Findings on Plutonium
~ both Military and Civilian ~

The floating of this idea is perhaps a natural move by those who want to exclude plutonium from strict controls. The obvious intention here is to create the impression that there is nothing to fear from separated plutonium derived from commercial power plants. This is not true.

This led to other careless assumptions: for example, that the technique of reactor safeguarding already in place -- inspections and audits -- would be adequate to provide the vital early warning of illicit attempts to divert separated plutonium, when it eventually began to accumulate in stockpiles; and also, that warning well in advance of illicit bomb fabrication was perhaps not really essential.

from "Spreading the Bomb Without Quite Breaking the Rules"

from Reactor-Grade & Weapons-Grade Plutonium in Nuclear Explosives

• Virtually any combination of plutonium isotopes -- the different forms of an element having different numbers of neutrons in their nuclei -- can be used to make a nuclear weapon. Not all combinations, however, are equally convenient or efficient.

• The most common isotope, plutonium-239, is produced when the most common isotope of uranium, uranium-238, absorbs a neutron and then quickly decays to plutonium. It is this plutonium isotope that is most useful in making nuclear weapons, and it is produced in varying quantities in virtually all operating nuclear reactors.

• As fuel in a reactor is exposed to longer and longer periods of neutron irradiation, higher isotopes of plutonium build up as some of the plutonium absorbs additional neutrons, creating plutonium-240, plutonium-241, and so on. Plutonium-238 also builds up from a chain of neutron absorptions and radioactive decays starting from uranium-235.

• These other isotopes   [ plutonium-240, plutonium-241, plutonium-238, etc. ]   create some difficulties for design and fabrication of nuclear weapons.

  1. First and most important, plutonium-240 has a high rate of spontaneous fission, meaning that the plutonium in the device will continually produce many background neutrons, which have the potential to reduce weapon yield by starting the chain reaction prematurely.

  2. Second, the isotope plutonium-238 decays relatively rapidly, thereby significantly increasing the rate of heat generation in the material.

  3. Third, the isotope americium-241 (which results from the 14-year half-life decay of plutonium-241 and hence builds up in reactor-grade plutonium over time) emits highly penetrating gamma rays, increasing the radioactive exposure of any personnel handling the material.

• Because of the preference for relatively pure plutonium-239 for weapons purposes, when a reactor is used specifically for creating weapons plutonium, the fuel rods are removed and the plutonium is separated from them after relatively brief irradiation (at low "burnup"). The resulting "weapons-grade" plutonium is typically about 93 percent plutonium-239.

  Such brief irradiation is quite inefficient for power production, so in power reactors the fuel is left in the reactor much longer, resulting in a mix that includes more of the higher isotopes of plutonium. In the United States, plutonium containing between 80 and 93 percent plutonium-239 is referred to as "fuel-grade" plutonium, while plutonium with less than 80 percent plutonium-239 -- typical of plutonium in the spent fuel of light-water and CANDU reactors at normal irradiation -- is referred to as "reactor-grade" plutonium.

• All of these grades of plutonium can be used to make nuclear weapons, The only isotopic mix of plutonium which cannot realistically be used for nuclear weapons is nearly pure plutonium-238, which generates so much heat that the weapon would not be stable. (International rules require equal levels of safeguards for all grades of plutonium except plutonium containing more than 80 percent plutonium-238, which need not be safeguarded.)

• Designing and building an effective nuclear weapon using reactor-grade plutonium is less convenient than using weapon-grade plutonium, for several reasons.
  1. Some nuclear weapons are typically designed so that a pulse of neutrons will start the nuclear chain reaction at the optimum moment for maximum yield; background neutrons from plutonium-240 can set off the reaction prematurely, and with reactor-grade plutonium the probability of such "pre-initiation" is large. Pre-initiation can substantially reduce the explosive yield, since the weapon may blow itself apart and thereby cut short the chain reaction that releases the energy.

     Nevertheless, even if pre-initiation occurs at the worst possible moment (when the material first becomes compressed enough to sustain a chain reaction). the explosive yield of even a relatively simple first-generation nuclear device would be of the order of one or a few kilotons. While this yield is referred to as the "fizzle yield," a one-kiloton bomb would still have a radius of destruction roughly one-third that of the Hiroshima weapon, making it a potentially fearsome explosive. Regardless of how high the concentration of troublesome isotopes is, the yield would not be less.

