The Nuclear Regulatory Commission (NRC) on Friday issued Interim Staff Guidance (ISG) to U.S. nuclear power plants to ensure adequate implementation of three orders it issued in March in response to lessons learned from the Fukushima Dai-ichi nuclear accident.

The ISGs are not mandatory. They representing what the NRC said are “acceptable approaches” to meeting the orders’ requirements before their Dec. 31, 2016, compliance deadline. However, U.S. nuclear power plants would have to seek NRC approval if they wanted to follow a different compliance approach.

The final ISGs follow draft versions issued on on May 31 and asked for public input. The NRC said the final ISGs reflect information gained from the month-long comment period and subsequent public meetings.

The first order requires all U.S. plants to better protect portable safety equipment put in place after the 9/11 terrorist attacks and to obtain sufficient equipment to support all reactors and spent fuel pools at a given site simultaneously. “The ISG for this Order endorses the industry’s updated guidance for dealing with a scenario that knocks out all of a plant’s alternating current electric sources,” the federal regulator said. The updated approach includes the use of backup power supplies for devices that would burn off accident-generated hydrogen before it could accumulate to explosive levels. The staff concludes the updated approach will successfully implement the Order.

The second order applies only to U.S. boiling-water reactors that have “Mark I” or “Mark II” containment designs. Mark I reactors must improve installed venting systems that help prevent core damage in the event of an accident; Mark II reactors must install these venting systems. “The ISG for this Order provides more detailed technical information on the vents, as well as how vent designs and operating procedures should avoid, where possible, relying on plant personnel taking actions under hazardous conditions,” said the NRC.
The third order requires all plants to install enhanced equipment for monitoring water levels in each plant’s spent fuel pool. The ISG defines in more detail the water levels the new equipment must accurately report, as well as standards for equipment mounting, powering and testing, personnel training, and other criteria. The final ISG notes several areas, including instrument qualifications and instrument protection from falling debris, where the industry revised its initial approach. An exception in the staff’s endorsement sets specific seismic criteria to ensure the instruments will survive an earthquake.

Source: NRC

—Edited by Sonal Patel, Senior Writer (@POWERmagazine)