Fukushima disaster, questions

Several questions are formulated about the Fukushima disaster. 2011 March 19, the link to these questions had been uploaded to the the Cabinet of the Prime Minister of Japan ; up to 2011 May 9, no reply has been received. These questions are repeated below; some answers are suggested.

q01, maps of contamination?
Why soon after the accident at Fukushima the maps of contamination of the area with unstable isotopes were not published in web (making similarity with the Chernobyl disaster)?

q02, is it worth to stop all reactors at the earthquake?
According to the publications, the problem at the Fukushima plant was caused by the tsunami that covered the emergency generators that were supposed to provide the cooling of the reactors after the emergency shut down. Would the accident occur, if at least one of the reactors would remain operating during the earthquake (and providing the cooling of other reactors after the tsunami)?

q03, reactors above the ground?
Usually, the reactors are built above the ground. This make expensive the construction of the sarcofags. Why the core of reactor is usually placed ABOVE the level of sea? Would it be below the sea level, wouldn't it be easier just to open the gateway to let the water merge the core of a problematic reactor, than to deliver water with pumps, helicopters and suicide fire-fighters?

Answer: In general, the underground reactors are safer than those above the ground. The idea is pretty old. In century 20, Nobelist Andrew Sakharov had expressed his opinion, that the reasons of safety require that all the reactors are placed below the ground, and the special international law is necessary to prohibit the above–ground reactors.

New question: The Fukuhima disaster is estimated to cost to TEPCO of order of \(10^{12}\) yen. (of order of \(10^{10}\) american dollars). Japan counts some tens of nuclear reactors. Would it be possible to make the deep caves in the ground and put the reactors there (allowing the passive cooling in the case of a disaster and simplifying the burying when necessary) for some \(10^9\) yen each?

q04, only water vapor?
In the most of reactors, the working medium is water vapor. This was natural solution for the first reactors of the past century, as analogy with even older steam locomotives. Does any company perform any research for use of other working media? Did anybody design a reactor, for example, on the vapor of UF_6 instead or water vapor? Is it difficult to make a ceramic turbine for such a reactor? Why the core of the most reactors is solid? Why there are no reactors with liquid core?

Partial answer: The reactors with liquid core were reported:

http://nextbigfuture.com/2007/12/fuji-molten-salt-reactor.html Fuji Molten salt reactor. DECEMBER 19, 2007.  The attractive features of this MSR fuel cycle include: the high-level waste comprising fission products only, hence shorter-lived radioactivity; small inventory of weapons-fissile material (plutonium-242 being the dominant plutonium isotope); low fuel use (the French self-breeding variant claims 50kg of thorium and 50kg uranium-238 per billion kWh); and safety due to passive cooling up to any size. (Upgrade of the question: Such reactors do not seem to be dominant: are they too expensive?)

http://www.ornl.gov/~webworks/cppr/y2001/pres/120507.pdf Charles Forsberg. (Oak Ridge National Laboratory) Safety and Licensing Aspects of the Molten Salt Reactor. (2004)

q05, reactor without forced cooling?
5Why there are no reactors that could remain without the forced water cooling after the shut-down? Would such a reactor be too expensive? Or just non-efficient?

q06, update of question 01
Does the non-publication of the map of contamination mean that the reactors will be in fire until the most of their content burns out and drops into the atmosphere? (The development of the events indicate that perhaps the answer should be "Does not".)

q07, push to the sea?
Is it possible to move the rest of the exploded reactors into the sea, push them into the pound seen at the satellite view, to merge them into water and to make a dam reducing the contamination of the Ocean? (After the successful cooling, this question becomes not so urgent, but still academic.)

q08, relaxation heat?
After to stop the chain reaction the heat generated in an active element gradually reduces. Did anybody plot the dependence of the power generated versus time? Where can one see such a graphic? For how long will the exploded reactors require the forced cooling? Is it question of several weeks or several years?

Answer. Some estimate and links are collected in the special article decay heat. After the shut down, the decay heat is more than sufficient not only to melt the core of the reactor and the containment vessel, but even to evaporate them both in the atmosphere; and only the continuous forced cooling prevents this. After the shut–down, the nuclear reactor becomes completely dependent on the external sources of the energy. If they are damaged by the same event that caused the shut–down (earthquake, tsunami, tornado, etc.), then the nuclear accident (or nuclear disaster) happens.

For some under–discussed reasons, the decay heat of a nuclear reactors after the shut town is difficult to use and usually it is not used; at the failure of the emergency generators, the reactor melts and burns.

