![]() ![]() This nucleus is unstable and decays with a half-life of 6.6 hours to xenon-135, which itself has a "natural" half-life of 9.1 hours. The energy release comes from the fact that the mass of the products is less than the mass of reactants.) About 6.5% of the fission events produce iodine-135. uranium-235) and a neutron combine, producing two smaller nuclei and a few free neutrons while releasing a lot of energy. ![]() In nuclear fission, a heavy nucleus (i.e. In any analogy, k > 1 cannot go on forever. Consider it this way: k is the amount of fission at one time, compared to what it was an instant before. So, k = 1 means that the fission rate is constant, less than 1 means the rate is spiraling down, and greater than 1 means it is increasing. This is where the term "chain reaction" comes from. Neutrons both initiate fission and are generated by fission. (HBO)Īs explained in episode 5 of Chernobyl, "Vichnaya Pamyat" (Ukrainian for "memory eternal"), there are positive (red cards) and negative (blue cards) drivers of reactor "reactivity." Think of this reactivity, call it "k," as the change in the energy released in the fission process with time. Jared Harris as Valery Legasov describes the positive (red cards) and negative (blue cards) drivers of reactivity. While no short presentation can do justice to the accident, HBO’s depiction of the reactor failure was masterfully done. To nuclear scientists, the idea that you could take a reactor that had been running at normal power, reduce it to an idling power level, and then bring it back up to full power, is foolish and known to be so from experience gained in the early 1940s from the Hanford, WA reactor that produced plutonium for the Manhattan Project. This essay offers a commentary on the HBO series, intended for those who watched all five episodes, focusing on the technical aspects but broaching the subject of how humans and societies construe nuclear technology. The creators of this series were not afraid of technical scientific details, as they realized the story had a scientific core wrapped in how humans, as well as the Soviet bureaucracy, responded to complex truths, both politically troublesome and culturally traumatic. Today, Chernobyl remains a cultural touchstone for the dangers of nuclear technology, serving as a comparison for any nuclear accident.Ī popular HBO series, Chernobyl, was aired this summer detailing, and dramatizing, what happened. ![]() There was a run on iodine pills and a dramatic increase in elective abortions. The reports from the USSR were not informative, but fission products (ash from the nuclear fission process) were being reported in air samples throughout Europe. The newest reactor (#4) at the Chernobyl site exploded, 50 miles north of Kiev in the Ukraine and only a few miles from the border with Belarus. At Uppsala, we’ve also calculated how much is produced by the destroyed reactor core and made models that can be used for modelling xenon production, decay and movement throughout the building.Those of us of a certain age remember that the world shook on April 26, 1986. What is your part in the project? “I was the one who came up with the idea that we can have radioxenon as a fission signature in the damaged reactor and that it can be useful. We want to evaluate whether it can be used for monitoring in Chernobyl.” It’s designed not to measure the radioactivity of a ruined reactor, but to detect nuclear test explosions. What kind of instrument do you have to use? “The Swedish Defence Research Agency (FOI) has developed an extremely sensitive radioxenon sensor, the Swedish Automatic Unit for Noble gas Acquisition (SAUNA). In Chernobyl today, they have a system using neutron sensors, but they’re positioned too far from the focus of interest, the fuel mass, and with unknown material in between.” Determining the cause requires a different way of measuring from the existing one. The reason is thought to be that it had rained before, and when the water evaporates it can increase – but also lower – reactivity. About a year ago, the media reported a rising neutron flux (a measure of the intensity of neutron radiation, determined by the neutrons’ flow rate). They need to know that the fuel mass from the destroyed reactor won’t suddenly become critical, and a chain reaction arise. Why does it need to be done? “Safety’s essential for the workers there. The advantage is that it can be measured in extremely small concentrations.” Xenon is a noble gas and its radioactive isotopes (radioxenon) arise during nuclear fission. “We plan to use xenon meters to monitor the fuel left in the ruined reactor. ![]()
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