Joining Oracle tables with 2 strings to be oa a single row (in a distinct SQL filter)
Simply do a GROUP BY instead of DISTINCT:

SELECT RAP.ID_PL, SES_RAP.AN,  RAP.DENUMIRE,
    A3T2.COD_DESEU, A3T2.TIP_AMB,
    coalesce(MIN(A32.COD_REC),'') || coalesce(MIN(A32.COD_VAL),'') 
FROM chest cht
    INNER JOIN raport rap
        ON cht.fk_id_raportor = rap.id
    INNER JOIN sesiune_rap ses_rap
        ON ses_rap.id = CHT.FK_ID_SESIUNE_RAP
    full outer join a3_t2_rows a3t2
        on A3T2.FK_ID_ANEXA = cht.id
WHERE A3T2.TIP_AMB ='LEMN'
GROUP BY RAP.ID_PL, SES_RAP.AN,  RAP.DENUMIRE,
    A3T2.COD_DESEU, A3T2.TIP_AMB