Draft Sixth Power Plan Comment

Uranium 238 (U-238) is a principal ingredient in the nuclear cycle. It is subject to "chain of custody" in that it must be sequestered from human contact. At issue is just how long it might be possible to gurantee that in even the best of scenarios...10 yrs.?, 100? 1,000? how about a million? Truthfully, we haven't a clue about being sure of our capacity to sequester this dangerous material more that a relatively very short time. Nuclear power generation is a Faustian bargain for this reason. In the decades since it's inception no reliable disposal system has been created. U-238 is an alpha radiation particle emitter, and compared to photo or beta radiation, is more effective at causing certain biological effects, notably either cancer or cell-death for equivalent radiation exposure. It is subject ot decay and the daughter nuclide of a radioactive decay event may also be unstable (radioactive). In this case, it will also decay, producing radiation. The resulting second daughter nuclide may also be radioactive. This can lead to a sequence of several decay events. Eventually a stable nuclide is produced. This is called a decay chain, which for uranium 238 is as follows: U238 decays, through alpha-emission, with a half life of 4.5 billion years to thorium-234 which decays, through beta-emission, with a half-life of 24 days to protactinium-234 which decays, through beta-emission, with a half-life of 1.2 minutes to uranium-234 which decays, through alpha-emission, with a half-life of 240 thousand years to thorium-230 which decays, through alpha-emission, with a half-life of 77 thousand years to radium-226 which decays, through alpha-emission, with a half-life of 1.6 thousand years to radon-222 which decays, through alpha-emission, with a half-life of 3.8 days to polonium-218 which decays, through alpha-emission, with a half-life of 3.1 minutes to lead-214 which decays, through beta-emission, with a half-life of 27 minutes to bismuth-214 which decays, through alpha-emission, with a half-life of 20 minutes to polonium-210 which decays, through beta-emission, with a half-life of 160 microseconds to lead-210 which decays, through beta-emission, with a half-life of 22 years to bismuth-210 which decays, through beta-emission, with a half-life of 5 days to polonium-210 which decays, through alpha-emission, with a half-life of 140 days to lead-206, which is a stable nuclide. The alpha-particles emitted by U-238 consists of two protons and two neutrons bound together (the equivalent of a Helium nucleus with atomic mass of 4 amu) with a total energy of about 5 Million electron Volts (MeV). They are a highly ionizing form of particle radiation. They are relatively harmless until/unless ingested (moving through many organisms up the food chain) or inhaled. In contact with living tissue, the massive (compared to a beta particle or gamma ray) alpha particle smashes through cellular DNA like a wrecking ball through a building, inducing aberrant cell growth and cancers. Being relatively heavy and positively charged, alpha particles quickly lose kinetic energy within a short distance of their source. This results in several MeV of destructive energy being deposited in a relatively small volume of material. This increases the chance of cellular damage in cases of internal contamination. In general, external alpha radiation is not harmful since alpha particles are effectively shielded by a few centimeters of air, a piece of paper, or the thin layer of dead skin cells. Even touching an alpha source is usually not harmful, though many alpha sources also are accompanied by beta-emitting radio daughters, and alpha emission is also accompanied by gamma photon emission which are harmful. If substances emitting alpha particles are ingested, inhaled, injected or introduced through the skin, then it could result in a measurable damaging dose. The Relative Biological Effectiveness (RBE) is a measure of the fact that alpha radiation is more effective at causing certain biological effects, notably either cancer or cell-death, compared to photo or beta radiation, for equivalent radiation exposure. This is generally attributable to the high Linear Energy Transfer (LET), which is about one ionization of a chemical bond for every Angstrom of travel by the alpha particle. The RBE has been set at the value of 20 for alpha radiation (U-238) by various government regulations. The RBE is set at 10 for neutron irradiation, and at 1 for beta and ionizing photon radiation. However, another component of DU's alpha radiation is the recoil of the parent nucleus, due to the conservation of momentum requiring the parent nucleus to recoil, much like the 'kick' of a rifle butt when a bullet goes in the opposite direction. This gives a significant amount of energy to the recoil nucleus, which also causes ionization damage. The total energy of the recoil nucleus is readily calculable, and is roughly the weight of the alpha (4 amu) divided by the weight of the parent (typically about 200 amu) times the total energy of the alpha. By some estimates, this might account for most of the internal radiation damage, as the recoil nuclei are typically heavy metals which preferentially collect on the chromosomes. In some studies[2] this has resulted in a RBE approaching 1,000 instead of the value used in governmental regulations. Normal functioning of mammalian kidney, brain, liver, heart, and numerous other systems can be affected by uranium exposure, because in addition to being radioactive, uranium is a toxic metal.[5] (2) Winters-TH, Franza-JR, Radioactivity in Cigarette Smoke, New England Journal of Medicine, 1982; 306(6): 364-365 (5) E. S. Craft, A. W. Abu-Qare, M. M. Flaherty, M. C. Garofolo, H. L. Rincavage, M. B. Abou-Donia (2004). "Depleted and natural uranium: chemistry and toxicological effects". Journal of Toxicology and Environmental Health Part B: Critical Reviews 7 (4): 297-317.