Kujala, May 24th 2011
This is an updated version of SFP 4 -theory, this time following completely TEPCO guidelines...
1. So where to begin? Seawater was sprayed to the pool between March 22nd and March 27th, first by the concrete pump and later also via the Fuel Pool Cooling Line:
March 22nd 17:17～20:32
March 23rd 10:00～13:02
March 24th 14:36～17:30
March 25th 19:05～22:07
March 27th 16:55～19:25
March 25th 06:05～10:20
2. Was seawater contaminated at that time? Yes it was.
From this chart it can be seen that on March 27th the levels of I-131, Cs-134 and Cs-137 were already elevated, I-131 levels being 250 times the limit:
And these were taken 330 m south from discharge canals 1 - 4. The levels must have been much higher near the plant.
Much depends where they put the hoses in the sea.
Here from more recent data (April 2nd) it can be seen that radioactive levels (I-131) of seawater at the screen were huge near unit 2 and further away to directions of unit 1 and 3 & 4 the levels are decreasing but are still big:
Unit 1: 19 000 Bq/cm3
Unit 2: 300 000 Bq/cm3
Unit 3: 15 000 Bq/cm3
Unit 4: 14 000 Bq/cm3
3. Has TEPCO admitted that contaminated seawater may be the reason for the radiation in the SFP 4?
It said the radioactive materials detected in the latest check could have come from seawater sprayed into the pool to cool the reactor.
4. If we suppose that seawater pumped to unit 4 SFP has been taken in front of unit 4 then the above level 14 000 Bq/cm3 would serve as some kind of maximum for the SFP. The highest level of I-131 so far has been 220 Bq/cm3 (April 12th):
As for the amount of radiation in mSv/h, this piece of news has been given:
84 mSv/h 6 meters above the SFP on April 12th:
5. The levels of cesium on May 7th were 63 % for Cs-134 and 72 % for Cs-137 from the values on April 12th:
This could indicate a small leak from the bottom of the SFP.
Concerning the situation of the unit 4 SFP the accuracy of this article has been questioned:
There is however one piece of information that seems to be reliable because it explains why TEPCO denied the possibility of a leak only one day after it had admitted the possibility of the leak:
The company checked the reactor facilities, suspecting water might be leaking from the pool, but cannot confirm water leakage into the bottom structures of the reactor building.
So what other explanations are there left if we exclude completely the possibility of a leak or something that behaves like a leak (an overflow for instance)?
a) Before the measurement on April 12th there was a long gap between water sprays meaning that the water level could have been low:
April 9th 17:07～19:24 Water spray
April 12th 12:00～13:04 Sampled the water in SFP.
April 13th 0:30～ 6:57 Water spray
The water level could have been higher on May 7th.
b) Because of the same reasons presented in a) the water could have been more evenly diluted on April 12th than on May 7th. If only one sample has been taken the result would be dependent on coincidence.
The fact is however that contaminated water has been found in the basement of the reactor building 4. Some explanation for this contaminated water is needed. So the decrease of cesium could still support a theory that a small amount of water from the SFP 4 is missing. We just have to find another explanations.
6. If the gate between SFP and RPV is broken there could be a flow of water from SFP to RPV. The big question is has TEPCO denied that RPV could be leaking? As far as I see it they have only checked the reactor building for SFP leaks but not for RPV leaks which would likely mean some additional checking. They have stated in their reactor status summary:
At this moment, we do not consider any reactor coolant leakage inside the reactor happened.
But as I see it this statement may come from the speculation that only checks for SFP leaks at the current moment are necessary or needed. Or in other words: if they restrict themselves only to the checks of leaks from the SFP they can give us the positive result that everything is fine although it may not necessarily be true.
However, in this post jpquantin makes some points against the gate is broken -theory:
And then again in this post:
Also if the RPV would be leaking the expected outcome would be to see a steady decline of the levels of cesium in the SFP 4 water. So the future measurements from the unit 4 SFP will show if the decline of cesium continues. If on the other hand the decline of cesium seems to stop it would rather indicate that the leak has stopped. This is the route I am predicting here.
7. The basics for the water found in the basements:
The water load from tsunami has been massive so it is only logical that this water will be later found somewhere. During tsunami the water may have found direct routes into the basements by braking some structures. This could explain the finding of two dead men in the basement of the unit 4 turbine building:
Afterwards there may have been more subtle routes like the tsunami waters infiltrating into the basements from outside through concrete. It is assumed that reactor buildings are waterproof but the functionality of these systems can be questioned. First of all, the waterproof systems may have become fragile over years. And secondly, the quake may have caused some damage to the waterproof systems.
Tsunami covered the whole area of every turbine and reactor building as can be seen from the page 30 of this document:
TEPCO is also thinking that the tsunami waters constitute the main part of the water found in the basements as presented here by Mr. Yoshida, TEPCO chief engineer:
The water is mainly concentrated from the tsunami that has leaked into the plant and then got contaminated...
So when putting this all together we are expected to find tsunami waters in the basements of the turbine buildings but it is not completely excluded that the same thing might happen also in the reactor buildings if we accept some kind of damage to the waterproof systems.
