The calculated distance (air line) between Vladivostok and Sŏnbong is approximately 92 miles respectively 148 kilometers.
By car or train, the actual journey to Sŏnbong is certainly longer, as only the direct route (as the crow flies) between Vladivostok and Sŏnbong has been calculated here.
Air line (approximately)
148 kilometers
80 nautical miles