11.   It was necessary to form teams to fill sacks with sand, which we later dropped into the reactor core.

12.   Later, he raised public alarms over nuclear waste left in the Arctic by submarine accidents and haphazard disposal of spent reactor cores.

13.   Radioactive gases began seeping into the reactor core.

14.   Rupture also could spill spent fuel pellets into the reactor core, forcing a costly and time-consuming cleanup that would delay restarting the reactor.

15.   The loss has been caused by a three-month closure of the plant to deal with a design flaw in the emergency shutdown system for the reactor core.

16.   The reactor was expected to return to service yesterday after a scheduled shutdown to change fuel in the reactor core.

17.   The scientists and engineers are working on the design of the reactor core for the next generation of submarines.

18.   The subs are largely deserted, some reportedly without security, even though highly radioactive reactor cores remain on board.

19.   The severed wire disabled a switch that turned on one of two high-pressure pumps that would flood the reactor core during an accident.

20.   The uranium-oxide fuel pellets would start to melt, releasing radioactivity into the graphite reactor core.