Let's kick the can...
It looks the cost-benefit ("performance-based") analysis argument by the Congressional Republicans in the House Energy and Commerce Committee won.
To recap the Committee's letter to the NRC chairwoman:
"With respect to these [safety] enhancements, we have particular concern about the potential requirement to install "filtered vents" for certain boiling water reactors which we understand to be significant, capital-intensive structures. As instructed by the Commission, the NRC staff has proposed four potential options but urged the Commission to choose "Option 3." Under this option, the Commission would issue an order requiring the installation of fintered vents rather than pursuing a performance-based process."
Now, the Nuclear Regulatory Commission will "study options" and won't make the final rule till March 2017. The Commission's thinking as you can read in the article below take the House Energy and Commerce Committee's thinking extremely seriously.
From Power News (3/21/2013; links are in the original, emphasis is mine):
NRC Delays Action on Vent Plan, Directs Staff to Study Options
The Nuclear Regulatory Commission (NRC) on Tuesday delayed approving a recommendation made by technical staff that calls for upgrades or replacements of "hardened" venting systems at the nation's 31 Mark I and Mark II boiling water reactors (BWRs), giving staff a year instead to assess other options and produce a "technical evaluation" on the proposal.
The NRC commissioners directed staff to follow a two-track approach for further improvements to systems for safely venting pressure during potential accidents at the reactors, in response to the Fukushima accident in March 2011. It gave the staff 60 days to finalize a March 2012 order, which will require vents to handle elevated pressures, temperatures, and radiation from a damaged reactor. The order will also ensure plant personnel can operate vents safely under these accident conditions.
It also gave the staff a year to produce a technical evaluation to support rulemaking on filtering, gathering more public input as it completes its analysis. Directing the staff to consider both the use of a filter to be placed on the vent, as well as a more performance-based approach using existing systems to achieve a similar reduction in radioactive release during an accident, the commission said the draft rule and final rule must be ready by March 2017.
A vent generally refers to a pipe connected to the primary containment of a nuclear power plant and leading to the plant’s exhaust stack. It is designed to allow gases inside the containment to be removed. “The major problem at Fukushima was getting the containment vents open,” said Doug True, president of ERIN Engineering and Research told Nuclear Insight last fall. “Significant delays in the decision to open the vents, combined with the Japanese decision-making process and difficulties in opening the vent valves, delayed the venting action, which in turn led to hydrogen explosions.”
The NRC's decision was widely viewed as a victory for the nuclear industry. The NRC has estimated that filtered vents could cost up to $15 million, but other estimates put costs of equipment at $30 million or more.
But media reports accusing the nuclear energy industry of opposing the installation of filtered vents on Mark I and II BWRs are incorrect, say Jason Zorn, assistant general counsel, and Steven Kraft, senior technical advisor at the Nuclear Energy Institute (NEI ). The issue is a technical one. "In the extremely unlikely event that an accident progresses to the point of the fuel melting through the reactor vessel onto the containment floor, it is imperative that water be injected into containment to cool the fuel debris on the floor," they say. "If not, radiation releases will occur from numerous locations in the containment building and bypass the vent. If the vent is bypassed, it doesn’t help if there is a filter on the vent, because it, too, will be bypassed."
Filtering strategies based on the individual plant evaluations could result in the installation of a vent filter, "if that’s what makes sense for a given plant," they said.
Sources: POWERnews, NRC, Nuclear Insight, NEI
“Significant delays in the decision to open the vents, combined with the Japanese decision-making process and difficulties in opening the vent valves, delayed the venting action, which in turn led to hydrogen explosions"?
The vents couldn't be opened for a long time because there was no power. There are experts and engineers who have proposed that instead of delay in venting leading to hydrogen explosion, venting may actually have caused hydrogen explosions in Reactors 1 and 3 because of the peculiar structure of the exhausts stacks and power loss. Instead of leaving via the exhaust stack, vented hydrogen gas came back inside the reactor building, they say.
Water under the bridge at this point, except that inaccurate understanding of the Fukushima I Nuclear Power Plant accident is being used as excuse.
"Performance-based" cost saving instead of "Defense in Depth", without properly defining "cost".
Defense in depth, in NRC's own words:
An approach to designing and operating nuclear facilities that prevents and mitigates accidents that release radiation or hazardous materials. The key is creating multiple independent and redundant layers of defense to compensate for potential human and mechanical failures so that no single layer, no matter how robust, is exclusively relied upon. Defense-in-depth includes the use of access controls, physical barriers, redundant and diverse key safety functions, and emergency response measures. For further information, see Speech No. S-04-009 (PDF), "The Very Best-Laid Plans (the NRC's Defense-in Depth Philosophy)."
I thought venting is an emergency response measure...