  2. Dealing with the second problem with reactor-grade plutonium, the heat generated by plutonium-238 and plutonium-240, requires careful management of the heat in the device. There are well developed means for addressing these problems and they are not considered a significant hurdle to the production of nuclear weapons, even for developing states or sub-national groups.

  3. The radiation from americium-241 means that more shielding and greater precautions to protect personnel might be necessary when building and handling nuclear explosives made from reactor-grade plutonium. But these difficulties are not prohibitive.

  4. While reactor-grade plutonium has a slightly larger critical mass than weapon-grade plutonium (meaning that somewhat more material would be needed for a bomb), this would not be a major impediment for design of either crude or sophisticated nuclear weapons.

• The degree to which these obstacles can be overcome depends on the sophistication of the state or group attempting to produce a nuclear weapon.
  1. At the lowest level of sophistication, a potential proliferating state or subnational group using designs and technologies no more sophisticated than those used in first-generation nuclear weapons could build a nuclear weapon from reactor-grade plutonium that would have an assured, reliable yield of one or a few kilotons (and a probable yield significantly higher than that).

  2. At the other end of the spectrum, advanced nuclear weapon states such as the United States and Russia, using modern designs, could produce weapons from reactor-grade plutonium having reliable explosive yields, weight, and other characteristics generally comparable to those of weapons made from weapons-grade plutonium.

     The greater radioactivity would mean increased radiation doses to workers fabricating such weapons, and military personnel spending long periods of time in close proximity to them, and the greater heat and radiation generated from reactor-grade plutonium might result in a need to replace certain weapon components more frequently.

  3. Proliferating states using designs of intermediate sophistication could produce weapons with assured yields substantially higher than the kiloton-range possible with a simple, first-generation nuclear device.

• Every state which has built nuclear weapons from plutonium to date has chosen to produce weapons-grade plutonium for that purpose.

• States have been willing to make large investments in some cases to acquire weapon-grade rather than reactor-grade plutonium: the United States, for example, in the 1980s, considered spending billions of dollars on the Special Isotope Separation facility to enrich reactor-grade plutonium to weapon-grade.

• The disadvantage of reactor-grade plutonium is not so much in the effectiveness of the nuclear weapons that can be made from it as in the increased complexity in designing, fabricating, and handling them.

• The possibility that either a state or a sub-national group would choose to use reactor-grade plutonium, should sufficient stocks of weapon-grade plutonium not be readily available, cannot be discounted.

• In short, reactor-grade plutonium is weapons-usable, whether by unsophisticated proliferators or by advanced nuclear weapon states. Theft of separated plutonium, whether weapons-grade or reactor-grade, would pose a grave security risk.

• The plutonium-240 content even in weapons-grade plutonium is sufficiently large that very rapid assembly is necessary to prevent pre-initiation. Hence the simplest type of nuclear explosive, a "gun type," in which the optimum critical configuration is assembled more slowly than in an "implosion type" device, cannot be made with plutonium but only with highly enriched uranium, in which spontaneous fission is rare.

  This makes HEU [Highly Enriched Uranium] an even more attractive material than plutonium for potential proliferators with limited access to sophisticated technology.

  Either material can be used in an implosion device.

  
  

  ---

  . . . back to TABLE OF CONTENTS

  ---

  
  
  

  Excerpts from: The Threat of Nuclear War testimony of Herbert Scoville former Head of Scientific Intelligence, (US Central Intelligence Agency) transcript of a British TV program broadcast by Granada Independent TV London, England March 29 1976.

  
  
  

  from Herbert Scoville, on The Threat of Nuclear War

• I participated in the first postwar atomic bomb tests at Bikini, and was myself in charge of a number of Defense Department nuclear weapons tests to measure the effects of such explosions. Later I became Head of Scientific Intelligence in the Central Intelligence Agency -- the CIA -- and studied the nuclear weapons programmes of other countries.

• [ I am ]   concerned that these weapons will soon fall into many hands in many corners of the world -- into the hands of unstable national governments, aggressive military cliques or irresponsible terrorist groups, with incalculable consequences for us all. This danger is the direct result of the uncontrolled growth of the nuclear power industry, which is making widely available the materials needed for such weapons. The peoples of the world must recognize the danger of what is going on and act to protect this and future generations.

