CSEWG Covariance Committee


The Covariance Committee (CovCom) of CSEWG was formally established by the Executive Committee of CSEWG during its annual meeting on 5 November 2007. It had been recognized for some time that CSEWG needed to devote more attention to this aspect of nuclear data evaluation in response to the growing demand for nuclear data uncertainty information from the nuclear applications community. Furthermore, it was felt by the CSEWG leadership that this could be accomplished best by maintaining a standing committee devoted specifically to this activity. This committee would operate on a par with, and in close collaboration with, the previously existing standing committees: Evaluation Committee, Formats and Processing Committee, Measurements Committee, and Data Testing Committee.


It is well recognized that covariances are an integral part of an evaluation, and their generation cannot be appropriately decoupled from the evaluation process. Therefore, it is not the objective of CovCom to unilaterally produce covariances for ENDF/B evaluations. Instead, the mission of this committee will be:

  • Encourage work within the U.S. nuclear science community devoted to the development of efficient and mathematically sound approaches to the production of reliable covariance information in the context of nuclear data evaluation for the ENDF/B Library.
  • Encourage evaluators who contribute to the ENDF/B Library to generate covariance files to accompany their evaluations. This will be carried out in close collaboration with the Evaluation Committee.
  • Work with the CSEWG Formats and Processing Committee to insure that adequate and appropriate formats exist within the ENDF system to represent covariance information.
  • Insure that procedures and software for testing and visualizing covariance information are readily available to the nuclear science community.
  • Establish "quality control" criteria for acceptance and inclusion of covariance information in the ENDF/B Library. This effort will complement the work of the Data Testing Committee.
  • Maintain close contact with applied users of covariance information so that CSEWG can understand and respond to their needs to the extent possible.
  • Provide guidance to ENDF evaluators concerning how best to generate covariance information for their evaluations.
  • Encourage experimentalists to provide the uncertainty information required by evaluators to generate reasonable covariances for measured nuclear data and to include them in their evaluations. This will be carried out in close collaboration with the Measurements Committee.
  • Encourage nuclear modelers to gain a better understanding of the uncertainties in calculated nuclear data and to generate reasonable covariances for model-calculated values.
  • Maintain contact with international nuclear data evaluation activities as they pertain to the generation of covariances.
  • Foster the consideration of advanced topics in the area of covariances, e.g., cross-reaction and cross-material covariances, new formatting and database management concepts, usage of covariances in systems analyses (both deterministic and Monte Carlo), etc.
  • Provide a resource of information dealing with covariances.

Methods of Operation

With the exception of quality control reviews of covariance information submitted for inclusion in ENDF/B, the activities of this committee normally will be task oriented but relatively unstructured. However, the following general features will characterize the workings of this organization:

  • A website will be maintained within the CSEWG framework. It will be devoted to an exchange of information within the U.S. nuclear data evaluation community. However, it will be open and easily accessible to everyone, worldwide (with no hidden URL or username and password requirements).
  • CovCom will have a standing Chair who is solely responsible to the CSEWG Executive Committee and will serve on this CSEWG leadership body.
  • The Chair of CovCom will be responsible for organizing a designated session devoted to covariance issues at the annual CSEWG meeting.
  • CovCom will interact with other standing committees of CSEWG in an informal manner as required to accomplish its mission and to further the objectives of CSEWG.
  • The Chair of CovCom will be solely responsible for interactions with BNL-NNDC concerning maintenance of the CovCom website and assignment of specific quality control review tasks. A well-defined chain of control is necessary to avoid confusion and overburdening of the personnel and resources of the NNDC. In other areas control can be more flexible. However, CovCom members are encouraged to keep the Chair informed of their activities and are further urged to copy all members of CovCom in e-mail communications dealing with covariance issues.
  • Much of the work of CovCom will be carried out by informal task forces of varying scope and duration that are established to address specific technical issues. Each task force will be led by a volunteer coordinator who reports to the Chair. Following completion of all task force projects the coordinator will prepare an informal report or memorandum in collaboration with the task force colleagues. This document will be posted on the CovCom website for the benefit of everyone.