RSH Data & Documents

"Health Effects of Low-level Radiation"

by Dr. Sohei Kondo

Chapter 1

Title Page: Front matter

Table of Contents

Terminology of radiation dose

Chapter 1 Comparison of the Acute Effects of the Hiroshima Nagasaki Atomic Bombings and of the Chernobyl Reactor Accident

People often ask the naive question: Which resulted in heavier casualties, the Chernobyl accident or the atomic bombings of Hiroshima and Nagasaki? The number of casualties caused by the atomic bombs dropped on either Hiroshima or Nagasaki was several thousand times greater than those caused by the Chernobyl accident. Yet, it is commonly believed by people, not only in the USSR but also in other countries, including Japan, the USA and Europe, that an atomic bomb and a nuclear reactor accident result in the same order of casualties among the public.

In a book about intelligence and evolution, I was shocked to encounter the statement, by Ruse (1988), that "in an age of Hiroshima--not to mention Chernobyl--I cannot believe that we shall not poison ourselves with radioactivity in the next 10,000 years". This conjecture shows that even a highly intelligent philosopher can make an emotional judgment about risk that disregards the relative magnitudes of the different contributing risks. Therefore, in this first chapter, I shall make a quantitative comparison of the casualties caused by the atomic bombs and those caused by the Chernobyl reactor accident.

1.1 Immense difference in the casualty rate after the Hiroshima- Nagasaki atomic bombings and the Chernobyl reactor accident

1.1.1 The Bells of Nagasaki and casualties after the atomic bombings

On 9 August 1945, at 11:02 am, Nagasaki City was wiped out by an atomic bomb that exploded 500 m over Urakami District at about the center of the Urakami Valley, which is 4 km long in a north south direction and 1.5 km wide. Among those wounded by the blast was a young doctor, Takashi Nagai, a professor of radiology at Nagasaki University School of Medicine, located about 600 m from the ground center of the atomic blast (Fig. 1.1). In 1949, Nagai wrote a book, Nagasaki no Kane (English translation in 1984: The Bells of Nagasaki), describing what he had seen and what he had heard from his associates (Nagai, 1949)

Fig. 1.1 Nagasaki City before the atomic bombing

(1) Hospital affiliated to Nagasaki University School of Medicine; (2) Nagasaki University School of Medicine; (3) Urakami District; (4) Urakami Cathedral; (5) Mitsubishi Heavy Industries, Nagasaki shipyard; (6) Nagasaki Port; (7) Nagasaki Railroad Station; (8) Nagasaki City offices; (9) Mt Konpira; (10) Nishiyama District; (11) Nishiyama Water Reservoir.

By about 20 minutes after the bomb had dropped, downtown Urakami district (Fig. 1.1) had become a flaming landscape. From the center of the hospital, flames were spreading throughout the campus. The only place that was not on fire was a hill on the east side of the hospital.

The classroom of fundamental medicine (Fig. 1.1) was housed in a wooden building located close to the center of the bomb explosion; the building was smashed and burned immediately after the blast, and all the professors and students in it were killed instantly. The classroom of clinical studies was slightly further away (Fig. 1.1) and was made of concrete, so there were some fortunate survivors, including Nagai.

No exact data are available about the numbers of human casualties caused by the atomic blasts in Hiroshima and Nagasaki. Early, conservative estimates were 45,000 and 22,000 instant deaths in Hiroshima and Nagasaki, respectively, and 19,000 and 17,000 deaths between two days and four months after the bombings (Table 1.1).

Table 1.1 Casualties and mortality after atomic bombings among citizens of Hiroshima and Nagasaki

 From Oughterson et al. (1955) and Oughterson and Warren(1956) with minor modification; the figures do not include military casualties. More accurate estimates for deaths by the end of 1945 are 90,000-120,000 in Hiroshima and 60,000-80,000 in Nagasaki (see Hiroshima-Nagasaki Committee, 1985; Watanabe, 1974)

More recent data, available in the Peace Memorial Park in Nagasaki, are as follows:

1.1.2 Comparison of casualties after the atomic bombings and the Chernobyl accident

After the Chernobyl accident that occurred on 26 April 1986, 31 persons working at the reactor died (two on the first day and 29 during the period 10 days to four months after the accident) and hundreds were injured; no casualties occurred among the general public (Table 1.2). It may be clear from a comparison of Tables 1.1 and 1.2 that the casualties resulting from the Chernobyl accident were negligible in comparison with those after the atomic explosions in Hiroshima and Nagasaki. This immense difference is a simple reflection of the different functions of the atomic bomb and of a nuclear reactor for generating electricity.

Table 1.2 Casualties and mortality after the Chernobyl nuclear reactor accident

From Gale and Hauser (1988); Guskova et al. (1988) and USSR Ministry of Health (1989)
a Crude estimate

The atomic bomb is produced as a weapon for killing people or destroying enemy bases. Figure 1.2 illustrates the approximate proportions of energy released as blast, heat and radiation after explosion of an atomic bomb (Br. Med. Assoc., 1983).