• I have spent many years of my life in the weapons business and in studying the effects of nuclear explosions. I have spent the last part of it in trying to get them under control. And I, too, am frightened of the dangers of a war involving nuclear weapons.

• I am particularly concerned that our senses have become dulled by the dry statistical calculations of millions killed and that we have forgotten the horrors that nuclear war can inflict on individuals. One small bomb on Hiroshima caused 100,000 dead and thousands more horribly scarred and mutilated by fire and blast. In a modern war there would be radioactive fallout too.

• I was in Bikini in March, 1954, when a single H-bomb spread lethal fallout over more than 5,000 square miles. I was put in charge of a team to measure the accidental radioactive contamination at Rongelap, an inhabited island on the southern edge of the fallout pattern and 120 miles from the explosion. If the people there had lived just one mile further north they would probably all have been killed. As it is, some twenty years later, they are now developing thyroid tumours, some of them cancerous. Think of the consequences today -- in England, Germany or France -- if this had occurred in Europe.

• I believe that the risk that a nuclear war will break out is growing day by day. With the spread of peaceful nuclear power, more and more countries have the opportunity to acquire bomb materials.... If the nuclear weapons powers are seeking to halt the spread of nuclear weapons they are certainly going about it the wrong way.

• This arms race is symbolic of a perverted world where the possession of nuclear weapons is taken as a sign that a country is important and should be listened to. Instead I believe we must create an international atmosphere where the possession of nuclear weapons is a cause for embarrassment and shame -- rather than for power and prestige.

• Unless those that have nuclear weapons show some evidence of restraint and all work together to establish a climate in which nuclear weapons are not assigned military or political value, we may see mushroom clouds over Tel Aviv and Cairo, and lingering radiation casualties throughout the Middle East. But no one knows how to limit a nuclear conflict. It could escalate out of control to Europe. These horrors, multiplied many times over, could equally well be visited on Washington and New York, London and Belfast, Paris and Marseilles, and Moscow and Leningrad.

  
  

  ---

  . . . back to TABLE OF CONTENTS

  ---

  
  
  

  Excerpts from: The Threat of Nuclear War testimony of George Rathjens former Director, Weapons Systems Evaluation World War II Atomic Bomb Project transcript of a British TV program broadcast by Granada Independent TV London, England March 29 1976.

  
  
  

  from George Rathjens, on The Threat of Nuclear War

• Nuclear war is most likely to be started by one of the newer nuclear powers, where the command and control systems may not be as refined or the government as stable as ours. The risk is particularly grave with nations that feel beleaguered or threatened and abandoned by the world community.

• Israel is the first one that comes to mind. It is feeling increasingly isolated and skeptical about continuing American support. Her differences with the Arabs are deep and unresolved. Israel has a strong nuclear technology which has been developed with help from France; for a dozen years it has had an experimental reactor operating that can produce enough plutonium for one nuclear weapon per year. I believe the Israelis could assemble nuclear weapons within a few weeks or months, if they have not already done so. They have the planes with which to deliver them, supplied by the United States and France.

• In a few years the Arab world is bound to surpass Israel in conventional military capability. They already have more men, tanks and money. Their ability to use these resources effectively is improving at an impressive rate. If Israel faces a war it knows it cannot win by conventional means, there is a terrifying possibility that she may use atomic weapons.

• The Nationalist Chinese Government on Taiwan faces an even bleaker future. It is confronted by eight hundred million sworn enemies on the mainland and it has been totally abandoned by the rest of the world. It has one of the most aggressive nuclear power programmes in the world. This may make sense in terms of their electricity needs. But it will also result in their producing enough plutonium in the next 10 years to make 1000 weapons, which I think is a very frightening number. If mainland China made a determined attempt to take Taiwan, the Taiwan government could only effectively respond by using nuclear weapons.

• But there's another, more alarming possibility. There have always been erratic and even mad heads of government. It's only thirty years since a man as dangerous as Adolph Hitler ran Germany. It's not easy to predict where the next unstable leader will emerge, but as nuclear power programmes expand, there is a risk that a change of government may place a madman in control of the potential to produce and use nuclear weapons. Or an unbalanced head of government of a non-nuclear country will be able to hire scientific mercenaries and buy black market plutonium to build his own do-it-yourself atomic bombs.

