REVIEW OF EVALUATIONS FOR THE TUNGSTEN
ISOTOPES
INTRODUCTION
Systematic comparison with experimental data from EXFOR was made with the ENDVER package was made for the following evaluations:
ENDF/B-VII http://www.nndc.bnl.gov/
TENDL-2008 http://www.talys.eu/tendl-2008/
FZK http://www.nea.fr/html/dbdata/jeff3.2-beta/#N
IAEA_ib21f http://www-nds.iaea.org/wolfram/wolfram.htmlx
The comparisons are presented for the natural element, which has the most abundant database of experimental data, although similar plots exist for individual isotopes.
The FZK and IAEA_ib21f files were processed with NJOY so that benchmark calculations could be run. Both libraries were processed with the same NJOY input decks. The plots generated by the ACER module of NJOY are presented.
The covariances were also processed in the standard Vitamin-J group structure. The plots generated by ERRORR and COVR modules of NJOY are presented.
NOTE:
To view the plots you must download the ZVView code and associate ZVD files with this application.
CROSS SECTIONS
The cross sections are generally in good agreement with measurements. Detailed graphical comparison can be viewed from nW-0.htm ; plot numbers in the text below refer to this list. General conclusions can be summarised as follows below.
TENDL-08
demonstrates the capability of predicting cross sections with default options.
FZK
Plot Comment
1 Total deviates somewhat from measured data between 1 and 15 MeV.
2 The elastic does not reproduce the most recent Schmidt data around 10 MeV.
4 The inelastic between 2 and 5 MeV has distinctly unphysical shape.
5 The (n,2n) cross section reproduces the original Frehaut data. Neither the renormalisation to the new standard, nor the systematic correction recommended by Vonach were taken into account.
11 Capture stops abruptly at 20 MeV. There is no contribution in MT5.
14,15 Radionuclide production cross sections (Ta-182, Ta-183) have an unphysical jump at 20 MeV.
IAEA_ib21f
Plot Comment
3 The non-elastic is higher than experimental data (like TENDL-08 and ENDF/B-VII) between 2 and 5 MeV. The FZK evaluation seems to be in better agreement, but see the comment about the inelastic, which has the peak in this energy range. The measurements are generally old and one could raise doubts about their interpretation.
6 The fission cross section is included as a dosimetry reaction to avoid treating the nuclide as fissile. Neither the neutron yields nor the spectra are given.
16 No other library gives W-183m isomer production.
ALPHA-PRODUCTION (Plot 428)
The FZK evaluation was adjusted to the measured data for Ta-181.
The IAEA-ib21f evaluation is somewhat higher, but within the associated uncertainty.
DEUTERON, TRITON AND HELION PRODUCTION
The IAEA_ib21f evaluation does not have the data for these particles explicitly.
ANGULAR DISTRIBUTIONS (Plots 17-76)
Some care is needed because in several cases the data are declared as "elastic", but from a more careful consideration it is evedent that some "contamination" with discrete inelastic levels is present. The data by Begum (Plot 37), Annand (Plot 38), Becker (Plot 39), Walt (Plot 40) and Hill (Plot 41) were re-classified as “scattering”.
At lower energies (300-1250 keV) IAEA-ib21f fits the data slightly better than FZK (e.g. Plot 18, 19, 21), although counterexamples can be found (incident neutron energy 475 keV, Plot 20). The FZK data resemble closely the ENDF/B-VII data and seem to follow the old Langsdorf data (Plots 58-70, e.g.: Plot 60, 65, 70).
At higher energies (1 to 7 MeV) the agreement between evaluations is generally better than the scatter in the experimental data.
The most recent data by Schmidt (Plots 42-50) cover the range from 7.19 to 14.1 MeV. The IAEA-ib21f give a distinctly better fit to the measured data, especially at the lower end of the measured range (e.g. Plots 42, 44, 45, 46, 47). At higher energies the differences between evaluations are smaller (e.g. Plots 48, 49, 50). In the EXFOR database the inelastic contribution was subtracted from the directly measured data.
At very high energies (>100 MeV) the angular distributions of some reactions in the IAEA_ib21f files may be negative. This is a formatting problem because tabular data representation has not been implemented for reaction channels other than the elastic.
ANGLE-INTEGRATED NEUTRON EMISSION SPECTRA (Plots 80-88)
At incident neutron energies between 7 and 10 MeV, IAEA-ib21f evaluation is the only one that reproduces the gradient of the spectrum in the range where inelastic contribution is dominant (e.g. Plot 80, 81, 83).
At higher energies, where the (n,2n) contribution becomes stronger, the slope of the spectrum shape is slightly underestimated, leading to some overprediction of the spectrum between about 2 and 5 MeV. However, in the range where the inelastic contribution is dominant, the IAEA-ib21f evaluation is again the only one that predicts the "flat" spectrum shape, as observed in the measurements (e.g. Plots 85, 86, 87).
DOUBLE-DIFFERENTIAL NEUTRON EMISSION SPECTRA (Plots 111-426)
Extensive database of double-differential spectra (particularly those by Schmidt) confirm the conclusions from the angle-integrated spectra.
