Pure potassium metal is not often used, but its alloys with sodium may substitute for pure sodium in fast breeder nuclear reactors.
pjˈʊɹ pətˈæsiəm mˈɛɾəl ɪz nˌɑːt ˈɔfən jˈuːzd, bˌʌt ɪts ˈælɔɪz wɪð sˈoʊdiəm mˈeɪ sˈʌbstɪtˌuːt fɔːɹ pjˈʊɹ sˈoʊdiəm ɪn fˈæst bɹˈiːdɚ nˈuːklɪɹ ɹɪˈæktɚz.