This is scary at first sight.Excerpt from the article

A potential problem with the emergency reactor core cooling system at the nation’s largest nuclear power plant went undetected from 1986, when it began producing power, until last week, the Nuclear Regulatory Commission(NRC) and the plant operator confirmed Thursday.

The issue was identified when engineers at the Palo Verde Nuclear Generating Station did an analysis after NRC inspectors raised questions at a detailed inspection early last week. The NRC was following up to see if earlier cooling system problems had been fixed.

The review showed the emergency cooling system may not operate as expected to provide water to reactor cores after a small leak in the reactor cooling lines, NRC spokesman Victor Dricks said.

Practically, for this flaw to lead to any kind of disatrous results, lots of redundant safety systems need to fail together. Well, i am not refuting the fact that such an incident could have happened anytime in the past 19 years of its operation but chances for a complete failure and a meltdown are slim. Nevertheless, this is definitely a serious issue and hopefully, the NRC will bring in a stricter system to check all the flaws in all operating reactors.

God, i dont even want to begin to imagine what the media fuss will be, on all this.