Short answer. Not a share of the indemnity. Article 609 obliges the owner either to replace the property with another of the same value and similar conditions, or to pay the usufructuary the legal interest on the indemnity for the whole period of the usufruct — and if he takes that option, to give security for it.
What the law says
Should the thing in usufruct be expropriated for public use, the owner shall be obliged either to replace it with another thing of the same value and of similar conditions, or to pay the usufructuary the legal interest on the amount of the indemnity for the whole period of the usufruct.
Civil Code, Article 609 — Expropriation of the Thing. Read the full provision →
The usufruct survives the taking
The instinctive assumption is that expropriation ends everything and the money is divided. The article assumes the opposite: the usufructuary's right continues, and what changes is only the thing it attaches to. That is why he is given either substitute property or a stream of interest running for the whole period of the usufruct. Both alternatives reproduce what he had — enjoyment for the term he was granted — rather than cashing him out. A usufructuary who was given the right for life is entitled to the replacement or the interest for life.
The choice belongs to the owner
The article says the owner shall be obliged either, so the election is his and the usufructuary cannot insist on one branch. What the usufructuary can insist on is that whichever branch is chosen actually delivers what the article describes. Replacement property must be of the same value and of similar conditions — not merely something of equal appraisal, but comparable in kind and in the enjoyment it affords, which is a real constraint where the original was productive land or a house someone lived in.
The security requirement is the usufructuary's protection
If the owner chooses to pay interest, he must give security for the payment. The reason is obvious once stated: the usufructuary has lost a tangible thing he was holding and is left with a promise from a person who now has the indemnity in hand and may have every reason to spend it. Security converts that promise into something enforceable over the whole term. A usufructuary faced with the interest option should treat the security as part of the arrangement rather than a formality to be sorted out later.
Get the usufruct on the record before the money moves
The practical failure in these situations is that the indemnity is released to the registered owner without anyone knowing a usufruct existed. So the instrument creating it, and any annotation on the title, are the first documents to surface — and to surface early, while the expropriation is still in progress rather than after payment. Keep the valuation figures too: the indemnity amount is the base for the interest computation, and the description of the property taken is what a replacement has to be measured against.