Patent Number: 060289066
Section: claims

1. A manufacturing method of a control rod for a boiling water reactor, comprising a tie rod having a cruciform cross section, sheaths having a U-shaped cross section attached to each end of the tie rod, and hafnium rods, plates or tubes contained inside the sheaths as neutron absorber material, comprising the steps of: providing an anodic oxidation film on a surface of said neutron absorber material; and assembling said neutron absorber material in the structure of the control rod.  said film providing step is carried out in an electrolyte of ammonium borate or oxalic acid, with a conductive material as cathode and said neutron absorber material as anode.  said film providing step is carried out in an elecrolyte of ammonium borate with a direct power source of 10-300V, with a platinum or stainless steel as cathode and said neutron absorber material as anode.  with a first cathode material inserted into the hafnium tube in order to provide an anodic oxidation film on inside surface of the hafnium tube;  a second cathode material is provided outside the hafnium tube in order to provide an anodic oxidation film on an outer surface of the hafnium tube and said neutron absorber material as anode. 2. A manufacturing method of a control rod for a boiling water reactor as claimed in claim 1, wherein, 3. A manufacturing method of a control rod for a boiling water reactor as claimed in claim 1, wherein, 4. A manufacturing method of a control rod for a boiling water reactor as claimed in claim 1, wherein, said film providing step is carried out by soaking gradually said neutron absorber material in an electrolyte for forming gradually said ahodic oxidation film on said surface of said neutron absorber material. 5. A manufacturing method of a control rod for a boiling water reactor as claimed in claim 1, wherein, said film providing step is carried out in an electrolyte,