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NEACRP-A-1080 Session B 3.6
International Comparison on Measuring Techniques of Tritium
Production Rate for Fusion Neutronics Experiments
--- Summary of Additional Questionnaire and Result for ANL Samples ---
Summarized by
Hiroshi MAEKAWA
Department of Reactor Engineering
Japan Atomic Energy Research Institute
Contributors :
ANL/U.S.A.
AECL-CRNL/Canada
IGA-EPFL/Switzerland
ENEA/Italy
CEN Cadrache/France
Univ. Tokyo/Japan
Osaka Univ./Japan
JAERI/Japan
K. G. Porges W. Workman, J. M. Miller, I. J. Hastings
S. Azam, M. Schaer
A. Moauro, P. L. Carconi
P. Michailli
T. Iguchi, M. Nakazawa
S.,Yoshida, A. Takahashi
H. Maekawa, F. Maekawa, T. Nakamura
The 33rd NEACRP Meeting
Oct. 15 - 19, 1990 Paris, France '
1. Introduction
The idea of the program, "International Comparison on Measuring
Techniques of Tritium Production Rate for Fusion Neutronics Experiments"
by using the 14 MeV neutron source, FNS, was first proposed from the
JAERI representative at the 30th NEACRP meeting. The representative of
Switzerland offered to use in addition the LOTUS facility to strengthen
the program. It was advised at the meeting that a work plan would be
prepared by a cooperation of the experimental groups at JAERI and
IGA/EPFL. The plan thus prepared through the exchange of opinions between
FNS and LOTUS staffs was endorsed at the 31st NEACRP meeting, and
participation in the program was solicited via the representatives of the
committee for research institutes in the member countries. Eight
institutes and Universities from six countries applied to this comparison
program. They are shown in Table 1.
Each participating group prepared Li-containing samples and sent to
the neutron source facilities. The irradiation experiments were performed
on April 27 and May 18, 1989 at FNS and LOTUS, respectively. The
irradiated samples were sent back to the participants to be measured the
tritium production rate. For the normalization of tritium counting system
used by each participating group, JAERI provided a blind sample and
distributed to all participants. Six out of eight groups submitted the
full set of results to JAERI by the middle of September, 1989. JAERI
examined and summarized the results with the assistance of LOTUS group.
At the 32nd NEACRP meeting, the summarized result was presented as an
interim report (NEACRP-A-1021).
From the inter-comparison described in the report, the followings
facts can be summarized:
(1) For the irradiation level of LOTUS, typically several tens Bq of
tritium per samples, agreement of tritium production rates from
different methods turned out to be around 10 % for one standard
deviation without any adjustment. The agreement for several Bq of
tritium production in FNS irradiation went worse to several tens %.
This shows that the degree of agreement depends on the tritium
amounts. The error assigned by the participants are not consistent
with the observation.
( 2 ) The interim result is against the requirement and expectation for a
benchmark experiment, i.e., the measured data are deviated among
the participants over the target accuracy of 5 %. The observation
suggests that there exist unidentified and organization-dependent
systematic errors not directly related to counting statistics nor
difference in tritium standards.
(3) It is most important to identify the causes that bring forth the
discrepancy by comparing and examining the whole procedures of the
participants before mentioning on the true accuracy of the current
measuring techniques. The examination includes the selection of Li-
containing probe, physical and chemical processing of irradiated
samples, preparation of liquid scintillation samples, counting of
foreground and background, efficiency determination and calibration,
tritium standard used, and error assignments on each factor.
According to the "Next Step" proposed to the 32nd NEACRP meeting,
the following two "Actions" have been done.
Action 1
JAERI asks the items relevant to tritium counting techniques to each
participant by a questionnaire, and examines and summarizes them.
Action 2
(1) Three types of diluted tritium water samples, i.e., around 10,000
Bq/g, several 10 Bq/g and several Bq/g, are made from the certified
HTO standard with high accuracy, and are distributed to each
participant.
(2) The participants measure the tritium concentration of the three
samples and report it to JAERI. JAERI examines and summarizes the
results reported.
