Iran, state of nuclear technology, scientific clarification - pp.1

[epenguin]

I would like to ask for scientific clarification on a less commented part of Iran's nuclear technology preparations. It is fine for us to do the politics here as well, but that is also discussed in lots of places. This site is particularly suitable for scientific/technological background you don't get elsewhere.

I remember being shocked reading how President Truman asked for the arguments about the use first ever use of nuclear weapons on one page, I think one side, of paper.

But faced with all there has been on Iran and nuclear technology here, which I have far from all read, I do see advantages in having it all on one page!

About Uranium enrichment I have more or less formed some picture. As fuzzy on the state of things as anyone's but a picture of the issues, to judge new announcements as they come along. To judge where people are coming from when they say the things they do.

Less talked about than Uranium enrichment was something I think about heavy water which has to do I think with Plutonium. A particular plant was mentioned at least in the news.

I have forgotten more than I remember e.g. I went through all the UNSC Resolutions. For the specific technologies you had to wade through annexes or documents cited by the Resolutions.

But it was said in the newspapers that one or more plants had no convincing non-military rationale. Specific technologies or materials were I remember mentioned in the Resolutions.

This is an invitation to explain (on less than a page) the nitty gritty about these things. What they mean, what is known, the rationale of the sanctions.

Not the politics, not the Ahmadejin is a much misunderstood and mistranslated guy, not the Israel has one too, not the human rights and elections in Iran.

We can get onto subjects arising later or elsewhere.

 

[russ_watters]

There aren't any specific questions in that post and the "request to explain" is exceedingly broad and most certainly covers both technical and political issues. Let's see if we can boil it down to a few keys, which I was thinking of bringing up myself:

1. What evidence has no (or at least a weak) non-military rationale? In particular, the new evidence was what I was going to bring up.
2. What are the stated violatons of the NPT that have the UNSC and IAEA after Iran?

I'm running out right now, but I can probably discuss some of them myself later.

...have you read through the wiki on this...?

 

[Astronuc]

I think epenguin is asking about the technical aspects of Iran's program that would point more to military than commercial applications of a nuclear program.

With respect to enrichment, it has to do with the number of centrifuges and how the cascades are configured. A commercial plant would have to produce on the order of 100 MTU/yr of enriched U (at 3-5% U-235). If a plant is only producing 100's of kgU per year, and if the centrifuges are configured for enrichments > 70%, then it's definitely a weapons program.

One can asked - does Iran have an operating commercial power plant? If not, why would they need an enrichment program? They can buy commercial fuel from US, EU, Russian, China, Korea, Japan, . . . . If they build enough plants - e.g. a dozen or so, then they could justify a small nuclear fuel fabrication plant. That's how all the other countries started out.

As for Heavy Water - that's used in a heavy water reactor, e.g. CANDU with natural or low enriched fuel. In addition, the neutron flux is harder which is beneficial for producing Pu-239 form U-238, and low enrichment is good from the standpoint of producing less U-236. CANDU's run fuel to low burnups, which means less Pu-240, Pu-241 and other transuranics in the Pu.

For a nuclear weapon, one wants as pure Pu-239 as possible.

 

[kyleb]

1. What evidence has no (or at least a weak) non-military rationale?

Is there anything in the NPT which makes this question relevant?

2. What are the stated violatons of the NPT that have the UNSC and IAEA after Iran?

From what I've seen, the UNSC is not declaring any violations of the NPT, and the IAEA has simply be doing their job to investigate the possibility of any, which their head recently stated he has found no evidence of anything of the sort, http://www.reuters.com/article/worldNews/idUSL312024420090703":

The incoming head of the U.N. nuclear watchdog said on Friday he did not see any hard evidence Iran was trying to gain the ability to develop nuclear arms.

"I don't see any evidence in IAEA official documents about this," Yukiya Amano told Reuters in his first direct comment on Iran's atomic program since his election, when asked whether he believed Tehran was seeking nuclear weapons capability.

So, what violations were you insinuating?

