For uninterrupted long term storage, freezing in a vacuum pack with a dessicant is best. Each time a batch of seeds goes through a freeze/thaw cycle, a few become unviable. For storage lengths of a few years or less, room temperature storage in an airtight container with a dessicant is satisfactory. Vacuum packing with dessicant and room temperature storage is best for access without the thaw and re-freezing that kills them. The problem with using the refrigerator for any period of time is the excessive amount of moisture constantly present. Each time the door is opened, moisture condenses on items inside, for which the dessicant is an inadequate deterrent for molds. A vacuum sealed container should not condense moisture on the inside. I have no knowledge of the effective lifespan of rice as a dessicant, but it could be replaced occasionally if suspected to be losing effectiveness. Using heat to remove any moisture present in rice or other "makeshift" dessicants will improve effectiveness and longevity. I have heard of vermiculite being used as a dessicant, but would recommend silica gel as a first choice. I heard of properly stored seeds over 10 years old still germinating at acceptable rates.