U.S. nuclear reactors are safer than they were before the Fukushima Daiichi meltdown that occurred three years ago in Japan, but automated data collection systems are still not prepared to operate in extreme conditions, according to a Government Accountability Office report.

The GAO report, which studied 16 countries and was requested by the State Department, recommended that the Nuclear Regulatory Commission quickly decide how and whether to upgrade data systems to withstand severe situations. Those systems are responsible for communicating critical power plant data to regulators.

"By delaying its decision on upgrades to enable the system to function under emergency conditions, the system may not function when needed most — during a severe accident," said the report, released Tuesday, which added that the NRC "might be missing a chance to lead by example."

The regulator said it does not consider such emergency response data systems a safety feature. It did not say whether it agreed or disagreed with GAO's recommendation to upgrade those units, noting it is working on areas it considers to be higher priority before rendering a decision on such systems.

Still, NRC Chairman Allison Macfarlane said the federal regulator has implemented a number of changes in response to the March 2011 disaster, which inspired a rethinking of nuclear safety around the world.

“The NRC staff’s work has focused on better positioning the reactor fleet to respond to future ‘unknown unknowns.’ We’ve learned and accomplished a great deal,” she said Tuesday.

The 9.0-magnitude earthquake and resulting tsunami knocked out the Japanese nuclear plant's electricity and caused a partial meltdown in three reactors, spewing radioactive material into the air and forcing more than 100,000 people to flee the area in what amounted to the largest nuclear disaster since the 1986 Chernobyl accident.

Following Fukushima, the NRC and regulatory bodies in other nations have been considering the possibility of "previously unimagined accident scenarios," such as those that would affect multiple reactors at a single power plant, the GAO report said.

Most of the countries studied also have imposed stricter rules governing emergency equipment — the NRC, for example, issued an order regarding water used to cool reactor cores — hydrogen control and filtered venting systems, which minimize the release of radioactive materials during emergencies.

The NRC has set a 2017 deadline for a final rule on filtered venting systems. The commission's staff has recommended installing them at the nation's 31 boiling water reactors with Mark I and Mark II containments, which are similar to those used at Fukushima.

The NRC also has directed plant operators to develop plans for alleviating problems faced during periods of long-term power loss.

"[A]s the most safety-significant changes draw nearer to completion, we’re confident that the requirements we’ve imposed, and the actions industry has taken, supplement an already rigorous oversight program," Macfarlane said.