Nuclear workers lost track this month of five shipments of radioactive garbage from West Germany but later found them, an official said Friday.

"The investigation has taught us a lesson," said Paul Ek, an engineer with the Atomic Energy Board. "We have to tighten our control of the transports."He said the five containers of nuclear waste arrived for disposal as planned at Sweden's Studsvik plant but they were not properly registered and were reported missing April 1.

The Atomic Energy Board traced the material through the West German Environmental Ministry and the Transnuklear company that organized the transports, according to Ek.

He said a stronger control system, including customs reports on all nuclear waste shipments, will be implemented during the next budget year.

"We will also demand that the nuclear plants and Studsvik inform us of transports within the country beforehand to make it possible to estimate what security is needed," he added.

The new reporting system will enable the board to monitor the waste transports step-by-step in the same way as shipments of atomic fuel, Ek said.