Ecology & Environmental Problems

• Dr. Ron Chesser

• Lecture #9

• Chernobyl, Nuclear Power, Environmental Disasters

Chernobyl particles after 10 days

Figure 2.5 Calculated (solid lines) and actual (dashed lines) distribution of radiation levels near Chernobyl on 29 May, 1986 (in µSv h-1). (From Israel et al., 1987.)

Since the moment of the accident a high-power stream of hot air was formed, which carried out radioactive substances from the reactor ruins into the atmosphere. Its power was maximal during the first 2-3 days. The height of the stream, as it was indicated in [1], reached more than 1200 m on 27 April, 1986, 30 km to the north-west from the Chernobyl NPP:

The level of radiation in the stream was about 1 mR/h at the height of 1200 m. In the following days the stream height did not exceed 200-400 m, as it is indicated in [14]. The level of radiation in the stream at the distance of 5-10 km and the height of 200 m was about 1 R/h on 27 April, and 0.5 R/h on 28 April. This estimation of the release height is true only for the relatively heavy fuel component. According to the data of [9], iodine and cesium radioisotopes were found at the heights of 6-9 km. The appearance of the iodine-131 traces in Japan and the USA not later 5 May indicates the same fact.

The qualitative picture of the release briefly presented above has not been subjected in its main details to changes in subsequent investigations (see, for instance, [2 and 14]), where the data on the initial amount of radionuclides in the reactor and the values of the release components were made more accurate. Only the statement about termination of significant releases in 10 days after the accident (see "New data on radioactive release") raises doubts.

The total amount of the radionuclides released out of the bounds of the Chernobyl NPP area is 50 MCi as of 6 May 1986, with the error of 50% (excluding radioactive gases and fuel) and the fuel component estimated in [1, 2] as 3.5%-0.5% of the fuel inventory in the core of the reactor with accuracy -50%, is confirmed by subsequent investigations [4, 5]. The estimation of the fuel release less than 1% presented in the USA work [16] can be explained by the fact that its authors used the data on fallouts and concentration of radionuclides in the air in the far zone, whereas the main part of the fuel component of the release is concentrated inside the 30-km zone.

137Cesium

• Main disagreements belong to the estimation of the release of iodine and cesium isotopes. The estimation of Cs-137 release made in as 13% was the subject of discussion in [1-4, 6, 14, 16-18], and subsequently increased up to 25 % in [4], over 25% in [17], 33% - 13% in [14], 33% - 10% in [2] bases on the measurement of Cs-137 in fuel masses inside the containment structure ("sarcophagus") of unit 4, up to 40% according to the data of [16] based on the data of global fallouts, and reached 60% in [6]. The authors consider the most convincing the estimation presented in [2]: 33% - 10%, or (2.3-0.7) MCi, which coincides with the estimation in [14, 16]. More detailed investigations of fuel masses inside the containment structure could possibly give more accurate information on this subject.

131Iodine• Still more ambiguous is the estimation of the release of iodine radioisotopes, first of

all of I-131, which has great practical importance for reconstruction of the doses to thyroid in population. Unfortunately, the measurements on 26 April are absent, and the first release of the short-lived radionuclides (not only of iodine-131, but also of tellurium-132, molybdenum-99,etc.) is not outlined completely. Besides, there is a circumstance unfavorable for measurements, the release of iodine partly in the aerosol and partly in the gaseous form. The measurement of the gaseous iodine requires special complex technique. Besides, the relation of the forms noticeably varied with time during the active phase of the accident [7]. The approximate constancy of the ratio of activities of I-131 and Cs-137 in fallouts observed in the majority of European countries gives an opportunity to estimate iodine depositions with cesium maps. In particular, such estimation was performed in [17], where the conclusion was made that the iodine release was least 45%. In different works the iodine release is estimated from 20% to 60% [3-5, 16, 17], up to 80% in [6].

• To our opinion, the most realistic is the estimation of iodine-131 release equal to 50-60% of its content in the reactor, or 40-50 MCi as of 26 April 1986. Accounting for radioactive decay in the reactor in the period of active release, this corresponds to total activity of 30-35 MCi released into the atmosphere in different days. According to the general estimation, about 80% of iodine came out from the reactor in the gaseous form.

