Factors to Consider in Long Term Reactivity Control for PWRs

In summary: They are inserted into the power plant at specific locations and their presence suppresses the power at those points.
  • #1
libertad
43
1
One of my tasks these days is reseaching about long term reactivity control on a typical PWR. As I know in the long term reactivity control we must consider to the role of burnable absorber and boric acid concentration in reactor core during its operation cycles.
So I want to do some calculation to analysis of these two factors.
If you think which I must do some other tasks or consider to other criteria please let me know.
Thanks.
 
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  • #2
Reactivity control is accomplished by radial and axial enrichment design, burnable poisons in the fuel, burnable poison clusters, boric acid in the coolant (which is then buffered by LiOH to maintain a pH above 6.9 at operating conditions) and in some plants by 'grey' rods for axial power shaping.

The U-235 enrichments can be tailored to reduce the local peaking and flatten the flux by flattening the power profile. Different enrichments are used in the blankets and in different rods within symmetric assemblies and in different assemblies.

In the fuel, one will find two main types - IFBA and Gadolinia. There was third type which used Erbia, but this has largely been replaced by IFBA. The IFBA fuel contains UO2 coated with ZrB2 with the boron enriched in B-10. The coating is fractions of a mil depending on design.

Gadolinia fuel involves the mixture of Gd2O3 (gadolinia) and UO2 in the same ceramic pellet. Disadvantages of Gd are the residual remaining toward end of the first cycle and the lower thermal conductivity. Enriching the Gd in isotopes 155 and 157 can allow one to reduce the gadolinia concentration thus reducing the penalties.

Solid burnable poisons include BPRAs (burnable poison rod assemblies) and wet annular burnable absorbers (WABAs) which look like control rod clusters. The burnable poison material (B4 in an alumina matrix or a borosilicate pyrex) are encapsulated in long stainless steel tubes and placed in the guide tubes of selected assemblies (which are obviously not locations under control rods).

Boric acid is a chemical shim. The concentration begins at high levels at BOC and gradually decreases throughout a cycle. The pH is controlled with LiOH. Ideally the boric acid concentration is close to zero.

In a few plants in the US and several in France, 'grey' rods containing Inconel are used to locally suppress the flux (and thus power). The grey rods are less absorbing than burnable poisons or control rods.
 
  • #3
Hello there! It seems like you have a very interesting research project on your hands. I think it's great that you are considering the role of burnable absorber and boric acid concentration in long term reactivity control on a typical PWR. These are definitely important factors to consider in your calculations.

In addition to these factors, you may also want to look into the effects of fuel burnup and reactor power history on long term reactivity control. These can also have a significant impact on the behavior of the reactor core over multiple operation cycles.

Furthermore, it may be helpful to consider the effects of temperature and pressure variations on reactivity control. These can also affect the behavior of the core and should be taken into account in your calculations.

Overall, I think you have a solid starting point with your current considerations. Keep up the good work and don't hesitate to reach out for any further assistance or brainstorming. Best of luck with your research!
 

1. What is "Long Term Reactivity Control"?

"Long Term Reactivity Control" refers to the methods and technologies used to manage and maintain the reactivity of a nuclear reactor over a longer period of time, typically months or years. This is important for the safe and efficient operation of nuclear reactors.

2. Why is long term reactivity control necessary?

Long term reactivity control is necessary to ensure that the nuclear reactor remains stable and does not experience dangerous fluctuations in reactivity. This helps to prevent accidents and maintain the efficiency of the reactor.

3. What are some common methods used for long term reactivity control?

Some common methods used for long term reactivity control include controlling the concentration of boron or other neutron absorbers in the reactor, using control rods to adjust the reactivity, and implementing burnable absorbers that gradually deplete over time.

4. How do scientists monitor and maintain long term reactivity control?

Scientists monitor and maintain long term reactivity control through various measures such as using reactor simulations and calculations to predict reactivity changes, regularly monitoring the reactor's parameters (such as temperature and power output), and conducting regular maintenance and testing of the control systems.

5. What are the potential risks associated with long term reactivity control?

The main potential risk associated with long term reactivity control is the possibility of a loss of control and a rapid increase in reactivity, leading to a nuclear accident. This is why it is crucial for scientists to carefully monitor and maintain the reactor's reactivity levels to prevent any dangerous situations from occurring.

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