...for enrichments > 70%, then it's definitely a weapons program.
...

For a nuclear weapon, one wants as pure Pu-239 as possible.

Highly enriched uranium and Pu-239 both have legitimate peaceful applications as fuel sources as well. It seems that your argument is along the lines of "as baseball bats can have been used to assault people, so acquiring baseball bats makes one a suspect of planning an assault". Or am I missing something in your argument that makes it anything but a guilty until proven innocent one?

Besides, your arguments seem to ignore the fact that http://www.nytimes.com/2006/04/06/opinion/06zarif.html?_r=2&scp=1&sq=zarif&st=cse", notably including:

• Refrain from reprocessing or producing plutonium;

• Limit the enrichment of nuclear materials so that they are suitable for energy production but not for weaponry;

• Immediately convert all enriched uranium to fuel rods, thereby precluding the possibility of further enrichment;

So, I'm left to wonder if concerns to the contrary have any more substance than Colin Powell's concerns of "mobile WMD labs" in Iraq, and seem to have much the same crowd backing them despite how poorly such claims turned out previously. Am I missing something here?

 

[Count Iblis]

Less talked about than Uranium enrichment was something I think about heavy water which has to do I think with Plutonium. A particular plant was mentioned at least in the news.

I think you mean the Arak nuclear plant. I'm not sure if that plant can produce the Pu-239 that Astronuc mentioned.

Astronuc wrote:

One can ask - does Iran have an operating commercial power plant? If not, why would they need an enrichment program?

Because they would want to make sure they can produce the fuel for the powerplants they want to build in the future first.

They can buy commercial fuel from US, EU, Russian, China, Korea, Japan, . . . .

They can't. A deal has been proposed under which Iran would have to sign away their right to produce their own fuel (close the Natanz facility, allow for more inspections etc.) and then in return the US would lift their policy of imposing sanctions on companies that deal with Iran on nuclear matters.

But such a deal (involving also other economic incentives) would be a severe violation of Iran's sovereignity, so it is a non-starter.

 

[Astronuc]

Highly enriched uranium and Pu-239 both have legitimate peaceful applications as fuel sources as well. It seems that your argument is along the lines of "as baseball bats can have been used to assault people, so acquiring baseball bats makes one a suspect of planning an assault". Or am I missing something in your argument that makes it anything but a guilty until proven innocent one?

What legitimate uses would that be?

Research reactors, e.g., TRIGA fuel used to be highly enriched, but such has been replaced with much lower enrichements.

If they are so innocent - then let the Iranians provide detailed records and allow surveillance and auditing of the material as appropriate.

 

[Astronuc]

Because they would want to make sure they can produce the fuel for the powerplants they want to build in the future first.

That's rather spurious.

They can't. A deal has been proposed under which Iran would have to sign away their right to produce their own fuel (close the Natanz facility, allow for more inspections etc.) and then in return the US would lift their policy of imposing sanctions on companies that deal with Iran on nuclear matters.

But such a deal (involving also other economic incentives) would be a severe violation of Iran's sovereignity, so it is a non-starter.

As far as I know the Russians are helping with the Bushehr VVER-1000 type reactor for which the Russians can supply fuel.

 

[Count Iblis]

If they are so innocent - then let the Iranians provide detailed records and allow surveillance and auditing of the material as appropriate.

Iran has already been told to stop enriching uranium by the UNSC and because they refused, sanctions have been imposed. So, I don't think it would be a good strategy for Iran to fully cooporate with the demands for more inspections than they are obliged to admit under the basic NPT rules.

Surely, you would offer to cooporate better with the IAEA on those extra points that are a result from the UNSC resolutions against you and are not part of the regular NPT regime, only in exchange for the West recognizing your right to produce your own fuel?

 

[Astronuc]

Iran has already been told to stop enriching uranium by the UNSC and because they refused, sanctions have been imposed. So, I don't think it would be a good strategy for Iran to fully cooporate with the demands for more inspections than they are obliged to admit under the basic NPT rules.

