Ultra Safe Nuclear Technologies Delivers Advanced Nuclear Thermal Prop

RobertDyck · 2020-12-14 20:30:31

https://usnc.com/ultra-safe-nuclear-tec … d5nzq-2_7E

SEATTLE – October 19, 2020 — Ultra Safe Nuclear Technologies (USNC-Tech) has delivered a design concept to NASA as part of a study on nuclear thermal propulsion (NTP) flight demonstration. NTP technology provides unprecedented high-impulse thrust performance for deep space missions such as crewed missions to the moon and Mars. The NASA-sponsored study, managed by Analytical Mechanics Associates (AMA), explored NTP concepts and designs enabling deep space travel.
“We want to lead the effort to open new frontiers in space, and do it quickly and safely,” said Dr. Michael Eades, principal engineer at USNC-Tech. “Our engine maximizes the use of proven technology, eliminates failure modes of previous NTP concepts, and has a specific impulse more than twice that of chemical systems.”
...
The USNC-Tech NTP concept uses a specialized variation of USNC’s FCM™ fuel, featuring high-assay low-enriched Uranium (HALEU) ZrC-encapsulated fuel particles. This variation enables high-temperature operation while maintaining the integrity of the fuel. FCM™ fuel is extremely rugged, enabling a new family of inherently safe space-optimized reactor designs that ensure astronaut safety and environmental protection. Using low quantities of HALEU, this unique NTP concept delivers high thrust and specific impulse previously only achievable through high-enriched uranium. Furthermore, FCM™ fuel leverages pre-existing supply chains and manufacturing facilities used by terrestrial nuclear reactor developers, reducing production risks and enabling sustainable industry involvement.

Uh huh. Another commercial company that utilizes "existing" technology. Their claim of "specific impulse more than twice that of chemical systems" sounds the same as NERVA. The problem with NERVA was high reactor mass resulting in low thrust:engine-mass ratio. Timberwind dramatically reduced reactor mass, but what exactly is this one? Lack of details makes me skeptical. And at a Mars Society convention, I spoke to an engineer who worked on NERVA. He said they already used greater than 99% enriched uranium. This news release says "low-enriched Uranium". Uh huh.

Does anyone have details?

tahanson43206 · 2020-12-14 21:30:11

For RobertDyck re new topic ...

Best wishes for a good run with this topic!

In order to try to refresh my memory of NERVA and previous nuclear propulsion projects, I asked Google, and it came up with:

https://en.wikipedia.org/wiki/NERVA

That Wikipedia article is quite comprehensive .... It was updated as recently as October of this year.

Many names I recognized are included in the narrative and in the list of references.

One detail I was looking for did not jump out at me ... the ISP planned for the engine designs.

However, the narrative ** did ** confirm that thrust was planned to be variable as a function of the amount of liquid hydrogen to be delivered to the heating elements, so I presume that ISP would vary depending upon the amount of thrust to be produced.

I look forward to a clarification on that point.

Regarding the engine design you've shown us in Post #1 ... I noted that the ISP to be produced was "twice" that of chemical rockets, and i presume (using hydrogen/LOX as the basis) the engine would hope to deliver an ISP of 900.

That figure seems low compared to the values I vaguely recall reading for NERVA.

(th)

RobertDyck · 2020-12-14 21:50:45

Astronautix: NERVA

Nuclear Engine for Rocket Vehicle Application. NASA/AEC Project of the 1960's to develop Nuclear Thermal Propulsion. NERVA stages, launched by the Saturn V, would have been clustered in earth orbit to send manned expeditions to Mars. Developed up to flight article test before cancellation.
AKA: Pluto;Rover. Status: Development 1971. Thrust: 867.41 kN (195,001 lbf). Gross mass: 178,321 kg (393,130 lb). Unfuelled mass: 34,019 kg (74,999 lb). Specific impulse: 825 s. Specific impulse sea level: 380 s. Burn time: 1,200 s. Height: 43.69 m (143.33 ft). Diameter: 10.55 m (34.61 ft). Span: 10.55 m (34.61 ft).

Astronautix: NERVA NTR

DoE nuclear/LH2 rocket engine. Study 1991. Late 1980's update of 1960's Nerva design.
Status: Study 1991. Thrust: 333.40 kN (74,951 lbf). Unfuelled mass: 8,500 kg (18,700 lb). Specific impulse: 925 s. Diameter: 5.00 m (16.40 ft).
Engine: 8,500 kg (18,700 lb). Area Ratio: 500. Thrust to Weight Ratio: 4. Coefficient of Thrust sea level: 0.

Aerojet Nuclear Systems Company: NERVA specification - this is a 142 page PDF document, scanned from print.

tahanson43206 · 2020-12-14 22:10:11

For RobertDyck re #3

SearchTerm:NERVA specification 142 page PDF

http://newmars.com/forums/viewtopic.php … 63#p174863

(b) Unmanned Deep-Space Injection - To place a large unmanned
payload on a deep space trajectory using the reusable nuclear shuttle from
262 nautical mile earth orbit and returning the shuttle vehicle to earth orbit
for reuse.

This is the mission I would most like to see for the delivery of passenger vessels to Mars ... by giving a vessel a shove from LEO, the tug would insure there would be enough fuel and oxidizer in the vessel so it can brake using propulsion at Mars, and (depending upon design) land one or more vehicles on the surface.

The document itself appears to be about as comprehensive as anyone could ask for, although I only skimmed it to get an impression.

The document clarified that the ISP sought was on the order of 950, or about twice the best chemical ISP, so the new design to which this topic is dedicated is comparable in target performance.

(th)

SpaceNut · 2020-12-15 09:27:56

Same topic US developing different versions of lunar nuclear power
With this one talking about the nuclear materials to be used...

tahanson43206 · 2023-06-10 06:19:41

It has been a while since this topic saw activity.

It is two+ years later than the most recent post.

Has anything happened to the company or the concept?

Updates would be welcome!

(th)

Calliban · 2023-06-11 04:23:13

Regarding a nuclear thermal rocket using Low Enriched Uranium. It can be made to work, but there are several reasons that HEU (90+ enriched) is prefered.

1. 238U dillutes the fissile 235U. As only 235U is fissioned, the 238U is dumb weight and bulk, making the engine larger and heavier than it needs to be.

2. In order to reach criticality with a LEU fuel, the neutrons need to thermalise outside of the fuel, to avoid 238U resonance peaks. The hydrogen propellant will provide some moderation, but at typical exhaust temperature >2000K, it will be insufficiently dense to do the job on its own. Most of the moderation must be provided by something else and the only material that has low enough atomic mass, low enough absorption cross section and high enough temperature tolerance, is graphite. The problem is that slowing down length in graphite is several inches. So the fuel channels need to be several inches apart, which makes the engine a lot bulkier.

3. At high temperatures typical of NTRs, doppler broadening of the 238U absorption peaks makes the 238U absorption problem even worse. This reduces excess reactivity, making the engine more vulnerable to xenon poisoning. If you shut it down, you may have to wait several hours for the xenon to decay, before you can restart. If you want a nuclear engine that can be started at any time and ramped up to high powers very quickly, then you need enough excess reactivity in the fuel at cold conditions to overcome both the doppler broadening and xenon poisoning. The only ways of gaining that extra reactivity are to increase enrichment, or increase overall engine size and power, though this is subject to diminishing returns. It can be quite dangerous restarting a reactor with high xenon concentrations if there isn't enough excess reactivity. This is because reactivity increases rapidly as xenon absorbs neutrons and is burned off. The accident at Chernobyl happened in exactly this way. They pulled out all control rods to 10p% to burn off the xenon peak. As they did, they got a power surge as the xenon burned off, which was amplified by the positive voud coefficient of the reactor. NTRs could be vulnerable to the same problem, unless they have enough excess reactivity that xenon poisoning is a small detrement to reactivity in percentage terms. This is why one of safety improvements to RBMK reactors involved increasing enrichment.