Section 2 describes the results of questionnaire mentioned above as
Action 1. Following Sections describe the results of Action 2, i.e., the
preparation and measured results of diluted tritium water samples. A
recommendation to "Next Step" is shown in Section 6. Additional results
reported after the 32nd NEACRP meeting are described in Appendix.
2. . Summary of Additional Questionnaire
Additional information based on the questionnaire are summarized in
a Tables 1 and 2. Three groups employed the Dierckx method to obtain a
liquid scintillation sample. The rest five groups adopted quite different
methods. In the case of Dierckx method, almost all tritium produced were transferred to the liquid scintillation sample except the tritium remained
in gas-phase. In the cases of ANL and JAERI, most part of tritium
produced was collected to make the liquid scintillation sample. While AECL
sampled only about one percent of tritium produced.
As a dry method was adopted at ANL, it was not necessary to consider
the tritium in gas-phase. CEN/Cadrache and JAERI considered it but the
other five groups ignored. In the case of JAERI, the quantity of tritium
in gas-phase was estimated separately using samples irradiated near the
target. Because the quantity of tritium in gas-phase for a Li20 pellet
irradiated in the simulated blanket assembly was too small to measure.
a The minimum of signal to background ratio was 1.6 shown in Table 2.
Though this value is not so high, we can still measure the tritium concentration with adequate error under a long measuring time.
From the additional questionnaire, we could not deduce any concrete reason why the tritium production-rate reported was deviated so large.
Table 2 Average counting rates of raw data during tritium counting for the samples irradiated by FNS and LOTUS.
[ Unit : cps / liquid scintillation sample I
ANL AECL/CRNL IGA/EPFL ENEA CEN/Cadr . U. Tokyo Osaka U. JAERI U.S.A. Canada Switzerland Italy France Japan Japan Japan
I Background I 0.08 1.8 0.896 0.15s0.41 0.190 0.485 0.254
FNS outer inner
LOTUS outer inner
*1 Data for liquid scintillation sample for the distillated part (about 80 % of total). *2 counts per min. / decay per min. *3 counts per min. / decay per sec. *4 Average signal to background ratio for the raw data of FNS experiment.
17 1.35 17 1.467 20 7.4 16 8.24
3. Preparation of Diluted Tritium Water Sample
The Analytical Chemistry Laboratory of Argonne National Laboratory
(ANL) prepared a set of three tritium solutions for this NEACRP
International Tritium Comparison, which were distributed on or about
March 5, 1990 from ANL. Each set was prepared by diluting NIS SRM 4926-D
tritium standard with deionized water. The data of tritium standard is
shown in Attachment. All dilutions were done by weight using an
analytical balance with a 1000 g ( 2 0.1 mg) capacity. All weighings were
performed in triplicate and the average used for the final value. The
solutions were prepared in Teflon weighing bottles and were mixed for
over 45 minutes prior to aliquoting. Ten ml aliquots were heat sealed a into engraved glass ampoules and distributed. Twenty ml aliquots of the
deionized water used in the preparation were also sent to the
participants. Aliquots of each prepared tritium solution were asseyed by
liquid scintillation counting to assure the quality of the solutions.
The specific activities (Bq/g) as of 1200 EST, July 25, 1989, are as
follows:
The uncertainties involved with the preparation of the standards
(weighings) were negligible in comparison to the uncertainty assigned to 0
the NIS standard, namely 0.86 percent.
The activity levels of Type "B" and "C" are corresponding to the
expected tritium concentration in the samples irradiated by FNS and LOTUS
at the 1989 experiment of this project, respectively. While the level of
Type "A" was selected to be high enough comparing any error sources.
4. Results for ANL Samples and Discussions
In the beginning of April 1990, JAERI sent a set of return form for
the report of measured tritium concentration in the diluted ANL samples
to the participants. The reports were sent back to JAERI from the
participants except the University of Tokyo by the end of July. Some of
ampoules were broken when they arrived at the University of Tokyo. JAERI
will receive the data soon after the new samples arrive at the University
of Tokyo. The results reported are summarized in Tables 3 and 4. The data
in the first column of Table 3 are the tritium concentrations on April 1,
1990 for three type samples and are corrected for. the decay from the date
shown in Section 3. Because the results reported by all participants are
the tritium concentrations of samples on the same date, i. e., April 1,
1990. The value in parentheses is the ratio of concentration measured to
that assigned by Dr. R. R. Heinrich (the value in the first column).
Though they used quite different tritium standard for calibration,
very good agreement is observed for three types of samples within 1 * 2 %
except some participants. The data of Osaka University deviate systemati-
cally by about 6 %. Their errors given in the Table 3 seem not to include
the error of tritiated water standard which is 4.7 %. The data of
background sample used at ENEA is very low comparing with that of ANL
Blank sample. This fact suggests that the correction for the contribution
of tritium (?) in the dilution water (Blank) used at ANL is necessary for
the data reduction. In the case of IGA/EPFL, it is difficult to
understand why the data of "B" and "C" are 6 % higher than the assigned
values.
From Table 4, the signal to background ratio for the sample "C"
distributes from 6.9 to 55.8 among the participants. This means that the
tritium concentration of a few Bq/g can be measured with high accuracy
even by the liquid scintillation counting system of the lowest signal to
background ratio.
Table 5 summarizes the conditions of measurements for each partici-
pant. The volume of ANL tritium water used and the volume percentage of
cocktail are distributed from 1 ml to 5 in1 and from 50 % to 95 %,
respectively for a liquid scintillation sample. Two groups used the
internal standard method for the calibration and three groups used the
most popular method, i. e., external standard method with a fitting
curve. The total measuring time for a sample was 1 to 9 hours.
Table 3 Measured tritium concentration on April 1, 1990 for ANL samples
[ Unit : Bq/g ]
Sample ID
Background Same 0.132'0.002 Same 0.110~0.007 Same - - - - - - - 0.459+0.030 0.049+0.009 as above as above as above
ANL AECL/CRNL IGA/EPFL ENEA CEN/Cadr . U. Tokyo Osaka U. JAERI U.S.A. Canada Switzerland Italy France Japan Japan Japan
I m I
* Data are assigned by Dr. R. R. Heinrich (ANL) and corrected for decay. ** Ratio to the assigned value.
C 3.81 t 0 . 0 3
Blank
3.893'0.021 3.88 '0.09 4 . 1 '0.13 4.69 20.38 3.198t0.023 ------- 4.172+0.090 3.898t0.057 (1.006) (1.003) (1.059) (1.212) (0.981) (1.078) (1.007)
0.134+0.003 0.142+0.006 ( 0 . 2 3 3 ~ ~ ~ ) 0.505+0.076 0.292t0.009 ------- 0.508+0.033 0.052t0.012
Table 4 Raw data of tritium concentration measurement for ANL samples
[ Unit : cps / vial 1
I Sample ID I ANL AECL/CRNL IGA/EPFL ENEA CEN/Cadr . U. Tokyo Osaka U. JAERI U.S.A. Canada Switzerland Italy France Japan Japan Japan I
I
+ Average ratio of the raw data "C" to background.
Blank
Background
0.075 0.130+0. 009 0.3 0.77350.1 0.327+0.010 ------- 0.195'0.013 0.096'0.007 * 0.085 0.200t0.013 0.099'0.003
Same 0.122t0.003 Same 0.119t0.006 Same - - - - - - - 0.197'0.013 0.090i0.007 as above as above as above 0.194'0.013 0.090i0.011
0.092i0.016
5. Conclusion of Present Comparison for ANL Sample
We can summarize the following conclusion from the international
comparison of tritium counting for the ANL diluted tritium water
samples. :
(1) Using an appropriate tritium water standard with high accuracy
for the calibration of liquid scintillation counting system, we can
expect a good agreement for a blind sample among the participants.
This is also supported by the result of JAERI's blind sample
described in Appendix.
( 2 ) All participants have the ability of measurement for the tritium
concentration level of several Bq/g. Namely, we can measure the
tritium production rate in a simulated fusion blanket under the
irradiation level of 7 x 1015. This total neutron yield can be
obtained by the D-T neutron yield rate of 2 x 1011 n/s and 10 hours
irradiation. This irradiation level is corresponding to the last experiment at FNS.
