Robert Ludlum's The Patriot Attack

Japan and China are thrown close to the brink of war when a Japanese warship is attacked. Meanwhile top Covert-One operative Jon Smith is sent to recover mysterious material from the wrecked Fukushima nuclear reactor.
Smith vanishes, and CIA agent Randi Russell goes on an unsanctioned mission to find him. She discovers that the missing samples may be evidence that Japan, led by Chief of Staff Masao Takahashi, has been developing next-generation weapons systems in preparation for a conflict with China.
The Covert-One team must prevent Takahashi from sparking a war, or the world will be dragged into a battle certain to kill tens of millions of people and leave much of the planet uninhabitable.