The calculated distance (air line) between Hérouville-Saint-Clair and Nantes is approximately 149 miles respectively 240 kilometers.
By car or train, the actual journey to Nantes is certainly longer, as only the direct route (as the crow flies) between Hérouville-Saint-Clair and Nantes has been calculated here.
Air line (approximately)
240 kilometers
130 nautical miles