+--------+--------+--------------------------------------------+

|Nuclide | T-1/2 |Activity [MCi] according to different works |

+--------+--------+-------------+--------+------+------+-------+

| | [19] | [1]([18]) | [13] | [16] | [14] | [12] |

+ +--------+-------------+--------+------+------+-------+

| Kr-85 | 10.7y | 0.9 | ------ | 0.55 | ---- | ----- |

| Sr-89 | 50.5d | 63 | 90 | 80 | 52 | ----- |

| Sr-90 | 29.1y | 5.5 | 6.2 | 4.2 | 5.2 | 5.9 |

| Zr-95 | 65.0d | 130 | 154 | 134 | 130 | ----- |

| Mo-98 | 66.0d | 150 | ------ | 137 | 130 | ----- |

| Ru-103 | 39.3d | 130 | 128 | 116 | 130 | ----- |

| Ru-106 | 368d | 56 | 33 | 29 | 52 | 23 |

| I-131 | 8.04d | 86 | 66 | 82 | 90 | ----- |

| Te-132 | 78.2h | 73 | 56 | 109 | 120 | ----- |

| Xe-133 | 5.24d | 170 | ------ | 193 | ---- | ----- |

| Cs-134 | 2.06y | 5.0 | 4.2 | 3.7 | 4.0 | 4.1 |

| Cs-137 | 30y | 7.7 | 8.2 | 5.6 | 7.2 | 7.0 |

| Ba-140 | 12.7d | 130 | 133 | 140 | 130 | ----- |

| Ce-141 | 32.5d | 150 | ------ | ---- | 130 | ----- |

| Ce-144 | 284d | 88 | 113 | 82 | 90 | 106 |

| Pu-238 | 87.7y | 0.027 | 0.022 | ---- | 0.026| 0.025 |

| Np-239 | 2.35y | 720(1340*) | 560 | ---- | 1300 | 1570 |

| Pu-239 | 24065y | 0.023 | 0.024 | ---- | 0.023| 0.04 |

| Pu-240 | 6537y | 0.033 | 0.05 | ---- | 0.033| 0.04 |

| Pu-241 | 14.4y | 4.7 | 5.7 | ---- | 4.6 | 5.0 |

| Am-241 | 432y | ------ | 4.2E-3 | ---- | 0.024|0.0037 |

| Pu-242 | 3.8E5y | 6.7E-5 | 6.7E-5 | ---- | ---- |5.6E-5 |

| Cm-242 | 163d | 0.7(0.4*) | ------| ---- | 0.7 | 0.83 |

| Am-243 | 7380y | ------ | 1.7E-4 | ---- | ---- |1.5E-4 |

| Cm-243 | 28.5y | ------ | ---- | ---- | 0.001| ----- |

| Cm-244 | 18.1 | ------ | 4.0E-4 | ---- |2.6E-3|4.8E-3 |

+--------+--------+-------------+--------+------+------+-------+

Radionuclide inventory in the unit 4 reactor at the Chernobyl NPP as of 26 April 1986 according to the data of different works.

* Figures in brackets are corrected according for individual burn-up of different fuel assemblies.

            Russian Research Center

"Kurchatov Institute"

Chernobyl Inventory released…whose numbers do you use?

• The April, 1989 issue of National Geographic states that 20% of the inventory of iodine and 10-20% of the cesium escaped.

• Zhores Medvedev states in Chernobyl Revisited that 90% of the core inventory remains in the sarcophogaus.

• Gregori Medvedev indicates in The Truth About Chernobyl that 49% of the core inventory escaped.

• A November, 1992 report by Friends of the Earth states that 10% of the core was released.

• Roger Milne says that just 3% of the core inventory was released. (New Scientist, April 27, 1991, p. 17).

