Author Topic: NASA boosts nuclear thermal propulsion with BWXT contract  (Read 6897 times)

Offline Joffan

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http://www.world-nuclear-news.org/ON-NASA-boosts-nuclear-thermal-propulsion-with-BWXT-contract-04081701.html

some quotes
Quote
The National Aeronautics and Space Administration (NASA) has awarded BWXT Nuclear Energy a $18.8 million contract to initiate conceptual designs for a nuclear thermal propulsion reactor in support of a possible future manned mission to Mars. BWXT Nuclear Energy is a subsidiary of nuclear components, fuel and services provider BWX Technologies, which is based in Lynchburg, Virginia.
The reactor, based on low-enriched uranium (LEU) fuel, would be part of a nuclear thermal propulsion (NTP) rocket engine designed to propel a spacecraft from Earth orbit to Mars and back. According to NASA, an NTP system can cut the voyage time to Mars from six months to four and "safely deliver human explorers" by reducing their exposure to radiation. That also could reduce the vehicle mass, enabling deep space missions "to haul more payload".
:
Part of NASA's Game Changing Development (GCD) Program, the NTP project "could indeed significantly change space travel", NASA said, largely due to its ability to accelerate a large amount of propellant out of the back of a rocket at very high speeds, resulting in a highly efficient, high-thrust engine. In comparison, a nuclear thermal rocket has double the propulsion efficiency of the Space Shuttle main engine, "one of the hardest-working standard chemical engines of the past 40 years". That capability makes NTP "ideal for delivering large, automated payloads to distant worlds", it said.

http://www.spacedaily.com/reports/NASA_taps_BWXT_for_spacecraft_reactor_design_999.html
Quote
"BWXT is extremely pleased to be working with NASA on this exciting nuclear space program in support of the Mars mission," Rex D. Geveden, president and chief executive officer of parent company BWX Technologies, said in a press release. "We are uniquely qualified to design, develop and manufacture the reactor and fuel for a nuclear-powered spacecraft."
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Online Elmar Moelzer

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #1 on: 08/06/2017 02:04 AM »
This is good news! Nuclear thermal engines are definitely something worth looking into.

Offline john smith 19

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #2 on: 08/06/2017 09:30 AM »
I think KiloPower offers a more near term deployment, mostly for surface power and as a source to drive ion thrusters of various types.

That said NTR is about the only approach that can deliver any significant improvement on Isp at thrust levels that can shorten human missions with a TRL that's anywhere close to deployment.

The shift to LEU is a big change though as historically these systems have assumed the availability of about 97% enriched U235, which with modern proliferation and safety concerns is a complete non starter.  :(
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline clongton

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #3 on: 08/06/2017 07:42 PM »
Humanity will never do anything truly substantial in space until it uses NTR of some type.
I have always been an avid supporter of NTR technology so this is really good news.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline john smith 19

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #4 on: 08/07/2017 07:33 AM »
Humanity will never do anything truly substantial in space until it uses NTR of some type.
I have always been an avid supporter of NTR technology so this is really good news.
I might agree with nuclear power but the single use NERVA architecture seemed epically wasteful to me.  :(

IIRC wasn't NTR in the DRM 5.0 mission a $13Bn line item? this is about 722x smaller.   :(

The KiloPower team managed to raise $63m to prove that you could run a Stirling generator off of a nuclear reactor and their reactor test (the first of a space rated design in the US since 1965) is costed around $200m. That unit operates at about 1Kw, with stretch potential up to 10Kw and will be complete except for the radiators, which are deemed too dependent on the final application. 

Incidentally radiator design is one of those areas where I think a lot of improvement is possible without hugely exotic TRL0 designs. I'd love to see more "tailored" emission surfaces that maximize heat radiation at the radiator operating temperature while minimizing heat absorption.

But NTR's are in the MW class for even small ones (the one studied here, an upgrade to the SNRE studied under NERVA
http://www.neofuel.com/Schnitzler-Borowski-2009_NTR_25klbs_3.5TtW_AIAA-2009-5239-234.pdf
is 550MW(th) for 25 000lb of thrust. 