8. The contamination of the basement of the reactor building:
The level of water in the basement of the reactor building 4 is 500 cm and radiation is 100 mSv/h:
If we speculate that the water is coming from the unit 4 SFP then the radioactive levels of SFP water serve as maximum for the water in the basement. 84 mSv/h was measured 6 meters above the SFP so the level on the surface of SFP water must be higher. 100 mSv/h on the surface in the basement is therefore on par with 84 mSv/h measured 6 meters above the SFP.
But what would be the routes of water from the SFP into the basement? This question is better answered negatively.
TEPCO has said the SFP is not leaking. So this is one route which should be excluded. We also exclude the leaking of the RPV as discussed previously.
So what is there left?
a) Some sprayed seawater may have missed the target and the water may have flowed through some unknown route into the basement.
b) Is it possible that SFP 4 has overflowed at some point? If so this water may again have flowed into the basement. The route may be same as in a).
c) Is it possible that there is a leak in the upper structures of the SFP where the water would flow some "outside" route into the basement? The main thing is here that this leak would not be detected by the checks they have made underneath SFP ("inside" route).
It might also be the combination of a) and b) or a) and c).
What is TEPCO's/government's view?
The water in the basement of the No. 4 reactor building at the Fukushima Daiichi nuclear power plant is now five meters deep following frequent water-spraying with outside equipment to cool its spent fuel pool, the Japan Nuclear and Industrial Agency said Monday.
They seem to suggest that water-spraying is the cause but they don't define any particular route.
9. The contamination of groundwater
The theoretical route presented here is from the basement of the reactor building. The idea is that the water is infiltrating through the concrete and mixing with groundwater. The supporting idea is that the waterproof systems are not working any more.
The result would be to see medium-level contaminated groundwater under unit 4. The radiation should be on par with 100 mSv/h found in the basement of the reactor building. As we don't know the radiation of groundwater in mSv/h we can also compare directly the radiation of the SFP with that of groundwater.
Groundwater between 6th of April and 27th of April in Bq/cm3:
Date: 6th 13th 16th 18th 20th 22nd 25th 27th
I131: 24 17 13 7,9 79 0,53 0,093 0,049
Cs134: 1,8 2,7 2,7 0,86 7,9 0,37 0,12 0,12
Cs137: 1,9 2,7 2,7 0,92 7,9 0,4 0,13 0,13
SFP between 12th of April and 28th of April in Bq/cm3:
Date: 12th 28th
I131: 220 27
Cs134: 88 49
Cs137: 93 55
And then we can compare maximum values:
Isotope: SFP Sub-drain
I131: 220 79
Cs134: 88 7,9
Cs137: 93 7,9
SFP gives us the maximum levels and so the levels of groundwater seem to be on par with the SFP levels.
10. The contamination of the basement of the turbine building
According to this source the level of water was +80 cm in the unit 4's turbine building. (dated March 29)
According to this source the level of radiation was less than in unit 1, 2 and 3. (dated March 28)
The radiation in the unit 1 turbine building was 60 mSv/h. (dated March 27)
So the conclusion is that around 27th - 29th of March the water level in the unit 4's turbine building was +80 cm and radiation less than 60 mSv/h.
Where is the radiation coming?
1) The first choice is directly from the SFP. In this case we could perhaps expect the radiation level to be about the same as in the basement of the reactor building because in this theory the water in the basement of the reactor building is coming also from the SFP. But there seems to be less radiation in the basement of the turbine building (< 60 mSv/h versus 100 mSv/h). There might be more water in the basement of the turbine building to dilute with. The height of water (80 cm versus 500 cm) doesn’t tell the whole truth as we must also know the surface area of the basements. Another option is that the leakage into the turbine building is smaller than the leakage into the reactor building.
2) The contaminated water could infiltrate from the basement of the reactor building through concrete into groundwater. Here we assume that the waterproof systems are not working any more. Then groundwater would move towards the sea and infiltrate again through concrete into the basement of the turbine building. The turbine building is perhaps not waterproof. Because contaminated water is diluting with groundwater we could expect the radiation level in the turbine building to be less than the level in the reactor building. In this case < 60 mSv/h is on par with 100 mSv/h.
3) Because unit's 3 and 4 turbine buildings are connected there might be a flow of contaminated water from unit 3 turbine building to unit 4 turbine building. The level of radiation in unit 3's turbine building has been 750 mSv/h:
This would indicate a small leak from unit 3 to unit 4 (750 mSv/h versus < 60 mSv/h).
In the case of 1) and 3) also a leak from the turbine building into groundwater is possible. So in this case groundwater would contain water both from the basement of the reactor building and from the basement of the turbine building.
In the case of 2) groundwater would contain water mainly from the basement of the reactor building whereas the turbine building would be the receiving side of this contaminated groundwater.
The water-spraying operations into the SFP of the unit 4 using seawater are enough to explain all findings of contaminated water found in four different places: 1) Spent fuel pool itself. 2) The basement of the reactor building. 3) The basement of the turbine building. 4) Groundwater underneath the unit 4.
The radiation levels in the different parts of the buildings and underneath the building (groundwater) are on par with each other.
The biggest weakness of this theory is the route from the SFP into the basement of the reactor building. This route has not been identified by TEPCO and TEPCO has denied the possibility of water leaking from the SFP into the room below it.
If we want to make an explanation completely without leaks the contamination of the basement of the reactor building could be the result of sprayed seawater that missed the target and SFP water that overflowed.
Further investigations are needed to confirm or discard this theory.