Request ID8 Type of the request High Priority request
TargetReaction and processIncident EnergySecondary energy or angleTarget uncertaintyCovariance
 1-H-2 (n,el) DA/DE  0.1 MeV-1 MeV 0-180 Deg 5 Y
FieldSubfieldDate Request createdDate Request acceptedOngoing action
 Fission Heavy Water Reactors 25-JUL-06 16-APR-07 Y

Requester: Kenneth KOZIER at CNLCR, CAN
Email:

Project (context): Critical experiments with high enriched uranyl fluoride in heavy water

Impact:
Different representations of the energy-angle neutron elastic scattering probability distributions (at energies <3.2 MeV) used in various releases of the ENDF/B-VI and JENDL-3.3 evaluated data libraries for deuterium cause differences of about: (1) 1000 pcm in simulations [1,2] of critical experiments involving solutions of high enriched uranyl fluoride solutions in heavy water (specifically the HST-004 and HST-020 series of measurements in the NEA ICSBEP handbook), and (2) 60 pcm in the calculation bias observed [2] in simulations of heavy-water coolant void reactivity (CVR) experiments performed in ZED-2. Moreover, both the HST and ZED-2 simulation results show a rising trend with neutron leakage, suggesting that further revision of the deuterium data evaluations may be needed. Modern measurements may help resolve a small positive bias of about 150 pcm in the simulation of ZED-2 heavy-water CVR experiments (corresponding to about 10% of the calculated CVR).

Accuracy:
About 5%, depending on energy and angle. At 220 keV, existing experimental data have uncertainties of about 16% and differ from the evaluated library values by about 35% at backward angles near 180 degrees. At 500 keV, some experimental data have uncertainties of about 5%, but differ from the library values by up to 50% at 180 degrees. At 1.0 MeV, existing experimental data have uncertainties of about 5%, but differ from the library values by up to 33% near 180 degrees. ENDF/B-VI.8 and JENDL-3.3 differ by about 15% at 180 degrees over this energy range. It is estimated that a 5% uncertainty would correspond to a reactivity uncertainty of about 300 pcm in the context of the HST simulations and about 20 pcm in the ZED-2 CVR simulations, and would be adequate to resolve the current discrepancy between results obtained using the ENDF-B/VI.8 (also VII) and JENDL-3.3 deuterium data files.

Justification document:
The available angular scattering experimental data for deuterium were reviewed [3, attached] and found to be 25 to more than 50 years old, sparse and inconsistent, particularly at backward angles near 180 degrees. The experimental data frequently differ from the evaluated library values by several standard deviations, especially at extreme backward and forward angles. In addition to the HST and ZED-2 simulation results [1,2], the neutronic importance of the deuterium scattering data has been investigated in empirical sensitivity studies of simple systems [4, attached], which suggest that the differences arise at energies up to about 1.0 MeV. A recent TSUNAMI sensitivity analysis of the CVR for an Advanced CANDU Reactor (ACR-700) type lattice cell showed [5] a large sensitivity to the deuterium elastic scattering cross section (34% change in CVR per % change in the cross section), although this methodology does not currently address the angular dependence.
References:
1. R.D. Mosteller, J.M. Campbell and R.C. Little, Reactivity Impact of ENDF/B-VI Cross Sections for Deuterium in Heavy-Water Solution Benchmarks, LA-UR-05-0330, 2005 Annual Meeting of the American Nuclear Society, June 5 - 9, 2005, San Diego, CA.
2. R.D. Mosteller, K.S. Kozier, J.M. Campbell and R.C. Little, ''Reactivity Impact of Deuterium Cross Sections for Heavy-Water Benchmarks'', LA-UR-05-0787, proceedings of the International Topical Meeting on Mathematics and Computation, Supercomputing, Reactor Physics, and Nuclear and Biological Applications, Avignon, France, September 12-15, 2005.
3. L.W. Townsend, ''Neutron-Deuterium Cross Section Evaluation'', Final Technical Report, AECL Purchase Order 217739, March 31, 2006 (copy attached).
4. K.S. Kozier, ''Sensitivity of MCNP5 Calculations for a Spherical Numerical Benchmark Problem to the Angular Scattering Distributions for Deuterium'', proceedings of the PHYSOR-2006 ANS Topical Meeting: Advances in Nuclear Analysis and Simulation, Vancouver, BC, September 10-14, 2006 (copy attached; to be issued).
5. M.L. Williams, J.C. Gehin and K.T. Clarno, ''Sensitivity Analysis of Reactivity Responses Using One-Dimensional Discrete Ordinates and Three-Dimensional Monte Carlo Methods'', proceedings of the PHYSOR-2006 ANS Topical Meeting: Advances in Nuclear Analysis and Simulation, Vancouver, BC, September 10-14, 2006 (to be issued).
6. J.P. Svenne, L. Canton, K. Kozier, and L. Townsend, "Re-evaluating low-energy neutron-deuteron elastic scattering using three-nucleon theory", International Conference on Nuclear Data for Science and Technology 2007, Contrib. #208.
7. K.S. Kozier, "Assessment of evaluated (n,d) energy-angle elastic scattering distributions using MCNP simulations of critical measurements and simplified calculation benchmarks", International Conference on Nuclear Data for Science and Technology 2007, Contrib. #594

Comment from requester:
Additional sensitivity studies are in progress. We are also looking into the possibility of having someone review the theoretical basis for the two distinctly different quantum mechanical formalisms used by ENDF/B & JENDL for the deuterium elastic scattering energy-angle distributions, and potentially undertake some new Faddeev three-body model calculations.

