Could a high / very high temperature nuclear reactor operate in Venus?

[xpell]

TL;DR

About the possibility of operating a VHTR or similar using the atmosphere of Venus as coolant.

Hi. I'm just a curious person with high-school-level scientific knowledge.

However, I was wondering if a specially-engineered Generation IV high or very high temperature (800-1,000ºC) nuclear reactor could work in Venus using the local atmosphere at 450ºC as "coolant", just like a "typical" reactor operating at 300ºC works on Earth. If not, why not, please?

Thank you in advance!

 

[.Scott]

It would be a tough engineering problem.
You can't use any semiconductor electronics.
You can't have any person attending it.

 

[xpell]

It would be a tough engineering problem.
You can't use any semiconductor electronics.
You can't have any person attending it.

Fully agreed. I'll leave the specific engineering details to the geniuses. But, if it would conceptually work, couldn't it be used to Stirling-refrigerate a chamber and keep the electronics and other stuff protected there or the like?

 

[PeroK]

Fully agreed. I'll leave the specific engineering details to the geniuses. But, if it would conceptually work, couldn't it be used to Stirling-refrigerate a chamber and keep the electronics and other stuff protected there or the like?

Are you talking about Venus, the planet; or Venus, Texas?

https://en.wikipedia.org/wiki/Venus,_Texas

 

[Rive]

if it would conceptually work, couldn't it be used to Stirling-refrigerate a chamber and keep the electronics and other stuff protected there or the like?

As a strictly theoretical issue, it might work.
But it's still an engineering nightmare.

Me, personally - I would rather opt for clockwork instead.

 

[.Scott]

Are you talking about Venus, the planet; or Venus, Texas?

https://en.wikipedia.org/wiki/Venus,_Texas

Venus, Texas ?! That would be way too hot.

 

[Astronuc]

Summary:: About the possibility of operating a VHTR or similar using the atmosphere of Venus as coolant.

However, I was wondering if a specially-engineered Generation IV high or very high temperature (800-1,000ºC) nuclear reactor could work in Venus using the local atmosphere at 450ºC as "coolant", just like a "typical" reactor operating at 300ºC works on Earth. If not, why not, please?

It is certainly an interesting idea to consider, and worthy of a homework problem in an advanced reactor and power plant course. One points to a domestic LWR with a peak temperature of ~300°C, which rejects heat at ambient temperature, ~25-35°C.

Thermodynamically, it is possible, although the thermodynamic efficiency would be limited. NASA puts the surface temperature at ~880°Fahrenheit (470°Celsius).
https://solarsystem.nasa.gov/planets/venus/in-depth/#otp_surface

One would probably want to use an open Brayton cycle, given that the atmosphere is mostly CO₂, some N₂ and traces of SO₂ (and sulfuric acid). "96.5% carbon dioxide, 3.5% nitrogen, and traces of other gases, most notably sulfur dioxide."
https://en.wikipedia.org/wiki/Atmosphere_of_Venus#Composition

One could consider a direct open Brayton cycle in which the compressed atmospheric gases are passed through the core directly, assuming one could ensure integrity of the fuel in the core. Then there is the matter of leaving the reactor on the surface at the end of the mission, or launching it back to orbit.

Bear in mind, the Russian Venera program had some limited success: "Due to the extreme surface conditions on Venus, the probes could only survive for a short period on the surface, with times ranging from 23 minutes (Venera 7) to ~two hours (127 minutes, Venera 13)."
https://en.wikipedia.org/wiki/Venera

One would require an material with a reasonably high melting temperature. If the peak operating temperature is 1000°C (1273 K), then one would want a melting temperature (assuming an maximum operating homologous temperature of 0.5) of at least 2273°C (2546K), which doesn't leave too many choices. If one can limit the maximum stress in the system, one might be able to use a homologous temperature of 0.6, which would decrease the melting temperature to 1848°C (2126 K). There is usually a tradeoff among creep (based on maximum stress and temperature), maximum temperature and anticipated lifetime (service life, or mission duration).

There there is the matter of find that high temperature material with reasonable resistance to corrosion (thermochemical) degradation. So, one needs a structural material (probably an alloy) with a reasonably high strength at operating temperature and a protective coating that resists the corrosion of the working fluid, i.e., the atmosphere of Venus.

Others have pointed out challenges to electronics, and consequently, control systems.

 

[xpell]

Thank you very very much, Astronuc, this is exactly the kind of thing that I had it mind. Just one (key) question, please:

If one can limit the maximum stress in the system, one might be able to use a homologous temperature of 0.6, which would decrease the melting temperature to 1848°C (2126 K).

I didn't understand this, my knowledge is limited as I said. And it's obviously very important. Would you be so kind to explain it "for dummies", please?

Others have pointed out challenges to electronics, and consequently, control systems.

Yes, well, since (in my mind) the most basic purpose of this reactor would be generating electricity to move a Stirling refrigerator and "create cold" before anything else, the very first thing that would be cooled would be the electronics. During landing and deploying / starting up / whatever is needed to get it up and running (fast), the electronics would be protected by more conventional methods that have already been proposed.

 

[Astronuc]

I didn't understand this,

For structural materials, e.g., alloys, ceramics or cermets, in a power system, it is important to know and understand how a material behaves at temperature (usually maximum service temperature) in its environment (fuel and working fluids) through the service (duty) period (service life). One must consider mechanical behavior, chemical environment (corrosion) and radiation environment (radiation effects). The latter two comprise the field of environmental degradation.

From a lot of experience over a large number of systems, rules of thumb have been developed with respect to performance and design. One of the rules is to limit the maximum operating temperature (hot spot) based on stress, temperature and lifetime (or time in service).

One rule of thumb is to design a component such that it operates at less than or equal to 0.5 homologous temperature. Homologous temperature is the ratio of applied temperature to the melting temperature (or incipient melting temperature). If the stress is very low (as determined by experiential judgement and experiment), one can shift the homologous temperature upward. Otherwise, 0.5 is useful, and preferably, it should be as low as possible.
https://en.wikipedia.org/wiki/Homologous_temperature

In a terrestrial LWR, the structural alloys typical operate at less the 0.3-0.35 homologous temperature.

So one can work with the 'thermodynamic (or process) temperature' and melting point of the material. If one wants to maximize process temperature, then one has to fine a material with the highest melting temperature. However, one must consider the thermomechanical properties of a material, e.g., elastic modulus, yield strength, ultimate tensile strength, ductility, impact toughness, fracture toughness, fatigue life, and creep, as well as corrosion or chemical interaction with the environment, which for a cladding material (which forms the barrier between fuel and working fluid or environment) means the fuel-cladding chemical interaction and cladding-coolant chemical interaction. One must determine how resilient that cladding is with the fuel and working fluid at temperature for however long. In a nuclear reactor, the neutron and gamma field changes the mechanical properties of the structural alloys and affects the thermochemical behavior of the material.

With respect to alloy design, consider the following: Some Thoughts on Alloy Design
https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-84-3612

Yes, well, since (in my mind) the most basic purpose of this reactor would be generating electricity to move a Stirling refrigerator and "create cold" before anything else, the very first thing that would be cooled would be the electronics. During landing and deploying / starting up / whatever is needed to get it up and running (fast), the electronics would be protected by more conventional methods that have already been proposed.

I'll take a look at the document cited, but please realize, there is nothing conventional about applying Earth based technology to the Venusian environment. One should read up on cooling systems and the theory of refrigeration systems or heat pumps. Start with Coefficient of Performance (COP) for a cooling system.

https://en.wikipedia.org/wiki/Coefficient_of_performance
http://labman.phys.utk.edu/phys136core/modules/m3/refrigerators.html

 

[xpell]

Thank you very very much again, Astronuc. That is exactly what I needed to know.

I'll take a look at the document cited, but please realize, there is nothing conventional about applying Earth based technology to the Venusian environment.

Well, it seems to be a NASA or NASA-affiliated idea, originally based on one of several Soviet concepts for a "Venerakhod", so I lend it some credence, but sure you'll be able to discern it better than me:

https://www.researchgate.net/publication/223235013_Venus_surface_power_and_cooling_systems

https://www.researchgate.net/publication/268569312_Venus_Rover_Design_Study

In "my" idea, an RTG-based system like this would be used to protect the electronics and other thermally fragile components of the reactor during descent, landing and set up / start up. Afterwards, the reactor itself would provide the electricity for cooling what needs to be cooled, with this other system as a backup. And once we have an operational reactor cooling things there, we can then send a second unit that doesn't need to be so ruggedized for temperature. Etc. Or something like that.

 

[hmmm27]

Why not (research/)build equipment that operates comfortably in that environs ?

 

[PeterDonis]

Why not (research/)build equipment that operates comfortably in that environs ?

If you think it's that easy, then go ahead and do it.

People who have researched it know that it's not easy, it's very hard.

 

[Astronuc]

In "my" idea, an RTG-based system like this would be used to protect the electronics and other thermally fragile components of the reactor during descent, landing and set up / start up. Afterwards, the reactor itself would provide the electricity for cooling what needs to be cooled, with this other system as a backup. And once we have an operational reactor cooling things there, we can then send a second unit that doesn't need to be so ruggedized for temperature.

What does it mean to be 'cooled' with respect to 'thermally fragile' components?

Consider that the atmosphere at the surface is at a temperature of about 470°C (878°F)! One may wish to study the refrigeration cycle and 'coefficient of performance' (COP). Cooling to room temperature means reducing the temperature to 25°C, or a reduction of 445°C, which is huge compared to conventional refrigeration.

Also, consider the pressure at the surface, "the pressure is 93 bar (1,350 psi), roughly the pressure found 900 m (3,000 ft) underwater on Earth."
https://en.wikipedia.org/wiki/Atmosphere_of_Venus

We would need to develop some high temperature electronics, which is an intriguing challenge. Otherwise, it might be feasible to land a craft with a 'cold reservoir' on the surface for a short period, e.g., 1 hour or 2 hours (based on Venera) and then launch it again.

Edit/update: NASA Glenn is looking at materials issues for a lander on Venus.
Experimental Study of Structural Materials for Prolonged Venus Surface Exploration Missions
Published Online:22 Oct 2020 - https://arc.aiaa.org/doi/10.2514/1.A34617

 

[x_engineer]

You should look at GE work on using supercritical CO2 as the working fluid of high temperature heat engines for power generation.

(I also participated in the HeroX competition for a clockwork rover for Venus, and ran across the GE work)