I think it's fair to say that for this project to get beyond the Powerpoint stage it's going to take a lot of commitment from NASA 
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline john smith 19

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #5 on: 08/07/2017 10:03 AM »
Update.

I found this on the NASA website for NTP

https://gameon.nasa.gov/gcd/files/2016/05/FS_NTP_160525.pdf

But there is something a bit odd about the description.  :(

An earlier report on the subject said that Graphite Composite fuels had much more maturity than cermets (20 reactors built Vs no cermet unit ever tested, not a trivial difference in this field).

One of the initial project goals is to purify Tungsten (the matrix material for the cermet designs) to 90% purity affordably, then to look at a reactor built with LEU at a regular engine test site IE Stennis).

I'm baffled by this.  ???

Going from HEU to LEU will make the core larger. I can only presume they think a thermal spectrum reactor (all that graphite makes it a thermal reactor, epithermal at most) will be simply too large to launch (IE from 97% U235 to <20%) and the only way to cope with the reduction is to go with a fast reactor, hence the cermet approach.

But TBH I did not realize there was any problem with W purity to begin with, unlike say the issue of all commercial Mo (low capture cross section) having enough Hf (high capture cross section) in it to affect its use in nuclear applications without serious processing.  :(

Clearly shifting to LEU changes the preferred options by a very long way.



 
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Joffan

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #6 on: 08/08/2017 12:14 AM »
Update.

I found this on the NASA website for NTP

https://gameon.nasa.gov/gcd/files/2016/05/FS_NTP_160525.pdf

The video referenced by that document - not really adding technical information but quite nicely done:



One of the initial project goals is to purify Tungsten (the matrix material for the cermet designs) to 90% purity affordably, then to look at a reactor built with LEU at a regular engine test site IE Stennis).

I'm baffled by this.

Hmm, I wonder if the clue is in the phrase "isotopically pure tungsten" - do they just want one isotope? That does sound difficult and expensive.
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Online yg1968

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #7 on: 08/08/2017 01:52 AM »
I don't know if this helps but they expand a little bit on this here:

Quote from: page 2
Initial project goals are to demonstrate the ability to purify tungsten to a minimum of 90 percent purity and determine the production costs at that purity level; to determine the technical and programmatic feasibility (pre-phase A level) of an NTP engine in the thrust range of interest for a human Mars mission; and to determine the program cost of an LEU NTP system and the confidence level of each major cost element.

Offline Propylox

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #8 on: 08/08/2017 03:34 AM »
I think it's fair to say that for this project to get beyond the Powerpoint stage it's going to take a lot of commitment from NASA
This seems like NASA dipping a toe in case they suddenly need to try and play catch-up to Russia. In 2016 Rosatom received experimental fuel for their NEP design, which began development around '09-'10, and are expected to unveil the prototype next year.
It's a 4MWt ~ 1MWe high temperature gas-cooled fast reactor for 100-150kw nominal ion propulsion.

January 2014 informative article http://osnetdaily.com/2014/01/russia-advances-development-of-nuclear-powered-spacecraft/
March 2016 short article https://sputniknews.com/business/201603211036691748-russia-rosatom-fuel/
« Last Edit: 08/08/2017 03:36 AM by Propylox »

Offline john smith 19

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #9 on: 08/08/2017 11:36 AM »
This seems like NASA dipping a toe in case they suddenly need to try and play catch-up to Russia. In 2016 Rosatom received experimental fuel for their NEP design, which began development around '09-'10, and are expected to unveil the prototype next year.
It's a 4MWt ~ 1MWe high temperature gas-cooled fast reactor for 100-150kw nominal ion propulsion.

Not really. Nuclear Electric <> Nuclear Thermal.  :(

The Russian NE is very big reactor by space nuclear standards (the biggest the US fielded was 30Kw(t) 500W(e) in 1965). It would mate very well with some of the NASA Ion thruster development projects.

