The question concerning Sahm-e Imam of Khums should be dealt with in its own appropriate place. However, we will answer the question briefly as under: A qualified Mujtahid can receive Sahm-e Imam (A.S.) during the period of the occultation of the Imam of Time (A.S.) and he can use and spend it wherever he deems appropriate. Here are a few reasons why a qualified can receive Sahm-e Imam:

1- Given the fact that qualified jurisprudents are the general representatives of the Imam of Time (atf) during the period of occultation[1], they (the Mujtahids) are allowed to spend the share of Imam for such purposes to which the Imam (A.S.) consents including those that serve the interest of Muslims and need of Islamic seminaries where Islamic sciences are acquired.  They can spend the portion of Imam (A.S.) for other purposes also such as helping people who are affected by flood and earthquake and also to provide social services for the needy.

2- A qualified jurisprudent holds guardianship over the property of an absent individual. The position is the same with the property of Imam of Time (may Allah hasten his reappearance). In fact, there is no one else other than a Mujtahid to be entitled to such guardianship over the Imam’s property. That is because a jurist who has guardianship over the property of an absent person for the good of people, then he must have more authority and be more entitled to having guardianship over the Imam’s property in the time of occultation. In the Imam’s absence, it is necessary that a qualified Mujtahid spend the Imam’s property for such purposes to which he consents.

3- There are many narrations as well as other proofs which indicate the validity of a qualified Mujtahid’s fatwa (verdicts) and which allow him to judge and have discretionary authority in non-litigious affairs (affair which do not have special guardian or caretaker and which God does not allow to remain unattended such as taking care of unprotected children and their properties, burying a Muslim who does not have a relative, protecting the property of an absent individual, etc.). That is to say, it is the duty of a just and eligible jurisprudent to undertake these tasks.[2] These traditions, by extension, allow the jurisprudents to have discretion over the portion of Imam, peace be upon him.[3]

Related answers:

18013 (site: en17646); 14024 (site: en13868); 3193 (site: 3450); 18014 (site: en17647); 7305 (site: 7438).