Surely, you would offer to cooporate better with the IAEA on those extra points that are a result from the UNSC resolutions against you and are not part of the regular NPT regime, only in exchange for the West recognizing your right to produce your own fuel?

I expect the nuclear program in Iran to be treated as any program anywhere in the world, including the US. Detailed records of the process are maintained and audited, and I've audited nuclear fuel fabrication in the US during which I checked enrichments and mass of U in the process. Others do a more detailed assessment as part of special nuclear material accountability.

 

[kyleb]

What legitimate uses would that be?

Again, as fuel, as such substances are used in many applications, http://www.nti.org/db/heu/civilian.html" .

If they are so innocent - then let the Iranians provide detailed records and allow surveillance and auditing of the material as appropriate.

If that is the standard by which we should be disputing innocence, then surely we should acknowledge that Iran has been far more forthcoming with their nuclear efforts than say, Israel, eh?

 

[Count Iblis]

As far as I know the Russians are helping with the Bushehr VVER-1000 type reactor for which the Russians can supply fuel.

Yes, and this had, since the 1990s, been a point of discussion between the US an Russia. Only a few years ago did the US stop pressuring Russia over this. But many other contracts Iran wanted to pursue under the NPT were blocked by US pressure, and that led to Iran's technical violations of the NPT in the first place.

Anyway, I think that the dispute is much more about distrust on both sides, also about sovereign rights etc. etc. Technical nuclear matters are not the main reason why this dispute exists.

 

[Astronuc]

Again, as fuel, as such substances are used in many applications, http://www.nti.org/db/heu/civilian.html" .

Those applications refer to enrichments of about 20%. My earlier post referred to enrichments above 70% for U-235 and as pure as possible Pu-239, which are not necessary for research reactors, medical isotope production reactors or naval cores. I'm not aware that Iran needs nuclear-powered, nor even conventional, ice-breakers.

Australia has a medical isotope reactor - but they do not make the fuel.

While vitually every reactor is unique, OPAL is one of a number of similar production facilities around the world, including the Safari-1 reactor in South Africa, the HFR nuclear reactor at Petten in the Netherlands and the NRU reactor at Chalk River in Canada. OPAL's operation staff cooperate with their international colleagues in sharing information and knowledge both directly through formal collaboration agreements and via various international organisations and forums.
. . .
The heart of the reactor is a compact core of 16 fuel assemblies arranged in a 4x4 array, with five control rods controlling the reactor power. OPAL uses low enriched uranium fuel with just under 20 per cent uranium-235. In terms of security and nuclear safeguards, this is a distinct advantage over earlier research reactors; some of which required as much as 95 per cent enriched uranium (weapons grade).

http://www.ansto.gov.au/discovering_ansto/anstos_research_reactor

Fast reactors use about 20% Pu in MOX fuel for the driver fuel.

I have only addressed the technical concerns. I have not made any claims about the intent if the Iranian program.

If that is the standard by which we should be disputing innocence, then surely we should acknowledge that Iran has been far more forthcoming with their nuclear efforts than say, Israel, eh?

Yes - the west has been tougher on Iran than Israel, and Israel should be held to the same standard. But then again, Israel's leaders have not been calling for Iran to wiped-off the face of the earth, although I'm sure they'd like to get rid of Ahmedinejad.

 

[Astronuc]

Anyway, I think that the dispute is much more about distrust on both sides, also about sovereign rights etc. etc. Technical nuclear matters are not the main reason why this dispute exists.

Yes - there is conflict between Iran and west over political and policy issues. However, I believe the OP was querying about the technical aspects of Iran's program and the potential implications.

 

[epenguin]

As for Heavy Water - that's used in a heavy water reactor, e.g. CANDU with natural or low enriched fuel. In addition, the neutron flux is harder which is beneficial for producing Pu-239 form U-238, and low enrichment is good from the standpoint of producing less U-236. CANDU's run fuel to low burnups, which means less Pu-240, Pu-241 and other transuranics in the Pu.

