New Horizons plutonium pinch

Date: Oct 6, 2004

New Horizons plutonium pinch

Date: Oct 27, 2004

Isn't there any other radioisotope that can be used for RTGs ?

And when it is the case, I guess NASA cannot consider cooperation with other countries that might have the capability to produce such exotic material (Russia, France...) with all the unused stockpile of weapon-grade Pu239 or U235.

Any comments ?

Alcor

Date: Oct 27, 2004

U235 and Pu239 have extremely long half-lives. This makes them unsuitable for power generation, as they simply won't disintigrate fast enough.

Sr-90 is an acceptable replacement that has been used on Earth bound RTGs. The only problem is that it takes significantly more Sr-90 to produce the same power output as Pu-238. In addition, I'm not sure how much Sr-90 governments keep around. The stuff has properties similar to Calcium and is treated as such by your body. This makes it somewhat dangerous if it gets into the environment.

Still, Sr-90 is nowhere near as bad as Iodine radioisoptopes.

Date: Oct 27, 2004

Good points there AKImBatman.

I would just add that the Pu-238 used in the RTG's already comes from Russia if memory serves.

There are a lot of different isotopes that could be used--Pu-238 just happens to be farily abundant and it is already a byproduct of fuel reprocessing. Gadolininum, Polonium, Curium, and Cerium also have good candidate isotopes (although I can't remember too many off the top of my head. Polonium 210 is an intense alpha emitter.)

The problem with the really energetic emitters is they decay too fast to process into a usable form. Pu-238 has a half life of 14 years which gives it a nice balance of power production (about 500 W of heat per Kilogram) and longevity needed for deep space missions. Polonium-210 can produce almost 100 times the power per unit mass, but it's half life is only about 4 months. So by the time a deep space probe has been traveling for 10 years, 30 half lives of Polonium-210 would have passed, while only about 2/3 of the Pu-238's first half life has expired. So the Pu-238 RTG will still be producing power (65% of original power) when a Polonium-210 RTG would be stone dead.

Date: Oct 27, 2004

Just a couple of clarifications....

Pu-238 just happens to be farily abundant and it is already a byproduct of fuel reprocessing.

Actually no -- although there is a small percentage (~1.5%) of Pu-238 in the Pu present in spent nuclear fuel (SNF). The majority of Pu in SNF is Pu-239, 240 and 241 (i.e. the heavy Pu isotopes, produced from neutron capture by U-238). To extract the small percentage of Pu-238 (a product of neutron absorbtion by U-235, by way of U-236, Neptunium-237 and 238), you would need to do isotopic enrichment, which is VERY complicated & expensive. Instead, Pu-238 is produced in its isotopically pure form by irradiating highly-enriched Uranium (HEU). Then the separation process is just a chemical one (the enrichment process having been performed at the Uranium stage, instead of Pu, which is much more difficult to handle in an enrichment plant, not least because the mass difference between Pu-238 and 239 is much less than that between U-235 and 238).

Also, the half-life of Pu-238 is 87.8 years, not 14. On a 10-year mission, the energy drop is pretty minimal. But an extended mission to Kuiper Belt objects could take some ten years on top of that, and if you've started out with a bare minimum to begin with, the power drop will then become fairly significant -- particularly as your power REQUIREMENTS actually SHOULD go up, due to the increased distance from earth, and the transmission signal power needed to maintain the same bit-rate.....

Date: Oct 28, 2004

Instead, Pu-238 is produced in its isotopically pure form by irradiating highly-enriched Uranium (HEU). Then the separation process is just a chemical one (the enrichment process having been performed at the Uranium stage, instead of Pu, which is much more difficult to handle in an enrichment plant, not least because the mass difference between Pu-238 and 239 is much less than that between U-235 and 238).

Interesting precisions indeed. Though not working in any nuclear-related industry, I had some vague remembrance that RTG plutonium was produced from enriched fissile material: this is why I assumed that excess military U235 could be well recycled for science use.

When considering the number of Cold War era nuclear warheads to be dismantled, there shouldn't be any shortage of basic material. Alas, the special manufacturing facilities may not follow...