(3) It is important to obtain a liquid scintillation sample keeping the loss of tritium produced as low as possible without any contamina- tion. Namely, the method and technique are essential for the
chemical treatment of irradiated sample with lithium. If all
participants adopt an appropriate method to extract the tritium
produced from the irradiated sample and a good liquid scintillation
sample, a good agreement is expected among the results of tritium
production rate measured by the participants.
6. Recommendation to Next Step
From the results of present international comparison for the ANL
diluted tritium water samples, JAERI recommends the same type experiments
as previous irradiations. JAERI will continue the organization of this
project. JAERI and IGA-EPFL will provide the same types of neutron fields
as previous ones by FNS and LOTUS facilities, respectively. The recom-
mended procedure and schedule for the next step are as follows:
1990 Nov. The member of NEACRP meeting will confirm the attendant of this
project to the participant(s) of their countries again and
inform the results to the host organization, JAERI by the end 0
of NOV. 1990.
1990 Dec. JAERI will ask and confirm the material and size of sample to
be used by each participant.
1991 Feb. All participants will send their Li-contained samples to JAERI
by the middle of March, 1991.
1991 Apr. Irradiation at FNS/JAERI.
1991 May Irradiation at LOTUS/IGA-EPFL.
a It should be a necessary condition that all participants will use a
suitable method to extract the tritium from an irradiated sample when we
proceed to the next step.
Acknowledgement
Author would like to thank Dr. Y. Kaneko of JAERI for his promotion
of this project. He is also grateful to Drs. R. R. Heinrich and K. G.
Porges of ANL for their preparation and distribution of the diluted
tritium water samples.
Appendix Additional Results Reported After the 32nd NEACRP Meeting
A participant has revised the data of blind sample supplied by
JAERI after the 32nd NEACRP meeting. Table A.l shows results of measured
tritium concentration in the blind sample. The reported data distribute
from 65.63 to 71.0 with average of 67.39 Bq/g, the standard deviation
being 2.8 %. Most of them agree each other within the experimental
errors.
One participant has reported their additional results after the
32nd NEACRP Meeting. The revised tables of measured tritium production
rates are shown in Tables A.2 and A.3 in the samples irradiated at
FNS/JAERI and LOTUS/IGA-EPFL, respectively. The C/E values (ratio of
calculated to experimental values) are presented in Table A.4.
Table A.l Measured tritium concentration in the blind sample
distributed by JAERI (Revised).
Organization Tritium concentration [Bq/g] (error)
Average*3 67.39 i 1.88 (2.8 %)
* Errors are assigned by each participant.
*1 Statistical error only (30). *2 Statistical error only (lo).
*3 Equal weight average.
Table A.2a Measured tritium production rate for outer samples
irradiated at FNS/JAERI (Updated).
Tritium production rate [T-atoms/Li-atom/source]
Organization
# 1 # 2 # 3
A 4.394 * E-29 lost in processing 4.432 * E-29
B not available 1.570'0.090 E-26 3.730t0.153 E-26
(5.7 %) (4.1 %)
C 1.612' ** E-29 1.804' ** E-29 1.808' ** E-29
D not available
F missing of sample 4.00 t0.13 E-29 3.94 t0.13 E-29
(3.3 %) (3.3 %) 0
* Experimental error is not assigned by participant. ** Statistical errors are bigger than 15 %.
Table A.2b Measured tritium production rate for inner samples
irradiated at FNS/JAERI (Updated).
Tritium production rate [T-atoms/Li-atom/source]
Organization
# 4 # 5
D not available
* Experimental error is not assigned by participant. ** Statistical errors are bigger than 15 %.
Table A.3a Measured t r i t i u m product ion r a t e f o r o u t e r samples
i r r a d i a t e d at L(YTUS/IGA-EPFL (Updated).
Tr i t ium product ion r a t e [T-atoms/Li-atorn/source]
Organiza t ion
# 1 # 2 # 3
A 2.378 E-29 2.415 E-29 2.420 E-29
D no t a v a i l a b l e
*Neutron y i e l d of 7.56 x 1016 i s used.
The e r r o r of neutron y i e l d i s not included i n above e r r o r .
Table A.3b Measured tritium production rate for inner samples
irradiated at LOTUS/IGA-EPFL (Updated).
