Sunday, August 17, 2008

Two, Four Six, Eight, We Don't Want to Proliferate

Members of the British House of Commons have the right to submit questions to members of the Government . In 1992, Labor MP Bob Cryer ask the following question:
"To ask the Secretary of State for Foreign and Commonwealth Affairs what information he has about how North Korea was able to build a military grade plutonium production reactor outside international safeguards based on blueprints of the United Kingdom military magnox plants at Calder hall, Sellafield."

The British Foreign Secretary Mr. Douglas Hogg responded : "Technical information about the Magnox reactors at Calder hall, Sellafield has been in the public domain for over 25 years. We continue to urge the Democratic People's Republic of Korea to fulfil her obligations under the non-proliferation treaty and sign an agreement with the International Atomic Energy Agency which would place all of her nuclear facilities under safeguards".

The British government, in its great wisdom, allowed the blueprints of the Calder Hall Magnox Reactors to be declassified. The Magnox reactor was, after all, a primitive power generating reactor, that had been offered for sale to other countries. By the mid 1960's its design was dated.

But the Calder Hall Magnox Reactors were not just innocent power reactor, they were graphite reactors capable of burning natural uranium as fuel. Natural uranium burning required frequent fuel changes, but military planners knew that it the fuel change cycle was speeded up, the post reactor fuel would be an excellent source of reactor grade plutonium. The primary function of the Calder Hall Magnox Reactors was weapons grade plutonium production. Power production was an after thought.

During the 1950's and 1960's the militant British Coal Miners Union, was a thorn in the flesh of the British Government, the British Economy, and the British public. Electrical power generation in the UK was dependent of Coal mined by Union Miners, and thus the possibility existed that the British ability to generate electric power would be lost in the event of a long coal miners strike. Thus the British government proposed to give the Calder Hall Magnox Reactors the ability to generate electricity. The catch was that electricity produced by Calder Hall Magnox Reactors would be far more expensive than electricity produced by coal fired plants, but the British government had an answer to that. The real function of the Calder Hall reactors was the production of weapons grade plutonium. Thus the British built a series of Magnox reactors for dual purpose use.

By the mid 1960's Magnox reactors were technologically obsolete, and the British saw no reason to withhold the blueprints from the public. Thus anyone who could cough up the considerable blueprint copying fee, could obtain a copy of the Calder Hall blueprints for his or her personal use and pleasure. There was one tiny question about this British government decision. The Calder Hall Magnox Reactors were built for decidedly military purposes. They were relatively simple, and easily to duplicate, by nations which possessed a far less substantial knowledge and industrial base than the United Kingdom. The plans for the Calder Hall Magnox Reactors, were open to be stolen by soviet spies, and probably were. The Soviets in turn would have been in a position to pass on the Magnox plans to what they regarded as friendly countries. The Soviets might well have regarded the technologically unsophisticated Magnox as a perfect "nuclear research starter kit", for North Korea, exactly because building one was within North Korea's industrial and technological reach. It would, however, not been beyond the capacity of North Korea to obtain the Magnox plans without Soviet help.

The Magnox reactor is the ideal type reactor for the anti nuclear types, and indeed the Greenpeace script sounds as if every reactor is a Magnox . This is not true, and the North Koreans knew exactly what they were doing, when they decided to focus their nuclear weapons program on plutonium production from the Magnox type reactor.

Only two nuclear moderators have been ever been used for Weapons grade plutonium production. They are Graphite, and Heavy Water. All of the major nuclear powers appeared to have exclusively relied on graphite reactors for military Plutonium production. Israel and India have used heavy water reactors for the same purpose. Which ever type of reactor is used, the presence of the moderator allows natural Uranium to be used as a nuclear fuel. The fuel is burned for a relative short period of time in order to maximize the production of Pu-239. The longer the fuel stays in the reactor, the more other types of Plutonium - Pu-238, Pu-240, Pu-241, and Pu-242 - build up. From the stand point of the weapons designer, the creation of other forms of plutonium in a nuclear reactor is an highly undesirable development.

