"Ladies and gentlemen, your captain speaking: we have a technical problem and we have to return to Beijing international airport. Thankyou".
You have to communicate with ATC and cabin crew, and onlyu reassure the passengers. For the ATC you give the usual: nature of failure, intentions, requests, endurance, pax, hazmats... and to the cabin crew the NITS. Then, if you have time and workload permitting, reassure the pax, which you achieve with the above phrase if you use a very calm, even boring tone.
If you say "there is no cause for alarm, or everything is under control" then they can get paranoid.
You can add "minor" to technical problem, or add "due to safety reasons" to intl airport, if you like, as if the problem is really small but airline policy obliges you to return.