• The prospect of leaders with the unpredictability of Colonel Gadaffi of Libya and the irrational aggressiveness of General Idi Amin of Uganda threatening the world with nuclear bombs is one that is simply terrifying. Yet if things continue as they are now, this is what we all face.

  
  

  ---

  . . . back to TABLE OF CONTENTS

  ---

  
  
  

  Excerpts from: The Threat of Nuclear War testimony of Theodore Taylor fomer Nuclear Weapons Designer, Los Alamos National Laboratory transcript of a British TV program broadcast by Granada Independent TV London, England March 29 1976.

  
  
  

  from Dr. Theodore Taylor, on The Threat of Nuclear War

• I believe that the uncontrolled spread of nuclear power to an ever-increasing number of countries is the world's number one problem, though it is not recognized as such.

• Governments and public opinion will not face up to the fact that we are moving inexorably into a new technology involving entirely new types of risk. This is true both of the risk of nuclear terrorism and of the risk of nuclear war between nations.

• On the threat from nuclear terrorism, urgent international action could, I believe, reduce the risk to an acceptable level. There would have to be much tighter security controls than now, and new technical measures concerned with the way nuclear power is generated. Also, sacrifices of national sovereignty; and perhaps sacrifices too in the civil liberties field. Pursuit of a terrorist who has stolen plutonium would require something other than the normal rules of police procedure. But given the will, the terrorist problem could be cracked. Every government, no matter how aggressive itself, has an interest in seeing that unauthorized groups do not get hold of bomb materials.

• But even if that were to be solved, the spread of nuclear power would still leave us with the threat of nuclear war between governments. There is the possibility that an aggressive or beleaguered country, or a deranged leader in charge of a national government, might seek a way out of their problems by using the most powerful weapon ever invented.

  
  

  ---

  . . . back to TABLE OF CONTENTS

  ---

  
  
  

  Excerpts from: The Threat of Nuclear War testimony of George Kistiakowsky Director of the Explosives Division Worl War II Atomic Bomb Project transcript of a British TV program broadcast by Granada Independent TV London, England March 29 1976.

  
  
  

  from George Kistiakowsky, on The Threat of Nuclear War

• For many years [I] worked inside the Government machine on matters related to nuclear weapons technology. I personally must confess that for a long time I saw myself as a technician there to put into effect the policies of Government leaders -- policies which I thought had been arrived at by men better qualified to judge than myself. I refer particularly of course to policies concerning nuclear weapons and nuclear power.

• During my stay in Government, I gradually came to believe that some policies in this area were wrong. And that one could not change them by working from the inside. I now find myself, like my friends here, out of the Government. But we all retain our knowledge of and interest in the subject. And since we believe that the dangers which we see concern you all, and us all, we have decided to speak out about them.

• The Atoms for Peace programme proposed by President Eisenhower about 20 years ago was intended to speed less developed countries to prosperity. Now this programme has become a threat to the nuclear peace of the world.

• What happened is this. A trade in nuclear technology has gradually developed between the nations that have nuclear power and those that do not. The nuclear "haves" have sold and built some twenty-five nuclear reactors and thirty-five or more are also under construction in the nuclear "have-not" countries. For a country without oil or coal, nuclear reactors may indeed be the best way to obtain electric power. But these reactors are also the only means for making plutonium -- the prime nuclear explosive material.

• Without going into technical details, let me say that in order to get plutonium one must have, in addition to reactors, a costly chemical factory called a fuel reprocessing plant.... Now, a country that has them both is separated from its first atom bombs only by a political decision and a year or two of inexpensive technical effort, about which I am familiar since I was involved in the making of the first atom bombs.

• Of course, the countries getting these plants argue that they need them for peaceful purposes only, not for bombs. But for electric power production, reprocessing is not now an economic or a necessary technology, especially for Third World countries. It isn't even in operation in the United States at present. For countries with only a few power reactors, the reprocessing plant is an outright wasteful investment. And yet many countries without nuclear weapons are interested in acquiring this technology. Why? There must be a non-economic reason, which probably is that these countries want to acquire the option to make nuclear weapons.

• Are international agreements always kept? Our times are those of political upheaval, of revolutions and military takeovers. International commitments have been broken time and time again. The atomic energy agreements are but a slender defence against the proliferation of nuclear weapons.

