IMPACT OF RESTRAINED THERMAL EXPANSION ON NPP KRSKO PRIMARY LOOP PIPING

Mechanical analyses of the Krsko NPP primary system piping subjected to the restrained thermal expansion due to insufficient pipe shim clearances are addressed in the paper. Reduction of clearance between a pipe and respective pipe restraints preclude free thermal expansion of the pipe system during the heat-up, thus causing a rise of excessive contact forces in the pipe - pipe restraint pairs. This results in a development of unfavourable strains and stresses both in pipes and restraints. A series of numerical simulations was performed which demonstrate sufficient strength resistance of the Krsko NPP primary piping, while supports are much more susceptible and need careful engineering consideration.Original Abstract: U ovom radu opisane su mehanicke analize primarnog cjevovoda Nuklearne elektrane Krsko, koje obraduju problem djelomicno onemogucene termicke ekspanzije cjevovoda uslijed nedovoljnog razmaka medu plocama ogranicavaca pomaka cijevi. Smanjenje razmaka izmedu cijevi i pripadajuceg oslonca sprijecava slobodno termicko prosirenje cjevovoda tijekom zagrijavanja sistema. Time se prouzrokuju jake tlacne sile izmedu cijevi i oslonaca, sto se rezultira kao nepovoljno stanje deformacija i naprezanja i u cjevovodu i u potporama. Izvedene su serije numerickih simulacija, koje potvrduju dovoljnu cvrstocu primarnog cjevovoda Nuklearne elektrane Krsko. Medutim, oslonci su puno vise osjetljivi na opterecenja te vrste i stoga je za njih potrebno izvesti brizljivo konstrukcijsko razmatranje.