By Thomas C. Reed on PhysicsToday.org:
For starters, Stillman asked the professor, 'Does the Chinese nuclear weapons program have a prompt burst reactor?' ... Yang's answer: 'Of course.'
Stillman pulled out a map of Sichuan Province. 'Can you show me where it is?' He thought he already knew the answer, but much to his surprise, Yang pointed to a location off in the mountains, a considerable distance west of the known Chinese nuclear weapons facilities.
Stillman fired a third fastball, right over the plate: 'Can you arrange an invitation for me to visit that facility?'
'Certainly,' the professor responded...
Thus began a most remarkable unveiling of the Chinese nuclear weapons program, a deliberate disclosure of its nuclear crown jewels to a central player in the American nuclear intelligence community.