Abstract: A coupon sampler for a reactor system includes a lower assembly having an in-line portion configured to receive a flow of a molten salt, and a lower assembly pipe portion extending transverse from the in-line portion and defining a lower channel therethrough. The coupon sampler further includes an upper assembly fluidically coupled with the lower assembly. The upper assembly includes an upper assembly pipe portion defining an upper channel therethrough and cooperating with the lower channel to define a sampling channel of the coupon sampler. The coupon sampler further includes a coupon device disposed fully within the sampling channel. The coupon sampler further includes an actuation mechanism operatively coupled with the coupon device and configured to move the coupon device axially into and out of the flow of the molten salt.