10/06/2010

Nuclear Poison

A nuclear poison is a substance with a large neutron absorption cross-section. Simply put, it can absorb neutron very effectively.

Where do these poisons come from? For starters, in the nuclear reactor, there will be material that is produce by the fission reaction that can absorb a lot of neutrons. Because we need neutrons to keep the reactor running, having less neutrons will result in less power being generated. In fact, if the poison level is unchecked, it may cause the nuclear chain reaction in the reactor to stop.

The radioactive materials in the reactor will decay. From time to time, there will be materials in the reactor that its decay process will result in a new substance that have a high neutron absorption cross section. This too will lead to an increase in the amount of nuclear poison.

Let's say that u have a jug of water. Then, a sponge is put inside the jug. After a while, you will noticed that the level of water inside the jug has decreased. Imagine that the water is the neutron and the sponge is the poison. Neutron level will be reduced by the existence of the poisons.  

But sometimes, you will need to keep some amount of poison in the reactor. Why you ask? It is because the poisons can be used to regulate the reactivity of the reactor. For example, you want to run the reactor with a 200 grams of U-235. Since the radioactive material will decay, the amount of fuel will decrease over time. In order to solve the problem, you will need to put more than 200 grams in the reactor. The more fuel you use, the reaction rate will be higher. So to effectively control the neutron level, poison is put inside the reactor.




33 comments:

  1. The poison u talking about is it the radioactive waste?

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    Replies
    1. Reactor poisons are simply nuclides that absorb neutrons other than the fuel nuclides. This is not the same thing as people normally call poisons that harm people. This is a "neutron poison" or the nuclide absorbs the neutron and goes to an energy state that does not release another neutron. The end result is that the neutron is no longer available for fission, so it has been "poisoned" or removed.

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  2. assalamualaikum..

    sincerely,i still dont get what u means by nuclear poison...i hope u can answer all my following questions...

    is it nuclear poison an addictive or catalyst?or just a waste material?

    but i also want ask about the neutron role in the nuclear activity.is it neutron reactivity that produce energy?

    u said that the nuclear poison also needed in the reactor to regulate the reactivity of the reactor.and u also said that materials in the reactor that its go through decay process will lead to an increase in the amount of nuclear poison.
    so,my question is,how to reduce the amount of nuclear poison in the reactor?

    muhamad danial bin dasuki
    me083590
    den_nell90@yahoo.com

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    Replies
    1. When a neutron is absorbed by an atom nucleus that does not cause fission, this atom nucleus is referred to as a "neutron poison", since the neutron is no longer available to be absorbed by a fuel atom that can cause a fission and a release of further neutrons. The neutron were removed or "poisoned". Look at a chart of the nuclides for little black triangles. These are the known fission fragments. Most of these fission fragments are "neutron poisons" or they absorb neutrons and do not produce another neutron.

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  3. is the poison in the reactor can affect the environment?

    muhammad fikri bin baharudin
    fiq.bahar@gmail.com

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    Replies
    1. Many of the fission fragments give off beta minus particles or gammas as they get rid of excess energy. From this sense you would not want to just dump used nuclear fuel in a normal dump. The term "poison" is simply confusing to common people. In this case "poison" means to absorb a neutron and not cause a fission. This is also commonly known as neutron absorption.

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  4. I sincerely thought this is a really nice summary of yesterday's lectures. Great job guys! However, please respond to your readers' enquiries.

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  5. The ones you see in the barrel with radioactive logo on it is the radioactive waste. It is the waste product of all the processes in the reactor.

    Nuclear poison is referring to the stuff that unintentionally absorbs neutron in the reactor. This poison come from the fission in the reactor. It's inside of the reactor.

    Maybe the term 'Neutron Poison' is clearer than Nuclear Poison.

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  6. Nuclear poison is not an additive nor is it a catalyst. It's the byproduct of the fission process in the reactor.

    In order for the reactor to function, you will need neutrons for the fission to occur. Meaning you need neutrons to bombard other atoms to create more neutrons. Hence the radioactive chain reaction.

    To simply put it, the reactivity is like the rate of neutrons to successfully to create more neutron. When these neutrons are created, heat will release inside the reactor as well. It's the heat that will be used to power up the turbine.

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    Replies
    1. A fission reaction causes heat by the addition of energy to the fission fragments, neutrons, betas, and gammas released from the nucleus during the fission process. A thermal neutron is required to cause fission. If the neutrons are absorbed by nuclides that do not cause fission then the neutrons are said to be "poisoned" or removed. They are no longer available to cause fission. If enough neutrons are absorbed the heat production will be greatly reduced and the reactor is called "shutdown". Even a shutdown reactor will generate some decay heat from the decay process of the fission product precursors.

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  7. Talking about the poison in the reactor, you need to know that there a few types of poison.

    1. Burnable poison (the name speak for itself :P)
    2. Soluble poison (the poison is actually circulated in the coolant)

    For Xe-135 poison, it will take 3 days of shutting down the reactor to lower it to small percentage.

