THIS PROPOSAL SEEKS TO INCREASE THE TRL OF NUCLEAR THERMAL PROPULSION SPECIFICALLY IN THE AREA OF ADVANCED COATING TECHNOLOGY. ATOMIC LAYER DEPOSITION (ALD) WILL BE USED TO APPLY A PINHOLE-FREE CONFORMAL NANOFILM TO BOTH FUEL PARTICLES AND FUEL ELEMENT CLADDING INCLUDING THE HIGH ASPECT RATIO HYDROGEN FLOW CHANNELS. THE FILM WILL ACT AS A BARRIER TOWARDS HYDROGEN DIFFUSION TO REDUCE EMBRITTLEMENT OF THE UNDERLYING CERMET FUEL. THIS WILL EXTEND THE LIFE OF THE FUEL AND PREVENT THE RELEASE OF HAZARDOUS FISSION PRODUCTS. THINNER FILMS ALSO HAVE A DECREASED THERMAL DIFFUSION RESISTANCE AND INCREASED ELASTICITY. GIVEN THE WEIGHT AND VOLUME RESTRICTIONS OF SPACECRAFT ALD NANOFILMS ARE IDEAL COATINGS. TUNGSTEN (W) MOLYBDENUM(MO) AND ALLOYS OF THE TWO ELEMENTS WILL BE USED TO FORM NANOFILMS VIA ALD FIRST ON SURROGATE FUEL PARTICLES AND THEN ON URANIUM FUEL PARTICLES. ALD OF CHEMICALLY-BONDED NANOFILMS UTILIZES SELF-LIMITING SURFACE REACTIONS TO ACHIEVE UNIFORM FILMS WITH THICKNESS DEPENDENT ON THE NUMBER OF ALD CYCLES. THE HIGH CONTROL OF THICKNESS ALLOWS FOR THE MINIMUM AMOUNT OF MATERIAL TO BE USED. SURROGATE FUEL PARTICLES WILL BE COATED AT THE UNIVERSITY OF COLORADO (CU) FOR COMPARING BARRIER MATERIALS AND FOR PROOF-OF-CONCEPT TESTING. ONCE SURROGATE TESTING IS COMPLETE A NEW ALD PROCESSING SYSTEM WILL BE CONSTRUCTED AT IDAHO NATIONAL LAB (INL) TO COAT URANIUM FUEL AND URANIUM FUEL ELEMENTS WITH THE BEST-PERFORMING MATERIAL. AFTER DEPOSITION ON SURROGATE PARTICLES FILMS WILL BE CHARACTERIZED AT CU TO ENSURE FULL COVERAGE AND MEASURE FILM THICKNESS. THE COATED SURROGATE PARTICLES WILL BE FORMED INTO FUEL ELEMENT SECTIONS AT INL WHICH WILL THEN BE RETURNED TO CU TO BE COATED WITH THE SAME ALD CHEMISTRY. THE COATED SECTION WILL THEN BE RETURNED TO INL FOR FILM EFFICACY TESTING USING THERMAL CYCLING. IN ADDITION HOT HYDROGEN TESTING WILL BE PERFORMED USING CFEET AT NASA MARSHALL SPACE FLIGHT CENTER. STATE OF THE ART TECHNOLOGY FOR PROTECTING FISSION MATERIAL CURRENTLY USES CHEMICAL VAPOR DEPOSITION (CVD) AND POST-PROCESSING. CVD ALLOWS FOR GAS PHASE REACTIONS SINCE IT DOSES SUBSTRATES WITH MORE THAN ONE PRECURSOR SIMULTANEOUSLY. THIS RESULTS IN THE DEPOSITION OF NANOPARTICLES AND POROUS FILMS WHICH OFTEN DELAMINATE FROM THE SUBSTRATE. TYPICALLY ANNEALING IS REQUIRED TO REDUCE POROSITY AND HELP BOND THE COATING TO THE SUBSTRATE. BY ITS NATURE CVD WILL CLOG ENTRANCES OF HIGH ASPECT RATIO CHANNELS. ALD HOWEVER WILL COAT THE LENGTH OF THE CHANNEL AND LITERATURE AS WELL AS CU REPORTS 100% COVERAGE OF SURFACES AND OF HIGH ASPECT RATIO PORES. THE REDUCTION IN FILM THICKNESS FROM MICRONS TO NANOMETERS WITH RESPECT TO CVD MEANS LESS FUNDS WASTED ON PRECURSORS LESS FUEL VOLUME DISPLACED BY COATINGS AND LESS OVERALL WEIGHT OF COATING REQUIRED. MATERIALS TESTED EXPERIMENTALLY WILL ALSO BE ANALYZED COMPUTATIONALLY. DENSITY FUNCTIONAL THEORY SPECIFICALLY NUDGED ELASTIC BAND METHOD WILL BE USED TO CALCULATE ENERGY BARRIERS TOWARDS ELEMENTAL HYDROGEN DIFFUSION. THE HIGHER THE THEORETICAL BARRIER THE HIGHER THE LIKELIHOOD OF THE COATING PREVENTING HYDROGEN EMBRITTLEMENT. THIS METHOD WILL ALSO BE USED TO PREDICT MATERIALS IN ADDITION TO W AND MO MOLECULAR DYNAMICS WILL BE USED TO SIMULATE HEATING OF THE COATING AND POTENTIAL DELAMINATION OR CRACKING. THESE COMPUTATIONAL STUDIES WILL INCREASE UNDERSTANDING OF HYDROGEN DIFFUSION. USING ALD FOR NANOFILM BARRIER COATINGS ON FUEL PARTICLES AND FUEL ELEMENTS WILL RAISE THE TRL OF NPT FUEL AND DECREASE THE COMPLEXITY OF FUEL ELEMENT FABRICATION. DEVELOPMENT AND CHARACTERIZATION OF EFFICIENT COATINGS CAN BE EXTENDED TO USES BEYOND THIS PARTICULAR APPLICATION. ALD COATINGS OF PROPOSED MATERIALS CAN ADDITIONALLY BE USED ON HYDROGEN CONDUITS AND STORAGE VESSELS. FURTHER ALD NANOSOLUTIONS A SPINOFF COMPANY OUT OF CU IS CURRENTLY WORKING WITH MAJOR GLOBAL INDUSTRIES TO COMMERCIALIZE THE CORE/SHELL ALD PARTICLE PROCESSING AND HAS SUPPLIED EQUIPMENT TO LLNL FOR CONFIDENTIAL APPLICATIONS.