Tritium production rate [T-atoms/Li-atom/source]
Organization
# 4 # 5
A 2.651 E-29 2.608 E-29
D not available
*Neutron yield of 7.56 x 1016 is used.
The error of neutron yield is not included in above error.
Table A.4 Ratio of calculated to experimental values
for the PNS experiment (Updated).
Sample number
Organization
# 1 # 2 # 3 # 4 # 5
SUPPLEMENT TO THE NEACRP REPORT
The International Comparison on Measuring Techniques of
Tritium Production Rate for Fusion Neutronics Experiments
- Summary of Additional Questionnaire and Result for ANL HTO Samples -
JAERI Nakamura, Tomoo
The content of this supplement should have been integrated in the
main paper. However, lack of time in adjustment the styles and some
what different approaches has resulted in a separate treatment.
I) Introduction
As explained in the main text, the international comparison
program was undertaken on the tritium production rate measurement
techniques for fusion blanket neutronics, as one of the benchmark
problems of the NEACRP activity.
The interim results summarized from the data reported
from the participating organization has shown large deviation each
other as shown in the Table 6.6 of NEACRP-1021. This is rather
astonishing because the accuracy in determining the tritium production
rates had been reported to be within lo%, at most 20%, in the papers
of individual experiments so far reported. And it has been generally
accepted that the irradiated Li-containing sample and liquid
scintillation counting method is well-matured technique in the fusion
neutronics experiments.
Whole procedure is divided roughly into three stages: Irradiation of
Li-containing sample pellets, chemical/physical processing of the
sample pellets into the HTO-containing samples and counting of the
samples combined with the calibration by tritium standard. The first
stage has been conducted in a way to assure an irradiation under
identical neutron spectrum and fluence, and there is little reason to
cause such a large difference. The second and third steps must
responsible for the cause(s) of the difference, since they were
conducted separately at individual organizations by different manners
of each own. The second stage has little common factors each other,
and most probable for the cause of the discrepancy. But before seeking
the cause of the difference in it, it is needed to confirm the
accuracy by a use of common standard, in the third stage which is
different each other yet follows the similar principle or procedure.
This is the motivation for the intercomparison by HTO samples provided
by ANL. Samples of three different concentrations were prepared to
examine the dependence on the tritium amount, because the results of
the last experiment had shown such dependence.
It is generally supposed or accepted that the technique to
measure the tritium production rate by the neutron irradiation of
Li-containing samples and liquid scintillation counting
11) Comparison of HTO samples provided by ANL, COM-ANL
The reported results from the participants are tabulated in Table
3 of the main text summarized by Maekawa. In the table it seems that
the error assignments have not been conducted on a same basis, because
the inclusion of error due to tritium standard is not clear in some
cases. In fact the errors from some organizations are apparently
smaller than the error component from tritium standard.
i) Simple Comparison
In the first place, a simple comparison was made on the reported
tritium concentrations for ANL HTO samples. An arithmetic mean and
deviation were calculated assuming an equal weight among the organiza-
tions rather than weighted mean taking error amplitude into considera-
tion.
Table S-1
Min. Max. Average D (in Bdg)
A: 253.6 - 270.9 261.8 t 6.5 (2.5%) 6.6%
B: 48.10 - 52.02 49.8 A 1.5 (3.1%) 7.9%
C: 3.80 - 4.69 4.06 t 0.31 (7.6%) 21.9%
D is the range of the deviation relative to the average defined by
Max. - Min. D =
Average
For the high tritium concentration samples of which errors due to
counting statistics are negligible, the 2.5% uncertainty as a whole is
by no means a good value. The deviation between the largest to the
smallest amounts to near 7%. For low concentration samples the
corresponding values rise to 7.6% and 21. 9%.
This indicates that a more close examination and discussion is
necessary on the the reported values.
ii) Absolute Value Comparison
Each experimenter assigned absolute values using the tritium
standard owned by his organization. Originally the problem of absolute
values rigorously is not an easy matter. I could be admitted, however,
that the tritium concentrations and errors assigned by Dr. Heinrich in
the Table 3 is a highly reliable measure of the absolute values of the
HTO samples distributed. They are based on the well certified value of
NIST standard and on a careful treatment in the dilution.
