238U cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where fast fission of one or more next-generation nuclei is probable.

[3] The decay of 238U to daughter isotopes is extensively used in radiometric dating, particularly for material older than approximately 1 million years.

The latter usually involves used "recycled" MOX fuel which entered the reactor containing significant amounts of plutonium[citation needed].

Also, Japan's Monju breeder reactor, which has been inoperative for most of the time since it was originally built in 1986, was ordered for decommissioning in 2016, after safety and design hazards were uncovered, with a completion date set for 2047.

[citation needed] DUCRETE, a concrete made with uranium dioxide aggregate instead of gravel, is being investigated as a material for dry cask storage systems to store radioactive waste.

This dilution, also called downblending, means that any nation or group that acquired the finished fuel would have to repeat the very expensive and complex chemical separation of uranium and plutonium process before assembling a weapon.

A tamper which surrounds a fissile core works to reflect neutrons and to add inertia to the compression of the 239Pu charge.

For example, an estimated 77% of the 10.4-megaton yield of the Ivy Mike thermonuclear test in 1952 came from fast fission of the depleted uranium tamper.

The Soviet Union's test of the Tsar Bomba in 1961 produced "only" 50 megatons of explosive power, over 90% of which came from fusion because the 238U final stage had been replaced with lead.

Beginning with naturally occurring uranium-238, this series includes the following elements: astatine, bismuth, lead, polonium, protactinium, radium, radon, thallium, and thorium.

While 238U is minimally radioactive, its decay products, thorium-234 and protactinium-234, are beta particle emitters with half-lives of about 20 days and one minute respectively.

As already touched upon above, when starting with pure 238U, within a human timescale the equilibrium applies for the first three steps in the decay chain only.

Thus, for one mole of 238U, 3×106 times per second one alpha and two beta particles and a gamma ray are produced, together 6.7 MeV, a rate of 3 μW.

[16] The Voyager program spacecraft carry small amounts of initially pure 238U on the covers of their golden records to facilitate dating in the same manner.

Significant internal exposure to tiny particles of uranium or its decay products, such as thorium-230, radium-226 and radon-222, can cause severe health effects, such as cancer of the bone or liver.