Can a priest, who is a recovering alcoholic and who has a congregation that is mostly recovering alcoholics validly substitute grape fruit juice in lieu of wine for the consecration ?
No, only valid matter can be used for confecting the Eucharist. With permission from his Bishop, a priest may substitute mustem, which is wine that has just barely started to ferment.
To add a bit to Corki’s answer, here is a document from the USCCB about communion for those with celiac disease or alcohol intolerance: usccb.org/prayer-and-worship/the-mass/order-of-mass/liturgy-of-the-eucharist/celiac-disease-and-alcohol-intolerance.cfm
Mustum is defined as grape juice in which fermentation has begun, but has been suspended with the result that its alcohol content (usually less than 1.0%) does not reach the levels found in most table wines. … Pasteurized grape juice in which all alcohol has been evaporated through high temperature preparations is invalid matter for Mass. …
Permission for priests, deacons, or the lay faithful without distinction to use mustum or low-gluten hosts is within the competence of the diocesan Bishop. The authority to permit the lay faithful to use mustum and low-gluten hosts in the reception of Holy Communion may be delegated to pastors under canon 137 §1 of the Code of Canon Law.