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  8. Ayyoh how can the poison in the reactor got effect on the enviroment....unless u go drill a hole at the reactor there let it leak

    -__-

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    Replies
    1. The "poisons" are really neutron absorbers. They are contained within the fuel pellets. "Poisons" are simply the smaller atoms that are formed when the fission process occurs. Look at the chart of the nuclides for little black triangles to identify the many fission fragments that are generated when the fission event occurs.

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  9. Assalamualaikum.
    I think the name nuclear poison is not a good name because in my opinion , poison is a negative words which effect dangerously to the environment, but in this case there is also a few reasons of using it. so maybe u should call it radio nuclear or something else. so that people will not scared of using it as it can regulate the reactivity of the reactor.
    Mohd Fazli bin Ramly
    mrfazli@rocketmail.com

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  10. thumbs up 4 fazli comment

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  11. This is certainly a very good way to introduce a nuclear substance with some useful benefits. As stated, nuclear poison can be used to regulate and control reactivity in a reactor. My only question is can nuclear poison be used to regulate and control objects in daily life for a better economical advantage?
    Roshen James a/l Jaya Krishnan
    james_thierry@hotmail.com

    ReplyDelete
  12. Correct me if I'm wrong, nuclear poison or to be specific burnable nuclear poison is also loaded into the core of the reactor to control the rate of fission of plutonium and uranium without control rods.
    Thirukumaran a/l Ramasamy Chettear
    thiru_5519@hotmail.com

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    1. When the material is added to the core to control excess reactivity, this is called a burnable poison. Atoms are added that are known to absorb neutrons. These atoms eventually become more stable and stop absorbing neutrons. The neutrons can then reach the fuel. The fuel is depleting at the same time so less fuel is present.

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  13. what determines the lifetime of nuclear fuel in a reactor long before all possible fissions have taken place?

    KESAVAN S/O MOHANADAS
    CE083434
    kesavan712554@gmail.com

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  14. assalamualaikum..

    as what you'd say that nuclear poison will cause the absorption of neutron but somehow it still need to be keep some amount in the reactor in order to keep the reaction higher. how can we know about the level of the nuclear poison?? is it still safe or is it need to be mend as it will cause the reaction to stop.

    MUHAMMAD SAFWAN BIN MOHD SHAKRI
    ME083869
    rises_alry@hotmail.com

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  15. As a forwading country towards globalization,the time has reach for Malaysia to involve actively in application of the nuclear reactor as an alternative to produce energy.Altough this title"nuclear poison" may scare us,but its actually a process which happens in the reactor.

    Kantharrajan sandaram
    me083559
    rajan_9849@yahoo.com

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  16. Im not sure why would anyone would want to use the poison for regulating objects in daily life.

    I can't think of anything that needs huge amount of neutron absorption. Flying car maybe? :D

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  17. Considering the effects of nuclear poison, which helps lower the high reactivity of their initial fuel load, based on my limited knowledge. Could u explain if they deplete in the reaction as they absorb neutrons or they itself is not involve in the process ie. like a catalyst.

    Muhamad Rifdy Bin Samsudin
    ed_dy12@hotmail.com

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  18. I think in the reactor normally it has some kind of indicator or equipment to monitor the poison level safely.

    Nowadays every power plant in the world has some kind of computerized monitoring system. The same thing goes for nuclear power plant.

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    1. Reactors contain both internal movable fission chambers and excore (external) nuclear detectors that measure the neutron flux within the core or the neutron flux that leaks from the core. The reactors also use thermal couples to measure the exit temperature of the core. Xenon and Samarium are the two most common neutron absorbers or "poisons". They cannot be measured directly. instead, we measure the effects my measuring the neutron flux or power level of the core.

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  19. Rifdy,

    i think the answers you're looking for are in the comments above.

    Thank you for visiting our blog. Don't forget to vote on the poll!!

    ReplyDelete
  20. A good summarized article about nuclear poison. Clearly it's needed to stabilize the reaction in the reactor. I have some questions though, firstly you said that to lower the percentage of Xe-135 in the reactor, it needs to be shut down for 3 days. Is there any other process introduced to perform this operation instead of shutting down reactors.
    Secondly, does the nuclear poison comes from a chain reaction from the reactor or it's introduced by putting it in the reactor.
    Thanks.

    Zulfadhli Bin Zahudin
    CE083466
    darhein_90@hotmail.com

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  21. How can we control the speed of the fission in the reactor? As stated above the nuclear poison is produced from the fission reactivity in the reactor and also if the nuclear poison is uncontrolled the amount of neutron will be less thus there will be less power generated. Another question is how to keep the nuclear poison checked? As i know from another source the best way to control fission reactivity is by using moderator and pressured H2O.Can the poison still be used with a high pressured H2O?

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  22. How can we control the speed of the fission in the reactor? As stated above the nuclear poison is produced from the fission reactivity in the reactor and also if the nuclear poison is uncontrolled the amount of neutron will be less thus there will be less power generated. Another question is how to keep the nuclear poison checked? As i know from another source the best way to control fission reactivity is by using moderator and pressured H2O.Can the poison still be used with a high pressured H2O?



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    Govinderan Mageswaran
    ME083544
    ninemoons_firing@yahoo.com

    ReplyDelete
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