For a nuclear weapon, one wants as pure Pu-239 as possible.

Thank you. It was that last bit I was asking for a rundown on. The Pu.

Most comment is about U enrichment. Iranians saying this is only for civil purposes, the other side saying they are not permitting the inspections under the NPT by IEAE that would guarantee they are not making the material for a nuclear weapon.

I.e. it could be civil only but is it? (And shouldn't it be guaranteed that it is under the NPT by inspections etc,? This has been extensively discussed also here and I know what I think.)

I read the Pu sites and programme on the other hand could not be civil only, not plausibly.

No nuclear physicist or technologist I would be glad of a guide and discussion of that. What are they known, thought, or suspected to be doing and how much of a worry of a route to a nuclear bomb there, how immediate, how likely, how easy etc. (rather than the political evaluations of e.g. post below)?

 

[kyleb]

Those applications refer to enrichments of about 20%.

Rather, it refers to enrichments "over 20%" and all the way up to "96% enriched fuel".

My earlier post referred to enrichments above 70% for U-235 and as pure as possible Pu-239, which are not necessary for research reactors, medical isotope production reactors or naval cores.

Yet such materials can be used for all three. Besides, are your arguments here based on any proof Iran doing anything of the sort, or are they simply speculative?

I'm not aware that Iran needs nuclear-powered, nor even conventional, ice-breakers.

Not that I suggested they did, but if they ever wanted to start competing more seriously in the international shipping market, the ability to produce their own nuclear-powered ice-breakers would be a plus.

Australia has a medical isotope reactor - but they do not make the fuel.

Well perhaps Iran could someday give them a better deal on what they buy.

...Israel's leaders have not been calling for Iran to wiped-off the face of the earth...

Rather, http://www.bbc.co.uk/blogs/theeditors/2007/03/wiped_off_the_map.html" .

 

[Astronuc]

Rather, it refers to enrichments "over 20%" and all the way up to "96% enriched fuel".

One will notice the discussion in the link to NTI addresses their efforts to reduce the use of HEU with LEU fuels. Please provide an example of civilian use of fissile material up to 96% enrichment.

A number of these reactors use fuel with a very high enrichment level, around 90% U-235, while many now use fuel enriched to about 36%. The amount of fuel the reactors require also varies dramatically, from just 1 kg in Miniature Neutron Source Reactors, to about 10 kg per year in many pool reactors, to over 100 kg per year in some of the most powerful reactors. Some of these reactors also have stocks of fresh and spent fuel on site, which makes them a potentially attractive target for thieves and terrorists seeking access to weapons-useable nuclear materials.

Since the late 1970s, efforts to convert research reactors to LEU fuel have developed new fuels and have reconfigured some reactors to minimize losses in neutron flux, and in some cases to even increase the flux.[2] As discussed on the "Past and Current Efforts to Reduce Civilian HEU Use" page, the United States, Russia, and other countries are working to develop higher density LEU fuels that could substitute for HEU fuels in existing research reactors. Several types of replacement LEU fuels have been developed already. Uranium-silicide fuel developed in the 1980s has a uranium density sufficient to convert the vast majority of reactors. Uranium-molybdenum (U-Mo) fuels with very high uranium densities are currently under development and testing and could potentially replace HEU fuel in the remaining reactors. Once development of U-Mo fuel is complete, and it has been licensed and put into production, virtually all present and future civil research reactors can be converted to LEU. Approval of U-Mo fuel currently is expected in 2010. This new LEU fuel will offer "unprecedented performance" that exceeds what could previously be achieved with HEU.[3] [For an additional briefing on research reactors, see "Highly enriched uranium in research reactors," prepared by the organizers of the June 2006 Oslo Symposium on Minimization of HEU in the Civilian Nuclear Sector.]

Yet such materials can be used for all three. Besides, are your arguments here based on any proof Iran doing anything of the sort, or are they simply speculative?

I'm not arguing that Iran is doing anthing specifically. Please don't attribute such statements to me.

