Sergio Final

Editor's Notes

• #4: To prevent the nuclear fuel from overheating, this heat had to be removed by cooling systems that were mainly run or controlled by electrical power* *The Fukushima Daiichi Accident REPORT BY THE DIRECTOR GENERAL of the International Atomic Energy Agency 2013
• #5: To prevent the nuclear fuel from overheating, this heat had to be removed by cooling systems that were mainly run or controlled by electrical power* *The Fukushima Daiichi Accident REPORT BY THE DIRECTOR GENERAL of the International Atomic Energy Agency 2013
• #6: In BWRs, due to the necessity of a steam dryer above the core, this design requires insertion of the control rods from beneath. 
• #7: The Nuclear System Protection System is a four channel electrical alarm and actuating system that monitors the operation of the reactor, which, upon sensing an abnormal condition, initiates action to prevent an unsafe or potentially unsafe condition. The system integrates the following functions : Reactor Trip: Nuclear System Isolation Engineered Safety Feature Actuation The NSPS uses solid state electronic technology from sensor output to actuation device inputs. Nuclear Engineering Handbook  edited by Kenneth D. Kok http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0046.html Code: 10CFR50.46
• #9: The Vallecitos boiling water reactor (VBWR) was the first privately owned and operated nuclear power plant to deliver significant quantities of electricity to a public utility grid. During the period October 1957 to December 1963, it delivered approximately 40,000 megawatt-hours of electricity. This reactor -- a light-water moderated and cooled, enriched uranium reactor using stainless steel-clad, plate-type fuel -- was a pilot plant and test bed for fuel, core components, controls, and personnel training for the Dresden project, a Commonwealth Edison plant built in Illinois five years later. The plant was a collaborative effort of the General Electric Company and Pacific Gas and Electric Company with Bechtel serving as engineering contractor. Samuel Untermyer, the GE engineer responsible for the initial design of the VBWR, had performed much of the conceptual research at Argonne National Laboratory while conducting heat transfer and nuclear physics experiments, including the BORAX (boiling reactor experiment) tests. https://www.asme.org/about-asme/who-we-are/engineering-history/landmarks/128-vallecitos-boiling-water-reactor The VBWR was shutdown in 1963 and NRC issued a possession only license in 1965. The license was renewed in 1973 and the license has remained effective under the provisions of 10 CFR 50.51(b). The facility has been maintained in SAFSTOR condition. The licensee plans to maintain the facility in SAFSTOR until ongoing nuclear activities are terminated and the entire site can be decommissioned. GE has a self-guarantee instrument. The spent fuel has been removed from the site. http://www.nrc.gov/info-finder/decommissioning/power-reactor/vallecitos-boiling-water-reactor-vbwr-.html
• #12: In BWRs, the heat is generated in the core that is composed of the fuel assemblies, which are the fuel pins bundled in square arrays and enclosed in a zirconium alloy fuel channel box72, and the control rods, which are cross-shaped arrangement of blades containing boron carbide (B4C) neutron poison. The fuel pins consist of low enrichment uranium oxide or mixed (uranium and plutonium) oxide (MOX) fuel pellets enclosed and sealed in zirconium alloy cladding tubes. The BWR fuel design and reactor core arrangements evolved over the years. The reactor cores in the Fukushima Daiichi NPP units at the time of the accident had some differences in their arrangements as shown in Table 1.2–8. Section 1.4 provides further details of the fuel composition. Pag 66 Volume 1
• #13: ABWR Seminar-Reactor, Core & Neutronics LE Fennern April 13, 2007
• #14: Dynamic Behavior of BWR Massachusetts Institute of Technology Department of Nuclear Science and Engineering Engineering of Nuclear Systems
• #15: When the flow increases, density increases
• #16: The Control rod design, susing boron carbide B4C compacted in stainless tubes. Control rods are used for power distribution shaping and for shim control of long term reactivity changes which occur as result of fuel irradiation
• #17: BWR/6 General Description of a Boiling Water Reactor. GE Nuclear Energy
• #18: In the Unit 1 design, there were two separate and redundant isolation condenser loops. In these closed loops, the primary side of the isolation condenser received steam generated in the reactor and condensed it by cooling inside the heat exchanger tubes that were submerged in colder water tanks (isolation condenser pools) located outside the primary containment vessel. Condensed steam was then sent as cold water back to the reactor by gravity (see the diagram below). Without mixing with the radioactive primary side water, the secondary side water in the isolation condenser pools boiled, and the evaporated steam was vented to the atmosphere, which served as the heat sink. The secondary side water volume of the isolation condenser (both trains together) was sufficient for eight hours of cooling before requiring replenishment from a dedicated water source.
