Nuclear engineer Arnie Gundersen (pictured at left), in a video now posted at the homepage of Fairewinds Associates, explains that a non-radioactive test performed at the Brunswick, North Carolina General Electric Boiling Water Reactor of the Mark I design 40 years ago, supports his theory that the primary reactor containment head at Fukushima Daiichi Unit 1 lifted, due to elongation of bolts, allowing hydrogen gas generated by the meltdown in the reactor core to escape into the secondary or outer reactor containment building. "It only took a spark" to then detonate the hydrogen gas, destroying the reactor containment building. Thus, and very significantly, all the talk (including in the U.S. Nuclear Regulatory Commission's Fukushima Task Force deliberations) about "hardening" the vents at U.S. and other Mark Is around the world is irrelevant. This is a flaw in the Mark I design that any hardening of the vents to make them "new and improved" cannot solve. Arnie shows a photo revealing that the vent at Fukushima Daiichi Unit 1 appears to have been functioning before the explosion -- steam is visible exiting the top of the Unit 1 "smoke stack." Despite this, it did not prevent the explosion that followed.