Review comment:
At the ND2007 in Nice two contributions were presented summarising the status at the time of the conference (April 2007, refs. 6 and 7). Theoretical calculations by L. Canton solving the AGS three-body equations using the Bonn-B nuclear potential tend to support the higher degree of backscattering in the ENDF/B-IV.4 evaluation. A 5% experimental accuracy for the differential cross section at 180 degrees would be sufficient to discriminate between ENDF/B-VI.4 and theory on the one hand and ENDF/B versions VI.5 to VII.0 on the other hand. Possibilities for experimental efforts are being investigated in the US and in Europe. Further theoretical efforts are planned to study the impact of three body forces and the use of other nucleon-nucleon potentials on the angular distribution.

Entry Status:
Work in progress (as of SG-C review of May 2018)

Main references:
Please report any missing information to hprlinfo@oecd-nea.org

Experiments

Theory/Evaluation

Validation

Additional file attached:AECL Final Technical Report.pdf
Additional file attached:Full_paper_152003.pdf



Request ID43 Type of the request Special Purpose Quantity
TargetReaction and processIncident EnergySecondary energy or angleTarget uncertaintyCovariance
 1-H-1 (n,el) SIG,DA  10 MeV-20 MeV 4 pi 1-2 Y
FieldSubfieldDate Request createdDate Request acceptedOngoing action
 Standard impact on all subfields 29-APR-11 13-MAY-11 Y

Requester: Dr Allan D. CARLSON at NIST, USA
Email: allan.carlson@nist.gov

Project (context): NIST, Neutron Cross-Section Standards (www-nds.iaea.org/standards), CSEWG, WPEC

Impact:
This neutron cross section standard is perhaps the most important of the standards [1]. All of the other standards have been measured relative to it. Any improvement in this standard improves all standards and other cross sections that have been directly or indirectly measured relative to this standard. It helps form the basis of the neutron cross section libraries. There is very large leverage associated with improvements in this cross section. A problem at about 14 MeV is shown in reference [2].

[1] A.D. Carlson, et al., International Evaluation of Neutron Cross Section Standards, Nuclear Data Sheets 110 (2009) 3215-3324.
[2] N. Boukharouba, et al., Measurement of the n-p elastic scattering angular distribution at 14.9 MeV, Phys. Rev. C 82, 014001 (2010).
[3] N. Boukharouba, et al., Measurement of the n-p elastic scattering angular distribution at 10 MeV, Phys. Rev. C 65, 014004 (2001).

Accuracy:
1%-2% over most of the angular range. Very little data are available at small center-of-mass angles so the emphasis should be placed there.

Justification document:
The nature of the standards makes a simple answer to the question difficult. Since essentially all cross section data depend on the standards, any improvement in this standard will improve data for any neutronics calculation.
This neutron cross section standard is perhaps the most important of the standards. All of the other standards have been measured relative to it. Any improvement in this standard improves all standards and other cross sections that have been directly or indirectly measured relative to this standard. It helps form the basis of the neutron cross section libraries. There is very large leverage associated with improvements in this cross section.

Comment from requester:

Review comment:

Arjan Plompen: New measurement efforts should seriously consider measuring the angular distribution for the outgoing neutron at the incident energies of 10 and 14.9 MeV tackled by the Ohio University collaboration while covering the forward angles and with good overlap with those data at backward angle [2,3]. Ideally they should answer the question concerning the degree of the Legendre polynomial required for the targeted uncertainty and allow the coefficients to be established accurately.

Don Smith: [...] improvements in the standards can almost always be justified. The H(n,n)H standard is certainly an important one. [...] this impacts on all technical areas but certainly more so at higher energies, e.g., in the HE tail of the fission neutron spectrum (or for fusion applications) [...]

Mark Chadwick: The sensivity of many experiments to this cross section is essentially one.

Allan Carlson in response to questions raised by Arjan Plompen:

A) It is very difficult to make absolute measurements of the hydrogen angular distribution with high accuracy. Instead it is much easier to make relative measurements. But to normalize the relative data to the hydrogen total elastic cross section requires either a rather complete measurement of the relative angular distribution or very good models to assist in the extrapolation to the angular region that was not measured (in the reference [2,3]). [...] it must be emphasized that this normalization aspect is very important.

B) It is disturbing that there are differences of 0.5 to 1% between the Arndt et al. and ENDF/B-VII evaluations of the total elastic cross section in the 10-20 MeV energy region. Part of this is because of the databases being used in the evaluations. For example, the Abfalterer et al. data were not used in the Arndt PWA analysis but they were included in the Hale (ENDF/B-VII) work. They had significant weight in the Hale evaluation due to the small experimental uncertainties so the evaluation is similar to those data. [...] It would be very valuable if each group used exactly the same database and compared their results.

C) Improvements in measurements of the total cross section are also worthwhile. The most recent work has used TOF techniques with white sources. These measurements are good but I would suggest that making a measurement at a single point with a (nearly) monoenergetic source for which very good background measurements are possible could provide even smaller uncertainty. In the 50’s and 60’s, a number of total cross section measurements were made in the MeV energy region with fraction of a percent uncertainties. I expect we could probably do a little better now. Note the detailed process described in Fast Neutron Physics for accurate total cross section measurements. An important point for the total cross section work (but not for the angular distribution work) is a very accurate determination of the energy of the neutrons. An error of 20 keV in the energy scale for a 1 MeV cross section measurement causes about a 1% error in the cross section. This effect is less however at higher neutron energies.

Entry Status:
Work in progress (as of SG-C review of May 2018)

Main references:
Please report any missing information to hprlinfo@oecd-nea.org

Experiments

Theory/Evaluation

  • A.D. Carlson et al. (G. Hale, M. Paris), Evaluation of the Neutron Data Standards, NDS 148 (2018) 143

Additional file attached:
Additional file attached: