diff --git a/.idea/vcs.xml b/.idea/vcs.xml
index 35eb1dd..7739d98 100644
--- a/.idea/vcs.xml
+++ b/.idea/vcs.xml
@@ -1,5 +1,11 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="GitSharedSettings">
+    <option name="FORCE_PUSH_PROHIBITED_PATTERNS">
+      <list />
+    </option>
+    <option name="synchronizeBranchProtectionRules" value="false" />
+  </component>
   <component name="VcsDirectoryMappings">
     <mapping directory="" vcs="Git" />
   </component>
diff --git a/examples/shield test.ncpf.json b/examples/shield test.ncpf.json
new file mode 100644
index 0000000..471fba3
--- /dev/null
+++ b/examples/shield test.ncpf.json	
@@ -0,0 +1 @@
+{"addons":[],"configuration":{"nuclearcraft:overhaul_sfr":{"blocks":[{"name":"nuclearcraft:solid_fission_controller","type":"legacy_block"},{"name":"nuclearcraft:fission_vent","type":"legacy_block","blockstate":{"active":false}},{"name":"nuclearcraft:fission_vent","type":"legacy_block","blockstate":{"active":true}},{"name":"nuclearcraft:fission_casing","type":"legacy_block"},{"name":"nuclearcraft:fission_glass","type":"legacy_block"},{"metadata":2,"name":"nuclearcraft:fission_source","type":"legacy_block","blockstate":{"type":"californium"}},{"name":"nuclearcraft:solid_fission_cell","type":"legacy_block","modules":{"ncpf:block_recipes":{"recipes":[{"oredict":"ingotHEU233ZA","type":"oredict"}]}}},{"name":"nuclearcraft:fission_cell_port","type":"legacy_block","blockstate":{"active":false},"modules":{"ncpf:block_recipes":{"recipes":[{"oredict":"ingotHEU233ZA","type":"oredict"}]}}},{"name":"nuclearcraft:fission_cell_port","type":"legacy_block","blockstate":{"active":true},"modules":{"ncpf:block_recipes":{"recipes":[{"oredict":"ingotHEU233ZA","type":"oredict"}]}}},{"name":"nuclearcraft:heavy_water_moderator","type":"legacy_block"},{"metadata":0,"name":"nuclearcraft:fission_shield","type":"legacy_block","blockstate":{"active":false,"type":"boron_silver"}},{"metadata":0,"name":"nuclearcraft:fission_shield","type":"legacy_block","blockstate":{"active":true,"type":"boron_silver"}}],"coolant_recipes":[{"elements":[{"name":"water","type":"legacy_fluid"},{"name":"condensate_water","type":"legacy_fluid"}],"type":"list"}]}},"designs":[{"design":[[[3,3,3,3,3,3,3,3,3],[3,0,1,2,7,8,4,4,3],[3,4,4,4,4,4,4,4,3],[3,4,4,4,4,4,4,4,3],[3,4,4,4,4,4,4,4,3],[3,4,4,4,4,4,4,4,3],[3,3,3,3,3,3,3,3,3]],[[3,5,4,4,4,4,4,4,3],[4,6,-1,-1,-1,6,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[3,4,4,4,4,4,4,4,3]],[[3,4,4,4,4,4,4,4,3],[4,9,-1,-1,-1,9,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[3,4,4,4,4,4,4,4,3]],[[3,4,4,4,4,4,4,4,3],[4,10,-1,-1,-1,10,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[3,4,4,4,4,4,4,4,3]],[[3,4,4,4,4,4,4,4,3],[4,9,-1,-1,-1,9,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[3,4,4,4,4,4,4,4,3]],[[3,4,4,4,4,4,4,4,3],[4,6,9,11,9,6,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[3,4,4,4,4,4,4,4,3]],[[3,4,4,4,4,4,4,4,3],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[3,4,4,4,4,4,4,4,3]],[[3,4,4,4,4,4,4,4,3],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[4,-1,-1,-1,-1,-1,-1,-1,4],[3,4,4,4,4,4,4,4,3]],[[3,3,3,3,3,3,3,3,3],[3,4,4,4,4,4,4,4,3],[3,4,4,4,4,4,4,4,3],[3,4,4,4,4,4,4,4,3],[3,4,4,4,4,4,4,4,3],[3,4,4,4,4,4,4,4,3],[3,3,3,3,3,3,3,3,3]]],"block_recipes":[[[0,0]],[[0,0]],[[0,0]]],"type":"nuclearcraft:overhaul_sfr","coolant_recipe":0,"dimensions":[9,7,9]}],"version":1}
\ No newline at end of file
diff --git a/index.html b/index.html
index 7e47541..66a4bc6 100644
--- a/index.html
+++ b/index.html
@@ -126,7 +126,7 @@
   </section>
 </aside>
 <footer>
-  <div>alpha 1.7</div>
+  <div>alpha 1.8</div>
   <div>
     <a href="https://discord.gg/Eq72HwPqfg">Discord server</a>
   </div>
diff --git a/scripts/dev-mode.js b/scripts/dev-mode.js
index 21948f3..48b97c4 100644
--- a/scripts/dev-mode.js
+++ b/scripts/dev-mode.js
@@ -39,7 +39,7 @@ registerLoadCallback(() => {
   });
 