Nuclear thermal is in the 100s of MW of thermal power. Even the Small Nuclear Engine ( basically a nuclear RL10) was around 350MW(t).

The upside of NTP for the US is they've had a substantial programme in it already, so there's a fair knowledgebase (although not perfect. It was shut down in some haste  :( ) to draw on and it converts heat directly into thrust with no intermediate conversion. That's important because radiators in space are true radiators (no convection  :( ). The more efficient your generator the lower its waste output temperature and the bigger the radiator you need.
For any system there will a  "break even" mass where making the generator 1% more efficient increases the radiator mass too much to be worth it.

I don't know if this helps but they expand a little bit on this here:

Quote from: page 2
Initial project goals are to demonstrate the ability to purify tungsten to a minimum of 90 percent purity and determine the production costs at that purity level; to determine the technical and programmatic feasibility (pre-phase A level) of an NTP engine in the thrust range of interest for a human Mars mission; and to determine the program cost of an LEU NTP system and the confidence level of each major cost element.
I'd already seen this in the presentation.
I took it to mean that normally tungsten has impurities (not a formally made alloy) that knock down its suitability as a reactor material, which is tough, but not as bad as requiring isotopic purity

Hmm, I wonder if the clue is in the phrase "isotopically pure tungsten" - do they just want one isotope? That does sound difficult and expensive.
That's the usual meaning and AFAIK you're right. For isotope sep you're talking exactly the sort of systems that do Uranium enrichment, which are specialized, complex and very expensive.   :(

I had sort of hoped they meant that Tungsten is normally found with other metals in it's chemical group in the same way that Molybdenum is found with Hafnium. Mo has a very low neutron capture cross section and very good high temperature strength, as does Hafnium, so most people don't bother to separate them.

Unfortunately Hf has a huge thermal neutron capture cross section (it's used in reactor control rods).

Fortunately there are chemical separation processes that work (but multiply the cost of "reactor grade" Mo  :( )

I can only presume that some of the natural Tungsten isotopes have very poor properties for a nuclear reactor and stripping them out makes a really big improvement.  If so that's going to be tough.  :(
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline john smith 19

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #10 on: 08/08/2017 03:29 PM »
Digging into the NASA progress report on the project they state they are looking for 90% pure Tungsten 184 isotope. Dynetics (who I associated with robotics, then the SLS boosters)  is the company doing the work. they need to deliver kilograms of Tungsten to test the fabrication process but so far they only managed about 50g+ of 50% pure W, but they think they know what the problem is.  :(
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline bradjensen3

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #11 on: 08/09/2017 06:03 AM »
Combine nuclear thermal propulsion with water from the Moon as reaction mass, and you could tool around the solar system at a high rate of speed. Get water from the Moon, drop to Earth orbit and pick up passengers, and get to Mars orbit in a month maybe?

Online KelvinZero

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #12 on: 08/09/2017 06:34 AM »
I think NTR basically always uses hydrogen. The point is that smaller particles move faster for the same temperature, so assuming you run you engine as hot as you can without melting it, you get better ISP if you use the smallest molecule for your propellant.

Lunar water does contain hydrogen though, so, yay.

Offline Asteroza

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #13 on: 08/09/2017 08:49 AM »
That's the usual meaning and AFAIK you're right. For isotope sep you're talking exactly the sort of systems that do Uranium enrichment, which are specialized, complex and very expensive.   :(

Would SILEX/laser enrichment schemes from uranium (re)processing be applicable here? I understood that the laser wavelength is output isotope specific so you can't use the same designs directly, but the basic principles should still apply, right?

Though there is the whole reprocessing taboo from the Carter era that made SILEX development run for so long. Trying to push SILEX tech for non-uranium use now may raise some technology dissemination concerns again.

