Spent nuclear fuel



Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant) to the point where it is no longer useful in sustaining a nuclear reaction.

activation products, and the reagents or solidifiers introduced in the reprocessing itself.

Alternatively, the intact spent fuel can be disposed as radioactive waste. The US is currently planning disposal in deep geological formations, such as Yucca Mountain, where it has to be shielded and packaged to prevent its migration to mankind's immediate environment for thousands if not millions of years.[1]

Nature of spent fuel

Large John H Radioactive Decay Characteristics of Irradiated Nuclear Fuels, January 2006 [2]

Nanomaterial properties

Spent cesium, hence many of these bubbles contain a lot of 137Cs.

 

In the case of the MOX the xenon tended to diffuse out of the plutonium rich areas of the fuel, and it was then trapped in the surrounding uranium dioxide. The neodymium tended to not be mobile.

 

Also metallic particles of an radioactive uranium active) simulation of spent oxide fuel exists.[1]

Fission products

  • 3% of the mass consists of fission products of 235U (also indirect products in the radioisotopes. But a considerable number are medium to long lived radioisotopes such as 90Sr, 137Cs, 99Tc and 129I. Research has been conducted by several different countries into partitioning the rare isotopes in fission waste including the Fission Platinoids (Ru, Rh, Pd) and Silver (Ag) as a way of offsetting the cost of reprocessing, however this is not currently being done commercially.
The fission products can modify the metallic nanoparticles slightly increases the thermal conductivity of the fuel.[2]


Table of chemical data

The chemical forms of fission products in uranium dioxide [3]
Element Gas Metal Oxide Solid solution
Br Yes - - -
Kr Yes - - -
Rb Yes - Yes -
Sr - - Yes Yes
Y - - - Yes
Zr - - Yes Yes
Nb - - Yes -
Mo - Yes Yes -
Tc - Yes - -
Ru - Yes - -
Rh - Yes - -
Pd - Yes - -
Ag - Yes - -
Cd - Yes - -
In - Yes - -
Sn - Yes - -
Sb - Yes - -
Te Yes Yes Yes Yes
I Yes - - -
Xe Yes - - -
Cs Yes - Yes -
Ba - - Yes Yes
La - - - Yes
Ce - - - Yes
Pr - - - Yes
Nd - - - Yes
Pm - - - Yes
Sm - - - Yes
Eu - - - Yes

Plutonium

  • 1% of the mass is 239Pu and 240Pu resulting from conversion of 238U, which may either be considered a useful by-product, or as dangerous and inconvenient waste. One of the main concerns regarding nuclear proliferation is to prevent this plutonium from being used by states other than those already established as Nuclear Weapons States, to produce nuclear weapons. If the reactor has been used normally, the plutonium is reactor-grade, not weapon-grade: it contains much 240Pu and less than 80% 239Pu, which makes it less suitable, but not impossible, to use in a weapon [4]. If the irradiation period has been short then the plutonium is weapon-grade (more than 80%, up to 93%).

Uranium

  • 96% of the mass is the remaining uranium: most of the original 238U and a little 235U. Usually 235U would be less than 0.83% of the mass along with 0.4% 236U.

236U which is not found in nature; this is one isotope which can be used as a fingerprint for spent reactor fuel.

Minor actinides

  • Traces of the minor actinides are present in spent reactor fuel. These are actinides other than uranium and plutonium. These include curium. The amount formed depends greatly upon the nature of the fuel used and the conditions under which it was used. For instance, the use of MOX fuel (239Pu in a 238U matrix) is likely to lead to the production of more 241Am and heavier nuclides than a uranium/thorium based fuel (233U in a 232Th matrix).

For natural uranium fuel: Fissile component starts at 0.71% 235U concentration in natural uranium). At discharge, total fissile component is still 0.50% (0.23% 235U, 0.27% fissile 239Pu, 241Pu) Fuel is discharged not because fissile material is fully used-up, but because the fission products have built up and the fuel becomes significantly less able to sustain a nuclear reaction.

Some natural uranium fuels use chemically active cladding, such as Magnox, and need to be reprocessed because long-term storage and disposal is difficult [5].

For highly enriched fuels used in marine reactors and research reactors the isotope inventory will vary based on in-core fuel management and reactor operating conditions.

Spent fuel corrosion

Uranium dioxide films

Uranium dioxide films can be deposited by reactive spluttering using an gold surface which was then studied with AC impedence spectroscopy.[3]

Noble metal nanoparticles and hydrogen

According to the work of the anode reacting and dissolving it is the hydrogen gas which is consumed.

See also

References

  1. ^ Microstructural features of SIMFUEL - Simulated high-burnup UO2-based nuclear fuel, P.G. Lucuta, R.A. Verrall, Hj. Matzke and B.J. Palmer, Journal of Nuclear Materials, 1991, 178, 48-60.
  2. ^ Dong-Joo Kim, Jae-Ho Yang, Jong-Hun Kim, Young-Woo Rhee, Ki-Won Kang, Keon-Sik Kim and Kun-Woo Song, Thermochimica Acta, 2007, 455, 123-128
  3. ^ F. Miserque, T. Gouder, D.H. Wegen and P.D.W. Bottomley, Journal of Nuclear Materials, 2001, 298, 280-290.
 
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