Not that I suggested they did, but if they ever wanted to start competing more seriously in the international shipping market, the ability to produce their own nuclear-powered ice-breakers would be a plus.

One linked to an article that provided 3 main uses of HEU for civilian use, of which nuclear marine propulsion was one. I addressed each use and indicated that HEU is not necessary. As far as I know, Iran doesn't have much of a shipbuilding industry, and developing an ice-breaker is a very specialized area. There is a lot more infrastructure necessary for a shipbuilding industry.

Well perhaps Iran could someday give them a better deal on what they buy.

Sure.

Rather, http://www.bbc.co.uk/blogs/theeditors/2007/03/wiped_off_the_map.html" .

Rather

Mr Ahmadinejad told some 3,000 students in Tehran that Israel's establishment had been a move by the West against the Islamic world.

He was addressing a conference entitled The World without Zionism and his comments were reported by the Iranian state news agency Irna.

"As the Imam said, Israel must be wiped off the map," he said, referring to Iran's late revolutionary leader, Ayatollah Ruhollah Khomeini.
http://news.bbc.co.uk/2/hi/middle_east/4378948.stm

Besides the topic of discussion is "Iran, state of nuclear technology, scientific clarification", so please don't interject politics. If one wants to discuss the politics, then start a different thread.

 

[Astronuc]

No nuclear physicist or technologist I would be glad of a guide and discussion of that. What are they known, thought, or suspected to be doing and how much of a worry of a route to a nuclear bomb there, how immediate, how likely, how easy etc. (rather than the political evaluations of e.g. post below)?

I think Paul Reynolds, BBC World Affairs correspondent, put it well:
"Iranian ambitions for this site are not known. It could be that they wanted a back-up in case their main plant at Natanz was attacked. But another fear is that they intended to enrich uranium more highly at the secret plant, to a level suitable for a nuclear explosion."
http://news.bbc.co.uk/2/hi/middle_east/8274903.stm

Because of the lack of transparency and forthrightness, the intentions of Iran's program are not known. A nuclear enrichment program can be dual use. There are certainly legitimate reasons to enrich uranium or produce Pu-239/241. But high levels of fissile material (>90% U-235 or Pu-239) can be used to make nuclear weapons.

In the west, commercial nuclear power plants use up to 5% enrichment in the fuel, which is in the form of UO₂. Such fuel would be used in the Bushehr VVER.

Highly enriched uranium is used in special types of research reactors, especially those which are compact, use little uranium, and use a lot of other material which absorbs neutrons, e.g., radionuclide (medical isotope) production.

Pu is normally used in MOX fuel in commercial nuclear plants, where it is enriched to about 6-8% Pu (mix of 239, 240, 241) with some Am isotopes. The Pu comes from reprocessed LWR fuel. Fast reactors, like Phenix or BOR-350/600/800 use MOX with about 20-30% fissile Pu.
http://www.insc.anl.gov/cgi-bin/sql_interface?view=rx_model&qvar=id&qval=12

http://www.world-nuclear.org/info/inf98.html

Enrichment can be reduced by using fuel materials with higher atom density.

 

[kyleb]

One will notice the discussion in the link to NTI addresses their efforts to reduce the use of HEU with LEU fuels.

I did notice that, but it does nothing to change the fact there are various applications in which HEU has and can be used for peaceful purposes, of which NTI provides multiple examples of.

Please provide an example of civilian use of fissile material up to 96% enrichment.

I said peaceful use. It was the Soviet government which used it for propulsion in space. To quote it here directly:

HEU USE FOR SPACE PROPULSION

HEU has also been used by the Soviet Union and the United States for space propulsion. Fission reactors (with HEU cores) have been used to power satellites in Earth orbit. Such reactors were used extensively during the Cold War by the USSR to power their Radar Ocean Reconnaissance Satellites (RORSATs). Notably, these reactors used 90% enriched HEU fuel. A second-generation TOPAZ reactor was also built (using 96% enriched fuel) and flown by the Soviet Union, although none are currently in operation.

So, there is one of many examples of very highly enriched fuel proving useful for peaceful purposes.

