Fukushima meltdown: HPCI and RCIC Rupture Disc?

Update:
By around 2:30 a.m., the pressure inside the vessel that forms a protective bulb around the reactor's core reached twice the level it was designed to withstand. Amid delays and technical difficulties, it was another 12 hours before workers finished releasing radioactive steam from this containment vessel, via reinforced pipes, to the air beyond the reactor building.

About an hour later, the reactor building itself exploded—a blast that Japanese and U.S. regulators have since said spread highly radioactive debris beyond the plant. The explosion, along with others amid overheating at reactors 2, 3 and 4, contributed to radiation levels that led to mandatory evacuations around the plant and the government's admission that the Fukushima Daiichi disaster ranks alongside Chernobyl at the top of the nuclear-disaster scale.

Tepco says pressure in the containment vessel likely hit 840 kilopascals (the metric equivalent of 121.8 pounds per square inch) around 2:30 a.m, roughly double the maximum pressure of 427 kilopascals the vessel was designed to handle.

BURSTING OF HIGH PRESSURE COOLANT INJECTION STEAM LINE RUPTURE DISCS INJURES PLANT PERSONNEL

This is how I came to talk about it...topix.
OK, so I am really talking about a rupture disc...I will corrected the title...

Questions for fukushima building explosions...

It is excessive pressure safety device on the piping between HPCI exhaust and the torus....if the HPCI exhaust piping or torus pressure gets too high, the blow out panel is designed to rupture.

It is beyond interesting with the WSJ saying the Japanese torus and primary containment got to be twice the design pressure...why didn't these blow out panels let go.

The HPCI or RCIC exhaust needs to go under water, to be condensed by the torus cool water, I think comes in from the bottom of the tous.

It would be interesting in the Fukushima plants how these blow out panels functioned.

If they are under water, did the panel rupture and did that lead to prematurely draining the torus.

If above the water line in the torus, did the lowering of the torus water uncover the blow out panel and lead to the leak of hydrogen into secondary containment that distroyed the buildings...