Time Out says
Paddy Considine (The Bourne Ultimatum, Hot Fuzz) is an electrifying actor waiting for the role that will make him a star, so any opportunity to see him in a leading part should not be ignored. The first half of Pu-239 is earnest and uneven in ways that may test the patience of those keeping an eye on him, but the film (the directorial debut of Bourne Ultimatum cowriter Scott Z. Burns) eventually hits its stride and becomes a powerful black comedy about corruption and organized crime in Russia.
Set in an unspecified year during the Boris Yeltsin era, Pu-239 takes its name from an enriched plutonium isotope used in nuclear warheads. Considine plays Timofey Berezin, a technician at an atomic plant so secret that the city surrounding it is found on no map. When an accident hits Timofey with a dose of radiation high enough to make him a walking corpse, he’s strong-armed into signing a waiver absolving his bosses of all responsibility. Out of spite, he steals 100 grams of the titular isotope, intending to sell the nuclear material on the black market so his wife (Radha Mitchell) and son will have something to live on when he’s gone.
While bin Laden would gladly sacrifice three limbs for some Pu-239, Timofey soon finds that unloading the stuff is a lot harder than expected—even though he wants a measly $50,000 for a booty worth millions. After heading to a Moscow street market, he teams up with Shiv (Oscar Isaac), an incompetent rookie racketeer who introduces him to an increasingly depraved array of potential customers (Steven Berkoff is ideally cast as the sleaziest of them all). The po-faced scenes between Timofey and his wife embody the worst qualities of issue-oriented dramas, but the ironic detachment of the Moscow sequences exemplifies the best.