Speaker
Description
Each release of the ENDF/B nuclear data library [1] pushes the limits of the processing codes through the introduction of new data and new data formats. Processing codes must be adapted to ensure that they are capable of using these new formats, or at the very least understand them. NJOY [2], the nuclear data processing code developed at Los Alamos National Laboratory is no exception to this. Since NJOY2016 is still the main production code for nuclear data libraries at LANL, we will continue to make the necessary changes in this version of NJOY to ensure full compatibility with the ENDF/B-VIII.1 nuclear data library. Where relevant, the modern NJOY21 components will also be updated.
The addition of the mixed elastic scattering option (LTHR = 2) for elastic thermal scattering (found in MF7 MT2) is one of the most anticipated changes for the ENDF/B-VIII.1 nuclear data library since it lifts the limitation of using either coherent or incoherent elastic scattering for moderators. For NJOY2016, this new format has required changes in various modules, the most important ones being THERMR (which processes the thermal scattering data) and ACER (which formats the data into an ACE file for use in application codes like the MCNP® code [3]). Figure 1 gives an example of what this mixed mode data looks like for D in 7LiD after processing through ACER in NJOY2016.65 which provides this new capability.
Because the coherent and incoherent data needs to be treated separately by MCNP6, the mixed mode scattering also necessitated an update to the ACE format itself by adding an additional elastic scattering data block [4], and a subsequent modification to MCNP so that the mixed mode elastic data can be used during a Monte Carlo simulation. Experimental support for this new format is available in MCNP, version 6.3.0 [5].
A second ENDF format change that will impact processing is the addition of R-matrix background elements for resonance channels in the R-matrix limited format (LRF = 7). Contrary to the mixed mode elastic scattering, the required changes to NJOY will be mainly limited to RECONR and NJOY21’s resonance reconstruction component.
In addition to these format changes, some processing limitations that were identified in the past will also have to be lifted to process ENDF/B-VIII.1 evaluations. Examples here would be MF34 covariance processing with multiple subsections in ERRORR or photonuclear data processing (in this case allowing for ACELAW=61 in the secondary photons).
In this paper we will give an overview of the most important changes that were made to NJOY2016 for processing ENDF/B-VIII.1 nuclear data, and where possible we will provide validation results that illustrate the impact that these changes will have for nuclear data users.
References
[1] D. Brown et al., “ENDF/B-VIII.0: The 8th Major Release of the Nuclear Reaction Data Library with CIELO-project Cross Sections, New Standards and Thermal Scattering Data,” Nuclear Data Sheets, 148, 2018, p. 1-142
[2] R. E. MacFarlane et al., “The NJOY Nuclear Data Processing System, Version 2016,” Los Alamos National Laboratory, LANL Technical Report LA-UR-20093
[3] J. A. Kulesza et al., “MCNP Code Version 6.3.0 Theory & User Manual,” Los Alamos National Laboratory, LANL Technical Report, to be published (2021)
[4] J. L. Conlin, P. Romano, W. Haeck, “A Compact ENDF (ACE) Format Specification,” Los Alamos National Laboratory, LANL Technical Report LA-UR-19-29016
[5] J. A. Kulesza, C. J. Josey, S. R. Bolding, J. C. Armstrong, J. E. Sweezy, J. S. Bull, M. E. Rising, E. J. Pearson, “MCNP® Code Version 6.3.0 Release Notes,” Los Alamos National Laboratory, LANL Technical Report, to be published (2021)