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10kBq Jaro


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Plutonium Pluto probe draws few protests
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http://seattlepi.nwsource.com/national/255900_pluto17.html


Tuesday, January 17, 2006


Plutonium Pluto probe draws few protests


By MIKE SCHNEIDER, THE ASSOCIATED PRESS


CAPE CANAVERAL, Fla. -- More than eight years ago, hundreds of protesters chanted anti-nuclear slogans before NASA launched a spacecraft to Saturn carrying 72 pounds of plutonium fuel. The noise before this week's launch of a craft with a similar payload has been more muted.


Only 30 anti-nuclear protesters showed up recently to oppose a plutonium-fueled mission to Pluto.


The most raucous it got was when protesters tied colorful origami birds to the fence of the Cape Canaveral Air Force Station.


"Folks tend to forget," said protest organizer Maria Telesca of the Global Network Against Weapons & Nuclear Power in Space.


[that's "Gnaw n'pis," by the way....]


But Telesca and other protesters said the threat of a nuclear accident is no less real with the New Horizons mission to Pluto than it was with the launch of Cassini to Saturn in 1997.


Plutonium fuel has been used on two other spacecraft taking off from the Cape Canaveral area since Cassini's launch. The two Mars rovers, Spirit and Opportunity, sent up in 2003, had much smaller amounts of plutonium, which creates energy from natural radioactive decay.


Twenty-four pounds of radioactive plutonium is in New Horizon's radioisotope thermoelectric generator, an aluminum-encased, 123-pound cylinder, 3 1/2 feet long and 1 1/2 feet wide, that sticks out of the spacecraft like a gun on a tank.


Inside the cylinder are 18 graphite-enclosed compartments, each holding 1 1/3 pounds of the plutonium dioxide. Similar generators previously have been used to power six Apollo flights and 19 other U.S. space missions.


NASA and the Department of Energy have put the probability of an early-launch accident that would cause plutonium to be released at 1 in 350 chances.


NASA last year estimated the cost of decontamination, should there be a serious accident with plutonium released during the launch, at anywhere from $241 million to $1.3 billion per square mile, depending on the size of the area.


If there was an accident during an early phase of the launch, the maximum mean radiation dose received by an individual within 62 miles of the launch site would be about 80 percent of the amount each U.S. resident receives annually from natural background radiation, according to NASA's environmental impact statement.


The space agency is setting up two radiological control centers and deploying 16 mobile field teams that can detect radiation around the launch site. Medical personnel at local hospitals also have been trained in the treatment of patients exposed to radioactive materials, and the launch required the approval of the White House.


The emergency plans are ready for today, "if need be, but hopefully not," NASA launch director Omar Baez said Sunday at a news conference.



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John


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Can anyone explain the process of make Pu-238?  I understand that Pu-239 is a result of      U-238 + n --> U-239 and then two beta decays to Pu-239.  Also, I read that Pu-238 some how starts with U-236 which is a rare outcome of U-235 + n --> U-236 (with now probability... it usually fissions).  Then the U-236 + n --> Np-237 +  n --> Pu-238.  So maybe you get it from spent rods from a fission reactor but then you would have more Pu-239 than 238 by far and it would be too had to separate so that's not it.  So how is it done?



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10kBq Jaro


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John wrote:

Can anyone explain the process of make Pu-238?  I understand that Pu-239 is a result of      U-238 + n --> U-239 and then two beta decays to Pu-239.  Also, I read that Pu-238 some how starts with U-236 which is a rare outcome of U-235 + n --> U-236 (with now probability... it usually fissions).  Then the U-236 + n --> Np-237 +  n --> Pu-238.  So maybe you get it from spent rods from a fission reactor but then you would have more Pu-239 than 238 by far and it would be too had to separate so that's not it.  So how is it done?

You got it -- except that the Np-237 is separated first, from HEU targets, before further irradiation. That way, you get pure 238, no isotope separation required.


I'm not familiar with the optimisation strategies, but I imagine there must be some part of the neutron spectrum that optimises absorption versus fission.


The most popular radiopharmaceutical, Tc-99m is, incidentally, produced in a similar way -- ie. irradiating HEU targets -- for generating Mo-99m fission products, which subsequently decay to Tc-99m.....  Of course lots of other FPs are produced as well in the process, but only a few, like I-131, are harvested for commercial medical application.



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