Here is what I learnt from some Russian scholars:

Soviets taught Chinese hands-on how to build the bomb from scratch. However, not sooner the Chinese learnt the tricks than they kicked their teachers out (under Mao's instructions). After Mao was told that the Chinese had learnt how to build the bomb, he felt it's time for him to face off with Khrushchov. Mao hated Khrushchov because he believed that Khrushchov stole his throne of the Communist Internationale that Stalin promised him in the eve of Korean War. Mao insisted sending hundreds of thousands military 'volunteers' to Korea in spite of little or no support from the top leaders. Mao wanted the opportunity to promote his international status--now that he'd become the Chinese emperor, why not push a little further and succeed Stalin as the emperor of the world (at least the comunist world)? Stalin, as canny as he was, could read Mao's mind and, dangling the throne of the communist world in front of Mao, used him as a fighting agent against Americans in a way that nobody in Soviet could dream of.