Some questions on nuclear safety of heavy-water power reactor operating in self-sufficient thorium cycle

In this paper the comparative calculations of the void coefficient have been made for different types of channel reactors for the coolant density interval 0.8-0.01 g/cm3. These results demonstrate the following. In heavy-water channel reactors, the replacement of D2O coolant by H2O, ensuring significant economic advantage, leads to the essential reducing of nuclear safety of an installation. The comparison of different reactors by the void coefficient demonstrates that at the dehydration of channels the reactivity increase is minimal for HWPR(Th), operating in the self-sufficient mode. The reduction of coolant density in channels in most cases is accompanied by the increase of power and temperatures of fuel assemblies. The calculations show that the reduction of reactivity due to Doppler effect can compensate the effect of dehydration of a channel. However, the result depends on the time dependency of heat-hydraulic processes, occurring in reactor channels in the specific accident. The result obtained in the paper confirms that nuclear safety of HWPR(Th) lies on the same level as nuclear safety of CANDU type reactors approved in practice. U ovom radu nacinjeni su uporedni proracuni koeficijenta supljine za razlicite vrste kanalnih reaktora sa gustinom hladioca u opsegu 0.8-0.01 g/cm3. Ovi rezultati pokazali su da kod teskovodnih kanalnih reaktora zamena D2O hladioca H2O hladiocem, osiguravajuci znacajne ekonomske prednosti, vodi ka bitnoj redukciji nuklearne sigurnosti postrojenja. Poredjenje razlicitih reaktora prema koeficijentu supljine pokazuje da je pri dehidraciji kanala porast reaktivnosti minimalan kod HWPR(Th) reaktora koji rade u samodovoljnom modu. Smanjenje gustine hladioca u kanalima praceno je u mnogim slucajevima porastom snage i temperature gorivnog sklopa. Proracuni pokazuju da smanjenje reaktivnosti usled Doplerovog efekta moze da nadomesti efekte dehidracije kanala. Medjutim, rezultati zavise od vremenski zavisnih toplotnohidraulickih procesa koji nastaju u reaktorskim kanalima u specificnom akcidentu. Rezultati dobijeni u radu potvrdjuju da je nuklearna sigurnost HWPR(Th) reaktora na istom nivou kao nuklearna sigurnost KANDU reaktora koja je potvrdjena u praksi.