Pu-238 is just plain hot, in addition to being radioactive. Managing the heat and radiation from from Pu-238 would be a significant challenge for weapons designers, because in a weapon incased with a outer shell of high explosives, the heat will build up until the layer of explosives melt, rendering the weapon useless. PU-240 poses an even bigger problem. Although it is not not fissionable under reactor conditions, it fissions spontaneously at an alarming rate. No less than 415,000 Pu-249 atoms fission every second, for every 2.2 pounds (1 kg) of Pu-240. Pu-241 is fissionable in a reactor, but it is quite radioactive. Furthermore, Pu-241 emits beta particles, and transmutes itself into even more highly radioactive Americium-241. When withdrawn from LWRs, Reactor grade plutonium is 53% Pu 239, 25% Pu-240, 15% Pu-241, 5% Pu-242 and 2% of Pu-238.

According to Carson Marks. "Reactor-grade material would generate more than 10.5 watts per kilogram. As Gerhard Locke has recently emphasized, a crude nuclear explosive containing perhaps eight kilograms of reactor-grade plutonium would put out nearly 100 watts of heat-much more
than the eight watts emitted from the approximately three kilograms of weapons-grade plutonium he suggests would be in a modern nuclear warhead. Since the high-explosive (HE) around the plutonium core would have insulating properties only a few times poorer than wood (about 0.4 watts m-oC-1 ) only 10 centimeters of HE could result in an equilibrium temperature of the
core of about 190°C.5 Apparently, the breakdown rate of many types of HE begins to become significant above about 100°C.

Johan Swahn of the Technical Peace Research Group of Chalmers University in Goteborg, Sweden has developed data indieating that the surface dose exposure rate of material such as the reactor- grade plutonium is about six times larger (and MOX-grade over eight times larger) than that from the weapons-grade material which, again, is handled routinely.Marks speaks of nuclear explosions with reactor grand plutonium, but not nuclear weapons.

Two nuclear weapons designers, Carson Marks and Alexander DeVolpe have debated the usefulness of reactor grade plutonium in weapons. DeVolpe pointed to two tests:
1. The two UK "Totem" 1953 experiments in Australia, which were designed to evaluate the yield reduction resulting from plutonium of less than weapons grade".
2. The 1962 United States nuclear test which appeared to involve an intermediate grade plutonium.

DeVolpe argues that "[a]lthough the Totem explosive yield was highly destructive, they evidently confirmed that it was not good enough for military-quality weapons. Because these results would have been shared with the US, we can guess that the [1962] Nevada test might have been conducted with plutonium closer to the low end (81%) of the definition". He adds, that the British were quite disappointed with their 1950's test results.

DeVolpe argued that information about the 1962 test was probably distorted for political reasons. Most of what we know about the test comes from a series of terse statements:

"The 1962 detonation involved plutonium of a quality below that of weapons grade. To reinforce its 1967 announcements that "high-irradiation level reactor-grade plutonium can be used to make nuclear weapons," the US government added in 1977 that "a nuclear test was conducted using reactor grade plutonium" and "it successfully produced a nuclear yield." As a result of the Openness Initiative formulated by Secretary O'Leary, DOE announced in 1994 that the plutonium was "provided" by the UK and the upper limit of explosive yield was 20 kt."

DeVolpe also pointed out, "[c]ompared to data released about other nuclear detonations, the information disclosed about the 1962 test has little substance". According to DeVolpe the French "scorned the US government affirmation that it successfully exploded a weapon made with 'reactor-grade' plutonium."

DeVolpe argues that the quality of the plutonium in the 1962 device would have then been considered "reactor grade", but in the 1990's it would have been classified as fuel grade. He argued that public accounts of the 1962 Nevada test was inconsistent with published data on the 1950's British "Totem" experiments.