GAMMA EMISSION SPECTRA
Angle-integrated spectra by Savin (Plots 89-109) are somewhat inconclusive (e.g. Plots 101, 105, 106).
The double-differential gamma spectra by Drake (Plots 418, 419, 420) indicate the following:
- The predictive power of the TENDL-08 generic calculations is remarkable.
- The IAEA-ib21f spectrum curves agree with the measured data well.
- In the FZK data the dominant contributions to the gamma spectra are missing.
NUCLEAR HEATING
Evaluations for all isotopes by FZK have "holes" in the heating between 1 and 10 MeV. The heating is negative at some energies. Recoil heating goes strongly negative.
Pages 16, 20 and 68 in w182_fzk_ace.pdf
Pages 10, 14 and 56 in w183_fzk_ace.pdf
Pages 10, 14 and 61 in w184_fzk_ace.pdf
Pages 12, 16 and 63 in W186_fzk_ace.pdf
The IAEA_ib21f evaluation does not seem to have such problems, except that for some nuclides the recoil heating at high energies has some saw-tooth structure, which is probably a numerical problem.
Page 60 in w180_ib21f_ace.pdf
Page 69 in w182_ib21f_ace.pdf
Page 75 in w183_ib21f_ace.pdf
Page 53 in w184_ib21f_ace.pdf
Page 65 in w186_ib21f_ace.pdf
PLOTS FROM THE ACER MODULE OF NJOY
The plots generated automatically by the ACER module of NJOY for the respective isotopes from the FZK and IAEA_ib21f evaluations are available from the links below.
w182_ib21f_ace.pdf w182_fzk_ace.pdf
w183_ib21f_ace.pdf w183_fzk_ace.pdf
w184_ib21f_ace.pdf w184_fzk_ace.pdf
w186_ib21f_ace.pdf W186_fzk_ace.pdf
PLOTS OF
COVARIANCES IN VITAMIN-J GROUP STRUCTURE
The plots were generated from the ERRORR output with the COVR module of NJOY.
w180_ib21f_cov.pdf
w182_ib21f_cov.pdf w182_fzk_cov.pdf
w183_ib21f_cov.pdf w183_fzk_cov.pdf
w184_ib21f_cov.pdf w184_fzk_cov.pdf
w186_ib21f_cov.pdf W186_fzk_cov.pdf
The general pattern is:
- The FZK covariances are represented for most of the reaction channels individually, while the IAEA_ib21f uses lumped reaction covariances to reduce the number of reaction channels.
- The FZK evaluation gives cross-reaction covariances only for the discrete inelastic levels and the continuum, while the IAEA_ib21f evaluation gives the full covariance information including cross-reaction covariances at least for the lumped reactions.
- There are no correlations between the cross sections in the resonance region and above in either of the two evaluations.
BENCHMARKING
The scope and nature of the benchmark test cases had already been presented elsewhere (e.g. Port Jefferson 2008), therefore only the main results are given:
FNG Benchmark
It has been shown already that the spectrum measurements are less reliable than the activation measurements. Differences between measured reaction rates and those based on calculations with the FZK and IAEA_ib21f tungsten evaluations are shown below. The IRDF-2002 data are used for the monitor reaction cross sections. Calculations were done with MCNP-5 using models from the SINBAD compilation, with material definitions corrected accordingly. Note from Authors: FZK benchmarks results' figure omitted at the request of FZK.
Criticality benchmarks
A variety of benchmarks from the ICSBEP compilation were executed. The ZPR-9 series of benchmarks in ICSBEP are modelled with homogenised regions. To remove the ambiguity of possible influence of the homogenisation on the results, detailed heterogeneous models for MCNP were obtained from ANL, but the differences in benchmark results were found to be much smaller than the discrepancies between the measured and calculated multiplication factors. The results presented below correspond to the detailed models. These benchmarks are interesting because tungsten appears in the core. In all other benchmarks tungsten is used as the reflector.
The table relating the benchmark names with the ICSBEP designation is the following:
|
IEU-MET-FAST-13_ |
ZPR9109V7A |
|
IEU-MET-FAST-14_ |
ZPR9213V7A |
|
IEU-MET-FAST-14_ |
ZPR9310V7A |
|
HEU-MET-FAST-60_ |
ZPR9410V7A |
|
HEU-MET-FAST-67_ |
ZPR9508V7A |
|
HEU-MET-FAST-67_ |
ZPR9613V7A |
|
HEU-MET-FAST-70_ |
ZPR9718V7A |
|
HEU-MET-FAST-70_ |
ZPR9811V7A |
|
HEU-MET-FAST-70_ |
ZPR9907V7A |
|
|
|
|
PU-MET-FAST-05_ |
Pu/W |
|
|
|
|
HEU-MET-FAST-084_14 |
Comet/W-1in |
|
HEU-MET-FAST-084_25 |
Comet/W-1/2in |
|
HEU-MET-FAST-085_06 |
Comet/W-2in |
|
U233-MET-FAST-004_02 |
|
|
|
|
|
HEU-MET-FAST-03_ |
ElsieWC19 |
|
HEU-MET-FAST-03_ |
ElsieWC29 |
|
HEU-MET-FAST-03_ |
ElsieWC45 |
|
HEU-MET-FAST-03_ |
ElsieWC65 |
