Good news on the Plutonium production issue

[AegeanBlue]

I've ready maybe 6 articles on the issue, all of them just copy the ORNL release. A few actually talked about missions, but in general when describing the production milestones it seems all they can do is copy the press release word to word

[sdsds]

I've ready maybe 6 articles on the issue, all of them just copy the ORNL release. A few actually talked about missions, but in general when describing the production milestones it seems all they can do is copy the press release word to word

I think DoE people tend not to be very talkative. In that world, when in doubt about whether something can be said in public, they seem to stay silent.

No, the Pu-238 itself isn't fissile. But don't you think its production requires something that is? So their caution is understandable.

That said, there must be plenty of other people who understand what it will take to ramp up Pu-238 production to the levels described, but I think those people aren't always the kind that journalists like to quote as sources.

All that is just my humble guessing. Take it with a big grain of salt.

[Burninate]

Meanwhile, outer planets mission proposals consists of 'a tennis field of solar panels with two tiny instruments attached to it' as some people on twitter quipped.

And this would be *perfectly fine*, except we resolutely refuse to prioritize the production of tennis courts worth of solar panels, a product that is useful in the inner system, the Earth orbit, and the outer system (as a first choice out to maybe Saturn, and a backup option farther out).  Lots of powerpoints, very few, very small grants.

Why is the 300kw Government Reference Array (3kw at Saturn, 300W at Neptune) still posed as being years off?  Why aren't we building and testing them by the dozen?

[Blackstar]

A lot of people who write articles for so-called news sites are either lazy or under extreme production/deadline pressures. So all they do is rewrite press releases. They don't call anybody or email anybody because that would take time and they don't have time. They just need to spit out new articles immediately.

There's lots of other information on this available if you just do a little digging. And there are people who will/can talk about it. For example, as I understand it, there are two ways to significantly increase production. One is the traditional method, just using more material. The other is switching to a different process that should work, but has to be tested first. There are people who could talk about the general outlines, pros and cons, and costs, of these two processes. But most people writing web articles don't care.

[baldusi]

I understand that the first method is to irradiate Neptunium-237. The other is to irradiate Americium, right? In both cases then you have to chemically separate the Pu.
Unless the other method is centrifuge separation which I understand is a lot more expensive.
I do know here they are working on laser Uranium enrichment, but I ignore if it is possible to apply to PU238 production.

[Blackstar]

I understand that the first method is to irradiate Neptunium-237. The other is to irradiate Americium, right? In both cases then you have to chemically separate the Pu.

No, I was referring to two methods to get Pu-238 out of Neptunium-237. The first method is the one they are currently using. To increase the amount of Pu-238 they produce, they have to put more Neptunium into the reactor and irradiate it. This is expensive, but I don't know why. I presume it is because they essentially "rent" spaces inside that reactor, and if they want more spaces, they have to pay more for them (because those spaces are being used for other things instead).

The other method is to cook the Neptunium-237 at a higher temperature inside the same reactor. Right now, the Neptunium is mixed in with an aluminum powder to keep it cooler so it does not melt inside the reactor. But if they make the containers out of zirconium, they do not need the aluminum powder. The Neptunium gets much hotter and produces more Pu-238. I described it earlier in this thread and provided a link to a DoE presentation about it.

[kevin-rf]

From what you described, it's not really cook it at a higher temperature, but pack it more densely (by not mixing it down with Al powder). The higher temperature is a side effect of denser packing with the same volume to radiate away heat generated by the decay of the Pu-238 and Neptunium-237.

[Star One]

Full-scale production of plutonium-238 still years away

“What we’re shooting for is to get to an interim production level of around 400 to 500 grams [14 to 18 ounces] per year in 2019, and then full-scale, a kilogram and a half [3.3 lbs.] — if everything goes right — in 2023,” Bob Wham, the Pu-238 project lead in the Nuclear Security and Isotope Technology division at Oak Ridge, said last month during a presentation with NASA’s Future In-Space Operations (FISO) working group.

http://spacenews.com/full-scale-production-of-plutonium-238-still-years-away/

[Blackstar]

This has me scratching my head, but I think I know what is going on.

When the U.S. stopped production of Pu-238 back in the late 1980s they were stopping what was essentially a small side-part of a much bigger operation. But soon a lot of that big operation got shut down too with the end of the Cold War. People retire, facilities are shut down, equipment is left to sit and rust.

Now here we are, a quarter century later (yeah, let's repeat that: A QUARTER OF A CENTURY LATER) and a lot of people have retired, and the infrastructure is either gone, or rusted. And so it has to not only be restarted, but in some ways re-invented because we cannot do it the way we previously did it.

I think that it's just turning out to be more complicated than anybody thought 6-7 years ago when people first started the ball rolling to get production restarted.

In a few months I'll be working with Ralph McNutt again and Ralph probably knows more about the overall history and the infrastructure issues than anybody. So I'll have to get some perspective from him on this.

[robertross]

...
{snip}
In a few months I'll be working with Ralph McNutt again and Ralph probably knows more about the overall history and the infrastructure issues than anybody. So I'll have to get some perspective from him on this.

That would be very much appreciated, thanks.

[baldusi]

The article also confirms that they have baselined the solvent separation method. If I understood you right the last time, this was something that even back then they wanted to do and they appear to have decided to do this time. It would make sense that if you are going to have to design, validate and certify the process again, to start with the cheap and easy one, since you don't have the nuclear weapon subsidy now.