   awaitEvent("config:end").then(() => {
-    void loadExampleFile("Pandora's Fission Reactor");
+    void loadExampleFile("shield test");
   });
 
   queueMicrotask(() => emitEvent("dev-mode:end"));
diff --git a/scripts/overlays.js b/scripts/overlays.js
index 786bb9c..69af7b3 100644
--- a/scripts/overlays.js
+++ b/scripts/overlays.js
@@ -3,6 +3,8 @@ import { getAtlasIndexFromMetadata, makeAtlasImage } from "./atlas.js";
 
 export function processCellOverlays(node, key = null, added = null) {
   if (key) {
+    node.replaceChildren(...node.querySelectorAll(`:scope > *:not([data-overlay="${key}"])`));
+
     const metadata = getCellMetadata(node, key);
     const atlasIndex = getAtlasIndexFromMetadata(metadata);
     if (atlasIndex && atlasIndex !== -1) {
@@ -12,15 +14,10 @@ export function processCellOverlays(node, key = null, added = null) {
       node.appendChild(overlayNode);
     }
 
-    if (key === "active" && metadata) {
+    if (key === "active" && added) {
       const overlayNode = makeAtlasImage(-1);
       overlayNode.dataset.overlay = key;
-      overlayNode.classList.add("planner--overlay");
-      node.appendChild(overlayNode);
-    }
-    if (key === "active" && !metadata) {
-      const overlayNode = makeAtlasImage(-1);
-      overlayNode.dataset.overlay = "inactive";
+      overlayNode.dataset.active = metadata ? "true" : "false";
       overlayNode.classList.add("planner--overlay");
       node.appendChild(overlayNode);
     }
diff --git a/scripts/solver.js b/scripts/solver.js
index 415cc2d..c311cf6 100644
--- a/scripts/solver.js
+++ b/scripts/solver.js
@@ -7,11 +7,14 @@ import {
   getPlannerMultiblockType
 } from "./planner.js";
 import { checkEquivalence, findFullEntry, findFullEntryFromAtlasMetadata } from "./ncpf-utils.js";
-import { deleteMetadata, getMetadata, setCellMetadata, setDomMetadata } from "./metadata.js";
+import { clearCellMetadata, deleteMetadata, getMetadata, setCellMetadata, setDomMetadata } from "./metadata.js";
 import { registerLoadCallback } from "./main.js";
 import { getAtlasMetadata } from "./atlas.js";
 import { initialize3dArray } from "./js-utils.js";
 
+const SFR_MODERATOR_MAX_LEN = 3;
+const SFR_MODERATOR_REFLECTOR_MAX_LEN = 2;
+
 registerLoadCallback(() => {
   listenTo("fileLoad:end", runSolver);
   listenTo("planner:cell:change", runSolver);
@@ -95,7 +98,8 @@ async function debugBlockSolver(data) {
 }
 
 export async function runSolver() {
-  emitEvent("solver:begin")
+  const startTime = performance.now()
+  emitEvent("solver:begin");
 
   const multiblockType = getPlannerMultiblockType();
 
@@ -107,6 +111,7 @@ export async function runSolver() {
       .map(idx => [idx, getAtlasMetadata(idx)])
       .map(([idx, md]) => [idx, findFullEntry("blocks", md, { configurationHint: multiblockType })]));
   plannerBlocks.forEach(v => v.tile = tileMap[v.tile]);
+  plannerBlocks.forEach(v => clearCellMetadata(v.dom, "active"));
 
   const plannerBlocksGrid = initialize3dArray(...getPlannerMultiblockSize());
   plannerBlocks.forEach(b => {
@@ -167,46 +172,70 @@ export async function runSolver() {
     while (activeCellIndex < activeCells.length) {
       const cell = activeCells[activeCellIndex];
       if (!cell.axes) return; // ignore bad cells
-      Object.keys(sixAxes).map((name, i) => {
-        let moderatorSum = 0;
+      Object.keys(sixAxes).map((directionName, i) => {
+        let valid = false;
         let moderatorPath = [];
+        let length = 0;
+        let reflectMultiplier = 1;
+        let reflect = false;
+        let fluxDestination;
         for (const block of cell.axes[i]) {
           if (!block) break;
 
