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Quaoar

Member

Registered: 2013-12-13

Posts: 665

INsTAR: the new Timberwind

Based of a 1970 design of James Powell, Timberwind was a high innovative partice bed NTR: it had T/W ratio of about 30, very high for a NTR, and a specific impulse of about 1000 s, higher than the 800 s of NERVA.

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

It also had some flaws: the random path of hydrogen between the particles creates hot spots where temperature went beyond the melting point of fuel cladding melting, so particles welded each other and damaged the frits, resulting a single-use engine.

Recently the old Timberwind was revisited and its flaws were addressed and solved with modern software simulation tools:

http://anstd.ans.org/NETS-2019-Papers/T … -130-0.pdf

The new design uses low enriched uranium particles with a diameter of 2 mm, with a core of 12% enriched uranium metal coated with a 0.2 mm thick alloy composed by 90% of tungsten 184, 5% of natural tungsten and 5% of rhenium. Each element is formed by particles arranged in hexagonal close packing (avoiding the random flow path of the old Timberwind) inside graphite frits and surrounded by an hexagonal graphite moderator. There are 37 elements surrounded by a beryllium reflector with six control drums. The whole core has a diameter of 140 cm and a length of 150 cm.

It has a chamber pressure of 69 bar (which may suggest that the turbopumps and the machinery comes from the old RL-10 like the old NERVA), a core exit temperature of 3300 K, a mass flow of 25.15 kg/s, a predicted exhaust velocity of 10.61 km/s, a thrust of 269 kN, a total mass of 2900 kg and a T/W ratio of 9.46 (3 with an external shield of 6000 kg for a crewed spaceship).

Last edited by Quaoar (2022-04-04 09:22:26)

tahanson43206

Moderator

Registered: 2018-04-27

Posts: 19,405

Re: INsTAR: the new Timberwind

For Quaoar re new topic...

Thanks for this update!  it looks important, and worth keeping this topic updated.

Out of curiosity, since you would have considered the four existing related topics before creating this new one, how does the INsTAR initiative compare to these?

Nuclear Pulse Propulsion starship. by Rune
Interplanetary transportation    16    2022-02-21 12:34:35 by SpaceNut

Nuclear Thermal Propulsion Module by Oldfart1939
Interplanetary transportation    1    2022-02-12 19:11:05 by Oldfart1939

A revival of interest in Nuclear Thermal Propulsion? by Oldfart1939 [ 1 2 3 ]
Interplanetary transportation    57    2021-12-18 09:34:39 by Mars_B4_Moon

Nuclear Ion Propulsion by Antius [ 1 2 ]
Interplanetary transportation    28    2021-12-11 13:52:35 by Mars_B4_Moon

Thanks again for the update!

(th)

Quaoar

Member

Registered: 2013-12-13

Posts: 665

Re: INsTAR: the new Timberwind

For Quaoar re new topic...

Thanks for this update!  it looks important, and worth keeping this topic updated.

Out of curiosity, since you would have considered the four existing related topics before creating this new one, how does the INsTAR initiative compare to these?

Nuclear Pulse Propulsion starship. by Rune
Interplanetary transportation    16    2022-02-21 12:34:35 by SpaceNut

Nuclear Thermal Propulsion Module by Oldfart1939
Interplanetary transportation    1    2022-02-12 19:11:05 by Oldfart1939

A revival of interest in Nuclear Thermal Propulsion? by Oldfart1939 [ 1 2 3 ]
Interplanetary transportation    57    2021-12-18 09:34:39 by Mars_B4_Moon

Nuclear Ion Propulsion by Antius [ 1 2 ]
Interplanetary transportation    28    2021-12-11 13:52:35 by Mars_B4_Moon

Thanks again for the update!

