5 ms·

Anyone can correct me if I'm wrong, but I believe for two years Tepco has been dumping about 150 tons of water a day on the melted cores at the bottom of the re

by marze 13y ago

Anyone can correct me if I'm wrong, but I believe for two years Tepco has been dumping about 150 tons of water a day on the melted cores at the bottom of the reactor buildings (or wherever they are), and pumping 100 tons of it out to filter and reuse. Obviously, 50 tons/days has disappeared every day for 2+ years. Since that water came in contact with the melted cores is extremely radioactive (not just tritium). Measurements of the water filling the lower levels of turbine buildings supports this thinking (something like 1 Seivert/hr). Since TEPCO has not allowed any independent measurements of the ocean within kilometers of the site, nor independent ground water measurements, and the independent ocean measurements taken at large distance from the site do not show a decrease in contamination vs. time, it appears likely they've been leaking substantial amounts of cesium and other radionuclides into the ocean for >2 years. If so, an impressive coverup. The math is simple, water in minus water out, and where did the missing water go.

VLM 13y ago
Hmm we'll lets run this thru the engineering filter and see how much is reasonable. Well, something that can't run forever, stops, and its been close enough to forever that you can assume we're evaporating away 50 tons/day. Where else could it be going? But is that a reasonable evap rate from an engineering perspective? 50 tons is about 50K kilograms. Takes about a KWH to boil away a kilo of water so we're looking at about 50K KWH or 50 MWH per day. Now there's about 25 hours in a day so thats about 2 MW continuous boiling away water, or at least on long term average. A big reactor runs in the GW range but decay heat starts around 10% and slowly drops over time. Actually a couple years in, most should be gone although the long tail is pretty long. So it was dumping out tens of MW continuously and now maybe much less. So we're looking at a couple MW generated, vs a couple MW to make that much water vapor. Seems reasonable. So I'm willing to believe from an engineering estimate, aside from solar heating and whatever, that 50 tons of water simply evaporates away. We can argue volumetric, if a ton is about 1K kilos and 1 L water is about 1 Kg, that would strongly imply a ton of water is about a 1K liters or about one cubic meter. I suppose we could have gotten to this same point by talking about mL vs cubic centimeters vs grams. Anyway you're claiming a cube of water a meter on a side, stacked 50 tall each day, for a couple years. I say that most of that has to have evaporated away otherwise you'd have 50 meters deep of water covering the entire site after a thousand or so days.
- marze 13y ago
  All good, but there is no boiling. Just evaporation from the surface of the pooled water flooding the buildings, which will not be significant, even if it wasn't at a humid oceanside location.
  - VLM 13y ago
    You're talking about a small decimal point variation in heat of vaporization aka enthalpy of vaporization. You are correct it does in fact vary by temp, but as a percentage, less than my vast rounding errors. One problem is heat of vaporization usually drops with temp. So evaporating water at 400 degrees in a boiler takes somewhat less energy than evaporating the same amount on a open to the air pond, and there's not much of a pressure vessel around the plant anymore anyway. For all intents and purposes given reasonable rounding the energy required to evaporate the water is more or less constant in that location. This has to do with the strength of the hydrogen bond in water. The energy require to vaporize the water is the same as hundreds of degrees of merely heating the water, thats why the starting temp has little effect on water boiling rate, etc. Still I stand by my numbers, 2 MW continuously can evaporate your 50 tons of water per day, to one sig fig. Note that we're not arguing about much. Sunlight is like a KW per sq meter so we're arguing about the energy from 2000 or so sq meters of sunlit area, which isn't much compared to a giant nuclear plant facility. It just doesn't strike me as much of an engineering challenge to evaporate 50 tons/day given that size of a facility and the decay heat and the solar insolation.
    - marze 13y ago
      Those are some awesome calculations. Since we are talking Japan's food supply and the Pacific Ocean, it would be nice to have some independent measurements taken on site, in addition to your nice back-of-the-envelope calculations. Keep in mind this water is all indoors, so unless you have some openings you are blowing air in, there will be no evaporation whatsoever.

by marze 13y ago

VLM 13y ago

Hmm we'll lets run this thru the engineering filter and see how much is reasonable. Well, something that can't run forever, stops, and its been close enough to forever that you can assume we're evaporating away 50 tons/day. Where else could it be going? But is that a reasonable evap rate from an engineering perspective? 50 tons is about 50K kilograms. Takes about a KWH to boil away a kilo of water so we're looking at about 50K KWH or 50 MWH per day. Now there's about 25 hours in a day so thats about 2 MW continuous boiling away water, or at least on long term average. A big reactor runs in the GW range but decay heat starts around 10% and slowly drops over time. Actually a couple years in, most should be gone although the long tail is pretty long. So it was dumping out tens of MW continuously and now maybe much less. So we're looking at a couple MW generated, vs a couple MW to make that much water vapor. Seems reasonable. So I'm willing to believe from an engineering estimate, aside from solar heating and whatever, that 50 tons of water simply evaporates away. We can argue volumetric, if a ton is about 1K kilos and 1 L water is about 1 Kg, that would strongly imply a ton of water is about a 1K liters or about one cubic meter. I suppose we could have gotten to this same point by talking about mL vs cubic centimeters vs grams. Anyway you're claiming a cube of water a meter on a side, stacked 50 tall each day, for a couple years. I say that most of that has to have evaporated away otherwise you'd have 50 meters deep of water covering the entire site after a thousand or so days.

marze 13y ago
All good, but there is no boiling. Just evaporation from the surface of the pooled water flooding the buildings, which will not be significant, even if it wasn't at a humid oceanside location.
- VLM 13y ago
  You're talking about a small decimal point variation in heat of vaporization aka enthalpy of vaporization. You are correct it does in fact vary by temp, but as a percentage, less than my vast rounding errors. One problem is heat of vaporization usually drops with temp. So evaporating water at 400 degrees in a boiler takes somewhat less energy than evaporating the same amount on a open to the air pond, and there's not much of a pressure vessel around the plant anymore anyway. For all intents and purposes given reasonable rounding the energy required to evaporate the water is more or less constant in that location. This has to do with the strength of the hydrogen bond in water. The energy require to vaporize the water is the same as hundreds of degrees of merely heating the water, thats why the starting temp has little effect on water boiling rate, etc. Still I stand by my numbers, 2 MW continuously can evaporate your 50 tons of water per day, to one sig fig. Note that we're not arguing about much. Sunlight is like a KW per sq meter so we're arguing about the energy from 2000 or so sq meters of sunlit area, which isn't much compared to a giant nuclear plant facility. It just doesn't strike me as much of an engineering challenge to evaporate 50 tons/day given that size of a facility and the decay heat and the solar insolation.
  - marze 13y ago
    Those are some awesome calculations. Since we are talking Japan's food supply and the Pacific Ocean, it would be nice to have some independent measurements taken on site, in addition to your nice back-of-the-envelope calculations. Keep in mind this water is all indoors, so unless you have some openings you are blowing air in, there will be no evaporation whatsoever.