How radiation-safe are short-term trips to the Chernobyl Zone?

Radiation warning sign in Pripyat

The Chernobyl Zone appeared owing to the radiation contamination of the area adjacent to the Chernobyl Nuclear Power Plant, when several decades ago its reactor 4 exploded. The bulk of the radiation, which escaped from it, fell within the borders of the contemporary Chernobyl Zone.

Up to now in the Zone there are places with considerably elevated and perhaps even deadly radiation. A prolonged, careless stay at such places can lead to radiation injuries of the body and, perhaps, even to chronic radiation sickness.

However, owing to clean-up of the Zone and the time passed (radioactivity naturally diminishes with time), high levels of radiation remain only in immediate proximity to the NPP, mostly at the traces of the most powerful western and northern releases from the reactor, and at some places at the NPP territory. The levels able to cause acute radiation sickness (ARS) remain only inside the Chernobyl Sarcophagus, the enormous "Object ‘Shelter’” construction, which keeps the reactor remnants behind the extremely thick reinforced concrete walls. In such places, only professionals can stay while doing necessary maintenance works.

The routes of our trips are far from such unsafe places. In our buses, for a short while only, we cross western and northern radiation releases’ traces. That is why total external dose obtained during usual 10-hour trip in the Zone is several times smaller then the one received during a transatlantic flight. (During flights at high altitudes the source of irradiation is not contamination but the outer space.)

The probability to swallow or breathe in a radioactive particle during 1-2-day trip to the Zone (if one follows the designated route and safety regulations) is rather low. Even if it happens, the probability that radioactive decay (disintegration) of the atom will take place while it will be in the body (and the irradiation occurs ONLY at the moment of this disintegration) is also very low. It is because radioactive atoms, which still exist in the Zone, are biologically removed from the human body hundreds and millions times more quickly then they physically disintegrate. However, if disintegration and ensuing irradiation nevertheless happen in the body, the resulting injury activates a system of powerful biochemical protective mechanisms. They work in our bodies all the time repairing them from massive routine everyday injuries, including those from natural radiation, which is everywhere and accompanies us from the moment of conception. These processes in healthy body eliminate a singular radiation injury. For short-time visits to the Zone with designated routes and radiation safety regulations followed, the combination of the above factors reduces the risk of internal irradiation’s negative effects practically to zero.

Until now there exists a wide spread misconception about the danger of so-called "radioactive iodine” in the contemporary Chernobyl Zone. Radioactive iodine was dangerous (if protective pills with the usual iodine had not been taken in advance) only in the first weeks after the explosion. Radioactive iodine had decayed almost completely in the first three months, and now is non-existent in the Zone.

After reading the paragraphs above, many of you may be perplexed: "If everything is so fine in the Zone, why the official radiation safety regulations are so strict?” In our view, some of requirements are already redundant: they were either important earlier, when the radiation levels in the Zone were much higher, or they remain valid for the places, which are inaccessible for ordinary visitors of the Zone. Nevertheless, during our trips we strictly follow and enforce these official requirements of the Zone authorities. To be on the safe side, as they say.

Now with some special terminology, and in more detail

Explorer shows the effect of radiation at the dosimeter

The result of some factor’s impact on the body depends on quantity – or dose – of the impact. An understandable example can be the case of mechanic impact: as the dose (amount of mechanic energy transmitted to the body) becomes bigger, the effect changes from pleasant rubbing to useful massage and further to bruises, fractures, numerous traumas and finis lethalis. Nobody prohibits massage: everybody understands that warming muscles up with hands is one thing and falling from the 10th floor is another. However, in physical aspect (that is, from the point of physics as science) – it is one and the same: just transmission of mechanic energy to the body.

There are big problems with understanding such simple fact about radiation. It is not surprising: humanity has known mechanic energy for tens of thousands of years, from the moment of its birth, and radiation (more correctly named "ionizing irradiation”) was discovered only a hundred years ago.

That is why additional explanations about what kinds of ionizing radiation and in what quantities are safe or dangerous. To be more specific: how dangerous radiation-wise is a one-to-several-day trip to the Chernobyl zone now, more than twenty years after the accident?

During such trip a person is subjected to additional radiation impact, which can consist of three types of ionizing irradiation: alpha, beta, and gamma.

A dose of gamma irradiation received during a regular day trip to the Zone is equal to the dose, received during two days in Kiev (New York, London …) or several hours of jet flight (in the plane, the source is space irradiation: it is the same gamma irradiation, differing only in origin). If you believe that two days in Kiev (New York, London …) or two hours in the plane present radiation danger, don’t go to the Zone.

Alpha and beta particles are shielded by clothes and human skin. Those small amounts of particles, which can fly in the Zone’s air, cannot cause any harm to the skin and subcutaneous layer. This is the principal difference of the Zone now from the Zone immediately after reactor explosion.