A little off-topic, I have always wondered why here in Europe, and particularly in France, with all the nuclear industry devoted to electricity production, no RTG has ever been considered for space science. That shouldn't be a financial problem, when you know the amount of money spent in reprocessing used nuclear plant fuel.

Realistically, because of the sensitive nature of this business, not even talking about the general political climate, cooperation could be fruitful but is delicate...

Date: Oct 28, 2004

Though not working in any nuclear-related industry, I had some vague remembrance that RTG plutonium was produced from enriched fissile material:

Actually, RTGs are produced from excess fission waste material. U235 & Pu-239 are the primary materials used in fission reactions. (There are a few others, but they're irrelevant to this discussion.) Pu-238, Pu-242, Cesium-137, Strontium-90, and other by products of U235 and Pu-239 fission tend not to be very useful for continuing the fission process. In some cases, the material is simply too hot to create a stable fission pile, in other cases neutron capture is insufficient to produce fission in the element.

this is why I assumed that excess military U235 could be well recycled for science use

You know what they say about assuming.

You need to keep in mind that RTGs function by taking the raditation from a radioisotope and converting it into electricity. (With a thermal conversion step in between.) If you look at the half life of U235, you'll find that half of it will disintigrate in 703,800,000 years. i.e. If you have 1 mole of U235 (6.02214199E23 atoms), you can expect that the U235 will produce about 13,566,415 disintigrations per second. While that may sound like a lot, it isn't. Each disintigration produces 4.679 MeV. Multiplying that by our disintigrations and converting to joules, we find that Uranium-235 produces a whopping 0.00001 watts.

Pu-238, OTOH, has a half-life of 87.74 years and a decay energy of 5.593 MeV. Using the same equation as before, we find that Pu-238 produces 6.529E15 disintigrations per second. Working that out, we find that Pu-238 produces 5.85 kilowatts of power. (Can someone check my figures? This seems a little high.) And that's not counting the spontaneous fission events!

Does that make the choice of radioisotopes a little clearer for you?

Date: Oct 28, 2004

Thanks for the corrections on the half-life of Pu-238--I didn't have my CRC Handbook in front of me, and I didn't look it up (Shame on Me!)

I didn't know about the Pu-238 coming from irradiated U-235, but I can see how that work! Multiple captures by neutrons that don't result in fission would progressively bump up the molecular weight of the nucleaus until, by beta-decay I assume, it ends up being Pu-238. I didn't know that it isn't found in spent fuel either--I assumed it formed like all the other 'common' isotopes of plutonium.

Multiple captures of neutrons in U-235 would account for the scarcity of the Plutonium-238. Still, with its relatively high activity level and its relative longevity it is an almost ideal fuel for deep space bound RTG's. I hope they continue to use it--it would be ashame to scrap promising future missions because there is no power source around to run them!

Date: Nov 19, 2004

here's a bit of an update on the RTG situation....

Idaho laboratory could house $230 million nuclear space-security program
Knight-Ridder Tribune
Thu 18 Nov 2004
Michelle Dunlop, The Times-News, Twin Falls, Idaho

Nov. 18--ARCO, Idaho -- The Idaho National Engineering and Environmental Laboratory might be the new home to a nuclear program that produces materials for national security and space exploration, according to Department of Energy officials.

The DOE announced its intent to consolidate the manufacturing of radioisotope power systems, like those used in NASA's recent Cassini mission to Saturn, to the INEEL site. INEEL's Advanced Test Reactor already is used in the production of the systems, in combination with production at two other DOE sites. Neither of the other two sites has a reactor readily available, thus eliminating the possibility of consolidation at those locations.

The department is asking for public comment on environmental impacts and other issues the DOE needs to consider in its initial assessment of consolidation.

"As part of this process, we're asking the public to identify what other things we should consider," said Timothy A. Frazier, program director of radioisotope power systems for the DOE. "We'll review the comments that we receive and revise the environmental impact statement with the comments. And then we'll make it final." If the process goes smoothly, the DOE expects to begin construction for the radioisotope power system facility at INEEL in October of 2007. The entire project is projected to cost $230 million, Frazier said. The facility would be operational by late 2010.