Offline john smith 19

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #14 on: 08/09/2017 05:00 PM »
Would SILEX/laser enrichment schemes from uranium (re)processing be applicable here? I understood that the laser wavelength is output isotope specific so you can't use the same designs directly, but the basic principles should still apply, right?
I know nothing of "The technology that must not be named,"  :) but I'd guess that broadly speaking you'd be right.

I might (semi randomly) observe that a lot more materials have been tested for laser action since the 1970's and I could imagine (but not know) that either a new laser type (AFAIK high power laser diodes in the visible range were science fiction then, today people are building actual weapon systems out of them), new laser material or new way way of using an existing material (EG harmonic generation) could produce a laser intense enough to be useful at just about the right wavelength to do the job in a way that systems of that era could not.

[EDIT One thing that did strike was the (no doubt superficial) resemblance between the descriptions of the various laser enrichment systems and atomic clocks designs, in particular using various combinations of light sources, RF and/or magnetic fields to get separation of atoms in different atomic states.
Obviously the clocks seek to minimize the number of isotopes to begin with so a "clock like" system would be the worlds least accurate atomic clock.  :) .
The materials used in clocks are also chosen for how easily the can be vaporized, which would not be the case for Tungsten, which is just about the hardest element to vaporize there is.  :(  TBH I'm still a bit vague why isotoically pure Tungsten is needed. Tungsten has multiple isotopes. I guess some of them have just too high a capture cross section before the fission neutrons get to the preferred operating energy of the design.  :( ]

TBH I quite liked the proposal that one of the National Laboratories had of dissolving it in molten Bismuth and centrifuging the mix so the stuff separated into layers. I presume you then inserted a hollow needle down to the right layer and extracted the relevant isotope after it had spun down, but before the layers mixed together. Sadly it didn't go anywhere as I guess it was just too tough to engineer. I think the physics didn't quite work.  :( .

Quote from: Asteroza
Though there is the whole reprocessing taboo from the Carter era that made SILEX development run for so long. Trying to push SILEX tech for non-uranium use now may raise some technology dissemination concerns again.
Just another thing about the US that seems completely crazy to outsiders  :(. All those reactors (the most of any country on the planet?). All that spent fuel. All that potential for recycled fuel. But instead it's left to sit in a storage, waiting for a long term solution that's been coming "real soon now" since the original "Star Wars" had it's cinema release.  :(

What I don't get is why no one has tried to put together a "reprocessing plant in a shipping container" that can (slowly) chew through the pile of fuel rods and make new ones without them ever leaving a site. Obviously the economics are very tricky, and you'd want to prepare as much of the new fuel rods as possible centrally (and of course engineering a system capable of surviving exposure to intense radiation and highly toxic, volatile, abrasive and chemically aggressive chemicals) , but I think it could be possible.

However that's completely OT for this thread.   :(
« Last Edit: 08/09/2017 06:28 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Joffan

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #15 on: 08/09/2017 08:08 PM »
Urenco actually offers isotope separation on elements other than uranium:

https://media.urenco.com/corp-website/74/stableisotopes_2.pdf (p14)

Quote
Naturally occurring Tungsten has five stable isotopes...

All of these isotopes can be enriched or depleted by URENCO to any required concentration. Using our centrifuge technology, concentrations can be enriched to exceed 99.9% or depleted below 1%.
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Offline john smith 19

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #16 on: 08/09/2017 08:28 PM »
Urenco actually offers isotope separation on elements other than uranium:

https://media.urenco.com/corp-website/74/stableisotopes_2.pdf (p14)

Quote
Naturally occurring Tungsten has five stable isotopes...

All of these isotopes can be enriched or depleted by URENCO to any required concentration. Using our centrifuge technology, concentrations can be enriched to exceed 99.9% or depleted below 1%.
And they are already doing "low activation" Tungsten.  :)

Given that URENCO has a US operation (although their non fuel operation seems to operate out of their Netherlands site) the simple answer would be for Dynetics to call them saying they are on a USG contract and order up a Kg or two.