Table Information• Table presents numerical data on the release of different radionuclides from

the destroyed reactor. The first column presents the estimations from the report by academician Legasov in 1986 [1] decay-corrected to 26 April 1986 [18]. The second column gives the estimations from the work by P.H.Gudiksen et.al. [16] decay-corrected to 26 April 1986. The third column is the summary of the most reliable (as to the expert evaluation of the authors) data on the release. The data on the radionuclide inventory in the reactor are taken in accordance with [12, 18]. Notice that the release of iodine-131, as well as of cesium radioisotopes, was evidently underestimated according to the results of [1, 18].

• The release of iodine-131 was assumed equal to the middle (45 MCi) of the estimated interval 40-50 MCi. The estimation of the cesium release as 33%, or 2.3 MCi, is based on the amount of cesium-137 in the destroyed reactor, which coincides with its global distribution in the atmosphere and deposition on surface. The Cs-134 release was assumed equal to 0.53 of the Cs-137 release (see section 3.2), i.e., 1.2 MCi. The data on the tellurium release have no discrepancies. Strong connection with the fuel matrix is assumed for the rest of radionuclides, at least during the explosion, and their release is calculated as 3.5% of the amount accumulated in the core.

Chernobyl Releases• During the process of the accident the nuclear fuel from the

destroyed reactor was subjected to high temperature and mechanical failure. Heating up to the temperatures of about 2000 C caused complete or partial evaporation of volatile radioactive elements from the fuel. A part of the fuel was released during the explosion in the form of fine-dispersed component which distributed in the atmosphere. Subsequent fires and natural fuel heating by radioactive decay caused that hot air continued to carry out of the reactor the products of graphite burning, radioactive gases, aerosols, and fine-dispersed fuel dust with dimensions of particles from parts of a micron to tens and even hundreds micron. Thus, radioactive releases from the destroyed reactor consisted of at least two different components: – radioactive nuclides included into the matrix of the dispersed fuel and

released in the form of radioactive dust, – separate volatile radioactive substances in the form of gases or

aerosols, which evaporated from the hot fuel

Chernobyl Releases• According to estimations, during the accident: • inert gases came out of the destroyed reactor completely [1.2]; • iodine-131 release was 50-60%, which is 40-60 MCi (on the

average, 45 MCi) as of 26 April 1986, <>[3, 4, 5, 16, 17]; • cesium release was (33 +/- 0.7)MCi; • strontium release was about 4%, or 0.2 MCi [1]; • fuel release outside the plant area was (3.5 +/- 0.5)% [1, 4, 5]. • Besides, some general remarks can be made: • In the modelling of radionuclide transport at the Chernobyl accident

one should differ the fuel and volatile components, and the transport of relatively refractory fuel component can be described by local and mesoscale models, whereas volatile (cesium and iodine) component require attraction of global transport models;

• the considerable release of radionuclides could continue even after 5 May 1986.

First Stage of Radionuclides Release.At the first stage the mechanical release of the dispersed fuel took place as a result of the initial explosion. Its radionuclide composition corresponds to fuel inventory of the core with enrichment by volatile nuclides of iodine, tellurium, and cesium.

Second Stage of Radionuclides Release.At the second stage, from 26 April till 2 May the power of the release fell, obviously because of the measures undertaken for extinguishing of burning graphite, and formation of the filtrating layer. The dependence of the release power on time Q(t) at this stage can be presented in the first approximation as Q(t) = 0.25.exp(-0.28.t), day , (1) where 0.25, day , is the part of the total release corresponding to the first day; t, days, is the time after the explosion. At this stage the release consisted of fine-dispersed particles of fuel dust entrained by the flow of hot air and of graphite burning products. The radionuclide composition is also close to the fuel one.

Third Stage of Radionuclides Release.The next, the third stage of the accident is characterized by fast increase of the release power, at first with predominance of the volatile component, especially of iodine, and then the composition became again close to the fuel one. The approximation of the release power in this period is the following: Q(t) = 0.09.exp(0.35.(t-5)), day . (2) The release at this stage was attributed to fuel heating over 2000 C by the residual heat release. As a result of temperature-dependent migration of decay products and chemical conversions of uranium dioxide, the decay products were released in the form of aerosols or of the particles of graphite burning products.