DeVolpe complains about the continued classification of information the 1962 test, long after far more information of conventional plutonium devices had been declassified. This would include general information on device design, plutonium quality, plutonium metallurgical chemical form, and Explosive yield. DeVolpe argues, "A lower yield would be suggestive of greater resistance to proliferant use. No nation with other options would choose such material as the basis for a nuclear-weapons program, and none are known to have done so".

Los Alamos chief weapons designer Carson Marks, together with Marvin Miller and Frank von Hippel, responded to DeVolpe's argument. Many of their arguments would seem very ambiguous. For example, they state, "The information disclosed about this test in 1977 represented a compromise between policy makers in the Carter Administration who wished to high-light the proliferation risks of of civilian plutonium use and those responsible for protecting classified weapons-design information".

This statement highlights the political influence on the 1977 statement, but does not respond to DeVolpe's argument that more was classified on the 1962 tests, than was classified on nuclear weapons test conducted at that time. If the goal of the Carter Administration was to high-light the proliferation risks of of civilian plutonium use, maintaining the classification of information that was inconsistent with that goal would have certainly been possible. DeVolpe argued that the classification of the 1962 was idiosyncratic, the Marks et al statement does not conflict with DeVolpe's argument.

Marks et al, made a further statement: "To our knowledge, all U.S. nuclear weapons use weapon-grade plutonium, i.e. plutonium with an isotopic fraction of at least 93.5 percent Pu-239. The same is probably true of the weapons in the arsenals of the other weapon states. There are several reasons for this. One of these is that the natural-uranium-metal fuel used in early production reactors had to be discharged after low U-235 burnup because of both reactivity and metallurgical fuel constraints. Such reactor operation naturally produces plutonium with a high Pu-239 fraction. It was also recognized that radiation exposure to workers fabricating plutonium weapons components in glove boxes would be minimized if the plutonium had a low fraction of the higher plutonium isotopes".

They added,

"However, the most important factor in motivating the high Pu-239 content plutonium in early nuclear weapons was the problem of pre-initiation of the chain reaction. In nuclear designs such as the Nagasaki weapon, where the chain-reaction was designed to be initiated at the point of maximum core compression, neutrons from the spontaneous fission of the even plutonium isotopes (primarily Pu-240) could pre-initiate the chain-reaction leading to significant reduction of the yield of the device.

Even with very high Pu-239 plutonium used in the Nagasaki bomb, there was an estimated 12 percent of reduced yield from this cause. For weapon-grade plutonium as defined today, this probability would have been considerably higher -- on the order of 50 percent -- unacceptably high to the U.S. military. This provided one of the many motivations for going to more sophisticated designs of fission weapons which incorporated faster assemblies and smaller quantities of fissile material. The introduction of "boosting," i.e. having a low-yield fission explosion ignite deuterium-tritium fusion in the primary releasing neutrons which increase the fission yield by an order of magnitude, further reduced the sensitivity to pre-initiation".

They conclude, "we are not arguing that a proliferator would not prefer weapon-grade plutonium or highly-enriched uranium to reactor-grade uranium. However, the possible use of reactor-grade plutonium cannot be discounted".

It is also important to note that Marks et al, did not challenge DeVolpe's discussion of to the British "Totum" tests.

A 1998 Indian test might be shine a little more light on the subject. In May, 1998, India tested a series of nuclear devices. At least one of those devices was believed to use reactor grade plutonium. The yield was reported to be between 0.2 and 0.6 kilotons, but some Indian scientists speculated that it was much smaller.

We ought to take a further note of the "Totum" experiments. These experiments used plutonium from the Calder Hall Magnox reactors and were conducted because plutonium from the Calder Hall reactors had a relatively high Pu-240 content, although probably >10%. The first test is reported to have produced an explosion on around 10 kilotons. But the exact sized of the second explosion is something of a mystery, with estimates running as high as 7 kilotons, and as low as 0.25 kts.

