WASHINGTON--The Three Mile Island accident has revealed a need for new safety measures that could affect nearly half of the atomic power plants in the country, Nuclear Regulatory Commission (NRC) staff members said yesterday.

The commission staff said the accident requires consideration of additional measures "on a priority basis" and the agency may issue a new directive today.

NRC staff members had earlier said further "actions" should be considered "for all light water power reactor facilities." All of the nation's 72 licensed nuclear plants except the one at Plattsville, Co. are light water facilities.

But Frank Ingram, an NRC spokesman, said later the staff meant to refer only to the 43 "pressurized water reactors," of which Three Mile Island Unit 2 is one example.

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The NRC issued safety bulletins concerning the nine plants built by Babcock and Wilson, the engineering firm that built the Three Mile Island plant in Pennsylvania. The new order could affect the other 34 pressurized water reactors designed by Westinghouse Corp. and Combustion Engineering Corp. Ingram said the NRC is not considering shutting down any nuclear plants.

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Ingram said the NRC staff "is expected to advise utility operators of pressurized water nuclear power plants of these new actions sometime tomorrow." He did not mention what the actions are.

The staff members said they discovered certain instruments in some power plants designed by Westinghouse can give conflicting and misleading readings about coolant water levels in the reactor. NRC officials have said a similar situation existed at Three Mile Island and may have contributed to the accident.