The Nuclear Regulatory Commission (NRC) has promulgated a draft Generic Environmental Impact Statement for public comment which outlines their plans and assurances for the continuing ability to safely deal with spent nuclear reactor waste. Their term is “waste confidence.” These are some of my comments concerning the accuracy and credibility of that draft which I submitted during their public comment period.
Scores of radionuclides of varying half-lives and activities combined in hundreds of chemical compound variations are produced by nuclear fission in both bombs and reactors. Although many of these decay quickly, others persist long enough to be incorporated chemically into animal and plant tissues, through a myriad of physiological and biochemical pathways, to become constituent building blocks of cells. These incorporated radioisotopes can cause mutagenic and oncogenic transformations in the host or adjacent cells. Each compound can be metabolized by a variety of anabolic and catabolic pathways with different biological outcomes. The simple-minded approach, used by the NRC, to estimate risk is almost entirely based on the external fluence of gamma and beta radiation, distributed uniformly over large areas, and largely ignores the multitude of specific risks due to in-situ radionuclide incorporation. Unlike other toxic biochemical reactions which require a certain minimum concentration of reactants (toxicants) or activation energy to proceed, nuclear processes emit particles or photons with sufficient energy to precipitate a chemical reaction from the decay of a single nucleus. Thus, there is no threshold concentration for nuclear induced chemical processes as there is with chemical toxins. In fact, some radionuclides such as polonium-210, which can be present in waste fuel, and is present in the neutron “spark plugs” of plutonium bombs are lethally toxic even in the sub-microgram range. To calculate the true risk from each type of nuclear waste an analysis of the radioisotope composition of that waste based on the starting fuel mixture, the degree of fuel burn-up and the stage in the cooling/aging process must be done. It is essential to fully evaluate the toxicity of all the different radioisotopes in the waste fuel which is a very difficult process.
Tritium is a strong biological toxin because it is readily incorporated into biological tissues. It doesn’t even require a chemical reaction since an organic molecule can incorporate tritium through an exchange mechanism between tritiated water and the hydrogen atoms of organic compounds by simple incubation in aqueous solution. Thus tritium can be absorbed from the environment by both ingestion and inspiration. Once incorporated into the body, tritium is particularly dangerous because hydrogen is ubiquitous in biological tissue. Tritium decays at a high activity rate but emits a low energy electron. Low energy electrons have a high linear energy transfer to their surroundings and therefore cause maximum biological damage in a small volume of tissue. This energy deposition in a very small area of an organ results in a very high micro-dose to specific cellular and tissue components, which can lead to cancer or mutation if a cell is transformed and not cleared by the immune system. Therefore, micro-dose calculation is important for assessing the carcinogenic potential of tritium decay, in situ, and this micro-dose is much larger than what would be expected if the dose were to be distributed uniformly throughout the organ.
Other radionuclides present in spent fuel are also selectively incorporated into certain biological tissue because they mimic some essential biological elements. For example: radioactive cesium and rubidium mimic potassium and so are concentrated in the muscles where they can cause wasting disease such as polymyocytis, or contribute to autoimmune disorders like multiple sclerosis or even heart disease. Plutonium and strontium mimic calcium and so concentrate in the bones near the bone marrow which can cause leukemia, lymphoma, multiple myeloma and other disorders of the blood forming units. Some alpha emitters in the circulatory system damage the vascular lining causing inflammation resulting in calcified arterial plaques which can cause infarcts and heart disease. Radioactive noble gases dissolve in fatty tissues and so concentrate in tissues like the brain, breast and bone marrow, causing cancers in these organs. A variety of radionuclides mimic iron and so are transported and stored in the body by transferrin and ferritin. Radio-iodine concentrates in the thyroid, but can also be incorporated into radioactive thyroxin which can damage the thyroxin receptors in the tissues. (Dioxin is so chemically toxic precisely because it disrupts this thyroxin/receptor binding site). It is not enough to say that these atoms are simply radioactive but one must also know where in the body they are concentrated and how their decay affects the adjacent tissue and its biochemistry. These pathways are so complex that it is virtually useless to attempt to predict biological risk based on the decay properties of radioisotopes themselves outside the body. Most of the NRC risk analyses are clearly done by physicists with limited knowledge of biology or biochemistry and so lack the insight of the biological disciplines. Physicists concentrate on the external radiation component of dose, in most cases, while ignoring the subtleties of the tissue “doses” at the molecular level. Radiation has also been shown to have other demonstrated statistical effects besides increasing cancer rates, such as depression of the normal bodily immune response against pathogens and a non-specific life shortening in irradiated populations.
It is therefore curious that the NRC has chosen to add an internal radon dose to their estimate of the Natural Background Radiation (NBR). This “radon” dose cannot even be generalized since it depends on so many factors such as smoking habits, house ventilation/air exchange systems and the composition of the underlying bedrock and soils. The NRC uses this approach when it suits their purpose of inflating the background dose for comparison purposes against NRC allowed exposure standards; but they ignore internal doses when they go against their otherwise optimistic risk projections. It is also curious that they add a significant dose due to medical procedures which are clearly not “natural” at all.
Since the earth’s life forms are carbon based, carbon-14 is a particularly noxious toxicant. Carbon-14-carbon dioxide has a long half-life and is also readily incorporated into biological organisms by photosynthesis, where it can be assimilated into bio-molecules such as DNA which are vital to life. Carbon-14 decays by beta emission and can cause disruption and mutation of bio-molecules in three different ways: (1) the emitted beta particle can ionize and disrupt adjacent bonds in the molecule; (2) the beta decay can cause the source nucleus to recoil and be expelled from its position in the bio-molecule causing bond disruption and recombination in deleterious ways; and (3) the decaying carbon nucleus can transform itself into a different element with different chemical properties and thus compromise the chemical integrity of the bio-molecule.