What year did construction start at Heysham 1
CREATE TABLE "current_agr_reactors" (
  "agr_power_station" text,
  "net_m_we" real,
  "construction_started" real,
  "connected_to_grid" real,
  "commercial_operation" real,
  "accounting_closure_date" real
);
SELECT "construction_started" FROM "current_agr_reactors" WHERE "agr_power_station"='Heysham 1';