Coincidentally, the United States currently has an agreement with Russia through 2010 to purchase the plutonium-238 needed to make radioisotope power systems. A 2003 audit report on plutonium-238 released by the DOE concluded the following: "Unless the Department accelerates its program to re-establish a plutonium-238 production capability, it risks being unable to meet future national security and NASA requirements." Brad Bugger, communications director for the DOE, elaborated on the report's findings.

"We cannot use the plutonium we purchase from Russia for national defense," Bugger said. "We would like to establish a domestic source." The United States relies on the plutonium-238 it has in inventory for national defense purposes, while procuring more from Russia for space-related projects. Frazier could not comment on which national security applications the systems are used in.

"They are helping safeguard the U.S.," he said.

However, he said, a large portion of the systems produced will go to NASA.

During the manufacturing of radioisotope power systems, DOE workers must first process plutonium-238 and secondly purify and encapsulate the material. These two steps generate some nuclear waste, Frazier said.

"We're going to take great pains to reuse the waste," he said. "There will likely be some remote-handled transuranic waste." According to a recent publication by the state of Idaho's INEEL Oversight Program, INEEL currently houses 63,000 cubic meters of transuranic waste. Some of the waste is in storage, the rest buried.

The transuranic waste generated during the production of radioisotope power systems at INEEL will be shipped to the Waste Isolation Pilot Plant near Carlsbad, New Mexico.

"We're expecting that to be minimum," Frazier said.

Transuranic waste includes plutonium and neptunium Ñ both used in the production of radioisotope power systems Ñ as well as americium. This classification of waste does not contain a high level of radioactivity, but remains radioactive for a long time. The Environmental Protection Agency lists the half-life of plutonium-238 at 87.7 years. Both the EPA and DOE maintain that plutonium-238 is not useful for nuclear weapons proliferation.

"Plutonium-238 is not weapons grade material," Frazier said.

Although Frazier expects moderate increases in security once the facility is complete, he does not anticipate a large build up.

"That is one of the really great things about locating at INEEL," Frazier said. "The Idaho site does have a high degree of security." Specifics on the economic impacts of the program's consolidation will be available when the draft assessment is ready, Bugger said. The DOE does not anticipate a significant increase in permanent jobs related to the project. However, the construction phase may provide work for contractors in the state.

"Our hope is that it would produce some trickle-down effects in Idaho," Frazier said.

Since the DOE will be involved in the design of the new facility, the department will be able to take into consideration environmental factors that have long been a concern to Idahoans Ñ such as waste polluting the aquifer, worker health and safety and air quality issues.

"We have the unique ability to design the facility from the ground up," Frazier said.

On Wednesday, at least one member of the Idaho delegation expressed his satisfaction over the DOE proposal.

"Senator Craig is pleased about the consolidation," said Mike Tracy, a spokesman for the senator. "NASA has been very pleased with what Idaho's DOE site has done."

TIMELINE FOR CONSOLIDATION PROCESS:

--December 2004 -- The DOE will conduct informational meetings.

--Jan. 31, 2005 -- End of initial public comment on the process for the DOE's environmental impact assessment.

--Spring 2005 -- A draft of the environmental impact statement will be released for additional public comment.

--Summer 2005 -- The DOE will finalize its assessment.

--September 2005 -- The Department anticipates the signing of the record of decision.

--October 2007 -- Construction will commence on a radioisotope power system facility at INEEL.

--Late 2010 -- The radioisotope power system facility should be operational.

