  The low-energy $U(1)_{B-L}$ gauge symmetry is well-motivated as part of
beyond Standard Model physics related to neutrino mass generation. We show that
a light $B-L$ gauge boson $Z{'}$ and the associated $U(1)_{B-L}$-breaking
scalar $\varphi$ can both be effectively searched for at high-intensity
facilities such as the near detector complex of the Deep Underground Neutrino
Experiment (DUNE). Without the scalar $\varphi$, the $Z{'}$ can be probed at
DUNE up to mass of 1 GeV, with the corresponding gauge coupling $g_{BL}$ as low
as $10^{-9}$. In the presence of the scalar $\varphi$ with gauge coupling to
$Z{'}$, the DUNE capability of discovering the gauge boson $Z{'}$ can be
significantly improved, even by one order of magnitude in $g_{BL}$, due to
additional production from the decay $\varphi \to Z{'}Z{'}$. The DUNE
sensitivity is largely complementary to other long-lived $Z{'}$ searches at
beam-dump facilities such as FASER and SHiP, as well as astrophysical and
cosmological probes. On the other hand, the prospects of detecting $\varphi$
itself at DUNE are to some extent weakened in presence of $Z{'}$, compared to
the case without the gauge interaction.