• #19: Reactor core isolation cooling. In the design of Units 2–6, there were open cycle cooling systems that needed a source for adding water to the reactor system. In the reactor core isolation cooling systems, the steam from the reactor drove a small turbine which, in turn, ran a pump that injected water into the reactor at high pressure. The steam that ran the turbine was discharged and accumulated in the suppression pool section of the primary containment vessel, which served as the heat sink for absorbing waste heat. The water lost from the reactor was replenished by taking fresh water from the condensate storage tank (see the diagram below). When the tank emptied or the suppression pool became full, the water that accumulated in the suppression pool could be used, making the system essentially a closed loop cycle. The reactor core isolation cooling was designed to operate for at least four hours.
• #20: In Unit 1, as the reactor pressure increased, both loops of the isolation condenser system started automatically and continued to cool the reactor. The operation of both isolation condenser loops lowered the reactor pressure and temperature so rapidly that the operators manually stopped them, in accordance with procedures, in order to prevent thermal stress on the reactor pressure vessel. Afterwards, only one of the loops was used by the operators to control the cooling rate in a range prescribed by the procedures.  In Units 2 and 3, the increase in reactor pressure automatically activated safety relief valves, which were designed to protect the reactor from over pressurization by releasing steam from the reactor vessel to the suppression pool section of the primary containment vessel. This resulted in a decrease in the reactor water levels. The operators manually activated the reactor core isolation cooling system in accordance with procedures. In Unit 4, the equipment for cooling and refilling of spent fuel pool water stopped working as a result of the loss of off-site power. The Unit 4 spent fuel pool, containing more than 1300 spent fuel assemblies, had the largest amount of decay heat to be removed among all the spent fuel pools of the units.  In Unit 5, the reactor pressure, which was being kept elevated by the use of a pump for pressure testing purposes at the time of the earthquake, initially dropped when the pump stopped as a result of the loss of off-site power. The pressure started to rise due to decay heat, but unlike in Units 2 and 3, it remained well below the levels to activate the safety relief valves.  In Unit 6, the reactor was near
• #22: However, about 10 minutes after the first wave, the second and largest wave, with a runup height of 14–15 m,
• #23: As the core degradation proceeds, leading eventually to melting of the core material, the fission products initially trapped within the nuclear fuel become volatile and released from the core material. The time and amount of release of the different fission product elements depends on their respective volatilization temperatures, as follows:  Highly volatility elements like the noble gases, i.e. xenon (Xe), krypton (Kr), caesium (Cs), iodine (I), or tellurium (Te) and relevant chemical compounds of these elements, are released completely from the core in the early phase of core degeneration, when the core is still inside the RPV.  Medium volatility elements like strontium (Sr) and barium (Ba) are released from the core during the in-vessel phase as well as during the ex-vessel phase. These medium volatile fission products dominate the release during the accident phase after RPV failure.  Low volatility elements like zirconium (Zr), niobium (Nb), and the actinides (U, Pu, Np, Am) and their oxides, have a boiling point well above the temperatures reached in a core melt, and so only trace amounts of them are released. When the RPV fails and the core material falls into the reactor pit, the core melt no longer contains significant amounts of volatile fission products. Thus, the release of highly volatile fission products is expected to be low in this late phase of a core melt accident.
• #25: At 06:14 on 15 March, an explosion was heard on the site and tremors were felt in the common main control room of Units 1 and 2. Unit 2 suppression chamber pressure had dropped to near atmospheric pressure57, indicating potential loss of the confinement function
• #26: TEPCO [7] also estimated the amount of hydrogen generated through a numerical analysis considering the oxidation of the zirconium cladding. he Sandia National Laboratory also analyzed the amountof hydrogen produced during the accident [12] utilizing thecode  MELCOR  The main sources of hydrogen that must be taken into account are the oxidation of  Zircaloy by steam, the radiolysis of water, the reaction between water and boron carbide and the interaction of the molten core with the concrete of the containment
• #27: About two hours later, white smoke (or steam) was observed being released from the Unit 2 reactor building near the fifth floor. A radiation dose rate measurement of nearly 12 mSv/h was recorded at the main gate at 09:00 on 15 March, the highest measurement since the beginning of the accident. Because of the high radiation levels, an order was issued by government authorities, two hours later, at 11:00, requiring all residents within a 20–30 km radius of the Fukushima Daiichi NPP to take shelter indoors
• #30: What did the world learn from the Fukushima accident? What did the world learn because of the Fukushima accident? Review in-depth
• #31: This not only helps preserve the integrity of the containment building, but can also help delay reactor core damage or melting