The Effect of Birthrate Granularity on the Release- to- Birth Ratio for the AGR-1 In-core Experiment Page: 4 of 10
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Proceedings of the HTR 2012
Tokyo, Japan, October 28 - November 1, 2012
Paper HTR2012-3-022IIB. Release Activity Computation
The performance of a nuclear fuel test is
typically evaluated using R/Bs the ratio of the
released activity (R) of an isotope from the fuel to
the predicted creation rate of the isotope because of
irradiation conditions (birth activity (B)). The
gamma-ray spectrum measurements from the HPGe
detectors in each FPMS were used to find the release
activities of several different isotopes of krypton and
xenon shown in Table 2. The acquired spectra were
automatically analyzed using the INL-developed
PCGAP gamma-ray spectral analysis code [5,6] and
were stored electronically. At the end of each
irradiation cycle the FPMS measured activities were
corrected to account for decay that occurred during
transport from the capsules to the detectors.
Transport times were calculated from outlet gas flow
rates recorded by the automated experiment data
control system of the ATR and the capsule-specific
volumes through which samples flow to reach the
respective monitoring stations [7].
Isotope
Kr-85m Xe-131m Xe-135m
Kr-87 Xe-133 Xe-137
Kr-88 Xe-135 Xe-138
Kr-89 Xe-139
Kr-90
Table 2: The table above contains the isotopes of
interest for release to birth calculations. Release
activities were measured with the FPMS, and fission
product birth rates were estimated using MCWO.
The activities measured from the spectra
collected by the FPMS, corrected for decay during
transport, were converted to released atoms per
second at the capsule. The proper correction for the
measured activity is calculated for equilibrium
conditions for the different components illustrated in
the simplified flow system in Fig. 3.
Transport volume (Vt)
c b
Sample volume (VS) d
Capsule Detector
Fig. 3: A simplified single capsule flow graphic to
aid in flow correction calculations.At equilibrium, when the rate of change of the
number of atoms of an isotope of interest in the
sample volume, 'a,' is zero, one can deriveSVf
A . f
R = "a e;-
-1where:
Rc = Release rate (atom/sec) of isotope at the
capsule exit (c)
Aa =Activity (Bq) of isotope in sample volume a
A =Decay constant of isotope (see-)
VT = Transport volume (mL) between (c) and (b)
V =Sample volume (mL) (a)
f =Capsule specific flow (mLlsec).
The flow rate is taken as the average of all values
with times during the spectrum acquisition. The
activities (A) provided by the INL-developed
PCGAP analysis are corrected for random summing
and detector efficiency. The first exponential
involving the transport volume (V) accounts for the
probability of decay before reaching the sample
volume, while the remaining factor (V) accounts for
the probability of decay while passing through the
sample volume. This equation is valid so long as the
specie involved remains entrained in the effluent gas
and travels through the gas lines and sample volume
at the flow rate, and the flow rate is fairly constant.
Any specie trapping prior to exiting the sample
volume or large variations in the flow rate during
acquisition would compromise the calculation [8].
The estimated uncertainty in R, can thus be
determined from standard error propagation
techniques to be(Eq. 2)
ak[j6 2+~ Rc(u
or mn terms of relative errors:
2
2 .1. 2 - 2
f.-e fs
Rc A 2s Y
f - f(Eq. 3)
(Eq. 1)
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Scates, Dawn & Walter, John. The Effect of Birthrate Granularity on the Release- to- Birth Ratio for the AGR-1 In-core Experiment, article, October 1, 2012; Idaho Falls, Idaho. (https://digital.library.unt.edu/ark:/67531/metadc841076/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.