Human error main cause of accident at Three Mile Island

Press, 4 August 1979, Page 9

Human error main cause of accident at Three Mile Island

NZPA-Reuter Washington i Investigators for the I United States Nuclear Regulatory Commission said] yesterday that the reactor: breakdown at the Three Mile, Island nuclear plant near Harrisburg, Pennsylvania, could be attributed to many factors, but most of all to human error.

The investigators concluded that the plant’s equipment and emergency procedures were “adequate to have prevented the serious consequences of the accident if they had been permitted to function or be carried out as planned.” But, the investigators said, a series of errors by plant operators made it impossible' for the plant to continue working as designed, thereby resulting in “the most serious accident in United States commercial nuclear power-plant operating history.”

The commission’s report was issued just as a Congressional committee completed a report highly critical of the commission’s plans and procedures for locating power plants and evacuating people living near them in emergencies. At the same time, the Presidential commission that is investigating the accident at Three Mile Island heard testimony about the difficulty that state and local emergency officials ex-

jperienced in dealing with •the crisis caused by the accident on March 28 at the nuclear generating plant. In its report on the causes of the breakdown, the comi mission’s investigators ex- > pressed particular concern about operator interference with the plant’s emergency cooling system. , "Had the operators allowed the emergency corecooling system to perform its intended function,” the i investigators said, “damage Ito the core would most likelv have been prevented.” When the accident occurred, the operators cut off emergency cooling pumps at several points because their interpretation of various dials indicated that the coolant fluid surrounding the fuel core was at the required level. In fact, it was escaping through a stuck valve and thus permitting the core to nverhoat. The investigators attributed the pumps’ shut-down to an unwarranted "mind set” among operators that overfilling the reactor with coolant was to be avoided “at almost any cost.” Operators at other plants had reacted in a similar manner when less serious accidents occurred, the investigators said, adding that the commission had ordered operators throughout the country to be retrained in an effort to “preclude recurrence.”

The investigators concluded that the amount of radiation that escaped when the Three Mile Island reactor was damaged presented “minimal risks” to people living in the surrounding But they said the plant, operated by the Metropolitan Edison Company, should have done a better job of containing the radiation. Besides blaming operator mistakes and equipment failures for the accident, the commission report was also critical of the implementation of emergency plans, and expressed concern about the paucity of information available at times about what was happening. Carrying out emergency plans, 'particularly by the Nuclear Regulatory Commission, was one of the main topics in the Congressional report on reactor accidents that was completed yesterday by the House Government Operations Committee. Although toned down somewhat from an earlier draft version, the report nevertheless accused the commission of being remiss in not requiring plants, states, and localities to prepare detailed emergency plans for plant accidents. Plants should not be allowed to operate in the absence of approved plans, the committee report added.