A report just released by the National Academy of Sciences bears two disturbing revelations. The cooling pools for nuclear waste at some reactor sites may be far more vulnerable to a devastating attack by terrorists than federal regulators are willing to admit. And the Nuclear Regulatory Commission is operating in a hermetically sealed cocoon that makes it difficult for anyone - even the academy, armed with a Congressional mandate - to tell whether the public is adequately protected.

The academy was brought into the fray after a group of scientists, analyzing reports published by the regulatory commission itself, issued a report suggesting that a terrorist attack could crack the pools that hold used nuclear fuel at reactor sites, thereby causing a leak of cooling water and setting off fires that could unleash radioactive plumes worse than those at Chernobyl. In asking for the study, Congress directed the regulatory commission and other federal agencies to provide the information the academy needed. That proved to be wishful thinking. The academy got only part of what it needed and was denied the rest on security grounds.

Even so, the academy was able to penetrate the myth put out by the regulators and the nuclear industry that spent-fuel pools at reactor sites pose an extremely low risk. In a report made public on Wednesday, a panel of experts assembled by the academy concluded that several types of credible terrorist attacks, using planes, truck bombs or a ground assault with advanced weapons, might be able to release large quantities of radioactive material into the environment. The likely contamination would not be on the scale of Chernobyl, panelists say, but it could be severe. The plants thought to be most vulnerable are those with above-ground pools in buildings not shielded behind other structures.

To reduce the potential for radiation-releasing fires, the panel suggested that plant operators reposition the spent-fuel assemblies in their pools to minimize the buildup of heat and, where warranted, install water-spray systems to cool the spent fuel should the pools be drained. It also called for an evaluation of each plant's vulnerability and suggested that, if the results justified it, the commission might want to speed up the removal of spent fuel from the cooling pools into dry casks, where the likelihood of major releases would be less.

The commission pooh-poohed the report even before it was released, suggesting that the academy overstated the risks, that the pools themselves are robust structures and that if water leaked out and the fuel overheated, a couple of fire hoses could save the day. That seems too glib, given the academy's acknowledged expertise and presumed objectivity.

It is disturbing that the commission, in the name of national security, denied the academy the information needed to assess the effectiveness of security improvements instituted since 9/11, refused to brief the panel on what kinds of threats it was prepared to guard against and slowed the release of this unclassified version of a classified report with endless fights over what could be said publicly. In general, the agency gave the academy what it needed to assess the physical vulnerability of spent-fuel pools but little of the information needed to assess the readiness of plant guards and technicians to hold off attackers and mitigate any damage they might cause. The commission is apparently now ready to supply additional information, but the lesson of this sorry episode is clear. The next time Congress asks for a National Academy of Sciences report, it needs to ensure that the agencies whose performance will be evaluated cooperate more fully.