Identifying Decay Heat Sources in Reactors Post-Trip

[Freddy_uk]

I am looking for some data that identifies the most significant source of decay heat for the first few days from a reactor trip. Something similar for 1month after or more would be useful.

Thanks

Dave

 

[Astronuc]

Start with these and hopefully others can contribute. I'll continue looking.

Validation of ORIGEN-S Decay Heat Predictions for LOCA Analysis
http://www.ornl.gov/sci/scale/pubs/C183.pdf

http://www.ornl.gov/sci/scale/spentfuel.htm
particularly - http://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6972/cr6972.pdf

http://www.studsvikscandpower.com/nuclear-reactor-analysis-software/snf/publications
http://www.studsvikscandpower.com/nuclear-reactor-analysis-software/snf


Unfortunately, most tabulated calculations are for months or years.

 

[Freddy_uk]

Its for a single slide (or two) on a presentation. I have a decay heat curve and was looking for something that helps describe why the energy initially falls sharply and why after that only a very gradual reduction in heat is seen due to the half life of some of the isotopes.

 

[Astronuc]

Its for a single slide (or two) on a presentation. I have a decay heat curve and was looking for something that helps describe why the energy initially falls sharply and why after that only a very gradual reduction in heat is seen due to the half life of some of the isotopes.

In that case, try this -
http://energyfromthorium.com/2006/07/14/new-visualization-tool-for-decay-chains/
and launch the java app.

The radionuclides on the bottom of the band, near they grey dots, and half-lives on the order of seconds. They decay away in minutes. Those radionuclides with half-lives on the order of minutes decay away in hours.

Some with half-lives of years are persistent.

One could plot several different decaying exponentials individually and as a group -

exp(-t), exp(-0.1t), exp(-0.01t) and exp(-0.001t)

One may need to weight them differently (e.g., 1, 0.1, 0.01, 0.001) to see the effect, and plot them on linear and log scales.

The activity of a radionuclide is given by λN_o exp(-λt), and N_o, the initial amount corresponding to some reference time, is dependent on the fission yield. When a reactor is operating at constant power many fission products reach an equilibrium concentration because the loss rate (decay + transmutation) balances the production rate.

At shutdown, some isotopes actually increase in concentration, e.g., Xe-135, because it is a decay product (from I-135), but it is no longer transmuted since the neutron flux drops dramatically. Similar behavior occurs when there is a power reduction, but it's not so dramatic, since the neutron flux doesn't drop off so much.

 

[Freddy_uk]

In that case, try this -
http://energyfromthorium.com/2006/07/14/new-visualization-tool-for-decay-chains/
and launch the java app.

The radionuclides on the bottom of the band, near they grey dots, and half-lives on the order of seconds. They decay away in minutes. Those radionuclides with half-lives on the order of minutes decay away in hours.

Some with half-lives of years are persistent.

One could plot several different decaying exponentials individually and as a group -

exp(-t), exp(-0.1t), exp(-0.01t) and exp(-0.001t)

The activity of a radionuclide is given by λN_o exp(-λt), and N_o, the initial amount corresponding to some reference time, is dependent on the fission yield. When a reactor is operating at constant power many fission products reach an equilibrium concentration because the loss rate (decay + transmutation) balances the production rate.

At shutdown, some isotopes actually increase in concentration, e.g., Xe-135, because it is a decay product (from I-135), but it is no longer transmuted since the neutron flux drops dramatically. Similar behavior occurs when there is a power reduction, but it's not so dramatic, since the neutron flux doesn't drop off so much.

Thanks for your help.

I forgot about the increase in Xe, which i believe has to decay away sufficiently before a shutdown reactor can restart (if an automatic shutdown has occurred).
Obviously the reason for the shutdown must also be investigated, and determine if all systems respond correctly post trip.

 

[QuantumPion]

In that case, try this -
http://energyfromthorium.com/2006/07/14/new-visualization-tool-for-decay-chains/
and launch the java app.

The radionuclides on the bottom of the band, near they grey dots, and half-lives on the order of seconds. They decay away in minutes. Those radionuclides with half-lives on the order of minutes decay away in hours.

Some with half-lives of years are persistent.

One could plot several different decaying exponentials individually and as a group -

exp(-t), exp(-0.1t), exp(-0.01t) and exp(-0.001t)

One may need to weight them differently (e.g., 1, 0.1, 0.01, 0.001) to see the effect, and plot them on linear and log scales.

The activity of a radionuclide is given by λN_o exp(-λt), and N_o, the initial amount corresponding to some reference time, is dependent on the fission yield. When a reactor is operating at constant power many fission products reach an equilibrium concentration because the loss rate (decay + transmutation) balances the production rate.

At shutdown, some isotopes actually increase in concentration, e.g., Xe-135, because it is a decay product (from I-135), but it is no longer transmuted since the neutron flux drops dramatically. Similar behavior occurs when there is a power reduction, but it's not so dramatic, since the neutron flux doesn't drop off so much.

While your link is really cool, it does not include the isotope responsible for the largest portion of decay heat immediately after shutdown, which is neptunium-239.

 

[QuantumPion]

Thanks for your help.

I forgot about the increase in Xe, which i believe has to decay away sufficiently before a shutdown reactor can restart (if an automatic shutdown has occurred).
Obviously the reason for the shutdown must also be investigated, and determine if all systems respond correctly post trip.

Reactors can restart with xenon just fine unless they are at the very end of their cycle and have no excess reactivity remaining.

 

[Freddy_uk]

Reactors can restart with xenon just fine unless they are at the very end of their cycle and have no excess reactivity remaining.

Ok I've got the wrong idea possibly. Although when this subject was discussed once it was regarding early commissioning of the reactor were it was only partly fuelled. So what your saying makes perfect sense now.