4. Power to weight ratio is limited by heat transfer rate out of the fuel and into the propellant. The best results are achieved if we have lots of very small fuel particles occupying the entire volume of the engine. If the fuel is mostly 238U, then resonance absorption peaks make that impossible, because they gobble up too many neutrons.

5. The NTR will require some shielding for safety. The hydrogen propellant will provide shielding against neutrons. But the engine will continue to emit gamma as fission products decay for months afterward. The more compact the core is, the easier this becomes.

This isn't to say that LEU NTRs are impossible. At one point I looked into a pebble bed NTR that could run on natural uranium. But it was big, heavier and had low thrust. It could have provided propulsion for a large ship, but would not have been at all useful for smaller vessels or in situation where decent levels of thrust/weight were needed.

Last edited by Calliban (2023-06-11 04:42:35)

tahanson43206 · 2023-06-11 06:37:40

For Calliban re #7

Thanks for your thorough review of the possible use of low enrichment Uranium for space propulsion!

Because this topic was created by RobertDyck, and because Large Ship is on my mind, I thought your closing paragraph was worth highlighting:

This isn't to say that LEU NTRs are impossible. At one point I looked into a pebble bed NTR that could run on natural uranium. But it was big, heavier and had low thrust. It could have provided propulsion for a large ship, but would not have been at all useful for smaller vessels or in situation where decent levels of thrust/weight were needed.

Since Large Ship is tentatively sized at 5,000 tons. it may be a candidate for a low enrichment fuel supply.

Because of the social disadvantage of enrichment, solutions that harness low enrichment fuel are likely to be preferred for commercial applications.

No doubt high enrichment will be standard for military vessels.

It is entirely possible that your many posts in this forum include specification for a reactor design optimized for Large Ship. If you have time, please see if you can find those posts and provide a collection of links in this topic.

Or as an alternative, if your previous posts have not considered the Large Ship scenario in detail, please note that GW Johnson has worked out the requirements for a voyage of Large Ship from Earth to Mars using a variety of techniques, including the Space Tug. I like the Space Tug scenario, because the Large Ship is only responsible for (on the order of) 10% of the impulse needed for a flight to Mars. That 10% might be achieved by a nuclear propulsion system of some kind, which would allow the chemical propulsion needed for arrival at Mars to be saved.

Your reminder of Xenon poisoning led me to ask Google about the phenomenon, and it provided a number of citations, including ones about Chernobyl.

It appears that a person could spend hours following all the branches from this aspect of nuclear reactor operation.

One thing that would be helpful is a guidance for future reactor operators about how to avoid the mistake made at Chernobyl. I would hope that training for reactor operators covers the Xenon situation, and numerous other scenarios that can (and do) occur. I picked up the impression that Chernobyl occurred because the reactor operators pulled out the control rods 10% in order to burn off Xenon. Without reading further, I deduce that was too much.

If there is a link to a concise summary of Chernobyl and lessons learned, it seems to me it would fit well into any of the Nuclear related topics, or perhaps all of them.

Follow up later: The Wikipedia article on Xenon-135 appears to contain a broad overview of the subject, including details of the error at Chernobyl.

Details of interest include the need for careful pacing of reactor power level changes, due to creation and decay of short lived elements.

(th)

tahanson43206 · 2023-06-11 06:50:48

As a follow up, I asked Amazon for a list of books it carries about nuclear reactor operation....

The list is long, but this title stood out:

How to Drive a Nuclear Reactor (Springer Praxis Books) 1st ed. 2019 Edition, Kindle Edition
by Colin Tucker (Author) Format: Kindle Edition
4.8 4.8 out of 5 stars 286 ratings
Part of: Popular Science (16 books)
See all formats and editions
Kindle
$7.13 - $14.74
Read with Our Free App
Paperback
$16.63 - $16.79
7 Used from $16.63
18 New from $16.79
Have you ever wondered how a nuclear power station works? This lively book will answer that question. It’ll take you on a journey from the science behind nuclear reactors, through their start-up, operation and shutdown. Along the way it covers a bit of the engineering, reactor history, different kinds of reactors and what can go wrong with them. Much of this is seen from the viewpoint of a trainee operator on a Pressurised Water Reactor - the most common type of nuclear reactor in the world. Colin Tucker has spent the last thirty years keeping reactors safe. Join him on a tour that is the next best thing to driving a nuclear reactor yourself!
Read more
ISBN-13
978-3030338756
Edition
1st ed. 2019
Next page
Due to its large file size, this book may take longer to download

(th)

Calliban · 2023-06-11 07:34:29

100% rod withdrawal, not 10%. Unfortunately, I am not writing on a proper keyboard. Typos abound!

Much is made of the unstable core physics of the RBMK. But the primary cause of the Chernobyl accident was an experiment that was conducted by an overbearing engineer who knew nothing about reactor physics. He disabled all of the reactor trip settings, disconnected the computer controls, ignored operating rules and manually withdrew control rods to 100%. After the xenon absorbed excess neutrons and its reactivity disappeared, this caused a power surge, which was amplified by boiling in the fuel channels. A light water reactor with negative void coefficient would have been more tolerant of the fault. But no reactor is safe from deliberate sabotage.

tahanson43206 · 2023-06-11 07:50:33

For Calliban re #10

Thanks for the clarification .... the 10% figure came from Wikipedia, or another source that Google found.

Now that I am alerted to the error, I'll try to set aside some time to find the 10% figure. If it is in Wikipedia, it can be corrected.

If I misread something, I'll be able to come back and report the error.

In any case, having the 100% withdrawal error clarified is helpful.

Something to think about in the context of reactor operation, is how to prevent a person unqualified for the position to end up able to create such havoc.

Those were Soviet times, so the culture must have encouraged elevation of this person.

However, a robust team structure, of everyone watching out for everyone else, was clearly not present.

I ** almost ** ordered the "How to Drive" book, but will wait until I have another book to buy, to save on shipping.

Update: I found another book to add to the order so now both books will arrive for free, since the total is over $25.

(th)

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#1 2020-12-14 20:30:31

Ultra Safe Nuclear Technologies Delivers Advanced Nuclear Thermal Prop

#2 2020-12-14 21:30:11

Re: Ultra Safe Nuclear Technologies Delivers Advanced Nuclear Thermal Prop

#3 2020-12-14 21:50:45

Re: Ultra Safe Nuclear Technologies Delivers Advanced Nuclear Thermal Prop

#4 2020-12-14 22:10:11

Re: Ultra Safe Nuclear Technologies Delivers Advanced Nuclear Thermal Prop

#5 2020-12-15 09:27:56

Re: Ultra Safe Nuclear Technologies Delivers Advanced Nuclear Thermal Prop

#6 2023-06-10 06:19:41

Re: Ultra Safe Nuclear Technologies Delivers Advanced Nuclear Thermal Prop

#7 2023-06-11 04:23:13

Re: Ultra Safe Nuclear Technologies Delivers Advanced Nuclear Thermal Prop

#8 2023-06-11 06:37:40

Re: Ultra Safe Nuclear Technologies Delivers Advanced Nuclear Thermal Prop

#9 2023-06-11 06:50:48

Re: Ultra Safe Nuclear Technologies Delivers Advanced Nuclear Thermal Prop

#10 2023-06-11 07:34:29

Re: Ultra Safe Nuclear Technologies Delivers Advanced Nuclear Thermal Prop

#11 2023-06-11 07:50:33

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