I'm not arguing that Iran is doing anthing specifically. Please don't attribute such statements to me.

You are taking about < 70% urianium enrichment and pultonum production, and my question is if Iran is currently working on either. Again, are your comments on such based on any evidence Iran doing as much, or are they purely speculative? I'll skip over the rest of the arguments in regard to such matierals for now as they have yet to be demonstarted as having any relevance here.

Besides the topic of discussion is "Iran, state of nuclear technology, scientific clarification", so please don't interject politics. If one wants to discuss the politics, then start a different thread.

I was not looking to discuss such political issues in this thread, but rather I was responding to your "wiped-off the face of the earth" argument. As back when that contrvesy started I looked though quotes of the original Farsi presented along with literal meanings of each word, and along with the context of the speech; and from that experience I see no reason to believe Ahmadinejad's statement suggested anything like what you claimed it did, and rather what I stated and quoted previously.

Put simply; the piecemeal quote of unsubstantiated translation you provided comes a long way from proving your claim. Surely if one makes a such a political argument in any thread, another should be free to contest it there? Granted, I do agree that if you want to attempt to substantiate your argument, the discussion would be best moved to a separate thread, but I doubt that you would maintain your argument after looking into the literal translation of the statement along with the context it was presented in.

 

[Astronuc]

I did notice that, but it does nothing to change the fact there are various applications in which HEU has and can be used for peaceful purposes, of which NTI provides multiple examples of.

I said peaceful use. It was the Soviet government which used it for propulsion in space. To quote it here directly:

So, there is one of many examples of very highly enriched fuel proving useful for peaceful purposes.

You are taking about < 70% urianium enrichment and pultonum production, and my question is if Iran is currently working on either. Again, are your comments on such based on any evidence Iran doing as much, or are they purely speculative? I'll skip over the rest of the arguments in regard to such matierals for now as they have yet to be demonstarted as having any relevance here.

I'm familiar with TOPAZ. The material (highly enriched uranium) came from the Soviet Union's nuclear weapons program.

Highly enriched U or Pu is dual use technology. It can be used for peaceful uses, e.g. compact cores for spacecraft propulsion or for military purposes such as nuclear weapons. Compact cores are desirable in order to minimize mass, which is desirable for reducing times in orbital transfer, or highly maneuverable satellites. As I understand them, the RORSATS were part of the Russian Navy's reconnaisance, surveillance and targeting system with the goal of tracking US naval vessels and targeting them for cruise or ballistic missiles. Not exactly a peaceful/civilian type use.

Commercial power reactors can use natural uranium (e.g., CANDU) or LEU (< 5%) in commercial LWRs. Anything about 5% would be viewed with suspicion, especially given the secretive nature of Iran's program. It is precisely the secretive nature and lack of disclosure by Iran that has the US, EU and others concerned about the actual nature of Iran's program.

HEU is really impractical for a power reactor. And certainly something like 90% Pu-239, and especially 96% Pu-239, is exceedingly impractical for a terrestrial based power reactor given the smaller delayed neutron fraction as compared to U-235. Even fast reactors tend to use on the order of 20% Pu-239 in MOX fuel.

Of course, naval cores use HEU, but they are designed for a longer lifetime before replacement than civilian reactors.

 

[WhoWee]

I'm familiar with TOPAZ. The material (highly enriched uranium) came from the Soviet Union's nuclear weapons program.

Highly enriched U or Pu is dual use technology. It can be used for peaceful uses, e.g. compact cores for spacecraft propulsion or for military purposes such as nuclear weapons. Compact cores are desirable in order to minimize mass, which is desirable for reducing times in orbital transfer, or highly maneuverable satellites. As I understand them, the RORSATS were part of the Russian Navy's reconnaisance, surveillance and targeting system with the goal of tracking US naval vessels and targeting them for cruise or ballistic missiles. Not exactly a peaceful/civilian type use.