 

[Astronuc]

Ok I've got the wrong idea possibly. Although when this subject was discussed once it was regarding early commissioning of the reactor were it was only partly fuelled. So what your saying makes perfect sense now.

Power reactors have a lot of excess reactivity at beginning of cycle. Only toward the end of cycle - last couple of weeks or so (when for BWRs, it's All Rod Out (ARO) or for PWRs, the soluble boron goes to a few or tens of ppm) does it become impossible for a Xe override. One would have to more or less shutdown or go to HZP and allow the Xe to decay.

 

[Freddy_uk]

Power reactors have a lot of excess reactivity at beginning of cycle. Only toward the end of cycle - last couple of weeks or so (when for BWRs, it's All Rod Out (ARO) or for PWRs, the soluble boron goes to a few or tens of ppm) does it become impossible for a Xe override. One would have to more or less shutdown or go to HZP and allow the Xe to decay.

Even when only 50% of the core is fuelled up? As when we 1st ran the plant up (80's) only 50% or less i think of the core was occupied with fuel, the remaining channels were dummy blocks of graphite. During this time the reactor would only operate for a week or 2 I am told, and each weekend they would refuel some more channels and start back up.

I wasn't even in kindergarden then, and the reactor type is and advanced gas (CO₂) cooled reactor . I will ask someone in our nuclear safety group or physics department when i am in work tomorrow.

 

[Astronuc]

Even when only 50% of the core is fuelled up? As when we 1st ran the plant up (80's) only 50% or less i think of the core was occupied with fuel, the remaining channels were dummy blocks of graphite. During this time the reactor would only operate for a week or 2 I am told, and each weekend they would refuel some more channels and start back up.

I wasn't even in kindergarden then, and the reactor type is and advanced gas (CO₂) cooled reactor . I will ask someone in our nuclear safety group or physics department when i am in work tomorrow.

Most of us on this forum are familiar with LWRs. AGRs are a slightly different beast.

If the core is 50%, it would not have much in the way of excess reactivity, especially if only capable of operating two weeks. Does one know if they used enrichments > 5%.

LWRs would not operate with half core loaded. It would not be worthwhile to irradiate a half core of dummy assemblies.

I will have to poke some folks familiar with AGR operation.

 

[Freddy_uk]

Most of us on this forum are familiar with LWRs. AGRs are a slightly different beast.

If the core is 50%, it would not have much in the way of excess reactivity, especially if only capable of operating two weeks. Does one know is they used enrichments > 5%.

LWRs would not operate with half core loaded. It would not be worthwhile to irradiate a half core of dummy assemblies.

I will have to poke some folks familiar with AGR operation.

We operate at around 3.5% now, but it wasn't as high back then. I didn't get chance to ask any questions today as we were busy interlock testing. I appreciate most members are unfamiliar with AGR's, all the new reactors planned in the UK are going to be PWR's from what i can tell.

 

[mheslep]

While your link is really cool, it does not include the isotope responsible for the largest portion of decay heat immediately after shutdown, which is neptunium-239.

Because that isotope is not significantly produced, as that particular simulation assumes a Thorium - U233 fuel cycle and very little transuranics, http://energyfromthorium.com/2006/07/14/new-visualization-tool-for-decay-chains/" :

One of the things to notice from this simulation is how that after about 300 years, most of the chains have decayed to stability.

Take a look here to get UOX activity and decay heat, which, as you say, is clearly dominated by neptunium-239 at the time of shutdown.
http://www.energyfromthorium.com/javaws/SpentFuelExplorer.jnlp

 

[mheslep]

I am looking for some data that identifies the most significant source of decay heat for the first few days from a reactor trip. Something similar for 1month after or more would be useful.

Thanks

Dave

Try this sim, will give you exactly what you want
http://www.energyfromthorium.com/javaws/SpentFuelExplorer.jnlp
Note: doesn't use only traditional U Ox fuel, though that is the default. Select 'Decay Heat' in the tabs at the bottom right.

 

[Freddy_uk]

Try this sim, will give you exactly what you want
http://www.energyfromthorium.com/javaws/SpentFuelExplorer.jnlp
Note: doesn't use only traditional U Ox fuel, though that is the default. Select 'Decay Heat' in the tabs at the bottom right.

I used this pie chart along with the original applet as a screenshot in a short presentation for my thesis which was a couple of weeks ago now.

Thanks

 

[NUCENG]

Start with these and hopefully others can contribute. I'll continue looking.

Validation of ORIGEN-S Decay Heat Predictions for LOCA Analysis
http://www.ornl.gov/sci/scale/pubs/C183.pdf

http://www.ornl.gov/sci/scale/spentfuel.htm
particularly - http://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6972/cr6972.pdf

http://www.studsvikscandpower.com/nuclear-reactor-analysis-software/snf/publications
http://www.studsvikscandpower.com/nuclear-reactor-analysis-software/snf


Unfortunately, most tabulated calculations are for months or years.

Do not neglect latent heat in the fuel, cladding, vessel and internals.

 

[NUCENG]

Start with these and hopefully others can contribute. I'll continue looking.

Validation of ORIGEN-S Decay Heat Predictions for LOCA Analysis
http://www.ornl.gov/sci/scale/pubs/C183.pdf

http://www.ornl.gov/sci/scale/spentfuel.htm
particularly - http://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6972/cr6972.pdf

http://www.studsvikscandpower.com/nuclear-reactor-analysis-software/snf/publications
http://www.studsvikscandpower.com/nuclear-reactor-analysis-software/snf


Unfortunately, most tabulated calculations are for months or years.

Do not neglect latent heat in the fuel, cladding, vessel and internals.