The US Nuclear Regulatory Commission (NRC) commissioners have voted to follow a "two-track approach" to improve the safety systems for venting pressure at 31 US boiling water reactors.

In a memorandum issued on 20 March, the NRC calls for enhancing a March 2012 Order that requires "hardened" venting systems at 31 boiling-water reactors with Mark I and Mark II containments.

The directive also starts rulemaking activities to produce requirements for those reactors to cool core debris and filter significant radiation releases.

NRC has given staff 60 days to finalize the enhanced Order, which will require the vents to handle the elevated pressures, temperatures and radiation levels from a damaged reactor, and for plant personnel to be able to operate the vents under those conditions

Staff will have a year "to produce a technical evaluation to support rulemaking on filtering." They must develop a proposed rule and a final rule by March 2017, NRC said.

The US Nuclear Energy Institute welcomed the news.

"The nuclear energy industry concurs that the Nuclear Regulatory Commission staff should develop the technical basis for a rulemaking for filtering strategies and severe accident management of BWR Mark I and II containments," said NEI senior vice president and chief nuclear officer, Anthony Pietrangel.

"The rulemaking process is the proper approach for consideration of this matter, as it affords all stakeholders the opportunity to participate," he added.

Caption: Oyster Creek, America’s oldest operating boiling water reactor, photo courtesy Exelon.