engine and power plant based on National Ignition Facility (NIF)-like fusion targets and a NIF-like laser operating at an energy of 1.4 megajoules (MJ) at a wavelength of 350 nanometers (ultraviolet), with a 2.5-meter-radius target chamber and with the final optics at a distance of 25 meters from the target. The National Ignition Campaign will begin during 2009, and ignition and fusion energy yields of 10 to 15 megajoules (MJ) are anticipated during fiscal years 2010 or 2011. Fusion yields of 20 to 35 MJ are expected soon thereafter. Ultimately fusion yields of 100 MJ are expected on NIF. The LIFE system is designed to operate with fusion energy gains of about 25 to 30 and fusion yields of about 35 to 50 MJ to provide about 500 megawatts (MW) of fusion power – about 80 percent of which comes in the form of 14.1 million electron-volt (MeV) neutrons with the rest of the energy in X-rays and ions. This is an approach which would be as good as and in some ways superior to liquid flouride thorium reactors. Improvements in lasers and cost reduction with laser components would meet the requirements of this project if current trends continue. A success with aneutronic nuclear fusion such as might occur with Bussard Inertial electrostatic fusion, dense plasma focus fusion would likely be superior to this. It would be worthwhile to fund several of these vastly superior approaches to nuclear fission and fusion for a billion or few billion each in order to get many multiple trillions of payoff with a homerun energy success. Even partial success with one of these approaches could deal with all of the current nuclear waste (unburned fuel) which would cost tens of billions to store in a place like Yucca Mountain.
This approach to fusion generates approximately 10**19 14.1-MeV neutrons per shot (about 10**20 neutrons every second). When used to drive a subcritical fission “blanket,” the fusion neutrons generate an additional energy gain of four to ten depending upon the details of the fission blanket, providing overall LIFE system energy gains of 100 to 300. (EROI 100-300)
The fission blanket contains either 40 metric tons (MT) of depleted uranium; un-reprocessed spent nuclear fuel (SNF); natural uranium or natural thorium; or a few MT of the plutonium-239, the minor actinides such as neptunium and americium, and the fission products separated from reprocessed SNF.
With the appropriate research, development and engineering program, LIFE engines could begin to provide electricity to U.S. consumers within 20 years, and could provide a very significant fraction of U.S. and international electricity demand by 2100.
Fusion-fission engines have not advance beyond the discussion stage because powerful high-average-power lasers and other required technologies did not exist. Similarly, accelerator-based schemes never advanced past the conceptual study phase, in part because a complete nuclear fuel cycle – including uranium enrichment and nuclear waste reprocessing – was still required to generate economical electricity.
Ignition experiments designed to accomplish National Ignition Facility (NIF’s) goal will begin in 2010, and successful demonstration of ignition and net energy gain on NIF will be a transforming event that is likely to focus the world’s attention on the possibility of ICF as a potential long-term energy option.
By integrating fuel generation, energy production and waste minimization into a single device, the LIFE engine requires neither enrichment nor reprocessing, and there is no need to remove fuel or fissile material generated in the reactor. LIFE engines can use fuels without prior enrichment and then burn them so completely that virtually no weapons-attractive material remains at the end of a plant’s life.
In addition to burning natural uranium, a LIFE engine can use for its fuel the two waste streams generated by LWRs – spent nuclear fuel (SNF) and depleted uranium (DU) left over from the process used to enrich uranium.
The LIFE engine extracts more than 99 percent of the energy content of its fuel, compared to less than 1 percent of the energy in the ore required to make fuel for a typical LWR. Higher fuel utilization means that far less fuel is required to generate the same amount of energy. A 1,500-megawatt LIFE power plant could operate for 50 years on only a small roomful of fuel.
A proof-of-principle LIFE fission cycle (from startup through greater than 99 percent fuel burnup) could be demonstrated with a one-fifth scale LIFE engine within less than 10 years.
Starting from as little as 300 to 500 MW of fusion power, a single LIFE engine can generate 2000 to 3000 megawatts thermal (MWt) in steady state for periods of years to decades, depending on the nuclear fuel and engine configuration. The source of “external neutrons” drives the sub-critical-fission blanket and makes the LIFE engine capable of burning any fertile or fissile nuclear material, including depleted uranium and spent nuclear fuel.
The LIFE engine is not without its challenges, however. In order for the LIFE project to manifest itself as a demonstration power plant by the year 2020, the price of fusion targets must be decreased, new long-lived materials must be developed, and low-cost DPSS lasers are needed to reduce the cost of the laser source itself.
“Experts predict that the cost of diodes used in DPSS lasers will continue to decrease significantly over the next several years,” says Diaz de la Rubia. “Building on the anticipated success of NIF, LIFE engines offer a pathway toward sustainable and safe nuclear power that significantly mitigates nuclear-proliferation concerns and minimizes nuclear waste.”
Meeting the Technical Challenges
A number of technical challenges must be overcome along the path to commercial LIFE engines by the year 2030. The key issues in the development of a LIFE fusion-fission engine are:
Achieving robust fusion ignition and burn on the National Ignition Facility (NIF).
Initial ignition experiments on NIF will begin in 2009, with the first credible attempts at achieving thermonuclear fusion in 2010 (see How to Make a Star). Success at NIF will pave the way for development of the fusion “front end” of the hybrid LIFE engine.
Development of a high-repetition-rate laser fusion driver.
NIF will execute one laser shot every few hours. A LIFE engine needs to execute 10 to 15 shots per second (see Inertial Fusion Energy). To achieve this high repetition rate, the LIFE fusion driver will need to use diode-pumped solid-state lasers (DPSSLs) instead of the flashlamp-driven lasers used in NIF. Experts predict that the cost of the diodes used in DPSSLs will continue to decrease significantly over the next several years, and many technologies required for DPSSLs have been demonstrated with the Mercury laser system at LLNL.
Inexpensive fusion targets.
LIFE engines will require several hundred million low-cost targets per year. The targets must be injected into the center of the LIFE chamber at a rate of 10 to 15 per second. Progress in the development of the technologies required to manufacture these targets has been made at General Atomics (GA) in San Diego, CA as well as at Livermore. Livermore and GA materials science experts believe technologies for low-cost, large-volume target manufacturing can be adopted from other industries.
Fission fuel and issues associated with the operation of the fission engine.
The “first wall,” or innermost shell, of the fission blanket will be exposed to large fluxes of fast neutrons and X-rays. Ongoing research in Japan, the European Community and the United States is focused on developing new structural steels that are suitable for both fusion and fission reactors and also to the LIFE engine environment. Researchers are also investigating and producing new forms of fission fuel capable of withstanding extreme environments for increasingly longer periods. Fissile material burn fractions as high as 85 percent have already been achieved in the kind of pellet fuel form required for a LIFE engine burning highly enriched fissile fuel or plutonium.