The 15% enriched heavy water is delivered to a finishing unit where, through vacuum distillation, the concentration is upgraded to 99.8% (reactor grade) deuterium oxide. The distillation unit consists of two towers containing special packing.
Deuterium is also enriched during the electrolysis of water since 1
1His more readily liberated as H2than 2
1Das HD. Hence, the first samples of heavy water were obtained from Norway where water electrolysis is the method of producing H2and O2since electricity is inexpensive there—even today where it is the major method of heating homes.
It is possible to increase the fuel efficiency by selecting the zirconium isotope94
40Zrwhich has the lowest neutron absorption cross section (0.08 barns; see Table7.2) for the fabrication of the zircaloy.
Several attempts have been made since the high cost of an enrichment process is a major capital investment which could be of continuous benefit since the 94
40Zrcan be recycled from spent fuel and reused with little reprocessing.
Fig.7.8MapofCanadashowingthedeuteriumconcentrationinppm(mg/g)invariouspartsofthecountry.Alsoshownarethesitesofheavywaterplantsandnuclear powerplants
7.7 The Hazards of Nuclear Energy 121
reactor on fire and releasing enormous amounts of radioactivity into the atmosphere. The radioactive cloud drifted across Europe and was first detected in Sweden, Monday morning, April 28, 1986.
Based on the prevalence of radioactive cobalt, iodine, and cesium, it was concluded that a nuclear bomb test was not the source of the activity but that a nuclear accident had occurred. This was acknowledged at 9:00 p.m. by Moscow TV news.
The radioactivity contaminated the vegetables and meats of central Europe. Millions of dollars were used to compensate farmers for the loss they suffered. Though about 31 deaths were associated with acute radiation exposure and fire, it is estimated that thousands of delayed cancers will result from the fallout.
Another nuclear disaster rated equal to Chernobyl happened at the Fukushima nuclear plant in Japan on the 11th of March 2011. Nuclear reactors were damaged by strong earthquakes and tsunami.
Crisis level at the Fukushima nuclear plant was raised to level 7 after 1 month of the disaster. Level 7 is classified by IAEA as the worst level on an international scale.
The accident at Three Mile Island released 15 curies and caused no direct fatalities. It has been estimated that not more than 1 delayed cancer victim will result.
However, we accept the construction of dams, some of which have failed and others, if they do fail, would cause hundreds of thousands of deaths. A list of some hydroelectric dam disasters is given in Table7.12.
We accept the occasional mine disaster and continue to mine coal. Since a tonne of uranium ore yields 300 times more energy than a tonne of coal, it is obvious that mining uranium leads to less mining deaths per energy unit (1/300) than mining coal. Again, it could be argued that the radon and radiation exposure in uranium mining is an additional hazard not encountered in coal mining.
However, black lung disease kills thousands of miners every year. It has been estimated that for every 1015We (watts of electricity) generated there are 1,000 deaths by black lung among coal miners and 20 deaths by lung cancer among uranium miners.
Fig. 7.9 Basic principles of heavy water production by the HDO + H2S!HDS + H2O equilibrium reaction
An indication of relative average risk of fatality by various causes is given in Table 7.13. The automobile remains the major cause of accidental deaths in our society, yet we accept this with minor token complaints. It is possible to predict that there will be 500 deaths in the USA due to automobile accidents (50 in Canada) during the Labor Day weekend holiday in September.
A comparison of man-days lost per megawatt-year output by various energy sources has been given by Inhaber and shown in Fig.7.10. Coal and oil show the highest losses, whereas natural gas shows the lowest loss. It may be surprising to note that solar energy sources are relatively hazardous.
Edward Teller—the father of the H-bomb—once pointed out that solar energy is not free of dangers because the ladder, which would be required to clean solar cells on the roof of our homes, causes more accidents in the home than any other device.
Table 7.12 Loss of lives due to hydroelectric and dam disasters
Date Place Lives lost
1923 Santa Paula, California, USA 450
1923 Gleno, Italy 600
1926 St. Francis, USA 430
1959 Malpasset, France 412
1961 Kiev, USSR 145
1963 Vaiont, Italy 2,000
1967 Kayna, India 180
1972 Buffalo Creek, WV, USA 118
Table 7.13 Average annual risk of fatality by various causes (USA)
Accident type Total number Individual chance per year
Motor vehicle 55,791 1 in 4,000
Falls 17,827 1 in 10,000
Fuels and hot substances 7,451 1 in 25,000
Drowning 6,181 1 in 30,000
Firearms 2,309 1 in 100,000
Air travel 1,778 1 in 100,000
Falling objects 1,271 1 in 160,000
Electrocution 1,148 1 in 160,000
Lightning 160 1 in 2,000,000
Tornadoes 91 1 in 2,500,000
Hurricanes 93 1 in 2,500,000
All accidents 111,992 1 in 1,600
Nuclear reactor 5,000a 1 in 200,000
Accidents (100 plants)
aThe British accident at Windscale in October 1957—a fire in the atomic pile—
resulted in the release of radioactive gas 131
50I (20,000 Cu), 210
82Po (37 Cu), as well as 103
44Ru; 106 44Ru; 95
40Zr; 95 41Nb; 137
55Cs (600 Cu), 89
38Sr (80 Cu), 90
38Sr (9 Cu), Ce-144, and Te-132
It has only recently been estimated that the number of deaths from leukemia and cancer which could be directly due to this accident is from 1,000 to 2,000 with the predomi- nant effect to children. Hence, we must distinguish between direct and indirect or more remote fatalities. If we add the direct deaths and the leukemia and cancer deaths for the Three Mile Island and Chernobyl nuclear accidents, we would estimate a total of about 5,000 deaths. This gives a risk factor of 1 in 200,000 which is still better than air travel
103 44Ru; 106
44Ru; 131
50I, 210 82Po,95
40Zr; 95 41Nb; 137
55Cs,89 38Sr, 90
38Sr
7.7 The Hazards of Nuclear Energy 123