Dear Jaakko,
Excuse me, two questions regarding LAMBDA in the delayed neutron parameters part of the output (SERPENT 2.1.24):
1) Is my understanding correct that LAMBDA=Lambda_eff, which is the prompt neutron reproduction time, and It is equal to l_eff (the effective prompt neutron lifetime)/keff (the effective multiplication factor)?
2) Is LAMBDA value in the SERPENT output in seconds?
Thank you very much in advance!
With best regards,
Sasha.
LAMBDA in the Delayed Neutron Parameters Output

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Re: LAMBDA in the Delayed Neutron Parameters Output
Hello Sasha,
It is my understanding that LAMBDA is the delayed neutron decay constant (units of 1/s), where the total delayed neutron decay constant is the first term and the six groups are the following terms. This corresponds directly with BETA_EFF.
The neutron lifetimes you are looking for will be:
*_LIFETIME for the prompt neutron lifetime
*_GEN_TIME for the prompt neutron generation time, which is the "l_eff (the effective prompt neutron lifetime)/keff (the effective multiplication factor)?" you are asking about.
The units for these are in seconds.
Which method you elect to use depends on your modeled system.
I hope this helps.
Best,
Jesse
It is my understanding that LAMBDA is the delayed neutron decay constant (units of 1/s), where the total delayed neutron decay constant is the first term and the six groups are the following terms. This corresponds directly with BETA_EFF.
The neutron lifetimes you are looking for will be:
*_LIFETIME for the prompt neutron lifetime
*_GEN_TIME for the prompt neutron generation time, which is the "l_eff (the effective prompt neutron lifetime)/keff (the effective multiplication factor)?" you are asking about.
The units for these are in seconds.
Which method you elect to use depends on your modeled system.
I hope this helps.
Best,
Jesse

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Re: LAMBDA in the Delayed Neutron Parameters Output
Hello Jesse,
Looking at the order of magnitudes of LAMBDA, *_LIFETIME, *_GEN_TIME, I think that you're right.
Thank you very much for the clarification!
With best regards,
Sasha.
Looking at the order of magnitudes of LAMBDA, *_LIFETIME, *_GEN_TIME, I think that you're right.
Thank you very much for the clarification!
With best regards,
Sasha.
Re: LAMBDA in the Delayed Neutron Parameters Output
Hi,
I am experiencing a problem when trying to understand the contents for ..._LAMBDA array. Basically I would expect that the 1 group constant is the result of > lambda = sum (lambda_i/Beta_i) * Beta , but when I perform such calculation, the results differ.
For example, for a given case run in jeff 3.2 using S2.1.24 I get:
ADJ_NAUCHI_BETA_EFF (idx, [1: 18]) = [ 7.58068E03 0.00232 2.49465E04 0.01285 1.14606E03 0.00603 7.21075E04 0.00757 1.49329E03 0.00519 2.46769E03 0.00404 7.01660E04 0.00752 6.20301E04 0.00815 1.81142E04 0.01519 ];
ADJ_NAUCHI_LAMBDA (idx, [1: 18]) = [ 4.10452E01 0.00376 1.24667E02 6.9E09 2.82917E02 0.0E+00 4.25244E02 7.3E09 1.33042E01 0.0E+00 2.92467E01 6.8E09 6.66488E01 4.1E09 1.63478E+00 0.0E+00 3.55460E+00 5.1E09 ];
Then I can calculate > sum (lambda_i/Beta_i) * Beta = 0.076866968 [1/s] but the first value in ADJ_NAUCHI_LAMBDA is 4.10452E01
Is this 1 group constant divided by another parameter in ADJ_NAUCHI_LAMBDA?
Thanks,
Diego
I am experiencing a problem when trying to understand the contents for ..._LAMBDA array. Basically I would expect that the 1 group constant is the result of > lambda = sum (lambda_i/Beta_i) * Beta , but when I perform such calculation, the results differ.
For example, for a given case run in jeff 3.2 using S2.1.24 I get:
ADJ_NAUCHI_BETA_EFF (idx, [1: 18]) = [ 7.58068E03 0.00232 2.49465E04 0.01285 1.14606E03 0.00603 7.21075E04 0.00757 1.49329E03 0.00519 2.46769E03 0.00404 7.01660E04 0.00752 6.20301E04 0.00815 1.81142E04 0.01519 ];
ADJ_NAUCHI_LAMBDA (idx, [1: 18]) = [ 4.10452E01 0.00376 1.24667E02 6.9E09 2.82917E02 0.0E+00 4.25244E02 7.3E09 1.33042E01 0.0E+00 2.92467E01 6.8E09 6.66488E01 4.1E09 1.63478E+00 0.0E+00 3.55460E+00 5.1E09 ];
Then I can calculate > sum (lambda_i/Beta_i) * Beta = 0.076866968 [1/s] but the first value in ADJ_NAUCHI_LAMBDA is 4.10452E01
Is this 1 group constant divided by another parameter in ADJ_NAUCHI_LAMBDA?
Thanks,
Diego

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Re: LAMBDA in the Delayed Neutron Parameters Output
Hi Diego,
shouldn't the one group decay constant just be a weighted average of the individual decay constants, where the weight of group i is Beta_i?
So lambda = sum (lambda_i*Beta_i) / Beta, which gives lambda = 0.41054 in your case. Reasonably close to the tallied one group lambda.
Ville
shouldn't the one group decay constant just be a weighted average of the individual decay constants, where the weight of group i is Beta_i?
So lambda = sum (lambda_i*Beta_i) / Beta, which gives lambda = 0.41054 in your case. Reasonably close to the tallied one group lambda.
Ville
Re: LAMBDA in the Delayed Neutron Parameters Output
Hi Ville,
Ussually we use the 1 gruop constant weighted by 1/Beta_i , but I suppose that both could be correct.
Thanks for the clarification,
Diego
Ussually we use the 1 gruop constant weighted by 1/Beta_i , but I suppose that both could be correct.
Thanks for the clarification,
Diego