Commercial power reactors can use natural uranium (e.g., CANDU) or LEU (< 5%) in commercial LWRs. Anything about 5% would be viewed with suspicion, especially given the secretive nature of Iran's program. It is precisely the secretive nature and lack of disclosure by Iran that has the US, EU and others concerned about the actual nature of Iran's program.

HEU is really impractical for a power reactor. And certainly something like 90% Pu-239, and especially 96% Pu-239, is exceedingly impractical for a terrestrial based power reactor given the smaller delayed neutron fraction as compared to U-235. Even fast reactors tend to use on the order of 20% Pu-239 in MOX fuel.

Of course, naval cores use HEU, but they are designed for a longer lifetime before replacement than civilian reactors.

Astronuc, it's a little off topic, but could you elaborate a little on the challenges and logistics of cooling with regards to a compact core for spacecraft propulsion - my imagination is running wild.

 

[Astronuc]

Cooling requires surface area in the reactor, and ultimately in space (waste heat) via a radiator. The size of the radiator is a function of temperature, T⁴, so to minimize the radiator area (and mass) one wants to make it as hot as poosible. BUT, making the radiator hot means the thermal efficiency of the thermomechanical cycle is diminished. So in designing a space nuclear power system for use in space, i.e. not on a planet or planetoid, one has to trade off the radiator against the thermodynamic cycle efficiency.

There were some rather interesting radiator designs, including a droplet type in which droplets would issue from a hot manifold and then collected in a cold sides manifold. The droplets could be guided by a magnetic fluid (if they use a ferrofluid) so that if there were any lateral acceleration, the droplets wouldn't escape. The planes of the radiators had to be aligned away from the sun (plane normal tangent to a solar orbit) as much as possible so they did not receive radiation (heat) from the sun.

Another challenge is the operating temperature of the reactor. In order for the reactor to maintain it's geometry, the peak temperatures are constrained to some maximum level (usually related to dimensional stability, e.g. material creep or swelling). The peak temperature is tied to the power density and heat flux. From a thermodynamic efficiency aspect, one wants to maximize core temperature, subject to the constraint of material and structural stability.

From a neutronics standpoint, the higher the enrichment and the smaller the core, the potentially less stable (controllable) the reactor becomes. In addition, there is also the excess fissile material that must be present to accommodate that which is consumed while still maintaining criticality. Unlike chemical fuel, fissile fuel is in place and not feed into the core - in most reactor designs. One could feed in a fluoride compound into a core, but that opens up the issue of fission products being expelled in the vicinity of the spacecraft and any nearby planet (would be problem for other orbiting craft), moon or asteroid.

Compact cores for propulsion and high power systems are rather challenging, but certainly some of the most interesting work one would do as a nuclear engineer.

I did one concept of using cryogenic propellant as a heat sink in order to minimize radiator/system mass.

Compact cores of high power are also dual use technology.


In the above discussion, I was addressing primarily closed-loop cycles/systems, which provide the bases for electric power systems. Nuclear propulsion can also be achieved by forcing propellant - usually hydrogen - through a very hot nuclear core. In this case there is no radiator because the cryogenic propellant draws all the heat from the core. However, due to high mass flow rates, such impulsive propulsive systems are used for a few days then shut off while a spacecraft coasts through most of the orbital transfer. The core sizing is a balancing act based on maximizing temperatures, accomodating the propellant flow through the core, and the thermo-mechanical constraints, control and reliability/safety of the nuclear systems.

A really great book on the subject is:
To the End of the Solar System: The Story of the Nuclear Rocket [ILLUSTRATED] (Hardcover)
https://www.amazon.com/dp/0813122678/?tag=pfamazon01-20
by James A. Dewar

The motivation behind the nuclear propulsion was to develop a means to achieve heavy lift for ballistic missiles - back when thermonuclear weapons were very heavy. Miniturization helped reduced the mass and size of nuclear warheads to the point where conventional chemical rockets were sufficient to deliver warheads. At that point, folks started to look for other missions for nuclear rockets.

