Patent Number: 
Section: claims

1. A sensor for measuring electrochemical corrosion potential in a nuclear reactor comprising: a tubular ceramic probe having a closed tip at one end packed with a metal and metal oxide powder;  a metal support tube having one end receiving an opposite end of said probe, and joined thereto by a braze joint therewith;  an electrical conductor extending through said support tube and probe, and having an end buried in said powder for electrical contact therewith; and  a plasma sprayed ceramic band locally coating said probe and tube at said braze joint for sealing thereof, wherein said plasma sprayed ceramic band has a coefficient of thermal expansion that is compatible with that of said tubular ceramic probe and wherein said plasma sprayed ceramic band spaced from said probe tip. 2. A sensor according to  claim 1  wherein both said probe and band comprise zirconia. claim 1 3. A sensor according to  claim 2  wherein said probe comprises magnesia-stabilized-zirconia, and said band comprises yttria-stabilized-zirconia. claim 2 4. A sensor according to  claim 3  wherein said powder comprises iron and iron oxide. claim 3