Do you not realize their is a difference between scanning and inspecting? I guess not.
This is from June 2005, so it must have been implemented by now:
Nation’s Busiest Seaports to Have Complete Radiation Detection Coverage by End of 2005
For Immediate Release
Office of the Press Secretary
Contact: 202-282-8010
June 3, 2005
Department of Homeland Security (DHS) Secretary Michael Chertoff today announced that the nation’s busiest seaports -- Los Angeles/Long Beach, California -- will have complete Radiation Portal Monitor (RPM) coverage by year’s end.
Three terminal locations, at Piers 400, 300 and Trans Pacific, within the Port of Los Angeles are scheduled to go on-line by the end of June. A total of ninety RPMs, which will screen all international container traffic and vehicles exiting the facility for nuclear materials or hidden sources of radiation, will be operational by December 2005.
http://www.dhs.gov/dhspublic/display?content=4530
====
The point is that they look to find the high risk containers, BEFORE they are shipped to the US, inspect the high risk containers, mostly also BEFORE they get here, then have additional screening in the US ports, for radiation.