diff --git a/src/reactor.cc b/src/reactor.cc
index 26b82a644b..e8d30ecb4d 100644
--- a/src/reactor.cc
+++ b/src/reactor.cc
@@ -57,7 +57,7 @@ void Reactor::InitFrom(cyclus::QueryableBackend* b) {
 
 void Reactor::EnterNotify() {
   cyclus::Facility::EnterNotify();
-  
+
   // If the user ommitted fuel_prefs, we set it to zeros for each fuel
   // type.  Without this segfaults could occur - yuck.
   if (fuel_prefs.size() == 0) {
@@ -98,6 +98,10 @@ void Reactor::EnterNotify() {
   }
 }
 
+bool Reactor::CheckDecommissionCondition() {
+  return core.count() == 0 && spent.count() == 0;
+}
+
 void Reactor::Tick() {
   // The following code must go in the Tick so they fire on the time step
   // following the cycle_step update - allowing for the all reactor events to
@@ -105,10 +109,32 @@ void Reactor::Tick() {
   // they
   // can't go at the beginnin of the Tock is so that resource exchange has a
   // chance to occur after the discharge on this same time step.
+
+  if (retired()) {
+    Record("RETIRED", "");
+
+    if (context()->time() == exit_time()) { // only need to transmute once
+      Transmute(ceil(static_cast<double>(n_assem_core) / 2.0));
+    }
+    while (core.count() > 0) {
+      if (!Discharge()) {
+        break;
+      }
+    }
+    // in case a cycle lands exactly on our last time step, we will need to
+    // burn a batch from fresh inventory on this time step.  When retired,
+    // this batch also needs to be discharged to spent fuel inventory.
+    while (fresh.count() > 0 && spent.space() >= assem_size) {
+      spent.Push(fresh.Pop());
+    }
+    return;
+  }
+
   if (cycle_step == cycle_time) {
     Transmute();
     Record("CYCLE_END", "");
   }
+
   if (cycle_step >= cycle_time && !discharged) {
     discharged = Discharge();
   }
@@ -158,10 +184,26 @@ std::set<cyclus::RequestPortfolio<Material>::Ptr> Reactor::GetMatlRequests() {
   std::set<RequestPortfolio<Material>::Ptr> ports;
   Material::Ptr m;
 
-  int n_assem_order =
-      n_assem_core - core.count() + n_assem_fresh - fresh.count();
+  // second min expression reduces assembles to amount needed until
+  // retirement if it is near.
+  int n_assem_order = n_assem_core - core.count() + n_assem_fresh - fresh.count();
+
+  if (exit_time() != -1) {
+    // the +1 accounts for the fact that the reactor is alive and gets to
+    // operate during its exit_time time step.
+    int t_left = exit_time() - context()->time() + 1;
+    int t_left_cycle = cycle_time + refuel_time - cycle_step;
+    double n_cycles_left = static_cast<double>(t_left - t_left_cycle) /
+                         static_cast<double>(cycle_time + refuel_time);
+    n_cycles_left = ceil(n_cycles_left);
+    int n_need = std::max(0.0, n_cycles_left * n_assem_batch - n_assem_fresh);
+    n_assem_order = std::min(n_assem_order, n_need);
+  }
+
   if (n_assem_order == 0) {
     return ports;
+  } else if (retired()) {
+    return ports;
   }
 
   for (int i = 0; i < n_assem_order; i++) {
@@ -189,7 +231,6 @@ void Reactor::GetMatlTrades(
   using cyclus::Trade;
 
   std::map<std::string, MatVec> mats = PopSpent();
-  std::vector<cyclus::Trade<cyclus::Material> >::const_iterator it;
   for (int i = 0; i < trades.size(); i++) {
     std::string commod = trades[i].request->commodity();
     Material::Ptr m = mats[commod].back();
@@ -233,8 +274,16 @@ std::set<cyclus::BidPortfolio<Material>::Ptr> Reactor::GetMatlBids(
 