Some hints to the recycle of the relaxation are suggested in ; but the author of that article does not justify such a hint, so, it is difficult to consider it seriously,

The testing of the emergency cooling is difficult. The Chernobyl disaster is reported to be caused by the intent to test the emergency system. The reactor was intentionally set to the dangerous regime; and the test failed, causing millions of victims.

q09, where are robots?
Is the price of a modern universal robot (that could bring the water tube to cool the reactor) higher, than the insurance fee the TEPCO pays to the families of the suicide nuclear workers?

q10, how deep into the earth does the melt-down go?
What happens with a core of reactor if it is melted-down and, while hot, buried with a 100m layer of the ground (stones, rocks, garbage, sand, borons, gumus)? Does it continue melting down deeper and deeper toward the core of the Earth?

q11, emergency pool?
Does it have sense, to arrange the emergency pool in vicinity of each reactor for the case of problem of the conventional cooling mechanisms, in order to drop the reactor into such a pool when it cannot be cooled with a civilized way?

Answer. To move the heavy, hot and radioactive smoking reactor, even if to emergency pool, it is difficult and dangerous operation. Much easier would be to mount the reactor in such a pool, in order to fill it with water (which seems to be the cheapest coolant) at the emergency; then, the boiling would provide the convectional cooling even at the total failure of all the mechanisms of the nuclear plant. According to Nobel laureate Antrei Sakharov, only the underground reactors can be sufficiently safe; in century 20, he had suggested the total prohibition of the above-ground reactors in his preface to the Chernobyl lessons by G.Medvedev, see Чернобыльская тетрадь 1 (In Russian).

q12 (update of question 8): recycle the relaxation heat?
One of problems at Fukushima is about the used active rods, that still produce heat in amount, say, two orders of magnitude lower, than in the case of the chain reaction, but still sufficient to melt and evaporate all their content if not cooled well. Why these rods are not used in some kind of "relaxer" that would recycle this heat for generating of electric power, or for warming buildings or greenhouses during the winter, compensating the maintenance expenses? Is such a re-use too difficult?

q13, save the contaminated milk?
Some milk and tap water are reported to contain the unstable isotopes of iodine; is it possible to reduce the radioactivity of such liquids by boiling? Is the concentration of iodine in the vapor the same as in the boiling liquid below? (With how many decimal digits is it the same?)

q14. Was the contamination at Hiroshima smaller?
Does the radioactive fallout due to the Fukushima accident already exceeds the fallout due to the Hiroshima and Nagasaki bombing in 1945? Is the mass evacuation of the citizen from the contaminated region (say, the red loop in the map at the top) performed?

Answer. No, the mass evacuation from the red loop in the top figure at the article Fukushima disaster is not performed; the only evacuation from the circle of radius of 30 km is prescribed. The figures indicate that the approximation of the contaminated region with the circle is very poor, irresponsible, non–professional solution.

q15. (update of q13)
Some farmers at the contaminated lands have to trash the radioactive milk. Would it be due to iodine-131 with lifetime of order of a week, or Caesium-137 with lifetime of order of a year, it would be sufficient to freeze the milk, or make a cheese of it, and keep it during several months, in order to let its radioactivity drop down. Does this mean that the main contaminants are Uranium and Plutonium?

q16. Why the contamination is as at Chernobyl?
The estimates show that the contamination of the Pacific Ocean in 2011 March becomes comparable to that due to the Chernobyl disaster. Such a huge contamination corresponds to the burning up into the atmosphere the significant part of the nuclear fuel from at least one reactor. One has to arrange some kind of the nuclear chimney, as it was done in Chernobyl, in order to achieve this. On the other hand, according to the reports, the most of the nuclear fuel at Fukushima remains confined and the reactors are kept at the temperature does not reach thousands of degree required for the efficient evaporation of the nuclear fuel. Does this mean that the main source of the contamination jet seen at the fit in the upper picture is not due to Fukushima, but due to some under-sea nuclear explosion, some nuclear chimney at some ship, submarine or the nuclear waste storage at the Shikotan island ( http://maps.google.com/?ie=UTF8&ll=43.826,146.75&z=17 )?

q17. Could a similar tsunami be caused by a nuclear device?
How strong tsunami would be caused by the synchronized under-bottom explosion of several devices of class http://en.wikipedia.org/wiki/Tsar_Bomba ?

For the answer, the naive hypothesis with some primitive estimates are suggested in the article Russia used the nuclear weapon in 2011.

q18. How does the hydrogen gets our from the container vessel?
The explosions at the Fukushima reactors are attributed to the detonation of the hydrogen between the high-pressure container vessel and the weather-protecting rough. The hydrogen is believed to be created in the reactor at the interaction of the hot zirconium alloys with water. How could it happen that this hydrogen filled the volume between the high-pressure vessel and the wether–protecting coat? Did this hydrogen just diffused through the walls of the high–pressure vessel?

q19, again about recycling of the relaxation heat (see q08, q12)
The heating of the spent fuel rods makes the serious problem at the storage; hence, how far is the heating power from the power which would allow the commercial use as source of heat for generation of electricity or at least for warming of some greenhouses?

q20. What are main contaminants?
Some evacuees are reported to visit their homes to pick up their belongings . Does it mean that the radiation is mainly due to some long-living isotopes? What is the isotopic content of the main contamination? How big are the particles of the contaminant? Are they just dust (say, 100 micron size)? How deep are they in the soil?

