PWRs usually report activity per unit volume of coolant, e.g., μCi/ml, or per unit mass μCi/mg, at least in the US. Activities are often reported for the Xe (133, 135, 138) isotopes, five iodine radioisotopes (131-135), Cs (134, 137) usually at shutdown, and Np-239.
Occasional leaking fuel is expected, even though utilities and their suppliers strive for zero defects. Plants are designed to handle a certain number of failures, but it is undesirable to have even one leaking (breach cladding) fuel rod.
Some failures coincident with a startup or restart may be indicative of debris failures, in which foreign objects, e.g., wire, from maintenance operations may become lodged in the fuel where the debris may wear (fret) a hole into the cladding. Otherwise, grid-to-rod fretting has a been a recent (last 20 years) problem for some plants and/or fuel designs. Activated crud (corrosion products) may also be an issue for some plants. Sometimes at shutdown, reactor cores might experience a crud burst. Rarely, one might find failures do to bad seal weld or primary hydriding (rod internal hydriding due to hydrogenous material contamination).Ukraine denies radioactive leak on Zaporizhzhya nuclear plant
http://news.yahoo.com/ukraine-denies-radioactive-leak-zaporizhzhya-nuclear-plant-195020745.html
http://www.reuters.com/article/2014/12/03/us-ukraine-crisis-power-minister-idUSKCN0JH12M20141203
It may take some time to get to the bottom of this. There is no reason that Westinghouse fuel should be less safe than Russian fuel. They are nominally the same. Coolability and reactivity control would be essentially the same.
Not sure about the use of Westinghouse fuel. If it was fresh, it would
not be the cause of a radiation leak. The older (Russian) fuel could be a source of radiation if the cladding was breached.
It would help to know which unit. One unit may be down for refueling.