Fourth Stage of Release.The last, the fourth stage began on 6 May and was characterized by abrupt decrease of the release rate because of the undertaken measures and of formation of more refractory compounds of radio nuclides in the process of interaction with the materials introduced into the core. The reason of such abrupt fall of the release power is still not clear, and noticeable releases of activity continued much later during the whole month.

Press

Contaminants Released, Chernobyl

• A retrospective view of the Chernobyl accident of Apr 26, 1986 assesses the total radiation release at about 100 megaCuries or 4 x 10^18 becquerels, including some 2.5 MCi of cesium-137. The cesium is the most serious release in terms of long term consequences. This is around 4% of the total accumulated activity of the core and compares to a release of 15 Ci at Three Mile Island. The release was then about 7 million times that at TMI. Anspaugh, et al. suggest that essentially all the noble gases and about half of the volatile elements (iodine-131, cesium-134 and cesium-137) were released . The cesium release from all of the atmospheric weapons tests is estimated to be about 30 MCi. The noble gas releases were estimated by Levi to be 45 MCi of xenon-133 and 5 MCi of krypton-85. About 3-5% of the core inventory of the relatively refractory elements such a strontium, plutonium, and ruthenium were released, much more than from a light water reactor meltdown.

Chernobyl Casualties

• There were 31 fatalities as of May 1987, all of whom were at the power plant, and most of whom were firemen fighting the blazes following the explosion. 237 persons were "removed to hospitals with acute radiation syndrome. About 500 were hospitalized altogether, including bus drivers who evacuated residents." An estimated 24,000 of the 116,000 evacuees received fairly serious radiation doses of about 45 rem. Thyroid doses from Iodine-131 as high as 250 rem were measured in children from Lelev, 9 km from reactor.

• Levi gives an estimated long term total exposure is 29 million person rems with an excess of 3000 cancer deaths above the 9.5 million cancer deaths projected in the same population. Largest effect from cesium. The later estimates by Anspaugh, et al. suggest 93 million person rem and a projection of 17000 additional fatal radiogenic cancers out of a total of 123 million cancer deaths. 97% of the health effects are projected to be in the Soviet Union and Europe.

Figure 1. Description of the radioactive plume behaviour and reported initial arrival times of detectable activity in air. (UNSCEAR, 1988; Persson et al., 1987).

Figure 7.1. Hot, radioactive gases were carried downwind from the breached reactor at Chernobyl by northwesterly winds in the wake of a low pressure system moving across the then-Soviet Union, evaporating clouds and forming a radioactive distrail. This was the first time in history that a radioactive distrail was photographed. The white arrows point to the distrail (courtesy of Hank Brandli).

This is BSIn my (RKC)Opinion.

Six days after the meltdown, hot, radioactive gases still escaping from the ruptured reactor were carried southeast in the wake of a compact low pressure system moving east over the Soviet Union.

Radioactive particles from the ruptured nuclear reactor at Chernobyl were circulated across Europe by a series of traveling high and low pressure systems in the days following April 26, 1986 (courtesy of Peter Gould).

Thermal Satellite Image

SCALES OF MOTION IN LAKE-INDUCED CIRCULATIONS

(nomenclature after Orlanski 1975)(table adapted from Kristovich et al. 2000)

SCALE DESIGNATIONEXAMPLES IN LAKE-EFFECT

CIRCULATIONS

MicrophysicalCloud and precipitation particles; moist

air thermodynamics; aerosols

Micro (< 20 m)Turbulent eddies; surface-layer

eddies; entrainment eddies

Micro (20-200 m) Surface layer lines

Micro (200 m - 2 km)Thermals; cloud-scale plumes;

surface-layer cells

Meso (2-20 km)Boundary layer rolls and cells; sub-

lake scale bands

Meso (20-200 km)Individual lake-scale circulations; lake

bands

Meso (200-2,000 km)Great Lakes aggregate-scale

circulations; secondary troughs

Macro (2,000-10,000 km)Secondary lake-aggregate responses;

synoptic flow; cyclones