Date: Nov 28, 2004

http://www.floridatoday.com/!NEWSROOM/spacestoryN1127PLUTO.htm

Nov 26, 2004

Plutonium pinch threatens mission potential
NASA hopes to launch Pluto-bound craft in 2006
BY CHRIS KRIDLER
FLORIDA TODAY
The first mission to Pluto will see what no other spacecraft has seen, but it could see less than hoped because of a plutonium shortage.
Security problems at Los Alamos National Laboratory halted production of plutonium, which NASA's New Horizons mission needs as its energy source. Though the mission is expected to get enough from the Department of Energy to get to Pluto, scientific ambitions might have to be curtailed.
"It is an upsetting issue," said project scientist Andrew Cheng of The Johns Hopkins University Applied Physics Laboratory.
Not only might the shortage prevent New Horizons from seeing more objects in the Kuiper Belt, the field of icy bodies where Pluto is king, but NASA also is considering a delay that could add expense and take away energy from the mission.
As it decays, the plutonium allocated for the mission produces less energy. In addition, if NASA waits to fly, Pluto moves farther away from the sun and farther out of the plane in which the other planets orbit.
"It takes more energy to get there," said project manager Glen Fountain of APL. In addition, with a delay, the craft won't fly by Jupiter, which would give it a gravity assist.
The radioactive energy source is necessary that far from the sun.
"The typical way to get power is to use solar panels," said Andrew Dantzler, director of NASA's solar system exploration division, "but sunlight's just far too dim out at outer-planet distances." With a planned January 2006 launch from Cape Canaveral on a Lockheed Martin Atlas 5 rocket, the earliest New Horizons would arrive at Pluto is 2015.
If NASA delays a year, it wouldn't arrive until 2019 or 2020. Getting to another Kuiper Belt object would take an additional two or three years.
"All this time, our plutonium is decaying," Cheng said. "We think that there's additional risk because you have a longer flight time," Fountain said, "so that issue says you want to get off earlier."
Because all of the spacecraft's parts have not yet been delivered, it's not clear just how much power they will require. "Five watts more or 10 watts less can make a big difference," Cheng said. The reduced power promised by the Department of Energy should be enough to allow at least a survey of Pluto, although with some gaps in coverage, he said.
"The Pluto mission is still on track," NASA chief scientist Jim Garvin said. "This is, as you know, an extraordinary opportunity to visit a unique piece of our solar system. It's a wonderful team with a great set of experiments, something we want to do as an agency."
The best photos taken of Pluto so far are blurry, distant images by the Hubble Space Telescope.
"We're going to try to get close enough to take pictures that will blow your socks off," said Cheng, lead scientist for New Horizons' narrow-angle camera, which will take high-resolution photos of the planet.
Scientists' knowledge of Pluto and its relationship to the Kuiper Belt is fairly recent, he said. The Kuiper Belt is thought to be full of icy bodies and a source of comets.
Pluto takes 248 Earth years to orbit the sun. It is locked in orbit with its moon, Charon, and like Earth and its moon, they always keep the same face toward each other.
"It's the last world where we're really going to have the moment of revelation," Cheng said.
Just how much revelation, and how soon, may depend on the launch date.
"In any delay, there's going to be additional cost," Dantzler said of the $650 million mission. " . . . I don't think we'll be getting any more plutonium than we have, so a delay wouldn't work to our advantage at all."
Although the schedule is tight, he said, "the development's on its way."
Fountain acknowledged the short preparation time poses a challenge, but he's optimistic about a 2006 launch. "We're feeling pretty good about getting there," he said.
Scientist Cheng also hopes for the best.
"It's the only planet that we have not ever gone to and visited with a spacecraft, so I'm still looking forward to that," he said. "If we mess it up this time, I don't know when we're going to do it."
Contact Kridler at 242-3633 or ckridler@flatoday.net

Some facts about Pluto:
Discovered: in 1930 by Clyde Tombaugh
Average distance from sun: 3.67 billion miles (outermost planet)
Diameter: 1430 miles, less than 1/5 Earth's
Length of day: About 6.4 Earth days
Length of year: About 248 Earth years
Minimum/maximum surface temperature: Minus 387/minus 369 degrees Fahrenheit
Moon: Charon
Source: NASA

Date: Nov 29, 2004

Yep. They keep waiting and the plutonium keeps decaying....

If we don't go soon, then Pluto will not be visited for perhaps another thirty years or more. RTG's are the only plausible power source for such a mission that will operate for years at cryogenic temperatures. I don't understand what the problem is--why don't we just buy some more Pu-238 from the Russians, or are we not on speaking terms with them anymore?

