Patent Number: 
Section: claims

1. A nuclear reactor, comprising:a nuclear fuel rod comprising a zirconium alloy tube;cladding on the nuclear fuel rod,the cladding comprising a layer coated on an outer surface of the zirconium alloy tube,wherein, under standard operating conditions that include a temperature of about 300° C., the layercomprises a homogenous polycrystalline diamond layer formed by chemical vapor deposition,is from 100 nm to 50 μm thick,includes crystalline cores, sizes thereof being in the range from 10 nm to 500 nm,has a maximum content of non-diamond carbon of 25 mol %,has a maximum total content of non-carbon impurities of 0.5 mol %,has a RMS surface roughness value less than 40 nm, andhas a thermal conductivity of the layer ranges from 1000 to 1900 W·m−1·K−1, andwherein, when the nuclear reactor is operated at a temperature above 850° C., the polycrystalline diamond layer undergoes a phase change and is transformed into a mixture of crystalline graphite, amorphous carbon, and graphene,wherein the transformation is configured to consume environment energy to lower environment temperature. 2. The nuclear reactor as set forth in claim 1, wherein the mixture forms a carbide. 3. The nuclear reactor as set forth in claim 1, wherein, after operation at a temperature above 1100° C., a thermally transformed carbon layer comprises a mixture of carbon, oxygen, and atoms from the zirconium alloy tube. 4. A method of protecting a nuclear reactor against corrosion, comprising:providing in the nuclear reactor a nuclear fuel rod comprising a zirconium alloy tube;providing cladding on the nuclear fuel rod,the cladding comprising a layer coated on an outer surface of the zirconium alloy tube,wherein, under standard operating conditions that include a temperature of about 300° C., the layercomprises a homogenous polycrystalline diamond layer formed by chemical vapor deposition,is from 100 nm to 50 μm thick,includes crystalline cores, sizes thereof being in the range from 10 nm to 500 nm,has a maximum content of non-diamond carbon of 25 mol %,has a maximum total content of non-carbon impurities of 0.5 mol %,has a RMS surface roughness value less than 40 nm, andhas a thermal conductivity of the layer ranges from 1000 to 1900 W·m−1·K−1;wherein, when the nuclear reactor is operated at a temperature above 850° C., the polycrystalline diamond layer undergoes a phase change and is transformed into a mixture of crystalline graphite, graphene, amorphous carbon, and atoms from the zirconium alloy tube,wherein the transformation is configured to consume environment energy to lower environment temperature,operating the nuclear reactor so that the polycrystalline diamond layer is still present and shows partial graphitization and amorphization. 5. The method as set forth in claim 4, comprising operating the nuclear reactor at a temperature above standard operating conditions so that the polycrystalline diamond layer undergoes a phase change and is transformed into a mixture of crystalline graphite, graphene, amorphous carbon, and atoms from the zirconium alloy tube. 6. The method as set forth in claim 5, wherein the mixture includes a carbide. 7. The method as set forth in claim 5, wherein the temperature above standard operating conditions is above 850° C.