Patent Number: 050283847
Section: description

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawing, a water cooled, boiling water nuclear fission reactor plant 10 for producing steam is shown combined with a steam powered turbine driving an electrical power generator. The nuclear fission reactor plant 10, as is typical, comprises a containment structure 12 housing the nuclear reactor and isolating the radioactive material and radiation produced products from the outer environment as a safety precaution. Housed within the protective containment structure 12 is the reactor pressure vessel 14 containing a core 16 of fissionable fuel. Circulating coolant water surrounds at least a majority of the reactor fuel core 16. Control rods 18 regulate the neutron sustained fission reaction of the fissionable fuel of the core 16, and in turn the occurrence and level of heat producing fuel fission for forming steam from the circulating coolant water. A steam separator and dryer system 20 is positioned above the fission heat emitting fuel 16 which produces steam from the surrounding coolant water, whereby the steam vapor rising from the fuel core is released from entrained liquid. Thus, the hot pressurized, steam discharged from the reactor pressure vessel is essentially free of ineffectual and corrosion causing liquid water, and thus suitable for turbine driving service. The dry steam vapor from the reactor pressure vessel 14 is passed through steam conduit 22 to a steam turbine 24, producing rotary movement which is transferred to an electrical generator 26 for producing electrical power. The spent steam exhausted from the turbine 24, now reduced to low pressure, is passed to a steam condenser 30 where it is cooled and converted to liquid form from recycling back through a condensed coolant water return conduit 32 to the pressure vessel 14 for reuse. Thus the coolant water, in the form of liquid or of gaseous steam, continuously circulation through the coolant system, removing heat energy from the heat producing fuel for the formation of steam, which in turn drives the turbine 24, is condensed back to liquid form, and returned to repeat the cycle. A practiced measure for inhibiting corrosion of certain types in nuclear reactor coolant water circulating systems such as described, consists of adding hydrogen to the recycling water as a means for reducing the free oxygen content, at least a portion of which is the result of radiation induced dissociation of some of the water. Accordingly, a hydrogen feed supply 34 can be provided to feed hydrogen into the coolant water system, such as into the condensed coolant water return conduit 32. However, as noted above, there is a negative effort to increasing the hydrogen concentration of the reactor coolant water. Hydrogen apparently promotes the conversion of non-volatile nitrogen compounds present in the coolant water to volatile nitrogen compounds such as ammonia. As noted, this phenomenon coupled with the radiations induced transmutation of oxygen atoms to the gamma ray emitting nitrogen16 isotope, results in volatile radioactive nitrogen compounds in the reactor coolant system. Such volatile radioactive nitrogen compounds, for example ammonia, entrained in the steam are carried beyond the reactor pressure vessel and the radiation retaining containment structure 12 and through the complete coolant circulating system. Thus, gamma ray emitting material passes through the turbine of power generating unit increasing the radiation level in the plant facility outside the enclosing protective containment 12. It has been observed, for example, that radiation levels within the steam system have been increased up to approximately five fold due to such circumstances. In accordance with this invention, the conveyance of radiation emitting volatile material, such as ammonia comprising the nitrogen16 isotope, out from the reactor pressure vessel and throughout the steam system including the steam turbine, thereby raising the radiation level outside the reactor containment and within the turbine/generator facility, is inhibited and controlled. Nitrogen containing compounds comprising any nitrogen16 isotope, in more volatile forms such as ammonia, are oxidized to non-volatile, water soluble forms comprising nitrates (NO-3) and/or nitrites (NO-2) by catalytic oxidation within the reactor pressure vessel to preclude their escape with the emerging steam. Oxidizing catalysts for use in the practice of this invention comprise metallic oxides having surfaces with oxidizing catalytic properties, such as oxides of group B metals of the periodic chart of elements, namely titanium dioxide and zirconium dioxide. Such catalytic oxidizing metals can be applied in the practice of this invention is a variety of arrangements for achieving the objective and advantages of chancing the safety of reactor plant operating and/or maintenance personnel performing outside of the protective reactor containment structure. One embodiment for the practice of this invention comprises constructing at least a potion or the conventional steam separator and/or dryer units from titanium or zirconium metal and oxidizing apt portion of it surface to provide the means for catalytic oxidation of ammonia to nitrates and/or nitrites. Another embodiment of this invention comprises surfacing at least a portion of the steam separator and/or dryer units, or other appropriate structure members within the reactor pressure vessel, with a suitable catalytic oxidizing metal such as titanium dioxide or zirconium dioxide. For example surfaces of conventional structural member can be plated by common means with titanium or zirconium metal, then oxidized on their exposed face. Alternatively catalytic oxidizers can be provided by affixing added component of high surface area bodies such as titanium dioxide and/or zirconium dioxide, for example metal oxide sponge, in effective locations within the reactor pressure vessel, or external thereto for catalytic oxidation prior to the steam leaving the containment structures. Such added catalytic oxidizing components can be located at any position providing high surface contract with the evolving or flowing steam and any vapor entrained therewith. According any apt arrangement will suffice whereby the produced steam and any entrained vapor are subjected to extensive contact with the surface of the catalytic oxidizing metal.