• If no action is taken, the spread of nuclear technology will soon advance beyond the ability of human societies to control it.

• The present gradual slide of humanity into nuclear war can be stopped only by the voice of the people. And it can be stopped, for nuclear installations take many years to build, and there is still time to act. A broad public movement must tell the governments of the seller countries that present policies of foreign trade in nuclear technology must change.

  
  

  ---

  . . . back to TABLE OF CONTENTS

  ---

  
  
  

  Excerpts from: The Threat of Nuclear War testimony of Dr. Bernard Feld Assistant Leader of the Critical Assembly Group Worl War II Atomic Bomb Project transcript of a British TV program broadcast by Granada Independent TV London, England March 29 1976.

  
  
  

  from Dr. Bernard Feld, on The Threat of Nuclear War

• Let me tell you about a nightmare I have. The mayor of Boston sends for me for an urgent consultation. He has received a note from a terrorist group, telling him that they have planted a nuclear bomb somewhere in central Boston. The mayor has confirmed that twenty pounds of plutonium is missing from Government stocks. He shows me the crude diagram and a set of the terrorists' outrageous demands. The diagram is familiar -- it is similar to one I saw about a year ago drawn up for fun by a student at M.I.T. [Massachusetts Institute of Technology].

  I know -- as one of those who participated in the assembly of the first atomic bomb -- that the device would work. Not efficiently, but nevertheless with devastating effect. What should I advise? Surrender to blackmail or risk destroying my home town? I would have to advise surrender.

• Let me explain the background to that nightmare. Plutonium is the stuff out of which atomic bombs are made. And the amount of plutonium in the world is increasing year by year as nuclear power spreads. Within the next ten years nuclear power plants will be producing around 100 tons of plutonium a year -- enough for 10,000 atomic bombs, each with the same power as the one that destroyed Nagasaki. It is hard to believe that a figure as big and as threatening as this is realistic -- but I assure you that this is what is being planned.

• So within the next ten years, there will be hundreds of tons of plutonium wandering around the world. It will be as easy as pie for a determined group to get hold of the 20 or so pounds needed for a Nagasaki-type bomb. And making a crude version of one of these bombs, once you've got the plutonium, is not all that difficult. Even a crudely-made bomb, much less efficient than the Nagasaki bomb, would be powerful enough to level whole areas of a city and to cause thousands or tens of thousands of immediate fatalities, not to speak of the further thousands condemned to slower death by lung or bone cancer from plutonium inhalation.

• This terrifying possibility will become an inevitability if the major industrialized nations persist in their current grossly irresponsible policies. Nuclear reactors, plutonium reprocessing plants, uranium enrichment facilities and the technologies needed to operate them are today being sold to any country with enough cash or oil to buy them. This irresponsible behaviour is not confined to any one country.

• The problem cannot be solved by the individual action of any one nation. If there is any solution at all it can only come about from the concerted action of all the industrialized nations. But little can be done if these nations continue to treat the problem as if it either does not exist or will somehow go away.

• Today the world stands at a crossroads. Will the needed steps be taken to avert the world-wide proliferation of nuclear bomb materials, or will it be another example of too little, too late?

  
  

  ---

  . . . back to TABLE OF CONTENTS

  ---

  
  
  

  Excerpts from: Explosive Properties of Reactor-Grade Plutonium by J. Carson Mark, Director of the Theoretical Division, Los Alamos National Laboratory, 1947-1972 reprinted in Science and Global Survival, Volume 4, pp. 111-128 adapted from an earlier paper prepared by Dr. Mark for the NCI Nuclear Control Institute Washington, D.C. 1993

  
  
  

  from Explosive Properties of Reactor-Grade Plutonium (NCI, 1993)

• from the Abstract:

  The following discussion focusses on the question of whether a terrorist organization or a threshold state could make use of plutonium recovered from light-water reactor fuel to construct a nuclear explosive device having a significantly damaging yield.

  Questions persist in some nonproliferation policy circles as to whether a bomb could be made from reactor-grade plutonium of high burn-up, and if so, whether the task would be too difficult for a threshold state or terrorist group.

  Although the information relevant to these questions is in the public domain, and has been for a considerable time, it is assembled here for use by policy makers and members of the public who are concerned about preventing the spread of nuclear explosives.