   bool gotmats = false;
   std::map<std::string, MatVec> all_mats;
-  for (int i = 0; i < fuel_outcommods.size(); i++) {
-    std::string commod = fuel_outcommods[i];
+
+  if (uniq_outcommods_.empty()) {
+    for (int i = 0; i < fuel_outcommods.size(); i++) {
+      uniq_outcommods_.insert(fuel_outcommods[i]);
+    }
+  }
+
+  std::set<std::string>::iterator it;
+  for (it = uniq_outcommods_.begin(); it != uniq_outcommods_.end(); ++it) {
+    std::string commod = *it;
     std::vector<Request<Material>*>& reqs = commod_requests[commod];
     if (reqs.size() == 0) {
       continue;
@@ -275,6 +324,10 @@ std::set<cyclus::BidPortfolio<Material>::Ptr> Reactor::GetMatlBids(
 }
 
 void Reactor::Tock() {
+  if (retired()) {
+    return;
+  }
+
   if (cycle_step >= cycle_time + refuel_time && core.count() == n_assem_core) {
     discharged = false;
     cycle_step = 0;
@@ -298,12 +351,15 @@ void Reactor::Tock() {
   }
 }
 
-void Reactor::Transmute() {
-  // safe to assume full core.
-  MatVec old = core.PopN(n_assem_batch);
-  MatVec tail = core.PopN(core.count());
+void Reactor::Transmute() { Transmute(n_assem_batch); }
+
+void Reactor::Transmute(int n_assem) {
+  MatVec old = core.PopN(std::min(n_assem, core.count()));
   core.Push(old);
-  core.Push(tail);
+  if (core.count() > old.size()) {
+    // rotate untransmuted mats back to back of buffer
+    core.Push(core.PopN(core.count() - old.size()));
+  }
 
   std::stringstream ss;
   ss << old.size() << " assemblies";
@@ -326,13 +382,12 @@ std::map<std::string, MatVec> Reactor::PeekSpent() {
 }
 
 bool Reactor::Discharge() {
-  if (n_assem_spent - spent.count() < n_assem_batch) {
+  int npop = std::min(n_assem_batch, core.count());
+  if (n_assem_spent - spent.count() < npop) {
     Record("DISCHARGE", "failed");
     return false;  // not enough room in spent buffer
   }
 
-  int npop = std::min(n_assem_batch, core.count());
-
   std::stringstream ss;
   ss << npop << " assemblies";
   Record("DISCHARGE", ss.str());
diff --git a/src/reactor.h b/src/reactor.h
index 8d9cfcecf4..a6aa645dbf 100644
--- a/src/reactor.h
+++ b/src/reactor.h
@@ -42,6 +42,15 @@ namespace cycamore {
 /// becomes full, the reactor will halt operation at the end of the next cycle
 /// until there is more room.  Each time step, the reactor will try to trade
 /// away as much of its spent fuel inventory as possible.
+///
+/// When the reactor reaches the end of its lifetime, it will discharge all
+/// material from its core and trade away all its spent fuel as quickly as
+/// possible.  Full decommissioning will be delayed until all spent fuel is
+/// gone.  If the reactor has a full core when it is decommissioned (i.e. is
+/// mid-cycle) when the reactor is decommissioned, half (rounded up to nearest
+/// int) of its assemblies are transmuted to their respective burnt
+/// compositions.
+
 class Reactor : public cyclus::Facility,
   public cyclus::toolkit::CommodityProducer {
 #pragma cyclus note { \
@@ -83,7 +92,16 @@ class Reactor : public cyclus::Facility,
   " operational cycle before the next begins.  If the spent fuel inventory" \
   " becomes full, the reactor will halt operation at the end of the next cycle" \
   " until there is more room.  Each time step, the reactor will try to trade" \
-  " away as much of its spent fuel inventory as possible.", \
+  " away as much of its spent fuel inventory as possible." \
+  "\n\n" \
+  "When the reactor reaches the end of its lifetime, it will discharge all" \
+  " material from its core and trade away all its spent fuel as quickly as" \
+  " possible.  Full decommissioning will be delayed until all spent fuel is" \
+  " gone.  If the reactor has a full core when it is decommissioned (i.e. is" \
+  " mid-cycle) when the reactor is decommissioned, half (rounded up to nearest" \
+  " int) of its assemblies are transmuted to their respective burnt" \
+  " compositions." \
+  "", \
 }
 
  public:
@@ -93,6 +111,7 @@ class Reactor : public cyclus::Facility,
   virtual void Tick();
   virtual void Tock();
   virtual void EnterNotify();
+  virtual bool CheckDecommissionCondition();
 
   virtual void AcceptMatlTrades(const std::vector<std::pair<
       cyclus::Trade<cyclus::Material>, cyclus::Material::Ptr> >& responses);
@@ -117,6 +136,10 @@ class Reactor : public cyclus::Facility,
   std::string fuel_outrecipe(cyclus::Material::Ptr m);
   double fuel_pref(cyclus::Material::Ptr m);
 