Dewar is a really great guy. Unfortunately, I didn't have my copy of his book with me when I met him. The price of the hardcopy would seem to indicate a limited supply. I think I paid half or a third the listed price when it first came out, and I probably pre-ordered it.

 

[kyleb]

It is precisely the secretive nature and lack of disclosure by Iran that has the US, EU and others concerned about the actual nature of Iran's program.

From what I've seen, Israel is the state most concerned about Iran's nuclear program, with the rest expressing various levels of interest in following that lead. So, why do you figure Israel is held to a different standard? You had mentioned the "wiped off the map" thing, but again that is just http://www.huffingtonpost.com/sam-sedaei/the-biggest-lie-told-to-t_b_70248.html" , regardless of the lack of any hard evidence of any ongoing efforts towards nuclear weapons production.

Considering the situation, it seems understandable that Iran would be hesitant to disclose their nuclear efforts, be they merely peaceful other otherwise. Also, imagining myself in their shoes, the increasing pressure would only make me more interested in pursuing nuclear weapons, simply to achieve the deterrence provided though MAD.

HEU is really impractical for a power reactor. And certainly something like 90% Pu-239, and especially 96% Pu-239, is exceedingly impractical for a terrestrial based power reactor given the smaller delayed neutron fraction as compared to U-235.

But again, there isn't any evidence of Iran perusing anything close to such grades of muscular fuel, is there?

 

[mheslep]

...regardless of the lack of any hard evidence of any ongoing efforts towards nuclear weapons production. ...

What would you consider hard evidence of a weapons program, if we assume a state is trying to hide the program?

 

[Count Iblis]

It is very clear that there isn't a shred of evidence for an existing Iranian weapons program. The current diplomatic approach of the West proves this. There is no way the US would demand anything less than an immediate suspension of all enrichment activities if the US was worried about an existing Iranian weapons program.

What the West is worried about is simply that Iran could produce nuclear weapons in the future. But the old Bush line of Iran not having the right to an industrial scale enrichment capacity has been abandoned. The UNSC resolutions formally do ask iran to stop enriching uranium, but further measures to enforce that resolution have been put on hold.

 

[mheslep]

...There is no way the US would demand anything less than an immediate suspension of all enrichment activities ...

UN SC Resolution 1737 from 2006, which has been posted again, and again, and again in these Iranian nuclear program threads:

[The Security Council] Acting under Article 41 of Chapter VII of the Charter of the United Nations
[...]
2. Decides, in this context, that Iran shall without further delay suspend the
following proliferation sensitive nuclear activities:
(a) all enrichment-related and reprocessing activities, including research and development, to be verified by the IAEA;

http://www.iaea.org/NewsCenter/Focus/IaeaIran/unsc_res1737-2006.pdf

 

[Count Iblis]

UN SC Resolution 1737 from 2006, which has been posted again, and again, and again in these Iranian nuclear program threads:

http://www.iaea.org/NewsCenter/Focus/IaeaIran/unsc_res1737-2006.pdf

Which was adopted while Bush was in power. Iran has rejected this as illegal and the World has now appeased Iran in their refusal to implement this UN resolution.

Iran is now not required by the West to immediately suspend their uranium enrichment program, despite it being formally illegal under UNSC resolutions.

My point is that given that the West is now not insisting that Iran suspend their enrichment program, we can conclude that the Western intelligence services do not have even a shred of evidence that Iran has a nuclear weapons program.

 

[mheslep]

Which was adopted while Bush was in power. Iran has rejected this as illegal and the World has now appeased Iran in their refusal to implement this UN resolution.

Iran is now not required by the West to immediately suspend their uranium enrichment program, despite it being formally illegal under UNSC resolutions.

Yes it is now 'formally illegal' because ... the US is the great Satan? Because you say so?

My point is that given that the West is now not insisting that Iran suspend their enrichment program, we can conclude that the Western intelligence services do not have even a shred of evidence that Iran has a nuclear weapons program.

Feel free to post an actual source for all these claims when ever you feel like it.

 

[Evo]

Locked pending moderation.