We ought to look at the 2006 North Korean nuclear test, which probably used "fuel grade plutonium from their Magnox type reactor. Prior to the test, the North Koreans told the chinese that they intended to set off a 4 kt nuclear device. Estimates of the actual size of the North Korean device varied widely with estimates running as low as 0.1 kts and as high 1.0 kt. Since the seismic reading fell into to the range of a large conventional explosion, some experts suggested that the North Koreans had not used a nuclear device at all. The Wall Street Journal suggested that the blast was equivalent to the explosive force of about $100,000 worth of ammonium nitrate. It was not clear if the North Korean test had been a success, a failure, or not even a test.

We should also to observe that all but one tests of nuclear devices with more than weapons grade levels of Pu-240 were conducted with Plutonium from Magnox reactors. The British 1953 Totum tests were conducted with a >10% level of Pu-240 and were deemed less than satisfactory. Given the published statement that the Plutonium for the 1962 Nevada test came from a UK source, it would appear that the source was a Magnox reactor. The Pu-240 content ran up to 15%. Finally the plutonium for the Indian sub lt test came from a heavy water reactor. The exact Pu-240 content was unclear.

Thus it would appear that no nuclear test has ever been conducted using plutonium extracted from LWR "spent fuel". Such Plutonium can include as much as 25% Pu-240. With so much Pu-240, the dangers of a spontaneous and premature explosion would be enormous. The amount of neutron radiation from such a device would be significant enough to require more than glovebox containment.

Finally it should be noted, that as Carson Marks has suggested, no nation has chosen to build nuclear weapons from using "reactor grade plutonium". Even North Korea chose to use plutonium that was near weapons grade, and their test of the explosive properties of that material may well have ended in failure.

Considering that no nation has ever even attempted to build a nuclear device using plutonium from spent light water reactor fuel, the case that reactor grade plutonium containing as much as 25% Pu-240 can be weaponized is open to question. In fact the history of nuclear proliferation efforts i9s not consistent with the notion that reactor grade plutonium woule ever be used as a nuclear proliferation tool. Even if such a reactor grade plutonium weapon were possible, easier routes to nuclear proliferation seem likely. The North Koreans seem willing to sell their possibly defective technology to the highest bidder. The many members of the A.Q. Kahn nuclear proliferation gang have never been arrested, and Kahn appears to be on the loose again. Kahn was able to procure of Pakistan the technology to build nuclear weapons, and the Kahn gang was known to have sold nuclear weapons technology to North Korea, Iran and Lybya. The South Africans developed an uranium separation technology that allowed them to enrich about 80 kgs of uranium every year to the 80% U-235 level, that is required for weaponized use.

The evidence is thus that even small nations like South Africa, given a determined government, may posses sufficient industrial, scientific and technical resources, may be able to develop the technology to produce a small number of nuclear weapons, without using reactor grade plutonium. The evidence is further that the cost of producing conventional nuclear weapons by conventional routes is not highly expensive, and the weapons produced are far more likely to produce predictable results. The probable continued survival of the A.Q Kahn criminal proliferation organization, and recent reports of North Korean involvements in building a reactor in Syria suggest that conventional proliferation resources are available to rogue states which wish to produce nuclear weapons. Thus alleged the civilian power reactor-proliferation link appears to be utterly without merit. Reactor grade plutonium produced by civilian power reactors, would appear to be a very undesirable proliferation tool, while inexpensive and far superior proliferation tools are available through criminal organizations and rogue states, to even small countries which wish to acquire nuclear weapon.

Ganted the availability of superior, low cost proliferation options, arguments that reactor grade plutonium from light water reactors constitute an added proliferation risk appear irrational. Thus the so called danger of nuclear proliferation risk ought to be taken off the table in discussions of the advantages and disadvantages of power production from reactors. building power reactors effectively adds no added risk of proliferation avove the super means already available to the would be proliferator.

2 comments:

David Walters said...

Charles, singularly the best written post I've seen yet here. I'm going to reference this as THE article on proliferation.

Can I use it on Left-atomics?

David

Charles Barton said...

David, You can use it.

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