Michele Kearney's Nuclear Wire: Plutonium

Showing posts with label Plutonium. Show all posts

Monday, September 20, 2010

Processing of Used Nuclear Fuel

(Updated September 2010)

Used nuclear fuel has long been reprocessed to extract fissile materials for recycling and to reduce the volume of high-level wastes.
New reprocessing technologies are being developed to be deployed in conjunction with fast neutron reactors which will burn all long-lived actinides.
A significant amount of plutonium recovered from used fuel is currently recycled into MOX fuel; a small amount of recovered uranium is recycled.

A key, nearly unique, characteristic of nuclear energy is that used fuel may be reprocessed to recover fissile and fertile materials in order to provide fresh fuel for existing and future nuclear power plants. Several European countries, Russia and Japan have had a policy to reprocess used nuclear fuel, although government policies in many other countries have not yet addressed the various aspects of reprocessing.
Over the last 50 years the principal reason for reprocessing used fuel has been to recover unused uranium and plutonium in the used fuel elements and thereby close the fuel cycle, gaining some 25% more energy from the original uranium in the process and thus contributing to energy security. A secondary reason is to reduce the volume of material to be disposed of as high-level waste to about one fifth. In addition, the level of radioactivity in the waste from reprocessing is much smaller and after about 100 years falls much more rapidly than in used fuel itself.
In the last decade interest has grown in recovering all long-lived actinides together (i.e. with plutonium) so as to recycle them in fast reactors so that they end up as short-lived fission products. This policy is driven by two factors: reducing the long-term radioactivity in high-level wastes, and reducing the possibility of plutonium being diverted from civil use – thereby increasing proliferation resistance of the fuel cycle. If used fuel is not reprocessed, then in a century or two the built-in radiological protection will have diminished, allowing the plutonium to be recovered for illicit use (though it is unsuitable for weapons due to the non-fissile isotopes present).
Reprocessing used fuel^a to recover uranium (as reprocessed uranium, or RepU) and plutonium (Pu) avoids the wastage of a valuable resource. Most of it – about 96% – is uranium, of which less than 1% is the fissile U-235 (often 0.4-0.8%); and up to 1% is plutonium. Both can be recycled as fresh fuel, saving up to 30% of the natural uranium otherwise required. The materials potentially available for recycling (but locked up in stored used fuel) could conceivably run the US reactor fleet of about 100 GWe for almost 30 years with no new uranium input.
So far, almost 90,000 tonnes (of 290,000 t discharged) of used fuel from commercial power reactors has been reprocessed. Annual reprocessing capacity is now some 4000 tonnes per year for normal oxide fuels, but not all of it is operational.
Between now and 2030 some 400,000 tonnes of used fuel is expected to be generated worldwide, including 60,000 t in North America and 69,000 t in Europe.

World commercial reprocessing capacity^1,2

(tonnes per year)
LWR fuel	France, La Hague	1700
	UK, Sellafield (THORP)	900
	Russia, Ozersk (Mayak)	400
	Japan (Rokkasho)	800
	Total (approx)	3800
Other nuclear fuels	UK, Sellafield (Magnox)	1500
	India	275
	Total (approx)	1750
Total civil capacity		5550

Products of reprocessing

The composition of reprocessed uranium (RepU) depends on the initial enrichment and the time the fuel has been in the reactor, but it is mostly U-238. It will normally have less than 1% U-235 (typically about 0.5% U-235) and also smaller amounts of U-232 and U-236 created in the reactor. The U-232, though only in trace amounts, has daughter nuclides which are strong gamma-emitters, making the material difficult to handle. However, once in the reactor, U-232 is no problem (it captures a neutron and becomes fissile U-233). It is largely formed through alpha decay of Pu-236, and the concentration of it peaks after about 10 years of storage.
The U-236 isotope is a neutron absorber present in much larger amounts, typically 0.4% to 0.6% – more with higher burn-up – which means that if reprocessed uranium is used for fresh fuel in a conventional reactor it must be enriched significantly more (e.g. up to one-tenth more) than is required for natural uranium^b. Thus RepU from low burn-up fuel is more likely to be suitable for re-enrichment, while that from high burn-up fuel is best used for blending or MOX fuel fabrication.
The other minor uranium isotopes are U-233 (fissile), U-234 (from original ore, enriched with U-235, fertile), and U-237 (short half-life beta emitter). None of these affects the use of handling of the reprocessed uranium significantly. In the future, laser enrichment techniques may be able to remove these isotopes.
Reprocessed uranium (especially from earlier military reprocessing) may also be contaminated with traces of fission products and transuranics. This will affect its suitability for recycling either as blend material or via enrichment. Over 2002-06 USEC successfully cleaned up 7400 tonnes of technetium-contaminated uranium from the US Department of Energy.
Most of the separated uranium (RepU) remains in storage, though its conversion and re-enrichment (in UK, Russia and Netherlands) has been demonstrated, along with its re-use in fresh fuel. Some 16,000 tonnes of RepU from Magnox reactors in UK has been used^c to make about 1650 tonnes of enriched AGR fuel. In Belgium, France, Germany and Switzerland over 8000 tonnes of RepU has been recycled into nuclear power plants. In Japan the figure is over 335 tonnes in tests and in India about 250 t of RepU has been recycled into PHWRs. Allowing for impurities affecting both its treatment and use, RepU value has been assessed as about half that of natural uranium.
Plutonium from reprocessing will have an isotopic concentration determined by the fuel burn-up level. The higher the burn-up levels, the less value is the plutonium, due to increasing proportion of non-fissile isotopes and minor actinides, and depletion of fissile plutonium isotopes^d. Whether this plutonium is separated on its own or with other actinides is a major policy issue relevant to reprocessing (see section on Reprocessing policies below).
Most of the separated plutonium is used almost immediately in mixed oxide (MOX) fuel. World MOX production capacity is currently around 200 tonnes per year, nearly all of which is in France (see page on Mixed Oxide (MOX) Fuel).

