The Tokyo Electric Power Company (Tepco) has used a new robot to inspect inside the Primary Containment Vessel’s (PCV) torus room of unit #2 at Fukushima Daiichi. The torus is a gigantic, donut-shaped tank containing about 600,000 gallons of water to suppress (condense) steam released from the reactor vessel during an over-pressure condition. The robotic inspection is the most detailed to date with respect to the inside of any containment structure at the power complex. The inspection seems to answer one long-standing question about unit #2, but at the same time presents two new, more troubling questions.
First, there is no evidence of any deformation, cracks, or physical compromise of the torus tank itself. In addition, there is no indication of damage to the steel shell of the walls surrounding the torus tank. In other words, there is no evidence of any water leaks with the unit #2 PCV itself. See : http://www3.nhk.or.jp/daily/english/20120418_34.html The pictures should finally put to rest the myth of a hydrogen explosion inside the PCV on March 15, 2011. The pictures released by Tepco show no evidence of any kind of hydrogen burn, either. In fact, if we didn’t know better we might conclude that nothing happened at all. See : http://photo.tepco.co.jp/en/date/2012/201204-e/120419-01e.html
A more important outcome of the robot’s inspection is two new, albeit over-lapping questions. First, unit #2’s rate of cooling water injection is about double the water flow for the same amount of cooling as units #1 & 3. Decay heat production in each core is now about the same, so double the water flow should mean twice the cooling. The numbers just don’t add up. Prior to this week, it was assumed that there must be a serious leak from the RPV into the PCV, and from there to the turbine building basement. But, there doesn’t seem to be any source of leaks from inside the PCV. The water is not going inside the “drywell” area either, where a surprisingly low water level was discovered a few weeks ago. So the question becomes…where is the water going? Since the temperature is about the same for unit #2 as is the case with the other two units, the flows indicate that about half the water Tepco is trying to inject into #2 RPV is not getting there! Only half of the water intended for injection is actually cooling the damaged core, while the other half is being lost before it gets there. It is very possible there is a serious leak from the feed-water piping somewhere before the pipes pass through the PCV and Drywell walls. The leak’s location is anybody’s guess at this point, but not inside the containment structure itself.
Which leads to the second new question…If only half of the water being pumped to the unit #2 RPV is actually getting there, what is happening to the water coming out of the system after it cools the damaged core? It’s not leaking into the Drywell and it doesn’t seem to be going into the torus room. The water levels in both are physically lower than the water level inside the turbine building basement. Unless the law of gravity has been repealed, there is no way the ongoing influx of water going into unit #2’s turbine basement is coming from the building’s PCV or drywell. Thus, there must also be yet another piping compromise outside the PCV from a system which has as not yet been speculated upon.
Tepco needs to go back to the computer-simulated drawing board and try to ascertain where the cooling water for unit #2 reactor core is really going, because their assumptions to date have been effectively quashed! By all indications, there has been no “melt-through” from the unit #2 RPV and there are no leaks going into or coming out from the unit #2 containment building. The previous “official” speculations on water leaks inside unit #2 at Fukushima Daiichi simply do not make sense any more.