The North restarted the reactor at the Nyongbyon complex only last summer, backtracking on a commitment of previous aid-for-disarmament negotiations.
A constant water supply from a nearby river is essential to cool the reactor and another reactor under construction. US-Korea Institute says satellite imagery show the recently restarted reactor may have been temporarily shut down or operated at a lower power level for repairs after flooding caused the river to change course.
The findings are being published yesterday on the institute's web site, 38 North.