Validation and Application of the AC2 Code COCOSYS

The GRS program package AC2 with its codes ATHLET/ATHLET-CD and COCOSYS aims for the reliable computational simulation of significant phenomena occurring during normal operation, design basis accidents, and severe accidents in the cooling circuit and containment of a nuclear power plant. To keep the modelling at the state-of-the-art, continuous development and validation is required. This is accomplished through participation in several national and international experimental research programs, where AC2 or one of its codes are assessed against both separate effect tests and integral tests. This paper exemplifies the status of validation and application of COCOSYS by means of calculations of iodine chemistry and molten corium/concrete interaction after reactor pressure vessel rupture. Further, calculations using the external 3D module CoPool coupled to COCOSYS on thermal stratification in large water pools are discussed. The examples given demonstrate the progress of the COCOSYS development and the capability to simulate phenomena in the containment during incidents and accidents with good results. Future applications comprise the entire spectrum of incidents and accidents for Generation III/III+ systems with just one program package.

Study on severe accidents and countermeasures for VVER-1000 reactors using the integral code ASTEC

The research field focussing on the investigations and the analyses of postulated severe accidents is an important part of the nuclear safety. To maintain the safety barriers as long as possible and to retain the radioactivity within the airtight premises of the containment, to avoid or mitigate the consequences of such events and to assess the risk, thorough studies are needed. This paper is focused on the possibilities for accident management measures in case of severe accidents. The analyses performed with the integral code ASTEC cover two accident sequences which could lead to a severe accident: a small break loss of coolant accident and a station blackout. The discussed issues concern the main phenomena during the early and late in-vessel phase of the accidents, the time to core heat-up, the hydrogen production, the mass of corium in the reactor pressure vessel lower plenum and the failure of the reactor pressure vessel. Additionally, possible operator's actions and countermeasures in the preventive or mitigative domain are addressed.

Investigation on primary side oriented accident management measures in a hypothetical station blackout scenario for a VVER-1000 pressurized water reactor

As a consequence of a total loss of AC power supply (station blackout) at a VVER-1000 leading to unavailability of major active safety systems, the safety criteria ensuring the safe operation of the nuclear power plant would be violated and core heat-up with possible core degradation could occur. A dedicated accident management measure (primary side depressurization) can be applied to reduce the primary pressure and to activate the injection from the passive emergency core cooling systems (accumulators). The analyses presented in this paper are aiming at both a detailed investigation of the accident sequence, taking into account the depressurization of the primary circuit, and the possibilities to prevent or at least to mitigate a damage of the reactor core so as to gain additional time for taking necessary countermeasures. The analyses are performed using the codes ASTEC and ATHLET developed by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and GRS (Gesellschaft für Anlagen- und Reaktorsicherheit mbH).

Selenium supplementation affects broiler growth performance, meat yield and feather coverage

(1) Selenium (Se) is an essential part of numerous selenoproteins, most of which are involved in the antioxidant system of the body. It is also required by poultry for the maintenance of optimal health and meat quality. This paper reports data from a study examining the effect of dietary source and concentration of selenium on broiler performance and meat quality. (2) Increased dietary selenium content markedly reduced feed conversion ratio (FCR) as a result of significantly lower feed intakes of birds while maintaining the same weight gains. (3) Selenium supplementation increased feathering, with organic selenium (selenised yeast) being superior to inorganic selenium (sodium selenite). (4) Birds receiving organic selenium in their diets had improved eviscerated weight, breast yield and reduced drip loss. (5) There were significant concentration x source interactions on yields of breasts and marylands (thigh plus drumstick), with elevated levels of organic selenium increasing the yields, whereas the opposite was true for the inorganic selenium.