Of course this does not necessarily mean the COM-ANL values is
the most probable ones. When the reported values are close enough to
this value yet different it is hard to say which is closer to the true
value, since the other standards from different origins should be
treated likewise reliable within the assigned accuracy. The accuracies
of the tritium standards are given below. Abbriviations are used to
0 denote the organizations
Table S-2
COM-ANL ANL AECL IGA/EPFL ENEA CENCAD UOT OU JAERI
In that meaning, the ratios relative to the Heinrich's values in
Table 3 do not necessarily mean the degree of correctness. In fact,
ANL and JAERI use the tritium from the same supplier, NIST, so that it
is natural, that their results are close to unity, if the counting has
been performed correctly.
However, the ratios help relative comparison within the uncer-
tainties in the standards. In other words, an appreciable deviation of
ratio from unity would mean something exist in the reported values.
As seen from Table 3, the results from ANL, AECL, CENCAD and
JAERI give agreement for the three samples of different concentrations
within t 2%, while IGA/EPFL, ENEA and OU give larger deviations in
positive direction except for A value of IGA/EPFL which is close
enough to value.
iii) Relative Comparison among Three Different Concentrations
Comparison of the relative ratios within an organization provides
interesting information. The request for three different concentra- .
tions of ANL HTO samples has intended to separate the issues depending 0
on the tritium content in the counting procedure. The relative
ratios among each organization are summarized in the Table S-3 taking
the highest concentration sample A as the denominator. It is based on
the natural assumption that A value can be determined most exactly
from the S/N viewpoint.
Table S-3
COM-ANL ANL AECL IGA/EPFL ENEA CENCAD OU JAERI
The ratios of COM-ANL are exact reference values, different from
absolute value issue, because the only concerned was the dilution
procedure which has been done with extreme care and high accuracy in weighing. From the table, ANL, AECL, CENCAD and JAERI give good
agreement with the reference values. No concentration dependence was
observed for them. The OU results give a little high values. Much
larger ratios were observed for the CIA of ENEA and B/A and C/A of
EPFL showing a dependence on the concentration
iv) Summary of HTO Comparison
From the comparison of COM-ANL samples, it is concluded that,
1) Simple comparison with equal weighting gives appreciable discre-
pancy beyond the presumed level.
2) Examination on absolute values and relative ratios discussed in
ii) and iii), show that the tritium counting procedures of ANL, AECL,
CENCAD and JAERI have consistency and good accuracy down to several
Bq/g samples.
3) ENEA and OU gave about 5% higher absolute values: this suggests the
calibration procedure including the tritium standards be re-examined.
The OU results might partly be attributed to the relatively large
error of 4.7% for the tritium standards. The IGA/EPFL and ENEA results
for relative comparison also indicate an improvement is needed in the
counting, data processing or else for low concentration samples. In
fact, the treatment of background results is very sensitive to several
Bq/g class samples.
4) For reference, the averages, in the same way as i), of above four
are given below. Reasonable agreement is observed.
Averaged value COM-ANL ( Bdg)
A: 258.18 + 3.57 (1.385%) 257.0 ?: 2.2
B: 48.66 i 0.482 (0.99%) 48.54 + 0.42 C: 3.868 i 0.0472 (1.22%) 3.87 + 0.03
5) Reasonable agreement of four different organizations proves that
the part of the liquid scintillation counting, if carefully
conducted, is reliable.
6) Hence, it is concluded that the main cause of the discrepancy in
the previous Li-containing sample experiment exists, as inferred, in
the stages prior to the preparation of samples for the liquid
scintillation counting.
111) Summary of the Questionnaire
The results of the questionnaire for the participants are
tabulated in the main text. They show a variety of basic information
on the measuring techniques for the tritium production rates. Detailed
comparison of sample, processing, counting, calibration procedure,
data deduction, correction, error assignment etc. on a unified basis
would provide valuable data each other on the final results and
uncertainty assessment for individual measurements, though the
analysis has not been completed yet unfortunately. However, while the
data are useful to discuss the cause of the discrepancy in reasonable
range and to adjust it, the deviation observed in the experiments is
beyond this. In other words, the answers to the questionnaire have not
given a hint to the possibility of such a large deviation
One item to be commented is on the sample of LiAL02. As is well
understood, the accuracy in measuring tritium production rates depends
on the tritium amount produced in the sample pellet, i.e., irradiation 0
fluence. The LiA102 sample gives low specific activity for counting . .
sample because large amounts of water is needed to dissolve them. For
that reason, LiAl02 is applicable only higher fluence irradiation
compared to the other samples used which can produce higher specific
activity counting samples. Hence it is concluded that LiA102 was not
an appropriate material for the neutronics experiment of the level of
LOTUS or FNS fluences.
