V večini vodno hlajenih jedrskih reaktorjev je med obratovanjem prisotna Čerenkova svetloba. Predvsem pri reaktorjih bazenskega tipa, med katere spada tudi reaktor TRIGA Mark II na Institutu ''Jožef Stefan'', je Čerenkova svetloba vidna s prostim očesom kot modri sij okrog sredice. Nastane kot posledica visokoenergijskih nabitih elektronov, ki potujejo skozi hladilo hitreje od hitrosti svetlobe v mediju. Meritev intenzitete Čerenkove svetlobe predstavlja osnovo pri preverjanju izrabljenosti goriva v bazenih za izrabljeno gorivo. V okviru obratovanja jedrskega reaktorja pa lahko meritev intenzitete Čerenkove svetlobe z nekaterimi omejitvami predstavlja redundantno meritev moči. V začetku naloge je predstavljeno fizikalno ozadje nastanka Čerenkove svetlobe. Sledijo principi delovanja silicijeve fotopomnoževalke, ki je bila izbrana kot detektor intenzitete svetlobe v okviru razvoja merilnika moči jedrskega reaktorja na podlagi Čerenkove svetlobe. Faze v razvoju merilnika so predstavljene in podprte z meritvami opravljenimi na reaktorju IJS TRIGA Mark II. Spektralne meritve in meritev intenzitete svetlobe v merilnem kanalu predstavljajo osnovo za izbiro komponent merilnega sistema. V okviru razvoja so nastali trije merilniki moči jedrskega reaktorja na podlagi svetlobe Čerenkova, ki so na koncu poglavja ''Razvoj in postavitev merilnega sistema'' primerjani med sabo. Razviti merilnik imenovan ''Nadgrajeni merilnik intenzitete Čerenkove svetlobe'' je bil dodobra preizkušen tako pri stacionarnem kot tudi pri pulznem delovanju jedrskega reaktorja. Vse opravljene meritve so bile primerjane z meritvami iz obstoječe jedrske instrumentacije in Fuchs-Hansen-ovim teoretičnim modelom. Iz primerjav je razvidno, da razviti merilnik deluje v skladu s snemalnikom pulzov jedrskega reaktorja, vendar z večjim dinamičnim razponom. Razviti merilnik omogoča vpogled v potek moči jedrskega reaktorja v območju nižjih pulzov, kar snemalnik pulzov v okviru jedrske instrumentacije ne omogoča. Ujemanje izmerjenih fizikalnih parametrov pulza s teoretičnim modelom je odlično. V primeru stacionarnega obratovanja reaktorja, pa je delovanje obstoječe jedrske instrumentacije boljše v primerjavi z razvitim merilnikom. V zaključku so predstavljene možnosti nadgradnje razvitega sistema v luči boljšega delovanja in pridobljeni rezultati v okviru opravljenega raziskovalnega dela. Cherenkov radiation is present in most water-cooled nuclear reactors. Especially in the case of pool-type reactors, including the TRIGA Mark II reactor at the ''Jožef Stefan'' Institute, Cherenkov light is visible as a blue glow around the reactor core. It is due to energetic charged electrons traveling faster than the speed of light in a dielectric medium. Cherenkov light intensity measurements are the basis for verification of spent nuclear fuel in spent-fuel pools for nuclear safeguards. During nuclear reactor operation, the measurement of the Cherenkov light intensity may, with some limitations, represent a possibility for reactor power monitoring. This work presents the physics of Cherenkov radiation, its production in nuclear reactors and the working principles of silicon photomultipliers. A Cherenkov light based nuclear reactor power meter is presented. Its development for the ''Jožef Stefan'' Institute TRIGA reactor is described. Spectral measurements and the measurement of light intensity in the measurement channel represent the basis for the selection of components of the developed measurement system. During the development three nuclear reactor power meters based on Cherenkov light were created. They are compared with each other at the end of the chapter ''Development and setup of the measuring system''. All measurements were compared with the Fuchs-Hansen theoretical model and measurements performed by reactor's nuclear instrumentation. The developed meter named ''Upgraded Cherenkov Light Intensity Meter'' has been thoroughly tested in both stationary and pulsed operation of the nuclear reactor. It is clear that the developed meter works in accordance with the pulse recorder of the nuclear reactor, but with a larger dynamic range. It allows insight into lower pulses, which is not possible with the pulse recorder, part of the nuclear instrumentation. The measured physical parameters of the pulse agree well with the theoretical model. In the case of stationary operation of the reactor, the performance of the existing nuclear instrumentation is better compared to the developed meter. In conclusion, possible upgrades of the developed system and obtained results are presented.