Inventory of separated recyclable materials worldwide³

	Quantity (tonnes)	Natural U equivalent (tonnes)
Plutonium from reprocessed fuel	320	60,000
Uranium from reprocessed fuel	45,000	50,000
Ex-military plutonium	70	15,000
Ex-military high-enriched uranium	230	70,000

More at link
http://www.world-nuclear.org/info/inf69.html

Friday, September 17, 2010

Blog Post: Fukushima to Restart Using MOX Fuel for First Time from Nuclear Power Industry News Edited By Tom Lamar

Tokyo Electric Power Co (TEPCO) said it was preparing to restart the 784 megawatt No.3 reactor at its Fukushima-Daiichi nuclear plant on Friday, at which it is set to burn so-called mixed-oxide (MOX) fuel for the first time. Fukushima Nuclear Plant

Fukushima is a nuclear power plant located in the town of Okuma in the Futaba District of Fukushima Prefecture. With 6 operating units located on site, Fukushima is one of the largest nuclear plant sites in the world. Fukushima is the first nuclear plant to be constructed and run entirely by TEPCO.
Asia's biggest utility said if all goes as planned, the reactor will start generating power on Sept. 22 and begin commercial operations on Oct. 26.
It had shut the reactor at the northern Japan plant for planned maintenance on June 19.
During the shutdown, TEPCO prepared for uranium dioxide as well as MOX fuel to be burned at the reactor, making it the first time the company will use the recycled fuel.
Other power companies have started using the recycled fuel as part of Japan's goal to move towards a closed cycle where it recycles its own spent fuel and then burns recovered uranium and plutonium as MOX fuel.

U.S. Detonates Explosives in Plutonium Study from GSN Daily News

Image via Wikipedia

The United States on Wednesday conducted an underground non-nuclear test detonation in Nevada to study the behavior of plutonium, the Associated Press reported (see GSN, Aug. 13).
The event, code-named "Bacchus," was the 24th subcritical test conducted since 1997 at what is now called the Nevada National Security Site. It was first such experiment since the "Unicorn" detonation on Aug. 30, 2006, at the installation, previously known as the Nevada Test Site, the National Nuclear Security Administration indicated (see GSN, Aug. 24).
Subcritical tests, which do not involve fission chain reactions that produce nuclear explosions, are key to ensuring the dependability of the U.S. nuclear deterrent, according to U.S. officials.
In the latest study, Los Alamos National Laboratory researchers detonated conventional explosives surrounding a cache of radioactive material in a uniquely built sphere, NNSA spokesman Darwin Morgan said. The test, conducted in a vault roughly 1,000 feet below the earth's surface, produced no nuclear reaction and emitted no radioactivity, he said.
Opponents of subcritical tests contend the experiments go against the purpose of the Comprehensive Nuclear Test Ban Treaty, a pact Washington has yet to ratify (see GSN, July 27; Ken Ritter, Associated Press/Reno Gazette-Journal, Sept. 16).

The Future of the Nuclear Fuel Cycle -- MIT Report

from PEN by Pace Law Library

This Report from the Massachusetts Institute of Technology Nuclear Fuel Cycle Study Advisory Committee finds that uranium supplies will not limit the expansion of nuclear power in the US or around the world for the foreseeable future, according to a major new interdisciplinary study produced under the auspices of the MIT Energy Initiative. The study challenges conventional assumptions about nuclear energy. It suggests that nuclear power using today’s reactor technology with a once-through fuel cycle can play a significant part in displacing the world’s carbon-emitting fossil-fuel plants and thus help to reduce the potential for global climate change. But determining the best fuel cycle for the next generation of nuclear power plants will require more research, the report concludes. The report focuses on what is known as the “nuclear fuel cycle”—a concept that encompasses both the kind of fuel used to power a reactor (currently, most of the world’s reactors run on mined uranium that has been enriched, while a few run on plutonium) and what happens to the fuel after it has been used (either stored on site or disposed of underground—a “once-through” cycle—or reprocessed to yield new reactor fuel).