[Blackstar]

The article also confirms that they have baselined the solvent separation method. If I understood you right the last time, this was something that even back then they wanted to do and they appear to have decided to do this time. It would make sense that if you are going to have to design, validate and certify the process again, to start with the cheap and easy one, since you don't have the nuclear weapon subsidy now.

Although I might have commented on the solvent separation method, I think the real upgrade is using zirconium as the containers instead of aluminum. That allows them to get rid of aluminum in the target material, which later has to be removed. With the zirconium, they can cook more material and at a hotter temp/radiation, and then they don't have to remove as many impurities. It speeds up and simplifies the process and produces more Pu-238 with very little change in the actual irradiation process. I don't know the status of that switch.

[as58]

Not really related to Pu-238 production, but interesting nonetheless: in May issue of Physics Today there's a nice article about the development of nuclear powered artificial hearts in the 60s and 70s. One AEC design from the early 70s was driven (mechanically, using flexible drive shaft) by a Stirling cycle engine powered by 60 grams of Pu-238. Artificial heart would have replaced patient's diseased heart, while the power source would have been implanted in the abdomen.

The article is available at http://scitation.aip.org/content/aip/magazine/physicstoday/69/5.

[iamlucky13]

I'm sorry for jumping back to relatively old posts. I don't have time to keep up with interesting topics like this regularly.

Which effort? If they build an ASRG and have confidence in it, that will use less Pu-238, meaning that more is available for other missions--with a caveat: some missions require the MMRTG because they need the excess heat that an ASRG does not produce. Also, there may be missions that people don't want to use the ASRG on.

Are you aware off the top of your head of specific mission studies where the lower heat output of an ASRG would have been a problem. It may only 1/4 as much waste heat as an MMRTG, but 400-500W still seems like a decent amount for keeping electronics boxes and bearings warm.

[iamlucky13]

Meanwhile, outer planets mission proposals consists of 'a tennis field of solar panels with two tiny instruments attached to it' as some people on twitter quipped.

And this would be *perfectly fine*, except we resolutely refuse to prioritize the production of tennis courts worth of solar panels, a product that is useful in the inner system, the Earth orbit, and the outer system (as a first choice out to maybe Saturn, and a backup option farther out).  Lots of powerpoints, very few, very small grants.

Why is the 300kw Government Reference Array (3kw at Saturn, 300W at Neptune) still posed as being years off?  Why aren't we building and testing them by the dozen?

Cost and mass. Current prices for multi-junction cells put the cost of a 300W array in the ballpark of $75 million. Costs would probably drop a moderate amount if such a large order were placed because as I understand it that would cause a big increase in the overall production, but we're probably still talking about the same rough order of magnitude. Such an expenditure is not going to happen unless a mission is actually committed to that needs it.

It won't happen for outer solar system missions because the estimated mass is around 4 tonnes:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140000360.pdf

It might be a possible trade for Saturn. Cassini's RTG's were rated for about 800 Watts at the beginning of the mission, so for a mission with similar energy requirements you'd be looking at ~1 tonne of mass. That would increase the dry mass of Cassini by almost 50%. That's not exactly encouraging, but probably not entirely out of the question.

[Blackstar]

I'm sorry for jumping back to relatively old posts. I don't have time to keep up with interesting topics like this regularly.

Which effort? If they build an ASRG and have confidence in it, that will use less Pu-238, meaning that more is available for other missions--with a caveat: some missions require the MMRTG because they need the excess heat that an ASRG does not produce. Also, there may be missions that people don't want to use the ASRG on.

Are you aware off the top of your head of specific mission studies where the lower heat output of an ASRG would have been a problem. It may only 1/4 as much waste heat as an MMRTG, but 400-500W still seems like a decent amount for keeping electronics boxes and bearings warm.

Yeah. There have been proposals for Titan balloons that would use an RTG power source. Apparently the RTG would produce enough heat for the balloon, but an ASRG would not. I imagine that any spacecraft that needs the heat for more than electronics boxes would have that problem. I think Ralph Lorenz of APL created a list.

[gongora]

[This is the most recent thread on the topic I could quickly find, if there is a more recent active thread let me know.]

The GAO released a report entitled "DOE Could Improve Planning and Communication Related to Plutonium- 238 and Radioisotope Power Systems Production Challenges."  I find it convenient that you can know their conclusion without even opening the report.  A copy is attached.

[Blackstar]

I watched the hearing. One of the speakers is somebody that I worked with on the Pu-238 issue back in 2009. I thought that many of the questions from the Congress members were rather dumb. The bottom line is that DoE and NASA are on the way to getting production up and running and there are no real problems now. But if you watched the hearing, you might have noticed a number of times that the witnesses were puzzled by the questions.

[Star One]

Plutonium supply for NASA missions faces long-term challenges

While NASA and the Department of Energy (DOE) have restarted production of a plutonium isotope used to power some space missions, a new report warns of challenges that could threaten its long-term supply.

The Oct. 4 report by the Government Accountability Office, tied to a House space subcommittee hearing on the subject, said that while there is sufficient plutonium-238 in stockpiles now for missions planned through the mid-2020s, scaling up production of the isotope faces a number of technical issues.

“DOE is making progress towards producing new plutonium-238,” said Shelby Oakley, director of acquisition and sourcing management at the GAO, in testimony at the hearing. “However, DOE faces challenges in hiring and training the necessary workforce, perfecting and scaling up chemical processing, and ensuring the availability of reactors that must be addressed or its ability to meet NASA’s needs could be jeopardized.”

http://spacenews.com/plutonium-supply-for-nasa-missions-faces-long-term-challenges/