+  bool retired() {
+    return exit_time() != -1 && context()->time() >= exit_time();
+  }
+
   /// Store fuel info index for the given resource received on incommod.
   void index_res(cyclus::Resource::Ptr m, std::string incommod);
 
@@ -131,6 +154,10 @@ class Reactor : public cyclus::Facility,
   /// fully burnt state as defined by its outrecipe.
   void Transmute();
 
+  /// Transmute the specified number of assemblies in the core to their
+  /// fully burnt state as defined by their outrecipe.
+  void Transmute(int n_assem);
+
   /// Records a reactor event to the output db with the given name and note val.
   void Record(std::string name, std::string val);
 
@@ -335,6 +362,9 @@ class Reactor : public cyclus::Facility,
                       "internal": True \
   }
   std::map<int, int> res_indexes;
+
+  // populated lazily and no need to persist.
+  std::set<std::string> uniq_outcommods_;
 };
 
 } // namespace cycamore
diff --git a/src/reactor_tests.cc b/src/reactor_tests.cc
index 8c743e5cf4..d67d14d897 100644
--- a/src/reactor_tests.cc
+++ b/src/reactor_tests.cc
@@ -461,6 +461,52 @@ TEST(ReactorTests, RecipeChange) {
   EXPECT_TRUE(0 < mq.mass(id("H1")));
 }
 
+TEST(ReactorTests, Retire) {
+  std::string config = 
+     "  <fuel_inrecipes>  <val>lwr_fresh</val>  </fuel_inrecipes>  "
+     "  <fuel_outrecipes> <val>lwr_spent</val>  </fuel_outrecipes>  "
+     "  <fuel_incommods>  <val>enriched_u</val> </fuel_incommods>  "
+     "  <fuel_outcommods> <val>waste</val>      </fuel_outcommods>  "
+     ""
+     "  <cycle_time>7</cycle_time>  "
+     "  <refuel_time>0</refuel_time>  "
+     "  <assem_size>300</assem_size>  "
+     "  <n_assem_fresh>1</n_assem_fresh>  "
+     "  <n_assem_core>3</n_assem_core>  "
+     "  <n_assem_batch>1</n_assem_batch>  "
+     "";
+
+  int dur = 50;
+  int life = 36;
+  cyclus::MockSim sim(cyclus::AgentSpec(":cycamore:Reactor"), config, dur, life);
+  sim.AddSource("enriched_u").Finalize();
+  sim.AddSink("waste").Finalize();
+  sim.AddRecipe("lwr_fresh", c_uox());
+  sim.AddRecipe("lwr_spent", c_spentuox());
+  int id = sim.Run();
+
+  int ncore = 3;
+  int nbatch = 1;
+
+  // reactor should stop requesting new fresh fuel as it approaches retirement
+  int nassem_recv =
+      static_cast<int>(ceil(static_cast<double>(life) / 7.0)) * nbatch +
+      (ncore - nbatch);
+
+  std::vector<Cond> conds;
+  conds.push_back(Cond("ReceiverId", "==", id));
+  QueryResult qr = sim.db().Query("Transactions", &conds);
+  EXPECT_EQ(nassem_recv, qr.rows.size())
+      << "failed to stop ordering near retirement";
+
+  // reactor should discharge all fuel before/by retirement
+  conds.clear();
+  conds.push_back(Cond("SenderId", "==", id));
+  qr = sim.db().Query("Transactions", &conds);
+  EXPECT_EQ(nassem_recv, qr.rows.size())
+      << "failed to discharge all material by retirement time";
+}
+
 } // namespace reactortests
 } // namespace cycamore