IV) Interpretation of the irradiation experiment
Since the last NEACRP meeting, new experimental results were
added by CEN/Cadarache. The Table 5-4 is the simplified revision of
the Table 6.6 of the Interim Report. This does not change the general
observation given in the interim report. The 1u deviation for LOTUS
irradiation is around lo%, while that for FNS irradiation amounts more
than 30%, both being inappropriate to examine the deficiency in the
nuclear data or methods.
Table S-4
Case ANL IGA/EPFL CENCAD UOT OU
( x 10-I 3 T Atom/Li Atom)
FNS(outer) 3.06 1.21 5.28 2.76 2.03
FNS(inner) 3.62 1.48 4.43 3.15 2.34
( x 10-l2 T Atom/Li Atom)
LOTUS(outer) 1.82 1.44 1.91 1.68 1.59
LOTUs(inner) 1.99 1.60 2.07 1.81 1.72
JAERI Average
* CENCAD data were converted from the values of Table A2.a.
So far, there have been no positive responses or modification
from the participant organizations on the results reported in the
interim report other than the addition of Cadarache data. Hence I have
to recognize that this is the reality of the current status in the
technique when a comparison is made with minimum limitation in the
whole procedure.
It should be pointed out this fact does not mean that any of the
means applied is not reliable. Somehow a measure has to be given to
the evaluation of the results in order to proceed to the next step,
even if there is no absolute standard, different from the common HTO . comparison For a rough screening, a comparison with calculation would
help judging the degree of the deviation. Of course, a calculated
value does not mean most probable value because it depends on the
nuclear data, calculation method, modeling and absolute neutron yield
normalization, and it is themselves that should be confirmed by the
experiments. Still, a deviation of as much as 50% in a very simple
experimental arrangement would be quite improbable. In that meaning, a
C/E comparison given for FNS irradiation in the Table A.4 in the main
text furnish some index. For the LOTUS results, similar comparison can
be made, but for smaller deviation judgement would be not easy as for
the FNS case. The stabilify is another measure of the reliability of
the results. This is inferred from the dispersion among the plural
number of the samples in the common irradiation and the ratio between
the LOTUS and FNS irradiations. Judging from these two measures, ANL,
UOT and JAERI get a better points down to the level of FNS
irradiation.
V) Summary and the next step
i) If carefully conducted, the accuracy of the liquid scintillation
counting is good enough down to the level of Bq/g from the results
of comparison of HTO samples.
ii) No evidence has been found to explain the cause of the
discrepancy in the irradiation experiment at FNS and LOTUS from
the the summary of the answers to the questionnaire.
iii)The main cause of the discrepancy must be in the stages prior
to the preparation of samples for the liquid scintillation
counting, most possibly in the processing of Li-containing
pellets.
iv) The present average level of tritium measurements seen from this
international comparison, gives an accuracy of about 10% for the
neutron fluence level of producing several tens Bq per sample.
V) When well prepared and cautiously conducted, an accuracy of 5-10%
will be achieved in the irradiation of neutron level producing
several Bq per sample.
vi) If the lesson learned and expertise in this comparison study is
properly reflected, all participants should be qualified for the
demonstration of the accuracy denoted above. I, vii)Upon the agreement of the all.participants, it is advised that
each to re-examine the whole procedures before the preparation of
the liquid scintillation samples including material selection,
chemical/physical processing appropriate for it and data process-
ing including necessary corrections. This is followed by a new
irradiation experiment to determine the ultimate value of the
uncertainty on the Li-sample and liquid scintillation counting
technique.
This supplement is a subjective view as one of the coordinators of
the program. To encourage the discussion on this subject, critical
comments or different opinions are welcomed. 0
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