TEPCO announced during the February 1 morning press conference that the valve of a pipe line connected to the reactor was found broken and at least 6 liters of water from the reactor had spilled.
The Reactor Well/Reactor Pressure Vessel of Reactor 4 is filled with water even if it does not have any fuel (since it was in maintenance when the accident happened), and the water goes back and forth freely between the Reactor Well and the Spent Fuel Pool as the gate separating them has been loose since the January 1 earthquake.
It is the water co-mingled with water from the Spent Fuel Pool that was leaking, as evidenced by the relatively high radioactivity of the water.
Information gleaned out of the three bumbling TEPCO people (without Matsumoto) who didn't seem to know much at all (except one), to the irritation of the reporters who attended:
At 10:30PM on January 31, a worker found the water leaking from the jet pump test line valve in the southwest corner on the 1st floor of Reactor 4 during the "patrol" (which is probably a lie, as you'll see later).
There are 20 jet pumps inside the Reactor Pressure Vessel.
The nature of damage of the valve is not known. It is probably not from freezing. It may have been broken when the explosion happened (last March).
The jet pump test line connects to the jet pumps inside the RPV.
The water stopped when they shut off the main line coming from the RPV, at 10:43PM.
It is hard to tell whether the test line valve broke recently or not, as the floor is littered with debris.
The leaked water is estimated to be about 6 liters as far as they could find on the floor full of debris.
The water is from the Reactor Well. The reactor has no fuel inside as it was on maintenance when the accident happened, but it is filled with water.
Radioactivity of the leaking water is 35.5 becquerels/cubic centimeter (but TEPCO couldn't say whether it was all-gamma radiation or something else). Therefore, it is the water from the Reactor Well which is connected to the Spent Fuel Pool.
The Reactor Well and the Spent Fuel Pool are separated by the gate, but the gate got loose after the earthquake on January 1 and the water from the Spent Fuel Pool comes in to the Reactor Well.
Actually, TEPCO knew something was amiss on January 30 when they noticed the water level of the Skimmer Surge Tank dropping rapidly at 3:50PM. The cooling system for the Spent Fuel Pool was re-started at 3:13PM that day, and they thought the Skimmer Surge Tank's level had something to do with the cooling system and decided to observe for one day and look for possible causes.
The water level of the Skimmer Surge Tank was dropping at 60 to 90 millimeters per hour.
Then on January 31, a worker found the broken valve at the jet pump test line. (See, it was not a routine "patrol"; they were looking for possible causes of the drop in the Skimmer Surge Tank level and found the leak.)
When the leak was stopped, the drop in the water level of the Skimmer Surge Tank stopped.
As the only person who was able to talk about anything technical explained, water goes back and forth freely between the Reactor Well and the Spent Fuel Pool, and if the water level of the Reactor Well goes down that means the water level of the Spent Fuel Pool goes down, and that is reflected in the water level of the Skimmer Surge Tank.
The Skimmer Surge Tank water level hardly changes in the cold weather like this.
The leak is probably confined within the reactor building, and the leaked water was probably led to the basement water.
Well well. When the water level drop in the Skimmer Surge Tank in Reactor 4 was first reported after the January 1, 2012 earthquake, the explanation was, as I clearly recall, that the water in the Spent Fuel Pool went into the Reactor Well when the gate got loose, and therefore not enough water went to the Skimmer Surge Tank. They also said the water level of the Skimmer Surge Tank would go down naturally due to evaporation.
Now they finally admit that the water level of the Skimmer Surge Tank is the direct indication of the water level of the Spent Fuel Pool.
6 liters of the contaminated water from the Spent Fuel Pool/Reactor Well doesn't make sense if the Skimmer Surge Tank water level was dropping 60-90 millimeters per hour for 29 hours. Several reporters pressed for a clear answer, but TEPCO said they would get back to them after calculation.
P.S. I just read a post by Ms. Emiko Numauchi as "Numayu" writing that there was nuclear fuel inside the Reactor Pressure Vessel of Reactor 4 and it had a meltdown, as she heard from a worker she trusts, and the English translation of the post by someone else.
If the fuel melted through the RPV and now on the floor of the Containment Vessel as she claims, I have no idea how the RPV/Reactor Well is able to retain water, as it clearly does, looking at the photographs. Of course she or anyone can claim they are fake photographs.
As for me, I want to find the facts as much as possible without resorting to calling everything fake. Even from TEPCO, the reporters on February 1 press conference were able to draw out more information than what TEPCO initially presented in the beginning of the press conference.
Well of course TEPCO can be lying 100%, but it simply would not make sense for TEPCO to hide a meltdown on Reactor 4 if it happened. There are already 3 meltdowns, and part of the melted fuel has eaten into the concrete floors of the Containment Vessels. What's the point of hiding another meltdown, after 10 months?