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Descriptive information to help identify this report. Follow the links below to find similar items on the Digital Library. Helium is insoluble and is eventually released to the interior of the fuel rod, where it produces an internal pressure. When sufficiently high, this pressure stress could cause separation of the cladding from the fuel, causing overly high centerline temperatures. Gadolinium has several very strongly absorbing isotopes, but not all have large cross sections and result in residual burnable poison reactivity worth at the end of the fuel life.
Even if the amount of this residual absorber is small and the penalty in operation small, the cost of this penalty, even if only several days, can be very high. The objective of this investigation was to study the performance of single isotopes in order to reduce the residual negative reactivity left over at the end of the fuel cycle. Since the behavior of burnable poisons can be strongly influenced by their configuration, four forms for the absorbers were studied: homogeneously mixed with the fuel, mixed with only the outer one-third of the fuel pellet, coated on the perimeter of the fuel pellets, and alloyed with the cladding.
In addition, the numbers of fuel rods containing burnable poison were chosen as 8, 16, 64, and Other configurations were chosen for a few special cases.
An enrichment of 4. A standard pressurized water reactor fuel core was chosen for the study, and state-of-the-art neutronic reactor core computer codes were used for analysis. Power distribution, fuel burnup, reactivity due to burnable poisons and other fission products, spectrum shift, core reactivity, moderator void coefficients, as well as other parameters were calculated as a function of time and fuel burnup.
The results not only showed advantages of separation of burnable poison isotopes but revealed benefits to be achieved by careful selection of the configuration of even naturally occurring elements used as burnable poisons.
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The savings in terms of additional days of operation is shown in Figure 1, where the savings is plotted for each of six favorable isotopes in the four configurations. The benefit of isotope separation is most dramatic for dysprosium, but even the time savings in the case of gadolinium is several days.
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For a modern nuclear plant, one day's worth of electricity is worth about one million dollars, so the resulting savings of only a few days is considerable. It is also apparent that the amount of savings depends upon the configuration of the burnable poison.
Unique identifying numbers for this report in the Digital Library or other systems. Reports, articles and other documents harvested from the Office of Scientific and Technical Information. What responsibilities do I have when using this report? Dates and time periods associated with this report. You Are Here: home unt libraries government documents department this report. Showing of pages in this report. Description Burnable poisons are used in all modern nuclear reactors to permit higher loading of fuel without the necessity of an overly large control rod system.
There are two types of micronuclear reactor power source Rowe, : 1 isotope generator, which converts decay heat into electric energy; 2 nuclear reactor power source, which converts fission heat into electricity energy. Comprehensively considering the reactor mass and volume, criticality safety, reliability, and maneuverability, heat pipe cooled fast reactor power source featured with compact structure, less movable parts, high reliability, and low noise level could be widely used in the power system of unmanned underwater vehicle in the future Rowe, Heat pipe cooled reactor has already been widely researched.
Various micro heat pipe cooled reactor power sources for space missions have been designed in the United States. Potassium or sodium heat pipe are adopted for cooling. MSR Bushman et al. SAFE Poston et al. China institute of atomic energy has put forward a variety of heat pipe reactor designs for space missions, such as the mars surface power plant, and the lunar surface power plant HPCMR Chengzhi et al.
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Based on a literature review, a micro heat pipe cooled nuclear reactor power source applied for underwater vehicle featured with 2. Lithium heat pipe cooled core, six control drums, tungsten, and an open water loop shield are adopted in this power source. Monte Carlo program and ORIGEN are used to preliminarily calculate design parameters and analyze the criticality safety and burnup characteristics of the design scheme, etc. The nuclear reactor power source consists of the following parts: core, control drums, shield, heat pipes, and thermoelectric generator.
The working principle is shown in Figure 1. In reactor core, fission fuels generate heat in chain reaction controlled by control drums. The heat is transferred by heat pipes and is converted into electrical power by thermoelectric generator. Waste heat is taken away by water. The core structure is shown in Figure 2 , and the key parameters of reactor core are shown in Table 1.
The core is made up of 90 fuel pins, 37 heat pipes, BeO reflector, and 6 control drums. Figure 3 shows the design parameters of fuels and heat pipes. The matrix is put in a barrel on whose inner surface is a coating of Gd 2 O 3 burnable poison. The barrel is surrounded by a BeO reflector and 6 control drums with B 4 C.
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Reactor core is stored in a cylinder Mo—14Re alloy barrel. Tungsten and an open water loop are used as shields in the power source system. Thermoelectric generator is used to convert heat conducted from heat pipes into electricity of kWe. Monte Carlo program has a significant advantage of simulating geometries without much approximation.
Effective multiplication factor k eff is one of the most important parameters in criticality calculation using MCNP. It is defined as the following equation Team, :. These three estimates are combined using observed statistical correlations to provide the final estimate of k eff and SD Urbatsch et al. As Figure 4 shows, a model is set up to simulate the core neutronics characteristics. The active zone is axially divided into 17 layers and cells per layer.
The importance of all the particles, neutron and photon, in all cells is defined to be equal to 1. The calculation requires an ACE format nuclear database. According to preliminary thermal analysis, the fuel temperature is assumed 2, K, temperature of the heat pipes and matrix is 1, K, and temperature of the control drums and reflector is K for neutronics analysis. MCNP5 is used to calculate the power distribution of the core.
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It can be seen from the Figure 7 that the power reaches a maximum value at the center of the active zone and decreases from the center to the periphery where control drums and reflector locate. Reflector has influence on radial power distribution, due to the neutron reflection effect. The radial power peak factor obtained is 1. Axial normalized power density of the hottest, the average, and the coldest channel are shown in Figure 6. The axial power peak factor is 1. The power peak factor of the core 1. The reactivity feedback is considered an important factor for reactor safety.
The impact of Doppler broadening effect and the density change due to thermal expansion are considered in the calculation. The thermal expansion coefficient of UN fuel is considered by the equation as follows:. The thermal expansion coefficient of B 4 C on six control drums is considered by the equation as follows:. The thermal expansion coefficient of BeO reflector is considered by the equation and data given by Kozlovskii and Stankus The reactivity change with the core temperature varying from cold condition K to thermal condition 1, K is shown in Figure 8.
Reactivity decreases as the temperature increases. Reactivity is mainly caused by neutron leakage for thermal expansion of the reflector. The thermal power is defined 2. The effective multiplication factor change during the core life is shown in Figure 9. The lifetime of the heat pipe cooled reactor core is 14 years. Due to the depletion of burnable poison and fast neutron breeding effect, the effective multiplication factor increases at the beginning of life and then deceases when burnable poison run out until the end of life.
As Figure 10 shows, a channel in active zone is defined as an area including a heat pipe and part of the surrounding fuels, air gaps, and matrix. One-dimensional calculation model for each channel is shown in Figure The temperature of the active zone channels is shown in Figure The maximum temperature of fuels is 2, K.
The maximum power of heat pipes is The temperature of thermocouple unit is also obtained by the same code. As shown in Figure 12 , temperature of thermocouple unit varies from to 1, K.