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Date: 29-3-2017
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Date: 26-11-2020
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Date: 5-4-2017
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Non-Burnable Poisons
A non-burnable poison is one that maintains a constant negative reactivity worth over the life of the core. While no neutron poison is strictly non-burnable, certain materials can be treated as non-burnable poisons under certain conditions. One example is hafnium. The removal (by absorption of neutrons) of one isotope of hafnium leads to the production of another neutron absorber, and continues through a chain of five absorbers. This absorption chain results in a long-lived burnable poison which approximates non-burnable characteristics. Absorbers with low neutron absorption cross sections can also be treated as non-burnable under most conditions. It is possible to make the reactivity of a poison material that is usually a burnable poison more uniform over core life through the use of self-shielding. In self-shielding, the poison material is thick enough that only the outer layer of the poison is exposed to the neutron flux. The absorptions that take place in the outer layers reduce the number of neutrons that penetrate to the inner material. As the outer layers of poison absorb neutrons and are converted to non-poison materials, the inner layers begin absorbing more neutrons, and the negative reactivity of the poison is fairly uniform.
The normal use of fixed non-burnable poisons is in power shaping, or to prevent excessive flux and power peaking near moderator regions of the reactor.
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اكتشاف تأثير صحي مزدوج لتلوث الهواء على البالغين في منتصف العمر
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زهور برية شائعة لتر ميم الأعصاب التالفة
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المجمع العلمي يكرم القرّاء المشاركين في الختمات الرمضانية بقضائي المدائن والنهروان
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العتبة العباسية تقيم ورشة علميّة عن عناصر الهُويّة الثقافيّة لوفدٍ من جامعة ذي قار
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قسم الشؤون الفكرية يقيم ورشة تعريفية حول مشاريعه الرقمية في جامعة المثنى
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العتبة العباسية تدعو للمشاركة في مسابقة القصّة القصيرة الثانية ضمن أسبوع الإمامة الدوليّ الثاني
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