Presumably for some reason they are not doing it that way (too expensive for a govt contract?) and it's proving tougher than expected to do in house.  :(
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Propylox

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #17 on: 08/10/2017 02:18 AM »
4MWt ~ 1MWe high temperature gas-cooled fast reactor for 100-150kw nominal ion propulsion.
(snips) The Russian NE is very big reactor by space nuclear standards ...
Nuclear thermal is in the 100s of MW of thermal power ... and it converts heat directly into thrust with no intermediate conversion. That's important because radiators in space are true radiators. The more efficient your generator the lower its waste output temperature and the bigger the radiator you need.
For any system there will a  "break even" mass where making the generator 1% more efficient increases the radiator mass too much to be worth it.
Well aware, as I'm sure you are that the higher the temperature - the faster the heat transfer through radiance and convection. Rosatom's fast reactor design's high temperature therefor needs smaller radiators to create the working fluid's temperature differential for power production. NASA's NTP would traditionally use high temperatures to excite the propellant as quickly as possible - but they call it a "reactor" instead of a "core" and set a relatively low bar of ~900s isp, but which seems high for the LEU they've also proposed. That's curious.
http://www.world-nuclear-news.org/ON-NASA-boosts-nuclear-thermal-propulsion-with-BWXT-contract-04081701.html
Quote
... The reactor, based on low-enriched uranium (LEU) fuel, would be part of a nuclear thermal propulsion (NTP) rocket engine ... In comparison, a nuclear thermal rocket has double the propulsion efficiency of the Space Shuttle main engine ...
Whatever NASA is envisioning, it'll need to produce electricity (turbine, stirling, thermoelectric) and for reliability/efficiency purposes will probably use a working fluid. No surprises there.
With LEU they'll need to increase nuclear activity (temperature) right before the throat after the propellant spends considerable time circulating around the core, building temperature. This choice of LEU adds incredible complexity to the design while decreasing its performance - so why do it?

Offline john smith 19

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #18 on: 08/10/2017 06:48 AM »
Well aware, as I'm sure you are that the higher the temperature - the faster the heat transfer through radiance and convection.
Again space radiators are true radiators. They are not surrounded by a gas layer as "radiators" are on Earth, which means convection, which is a very efficient way to move heat, doesn't exist.
Quote from: Propylox
Rosatom's fast reactor design's high temperature therefor needs smaller radiators to create the working fluid's temperature differential for power production.
True, but you sacrifice efficiency because you can only use a limited amount of that high temperature if you want the waste heat temp to be high. Conversion efficiency Vs radiator weight impacts overall system efficiency.

Quote from: Propylox
NASA's NTP would traditionally use high temperatures to excite the propellant as quickly as possible - but they call it a "reactor" instead of a "core" and set a relatively low bar of ~900s isp, but which seems high for the LEU they've also proposed. That's curious.
http://www.world-nuclear-news.org/ON-NASA-boosts-nuclear-thermal-propulsion-with-BWXT-contract-04081701.html
Quote
... The reactor, based on low-enriched uranium (LEU) fuel, would be part of a nuclear thermal propulsion (NTP) rocket engine ... In comparison, a nuclear thermal rocket has double the propulsion efficiency of the Space Shuttle main engine ...
Whatever NASA is envisioning, it'll need to produce electricity (turbine, stirling, thermoelectric) and for reliability/efficiency purposes will probably use a working fluid. No surprises there.
With LEU they'll need to increase nuclear activity (temperature) right before the throat after the propellant spends considerable time circulating around the core, building temperature. This choice of LEU adds incredible complexity to the design while decreasing its performance - so why do it?
Not really. Historically reactor flow through they NASA cores has been pretty simple. In one end, out the other. I'd expect a longer core. Basically it will be a question of heat release per unit length of the core. Look at an Earth based AGR. It's gas temperature is around 500c but the clad fuel was much hotter, and the UO2 pellets higher still (because UO2 is a very poor heat conductor) operating at the 10s of bar level.

