Induced nuclear reactions: processes – systems – and elements – Nuclear transmutation – By neutron bombardment
Patent
1998-01-05
1999-10-12
Wasil, Daniel D.
Induced nuclear reactions: processes, systems, and elements
Nuclear transmutation
By neutron bombardment
376171, G21C 108
Patent
active
059664185
DESCRIPTION:
BRIEF SUMMARY
This invention concerns the destruction of plutonium, especially of weapons grade plutonium.
The relaxation in tension between the United States and the former Soviet Union, witnessed over the past few years, has given rise to tens of thousand of nuclear warheads on both sides which have been declared excess to current needs. According to a recently published U.S. National Academy of Sciences report on Management and Disposition of Excess Weapons Plutonium, the excess amounts to 50 tons of weapons grade plutonium (W-Pu) in the U.S.A. At a recent NATO Advanced Research Workshop on managing the plutonium surplus Russian experts consider the Russian excess of W-Pu to be 100 tons.
At present W-Pu and highly enriched uranium (W-U) are present in warheads and will have to be transferred for dismantling. In this process a major problem will arise with regard to proliferation of nuclear weapons to national powers or sub-national groups by theft or unauthorised diversion.
One option is to dispose of this material by "burning" it in nuclear reactors and this is the subject of the present invention. The problem with this approach is the fact the even the "ashes" resulting from burning of W-Pu (i.e. the spent fuel) can be used to make a nuclear explosive. Following irradiation in the reactor, the spent fuel can be removed from the reactor, dissolved, and chemically processed to separate the plutonium which could then be used to construct a nuclear device. The compositions of different types of uranium and plutonium are given in tables I and II.
Although more difficult than with W-Pu, reactor plutonium (R-Pu) can be used to construct a nuclear explosive. It should be noted that although the critical mass of R-Pu is greater than that of W-Pu (see table III), the critical mass of R-Pu is less than that for weapons grade uranium (W-U). In addition, heat generation in R-Pu is about a factor five higher than in W-Pu and the spontaneous emission of neutrons is about a factor 6 higher than in W-Pu. In table III a summary of critical masses, heat production and neutron emission rates is given for various isotopes and isotope mixtures.
Accordingly the present invention intends to optimise the destruction rate of Pu and increase the proliferation resistance of spent fuel by increasing the relative amounts of the isotope .sup.238 Pu present in the "ash". Another aim is to avoid any reprocessing of the irradiated plutonium. These aims are achieved according to the invention by the method as defined in claim 1. As far as features of a preferred embodiment of this method are concerned reference is made to the secondary claims.
The use of weapons grade U requires an extended burnup to avoid proliferation problems associated with .sup.235 U in the spent fuel. Only after about 2000 days irradiation in a PWR neutron spectrum (total flux=3.times.10.sup.14 cm.sup.-2 s.sup.-1) is the percentage of .sup.235 U in the uranium less than 20% i.e. the concentration below which enriched uranium is not considered as a proliferation risk (the bare critical mass of a 20% mixture of .sup.235 U in .sup.238 U is approximately one ton). This long irradiation, of course, then leads to a high level of Pu destruction.
The invention will now be described in more detail by means of a preferred embodiment and the annexed drawings.
FIG. 1 shows the main pathways for the production of .sup.238 Pu from .sup.239 Pu and .sup.235 U.
FIG. 2 shows the Pu isotopic masses per ton of matrix: in fresh fuel (A) and after 1, 2, and 2.3 cycles (B, C, D respectively) in a PWR (one cycle=878 days). Fresh fuel contains 2.5% W-Pu+2.5% W-U in an inert matrix.
FIG. 3 shows the U isotopic masses per ton of matrix: in fresh fuel (A) and after 1, 2, and 2.3 cycles (B, C, D respectively) in a PWR (one cycle=878 days). Fresh fuel contains 2.5% W-Pu+2.5% W-U in an inert matrix.
FIG. 4 shows isotopic heating rates per unit mass of total Pu: for fresh fuel (A) and after 1, 2, and 2.3 cycles (B, C, D respectively) in a PWR.
FIG. 5 shows isotopic neutron emission rates per unit mass of tot
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patent: 5513226 (1996-04-01), Baxter et al.
patent: 5737375 (1998-04-01), Radkowsky
Magill Joseph
Matzke Hansjoachim
Nicolaou George
Peerani Paolo
Van Geel Jacques
European Atomic Energy Community
Wasil Daniel D.
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