Detection gross and Fine Leaks in Nuclear Fuel Elements

摘要

Nuclear fuel tightness of light water reactor is a necessary requirement ofrntheir successful operation and safety. Therefore a series of strict nondestructivernmonitoring methods apply to constructional materials and jointrnwelds of fuel elements on their production. Besides they use helium leakrntesting of all manufactured fuel rods. However this aspect of monitoring hasrnthe features, which need to be taken into account at its using.rnThe leak testing method has both low detection limit for fine leakage andrnupper limit for gross leakage. Each kind of leakage has its optimal testingrnconditions for detection. Sometimes preferably to carry out gross leaksrntesting by separate stage and may be done by another method, for example byrnmanometric one.rnBehavior of the leaky fuel rods of different types during manufacturing andrnoperation is investigated completely. Therefore in some cases a fuelrndesigners shell to carry out leak tests under elevated temperature. Hot leakrndetection has additional problems of suitability estimation of fuelrnelements. It is necessary to have temperature correlation for leakage flowrnrate.rnThe rigour requirements to fuel rod tightness and on the other hand the lackrnof a noticeable amount of rejected product provoke necessity of leakrnsimulation and determination of their behavior under different conditions.rnThere is special computer code developed by Moscow research instituternVNIINM, which allow to do it in dependence of defect size. It is convenientrnto consider all questions of leaky fuel detection on base of conditionalrndefect size which is equal to real one with same leak flow.rnSome results on mentioned questions, obtained at Novosibirsk ChemicalrnConcentrates Plant, which have allowed manufacturing of non-defective VVERrnfuel rods, are given in this report.