It is believed, that the main contaminants are still Iodine 131, Cesium 134 and Cesium 137 and for 2011 April 8, they give the comparable contribution ; the iodine slightly dominates. If this content of contaminants corresponds to the whole evacuation zone, then, after two weeks (say, in the end of April 2011) and no more leakage, then one may expect the radiation the decrease to its half (as the half-decay of the Iodine 131 is of order of a week; then, after a pair of years, is should drop to the half of the rest. However, the washing-out of the Cesium from the land may boost this process. Delivery of enormous amount of clean water could help to wash out the dust. Some big typhoon could provide the strong shower to the area of some thousand of square kilometers.

Putonium is also reported in the soil in vicinity of the plant , but the amount is not considered as dangerous for the health. However, the precision indicated with four decimal digits in the specification "1.000 millisieverts" cause doubts in the message of that publication and may indicate that the estimate is just wrong.

q21. Why the evacuation zone is circle?
21. Why the evacuation zone is just a ring ? Did the authorities try to determine the shape of the contaminated region with more details?

The I.A.E.A., based in Vienna, said on Sunday that its team had measured radiation on Saturday of 0.4 to 3.7 microsieverts per hour at distances of 20 to 40 miles from the damaged nuclear reactors ; but no data are suggested about the shape of the contaminated region, that could confirm or reject the approximation shown in the article Fukushima disaster and help the refugees to make decisions about the evacuation.

Answer. The aerial map of contmination by the U.S. Department of Energy released 2011 April 22 is shown at right. The figures indicate that the approximation of the contaminated region with the circle is very poor, irresponsible, non–professional solution.

2011 May 2, the asymmetric zone of evacuation is suggested in he report, see figure at left. The continuous leak of radiation mentioned there may be one of reasons against the specification of the boundary of the evacuation zone along the line of constant level of radiation.

2011 May 10, the map of contamination for April 29 is suggested by James ; it reproduces the main details seen in the map for April 21, although both maps might use the same data.

The publication, at least non-official, of the maps of contamination indicated that, first, the leak of radiation reduces. Also, such maps help to adjust the shape of the evacuation zone to the shape of the contaminated region.

The first-weeks contamination (shown at the top of the article Fukushima disaster may be attributed to the unstable isotopes of Iodine and Xenon (whenever they came from the Fukushima Daichi or from another sources); and formed the long trend from Notrh-East to South-West. The more recent maps indicate the short trend from South–East to North–West; perhaps, the first trend was formed by highly volatile isotopes (Xe, I, etc.) that go far (say, hundreds kilometers) but do not remain for a long time. The last trend may be formed, al least partially, by the heavy isotopes (cesium, plutonium, uranium, etc.) that do not go farer than a hundred kilometers, far, but remain longer. (Namely these isotopes should be taken into account determining the evacuation zone.) The suggestion of evacuation at left catches the main shape of the contaminate region. However, it is not clear, wether the residents should be evacuated from the coast in vicinity of Minamisoma: the contamination of sources of water (that is not detected at the aerial measurements) may be also important parameter.

q22. How high was the tsunami?
Reuter had reported the tsunami of 10 meter . Asahi suggests the estimate 10 m for the Sendai . According to Yomiuri the height of the wave was from 6.6m to 14m. The Japan Broadcasting Corporation indicates that the height of the tsunami reached 30 meter . Mainichi suggests the estimate 37.9 meters for the Miyako .

It seems, the estimate of the height of that tsunami shows the growing trend being considered as function of date of publication. On the other hand, even March 27, the same Yomiuri offered the estimate by Yasushi Kaneko of 40 meter ; The momentum of the tsunami waves considered as an equivalent of momentum of 250 jumbo jets at 1000km/h. However, the method of counting of those jets is not revealed in the publication. (Did anybody try to stop a tsunami employing few hundreds of jumbo jets?)

Well, how did the elevation of water at that tsunami depend on the distance along the coastal line?

q23. Does the reactivity increase?
In the nuclear reactor at the mixture of isotopes of Uranium, the U-238 gradually converts to plutonium. The critic mass of plutonium is smaller than that of U-235. Does this mean that, by default, the reactivity of the nuclear reactor increases?

q24. Farmer's debths
According to Yomiuri, the farmers who could not sell the radioactive cattle cannot pay their debs. . Why these debts are not transferred automatically to TEPCO?