           if (block.tile.modules["nuclearcraft:overhaul_sfr:moderator"]) {
-            moderatorSum += block.tile.modules["nuclearcraft:overhaul_sfr:moderator"].flux;
             moderatorPath.push(block);
             seenModerators.add(block);
-            if (!block.flux) {
-              block.flux = {};
-            }
-            block.flux[name] = moderatorSum;
+            length += 1;
+            continue;
+          }
+          if (block.tile.modules["nuclearcraft:overhaul_sfr:neutron_shield"]) {
+            length += 1;
             continue;
           }
           if (block.tile.modules["nuclearcraft:overhaul_sfr:fuel_cell"] || block.tile.modules["nuclearcraft:overhaul_sfr:irradiator"]) {
-            block.flux = (block.flux ?? 0) + moderatorSum;
+            valid = length <= SFR_MODERATOR_MAX_LEN;
+            fluxDestination = block;
           }
           if (block.tile.modules["nuclearcraft:overhaul_sfr:reflector"]) {
-            const backAxis = name.replace(/^[+-]/, s => s === "+" ? "-" : "+");
-            for (const blockBack of moderatorPath.toReversed()) {
-              moderatorSum += blockBack.tile.modules["nuclearcraft:overhaul_sfr:moderator"].flux;
-              moderatorPath.push(blockBack);
-              blockBack.flux[backAxis] = moderatorSum;
-            }
-            cell.flux = (cell.flux ?? 0) + moderatorSum;
-          }
-          if (block.tile.modules["nuclearcraft:overhaul_sfr:fuel_cell"] && !block.active) {
-            if (!block.recipe) break; // FIXME
-            const fuelStats = block.recipe.modules["nuclearcraft:overhaul_sfr:fuel_stats"];
-            if (fuelStats.criticality <= block.flux) {
-              block.active = true;
-              activeCells.push(block);
-            }
+            valid = length <= SFR_MODERATOR_REFLECTOR_MAX_LEN;
+            reflect = true;
+            reflectMultiplier = block.tile.modules["nuclearcraft:overhaul_sfr:reflector"].reflectivity;
+            console.log(reflectMultiplier)
+            fluxDestination = cell;
           }
           break;
         }
-        if (moderatorPath.length > 0) {
-          moderatorPath[0].active = true;
+        if (moderatorPath.length < 1) {
+          valid = false;
+        }
+        if (!valid) return;
+
+        moderatorPath[0].active = true;
+        let totalFlux = 0;
+        for (const mod of moderatorPath) {
+          totalFlux += mod.tile.modules["nuclearcraft:overhaul_sfr:moderator"].flux;
+          if (!mod.flux) {
+            mod.flux = {};
+          }
+          mod.flux[directionName] = totalFlux;
+        }
+        if (reflect) {
+          totalFlux *= reflectMultiplier;
+          const backAxis = directionName.replace(/^[+-]/, s => s === "+" ? "-" : "+");
+          for (const mod of moderatorPath.toReversed()) {
+            totalFlux += mod.tile.modules["nuclearcraft:overhaul_sfr:moderator"].flux * reflectMultiplier;
+            mod.flux[backAxis] = totalFlux;
+          }
+        }
+        fluxDestination.flux = (fluxDestination.flux ?? 0) + totalFlux;
+
+        if (fluxDestination.tile.modules["nuclearcraft:overhaul_sfr:fuel_cell"] && !fluxDestination.active) {
+          if (!fluxDestination.recipe) return; // FIXME
+          const fuelStats = fluxDestination.recipe.modules["nuclearcraft:overhaul_sfr:fuel_stats"];
+          if (fuelStats.criticality <= fluxDestination.flux) {
+            fluxDestination.active = true;
+            activeCells.push(fluxDestination);
+          }
         }
       });
 
@@ -249,7 +278,8 @@ export async function runSolver() {
           if (n.tile.modules) {
             return n.tile.modules["nuclearcraft:overhaul_sfr:reflector"]
                 || n.tile.modules["nuclearcraft:overhaul_sfr:irradiator"]
-                || n.tile.modules["nuclearcraft:overhaul_sfr:casing"];
+                || n.tile.modules["nuclearcraft:overhaul_sfr:casing"]
+                || n.tile.modules["nuclearcraft:overhaul_sfr:neutron_shield"];
           }
           return false;
         });
@@ -277,6 +307,9 @@ export async function runSolver() {
 
     await debugBlockSolver("heatsinks");
   }
+
+  const endTime = performance.now()
+  console.log(`Solver took ${endTime - startTime}ms`);
 }
 
 function checkHeatSinkRule(hs, rule, activeNeighbors) {
diff --git a/style.css b/style.css
index d31436d..08cc605 100644
--- a/style.css
+++ b/style.css
@@ -271,11 +271,11 @@ input:not([type="checkbox"]):not([type="radio"]):not([type="file"]) {
 .planner--cell > .planner--overlay[data-overlay="block_recipe"] {
     transform: scale(var(--recipe-scale-factor, 0.8));
 }
-#planner .planner--cell > .planner--overlay[data-overlay="active"] {
+#planner .planner--cell > .planner--overlay[data-overlay="active"][data-active="true"] {
     outline-offset: calc(var(--scale-factor) * -1px);
     outline: calc(var(--scale-factor) * 1px) solid var(--cell-active-outline, #0f08);
 }
-#planner .planner--cell > .planner--overlay[data-overlay="inactive"] {
+#planner .planner--cell > .planner--overlay[data-overlay="active"][data-active="false"] {
     outline-offset: calc(var(--scale-factor) * -1px);
     outline: calc(var(--scale-factor) * 1px) solid var(--cell-inactive-outline, #f008);
 }