The temperature of the reactor vessel is like that of a rockets thrust chamber so it's regeneratively cooled. Piping some of that flow through a generator would be no problem. The issue is with the reactor shut down can you get enough heat of the core without a propellant flow between the core and the walls to extract the heat? If not you're looking at sticking some kind of plug in the throat to trap recirculating gas, or keep a (hopefully small) constant stream of propellant running through it for a very long period.  :(
Personally I like heat pipes. They can move a lot of heat and they can be made one way and switchable. IE turned off while the reactor is running but switched on to extract decay heat for electrical power.

As to why NASA are doing this. AFAIK HEU (or "weapons" grade) is quite cheap, hence it's interest by the Kilopower team.

However those systems can be delivered to the launch site as black boxes.

An engine needs a lot of testing at various NASA sites which are not geared up to the level of security and hazmat containment that has not existed at those sites for decades.  IOW in principal going LEU saves a lot of money
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Propylox

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Re: NASA boosts nuclear thermal propulsion with BWXT contract
« Reply #19 on: 08/10/2017 04:38 PM »
Rosatom's fast reactor design's high temperature therefor needs smaller radiators to create the working fluid's temperature differential for power production.
True, but you sacrifice efficiency because you can only use a limited amount of that high temperature if you want the waste heat temp to be high. Conversion efficiency Vs radiator weight impacts overall system efficiency.
That doesn't make any sense. Please elaborate and/or correct your comment.

(snips) Historically reactor flow through they NASA cores has been pretty simple. In one end, out the other. I'd expect a longer core. ... The temperature of the reactor vessel is like that of a rockets thrust chamber so it's regeneratively cooled.
Piping some of that flow through a generator would be no problem. The issue is with the reactor shut down can you get enough heat of the core without a propellant flow between the core and the walls to extract the heat?
Personally I like heat pipes. They can move a lot of heat and they can be made one way and switchable. IE turned off while the reactor is running but switched on to extract decay heat for electrical power.
You're talking about HEU systems, which this is not, and contradicted your desire for efficiency by proposing a low temperature generator and associated systems.

AFAIK HEU (or "weapons" grade) is quite cheap, hence it's interest by the Kilopower team.
IOW in principal going LEU saves a lot of money
Another contradiction, and a cost claim without argument.
Based on your previous posts, I'd request the old JS19 reply  ;)

-- Previous quote --
1) An earlier report on the subject said that Graphite Composite fuels had much more maturity than cermets (20 reactors built Vs no cermet unit ever tested, not a trivial difference in this field). One of the initial project goals is to purify Tungsten (the matrix material for the cermet designs) to 90% purity affordably, then to look at a reactor built with LEU at a regular engine test site IE Stennis).
.. and ..
But TBH I did not realize there was any problem with W purity to begin with, unlike say the issue of all commercial Mo (low capture cross section) having enough Hf (high capture cross section) in it to affect its use in nuclear applications without serious processing.

2) Going from HEU to LEU will make the core larger. I can only presume they think a thermal spectrum reactor (all that graphite makes it a thermal reactor, epithermal at most) will be simply too large to launch (IE from 97% U235 to <20%) and the only way to cope with the reduction is to go with a fast reactor, hence the cermet approach. 
Re1) Why have you proposed tungsten will be part of the core and not part of the rocket - ie; the throat and upper nozzle? Isotopic requirements on neutron absorption/reflection would be much more applicable to the rocket architecture or core's casing than the core's matrix.

Re2) Agreed, but a LEU fast reactor still doesn't produce the heat desired for NTP without reflecting (W?), or otherwise encouraging, neutrons back into the matrix to accelerate fission and temperature. This is why I asked about creating higher temps or use of tungsten around the throat - the LEU doesn't cut it otherwise. And there's still the issue of keeping propellant in contact long enough to extract temperature - conflicting with keeping it moving and building velocity. I don't see how that's solvable without a working fluid. Thoughts?
« Last Edit: 08/10/2017 04:44 PM by Propylox »

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