  As part of the main focus of the BDF Working Group in 2021, this document
reports on the study of alternative locations and possible optimisation that
may accompany the reuse of existing facilities with the aim of significantly
reducing the costs of the facility. Building on the BDF/SHiP Comprehensive
Design Study (CDS), the assessment rests on the generic requirements and
constraints that allow preserving the physics reach of the facility by making
use of the $4\times 10^{19}$ protons per year at 400\,GeV that are currently
not exploited at the SPS and for which no existing facility is compatible. The
options considered involve the underground areas TCC4, TNC, and ECN3. Recent
improvements of the BDF design at the current location (referred to as
`TT90-TCC9-ECN4') are also mentioned together with ideas for yet further
improvements. The assessments of the alternative locations compiled the large
amount of information that is already available together with a set of
conceptual studies that were performed during 2021.
  The document concludes with a qualitative comparison of the options,
summarising the associated benefits and challenges of each option, such that a
recommendation can be made about which location is to be pursued. The most
critical location-specific studies required to specify the implementation and
cost for each option are identified so that the detailed investigation of the
retained option can be completed before the end of 2022.