(th)

Probably in this: A revival of interest in Nuclear Thermal Propulsion? by Oldfart1939

What is very interesting is the use of LEU, that can be  managed even by private company like SpaceX

Calliban

Member

From: Northern England, UK

Registered: 2019-08-18

Posts: 3,793

Re: INsTAR: the new Timberwind

One of the difficulties of NTR is maintaining an even fission rate across the core.  To get the best power density and coolant temperature, you want the same heat generation in every part of the core.  The neutron flux is a parabola.  If enrichment is uniform, fission rate and heat generation will be a function of local flux.  The burn up of the fuel will also be uneven.  You can deal with that by altering local enrichment or using burnable poisons.

Tungsten is a good cladding material, as it retains strength at high temperature.  The problem is it also has a high absorption cross section, which pushes up the required enrichment level.  By encasing the fissile fuel in discrete tungsten spheres, the designer must accept limits on the burn up of the fuel and power density.  Beyond a certain burn up, the fission gases will burst the cladding.  The need for heat transfer across the cladding, also limits power density.  The alternative is to put the Uranium particles within the graphite moderator and allow a large fraction of fission products to leak out.  That wouldn't be acceptable for Earth take off.  But it may be acceptable for purely orbital transfers.  Like Robert's large ship.

---

"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

Quaoar

Member

Registered: 2013-12-13

Posts: 665

Re: INsTAR: the new Timberwind

which pushes up the required enrichment level.  By encasing the fissile fuel in discrete tungsten spheres, the designer must accept limits on the burn up of the fuel and power density.  Beyond a certain burn up, the fission gases will burst the cladding.  The need for heat transfer across the cladding, also limits power density.  The alternative is to put the Uranium particles within the graphite moderator and allow a large fraction of fission products to leak out.  That wouldn't be acceptable for Earth take off.  But it may be acceptable for purely orbital transfers.  Like Robert's large ship.

That's the reason for using tungsten 184 instead of natural tungsten: W184 has a lower neutron cross section than natural tungsten (a mix of W180, W182, W183, W184 and W186) and and is mandatory for all the NTR made with low enriched uranium (even the canadian BWXT uses a W184-UO2 cermet for its LEU-NTR). The only drawback is that W184 can be obtained by centrifugation and is more expensive.

Last edited by Quaoar (2022-04-04 15:09:27)

Calliban

Member

From: Northern England, UK

Registered: 2019-08-18

Posts: 3,793

Re: INsTAR: the new Timberwind

For applications that are intended for use entirely in space, like Robert's large ship, thrust-weight ratios are less important.  In this situation, a NTR could be fuelled using vented tungsten clad fuel rods.  Uranium dioxide would allow fuel temperature up to 2800°C.  If kinetic impact Fusion can provide a source of neutrons, the rocket engine can be fuelled with natural Uranium and burn up can be taken as high as 20%.  The large ship would not likely need refuelling in a 30-year operating life.  The hydrogen propellant would be low pressure, with low number density.  This will have minimal effect on neutron energy.  As burn up increases, plutonium bred in the fuel will gradually increase its reactivity.  The frequency of Fusion pulses can be tapered down.

Last edited by Calliban (2022-04-05 12:42:10)

---

"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

Quaoar

Member

Registered: 2013-12-13

Posts: 665

Re: INsTAR: the new Timberwind

For applications that are intended for use entirely in space, like Robert's large ship, thrust-weight ratios are less important.  In this situation, a NTR could be fuelled using vented tungsten clad fuel rods.  Uranium dioxide would allow fuel temperature up to 2800°C.  If kinetic impact Fusion can provide a source of neutrons, the rocket engine can be fuelled with natural Uranium and burn up can be taken as high as 20%.  The large ship would not likely need refuelling in a 30-year operating life.  The hydrogen propellant would be low pressure, with low number density.  This will have minimal effect on neutron energy.  As burn up increases, plutonium bred in the fuel will gradually increase its reactivity.  The frequency of Fusion pulses can be tapered down.

Instar uses metallic uranium particles coated with W184: metallic uranium melts and become liquid inside the tungsten coating which operates at 3300 K.