But what will happen when a dust particle with radionucleus – i.e., a nucleus of radioactive atom able to disintegrate and emit an alpha or a beta particle – makes its way inside human body? For example, it may enter through the mouth with the air (it is prohibited to eat in the Zone!) and with saliva – to the digestive tract? Surprising as it may seem to many – most probably nothing will happen: "With small exceptions, radionuclides are transferred from digestive tract to the blood flow in a very small amount <4-10% from the total mix of uranium fission products).” (Sivintsev Y.V. "How Dangerous Irradiation Is: Radiation and Human”. Moscow, IzdAT, 1991. Pp. 52, 62.) That is, most probably (the probability being within (25 - 10) to 1) this dust particle, this radionuclide will just travel over digestive tract for 24 hours and then leave it and the person for good. The probability of radionuclide disintegrating and emitting an alpha or a beta particle during these 24 hours is also very small; e.g. with half-disintegration period of 30 years (and this type of radionuclides are now relevant for the Zone) this probability can be estimated as 0.01% (1 day / (30 x 365) days). As we can see, the probabilities are very small. Still, they are not equal to zero. We will come back to that a bit later.

Dosimeter radiation near the Chernobyl nuclear power plant

Let’s consider a different pathway for the radionuclides – through the lungs. Firstly, the particle might not make it to the lungs: about 80% of particles with the size exceeding a thousandth of a millimeter are detained by nasopharynx (same source, p. 52), and a human will either sneeze or spit out this dust, or it might make it to the digestive tract with saliva (it was already described). And it won’t get to the lungs.

However, if it was not detained by nasopharynx, it does not mean that the particle made it to the lung: the particles stick on the walls of closest big airways – the "tubes” of trachea and bronchi (the bigger and more dangerous the particle, the quicker it will stick). The trachea, big, small and medium bronchi are not just smooth tubes over which the air moves. Their internal surface is covered with microscopic hairs, the ciliae. These ciliae rise and lower in a coordinated fashion: up and down, up and down… In this way they make waves, which move from the depth of lungs outside. On the crest of this wave, being carried from one cilium to another, all alien particles are taken out. In 30 to 40 hours they eliminate the dust and dirt out from the lungs. (This elegant and constantly working mechanism of self-cleansing is named "epithelial escalation”.)

There is a small probability that a "hot” radioactive particle got stuck in the depth of a lung (or on digestive tract wall; or the radionuclide was carried by blood flow into the organism) – and alpha or beta irradiation damaged the cell. Does it mean finis lethalis? Nothing of the sort: the damage activates other powerful and sophisticated protection mechanisms – those on the cell level of the organism. The first line of such protection is the repairing one: the organism identifies the defect in the cell and repairs it, making the cell healthy and normal (actually, the organism does it in an intensive and constant manner every moment of our lives no matter where we may be). If for some reasons it is impossible to repair the cell, there is one more line of fight for health, which can be referred to as "sanitary”: the cell with irreparable defect is liquidated – killed and removed…

We should not forget that in normal life a person is subjected to the impact of alpha and beta irradiation – from natural radiation, which is present everywhere. That is why the additional amount of alpha and beta impact s/he may receive in the visited areas of the Zone has practically no effect. And if you are for taking into account such small risks – then like real perfectionists be consistent: don’t cross the roads, don’t ride in cars, don’t eat food made of products bought in a supermarket, never bathe in rivers and seas… These are all much more tangible dangers than those which may be associated with radiation during a short visit to the Chernobyl zone.

What has been said above can be further elaborated in even more detail. But the fact persists: a human organism is able to sustain even bigger radiation doses than those taken by the Zone’s visitor during a one- or a two-day-trip. Moreover, it has been reliably established by experiments (long ago for plants, recently for mice) that ionizing irradiation in low doses and irradiation rates (radiation levels) is BENEFICIAL for living organisms. Radiation hormesis, the beneficial impact of ionizing irradiation at low levels, has been confirmed by UN Scientific Committee on the Effects of Atomic Radiation as general biological phenomenon in a special report (document ref. A/AC 82/R 542, 1994 ).

A group of tourists Chernobyl zone near the Chernobyl NPP on an excursion

For a human beings, hormesis has not been experimentally documented. There are two reasons for it: on the one hand, one may note irradiate humans on purpose in the doses, possibly sufficient to achieve hormesis; and on the other, one cannot confirm the effect of small radiation doses studying large populations because a person is subject to thousands of various small impacts every day, and it is practically impossible to establish which one is responsible for his/her health improvement or impairment. (By the way, the latter cause explains the "conclusions” of numerous "studies”, in which the effects of other factors, very important for health (like diet, harmful effects and mere availability of job, salary amount, etc.), which had been in no way controlled during the research, were attributed to low doses of radiation.)

In conclusion one might say that, firstly, the issue of radiation and Chernobyl is still heavily politicized: enormous political and economic interests are behind each viewpoint. From both sides of the debate there is research with fraudulent results, the media further heats up this situation – and all this mess around the issue does not let a regular person find his/her way and make simple practical conclusions. For example, how risky it is visiting a most interesting spot on the planet – Chernobyl.



Secondly, over two decades of such socially unhealthy environment formed in some people painful reactions to the very words "radiation” and "Chernobyl”. I hope that the above brief and coherent explanation of some aspects of the problem will help them.

(c) Sergii MIRNYI