• from "Criticality Properties of Reactor-Grade Plutonium":

  All of the plutonium isotopes are fissionable.... The bare critical mass of plutonium-240 [the minimum amount needed for a nuclear chain reaction, without the use of a neutron reflector] ... is about 40 kilograms. Since the bare critical mass of weapons-grade uranium (94 percent uranium-235) is 52 kilograms, plutonium-240 may be said to be a more effective fissionable material than weapons-grade uranium....

  In practice, at all burn-up levels and at any time following discharge, the critical mass of reactor-grade plutonium is intermediate between that of plutonium-239 and plutonium-240, which is more reactive than weapons-grade uranium.

  Reactor-grade plutonium can be brought to a supercritical -- and, hence, explosive -- state by any assembly system that can handle uranium-235.

  The bare critical masses are not the masses one would need to construct a device, since by the use of a neutron reflector a few inches thick, the critical mass of each of these materials can be reduced by a factor of two, or so, below the bare critical mass.

• from "Effects of Pre-initiation on Yield Distribution"

  One week after the first fission explosion on 16 July 1945, Robert Oppenheimer wrote to General Leslie R. Groves' deputy and described the expected performance of the Trinity device [code name for the plutonium bomb detonated at Alamogordo, New Mexico] in combat:

  "The possibility that the first combat plutonium Fat Man [code name for the Nagasaki bomb] will give a less than optimal performance is about twelve percent. There is about six percent chance that the energy release will be under 5,000 tons [of TNT equivalent] , and about two percent chance that it will be under 1,000 tons. It should not be much less than 1,000 tons unless there is an actual malfunctioning of some of the components."

  One week later General Groves wrote to the Chief of Staff,

  "There is a definite possibility -- 12 percent rising to 20 percent, as we increase our rate of production [of plutonium] at the Hanford Engineer Works, with the type of weapon tested -- that the blast will be smaller [than the "nominal yield" of 20,000 tons of TNT] due to detonation in advance of the optimum time. But in any event, the explosion should be on the order of thousands of tons."

  Evidently, both Oppenheimer and Groves were referring to what has been identified as the "fizzle yield".... The principle effect of using reactor-grade plutonium in place of the high-purity plutonium available in summer 1945, would be to increase the probabilities that the yield would fall short of the nominal yield, but it would not greatly change the value of the fizzle yield, which would always be equalled or exceeded....

  Though much smaller than the nominal yield (by a factor of about 20 in the particular case considered -- the so-called "primitive" Trinity-style device) these near-fizzle yields would still constitute severely damaging explosions. Very heavy damage and acute hazard from the blast, thermal, and prompt radiation effects, which extended out to a radius of about a mile in the case of the weapons used in Japan, would, for these "small" yields, extend "only" out to a radius of one-third or one-half a mile.

• from "Heat"

  There will be a wide range in the heat and radiation emitted by these materials. Weapons-grade material (which is handled routinely) generates about 2.5 watts per kilogram, whereas the reactor-grade material would generate more than 10.5 watts per kilogram [due to increased alpha radiation]. As Gerhard Locke has recently emphasized, a crude nuclear explosive using 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....

  The design of a crude nuclear explosive using reactor-grade plutonium will have to account for the extra heat generation and radiation exposure, but provisions can certainly be devised to cope with these features. For example ... a thermal bridge [made of aluminum] with a total cross-section ... of only about one square centimetre would halve the temperature increase induced by the reactor-grade plutonium.

• Conclusions (unabridged)
  • Reactor-grade plutonium with any level of irradiation is a potentially explosive material.

  • The difficulties of developing an effective design of the most straightforward type are not appreciably greater with reactor-grade plutonium than those that have to be met for the use of weapons-grade plutonium.

  • The hazards of handling reactor-grade plutonium, though somewhat greater than those associated with weapons-grade plutonium, are of the same type, and can be met by applying the same precautions.

    This, at least, would be the case when fabricating only a modest number of devices. For a project requiring an assembly line type of operation, more provisions for remote handling procedures for some stages of the work might be required than would be necessary for handling weapons-grade material or for handling a limited number of items.

  • The need for safeguards to protect against the diversion and misuse of separated plutonium applies essentially equally to all grades of plutonium.