Date: Dec 9, 2004

http://www.space.com/news/rtg_meetings_041209.html

Space Nuclear Power Spotlighted in Public Meetings

By Leonard David

Senior Space Writer

posted: 09 December 200412:56 pm ET

The U.S. Department of Energy (DOE) has scheduled public meetings regarding a proposal to consolidate the operations required to support the production of radioisotope power systems at the new Idaho National Laboratory at Idaho Falls, Idaho.

The expanded use of radioisotope power systems for future Moon, Mars and beyond space ventures is being advanced by NASA as well as the DOE.

NASA has used radioisotope thermal generators (RTGs) to energize a variety of probes, including the Galileo mission to Jupiter, as well as the Cassini spacecraft now circling Saturn. This type of power technology is utilized on certain spacecraft because they provide electricity and heat over long periods of time without any maintenance.

Nuclear power is also essential to the now being built New Horizons mission to Pluto, slated for a 2006 sendoff.

The DOE announced the environmental review of the proposed consolidation of nuclear operations related to the production of radioisotope power systems (RPS) -- technology that enables space exploration projects as well as certain national security-related missions.

The RPS is a unique technology for missions that require a long- term, unattended source of heat and/or electrical power for use in harsh and remote environments -- such as deep-space. The Pu-238 in these units serves as the source for generating heat and electricity. The heat source can be used directly to warm critical spacecraft components.

Consolidate operations

Currently, DOE plans to produce RPS in support of Government national security and space exploration missions at three geographically separate and distant DOE sites: the Oak Ridge National Laboratory (ORNL), Tennessee; Los Alamos National Laboratory (LANL), New Mexico; and the Idaho Site, Idaho. The department is proposing to consolidate all these operations at one highly secure site to increase the security of the nuclear material while reducing costs and risks from transportation.

According to the DOE: "The proposed consolidation of these operations, which includes production, purification, and encapsulation of plutonium-238 (Pu-238), would be consistent with DOE's approach on consolidating nuclear materials, increasing the security of nuclear materials, and reducing risks associated with transportation of nuclear materials. The EIS will analyze all reasonable alternatives for the consolidation of the RPS operations as well as the No Action alternative." Under the No Action Alternative, DOE would continue the RPS production operations as currently planned.

Space and Security Power Systems Facility

Last October, Deputy Secretary of Energy Kyle McSlarrow announced the commissioning of the new Space and Security Power Systems Facility, the new radioisotope facility, at Idaho’s Argonne National Laboratory-West site.

The new facility will assemble and test radioisotope power systems that the DOE builds for NASA and various national security agencies. When the new facility begins operations later this year, its first major mission will be to assemble, test and deliver a power system to NASA for the 2006 New Horizons mission to Pluto.

"More than 40 of DOE’s radioisotope power systems have flown on spacecraft, beginning in the 1960s with the manned missions to the moon and continuing today with the three systems providing electricity to the Cassini spacecraft now orbiting Saturn," Deputy Secretary McSlarrow said. "The completion of this facility is an important new mission for Idaho and we look forward to continuing our work with NASA."

Public meetings

These radioisotope power systems are effective for use in space exploration because they can safely and reliably produce electricity 24 hours a day, seven days a week for several decades. They are particularly advantageous when distances from the sun are so great that solar panels would not be feasible.

Comprised of two principle parts -- a heat source and an energy conversion system -- they work by converting the heat from radioactive decay of plutonium-238 into electricity using a thermocouple. The largest of the radioisotope power systems are the three that are currently onboard the Cassini spacecraft, each system producing about 285 watts of electricity, roughly equivalent to three 100-watt light bulbs. DOE’s power systems have proven to be very reliable and durable: the Voyager 1 spacecraft, launched in 1977, was still sending signals back to Earth when it left the solar system late last year.

Several of the meetings have already taken place. Future public-invited meetings are slated for Dec. 13: Los Alamos County Golf Course, Los Alamos, New Mexico; Dec. 15: Oak Ridge Comfort Inn, Oak Ridge, Tenn.; and Dec. 17: Hyatt Regency on Capitol Hill, Washington, D.C.

More information can be found on the Internet at http://ConsolidationEIS.doe.gov