Residents near the Monju fast-breeder reactor in Fukui Prefecture are preparing a lawsuit to demand the experimental nuclear plant be closed for good, sources familiar with the matter said Saturday.

The lawsuit, which will be filed soon with the Tokyo District Court, possibly later this month, will assert the government never should have authorized construction of the trouble-prone prototype. The filing will be announced Tuesday to mark the 20th anniversary of the sodium leak accident there, the sources said.

Regulators recently recommended that the operator of Monju be replaced because of the plant's recurring safety lapses.