Fig. 1.2 Ground-burst of a nuclear bomb

(from The Medical Effects of Nuclear War , John Wiley & Sons, Chichester. Copyright 1983 by The British Medical Association. Reproduced by permission)

Of the atomic bomb casualties, about 80% died within one day after the explosion (Br. Med. Assoc., 1983; Table 1.1) due to thermal radiation and blast emitted by the exploded bombs, as vividly described in Nagai's book The Bells of Nagasaki (Nagai, 1949). The number ratio of deaths caused by blast, by heat and by radiation was about 2:2:1, which is similar to the energy fractions of 50, 35 and 15% released as blast, heat and radiation (including radioactive fall-out), respectively, after the atomic bomb explosion (Fig. 1.2). Nearly all of the human casualties that result from an atomic bomb explosion or an accident at a nuclear reactor are therefore quantitatively related to the amount of energy given off.

In contrast, as will be seen in the following sections, the available evidence suggests that low levels of radiation are not measurably dangerous to human populations. There were no blast or heat casualties at Chernobyl, because the damaged nuclear reactor emitted small amounts of energy in this form, and the explosion actually resulted in casualities of the same order of magnitude as those that would be caused in a major accident in a coal mine.

Fig. 1.3 Acute radiation syndrome in residents of Hiroshima exposed to the atomic bomb explosion

Time-dependent changes in relative mortality rates (heavy line; excluding deaths from burns, blast and other non-radiation injuries), epilation (solid circles), purpura (open circles) and oropharyngeal lesions (crosses) (modified from Ohkita, 1975; mortality rates after Oughterson et al., 1955 and other data after Kajitani and Hatano, 1953)

Fig. 1.4 Follow-up studies of leukocyte counts immediately after the Hiroshima atomic bomb explosion

Solid lines, recovered; broken lines, dead; open circles, recovered after single leukocyte count; solid circles, dead after single leukocyte count (from Amano et al., 1953, with minor modification)

In the victims of the Chernobyl reactor accident, the major causes of radiation-induced death were skin burns and intestinal injuries, due to irradiation with beta rays from externally or internally deposited radioactive nuclides; all of the victims except one also had injuries to the bone marrow as a secondary cause of death (Table 1.3).

Table 1.3 Major causes of death in patients with acute radiation sickness after the Chernobyl accident

Bone marrow dose (rad)	Bone marrow transplantation	Major cause of deatha	Number of deathsb	Time to death (days)
400 - 1400	-	Burns	13	10-24
600 - 800	-	Respiratory	3	30-48
insufficiency - 400	-	Infection	1	96
800 - 1200	+	Burns	5	15-24
600 - 700	+	Others	2	20-25
400 - 1000	+	Infection	4	34-91

Adapted from Guskova et al., al (1988)
^a In addition, most of the patients had injuries to bone marrow or intestine and other secondary diseases.
^b Two victims who died from causes other than radiation within 12 h of the reactor accident were not included.

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1.3 Health effects on Japanese fishermen of radioactive fall-out from the Bikini hydrogen bomb

On 1 March 1954, a hydrogen bomb test was performed on Bikini Island and 23 Japanese fishermen, 18 to 39 years old, were exposed to 'lethal' radioactive fall-out (about 1 mCi/g by a crude estimate). A brief description of the event and its effects is given here because these men can be regarded as having received a level of radiation intermediate between that of the Hiroshima Nagasaki atomic bombings and that of the Chernobyl accident (see Kumatori et al., 1980, for details).

Estimates of whole-body doses of gamma rays from the external fall-out, which were received during the first two weeks up to 14 March when they returned to Japan, were 200-295 rad for 11 fishermen, 325-395 rad for five, 415-475 rad for three, 545-575 rad for three and 670 rad for one. The acute effects of chronic irradiation at these doses were estimated to be approximately equivalent to those of a single, acute irradiation with half of the doses, i.e., total acute doses of 80-320 rad. Estimates of the additonal doses of radiation in the thyroid, on the basis of radioactive iodine nuclides incorporated, were 230-550 rad.

One fisherman with hematologic disturbances (anemia, leukopenia and thrombopenia) and hepatitis died 206 days after the accident, and one with ascites caused by cirrhosis died 21 years later. No malignant disease has been observed in the remaining men. Follow-up studies of peripheral leukocytes and platelets from the exposed fishermen were carried out from the time they returned to Japan. A summary of the 25-year follow-up is given in Figure 1.5. Average leukocyte and platelet counts were markedly depressed for about two years after the exposure and then recovered gradually, reaching normal levels two to five years after the exposure and then showing several excesses for about two years thereafter. More than 20 years after exposure, the average leukocyte counts were slightly depressed. In two fishermen exposed to high doses, neutrophil counts were depressed continuously for 25 years when compared with the counts on the first day after their return to Japan.

Fig. 1.5 Peripheral leukocyte and platelet counts in fishermen exposed to radioactive fall-out from the Bikini hydrogen bomb

Average counts of leukocytes and platelets were compared with those for normal males, and the differences between the two values were plotted against time of follow-up. (from Kumatori et al., 1980. Reproduced with permission)

References

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Chapter 2. Radioactive Fall-out from the Chernobyl Accident, Risk Assessment and the Aftermaths

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