Reaction of Boron with Alkali
Boron react with $\ce{NaOH}$ but under certain conditions. Boron exist in two form (1) crystalline form (2) amorphous form. Both forms are generally inert to chemical reactions and is unaffected by acids and alkali at normal conditions but at elevated temperature, concentrated oxidizing acids like nitric or sulfuric acids react with boron to yield boric acid. On the other hand, amorphous boron does react with fused alkali at high temperature to obtain trisodium borate:
$$\ce{2B(s) + 6NaOH(s) -&gt;[t &gt; 773K] 2Na3BO3(s) + 3H2(g) ^}$$
High purity, hydrated sodium metaborate(sodium tetrahydroxoborate, $\ce{Na[B(OH)4]}$) can also be produced from boron in a $\ce{NaOH-H2O}$ system. The process applied was called pressure alkaline leaching.
When fused in the presence of air at $\pu{350-400 ^\circ C}$, sodium metaborate is formed. You can find the reaction in this answer by @andselisk.
References

https://onlinelibrary.wiley.com/doi/abs/10.1002/0471743984.vse1217
Yin, B.W &amp; Qin, S.Y &amp; Zhang, Y.F &amp; Zhang, Y (2014). Preparation of hydrated sodium metaborate from boron concentrate via pressure alkaline leaching. Guocheng Gongcheng Xuebao/The Chinese Journal of Process Engineering. 14. 258-265, (link)