"The highest priority now is to get the K reactor started safely," he said.

It cuts a path beneath the surface that is within a half-mile of the K reactor, which the Energy Department hopes to restart first this year.

The full complement of fuel rods from which tritium is produced will not be retrieved from K reactor until near the end of 1991.

The accident occurred in the K reactor during a test of the system that cools heated water from the reactor vessel.

None of the reactors have run since April, with the exception of an abortive attempt to restart the K reactor in August.

Some say privately that K reactor may not restart until at least 1990 and that it could be years before all three reactors operate again.

This occurred in the K reactor on Jan. 20, 1970, when four fuel assemblies failed after burning out, the study said.

The Energy Department decided earlier this year it only needed one reactor to operate, and late last week K reactor began a series of tests.

The Energy Department said earlier this month that more than $1 billion was needed to complete the repair project on K reactor.

The Energy Department also has spent more than $1 billion in the last two years designing a new reactor to replace K reactor.