In the last decades, several rules have been developed to anticipate the thermal-hydraulic behaviour of nuclear reactors - like ATHLET, CATHARE, RELAP, RETRAN. However, these codes were developed to power reactors perform. To increase the application form for the analyses of research reactor some changes or addition of some strategies have been done. This section presents some things to consider for using of RELAP/SCDAP and MELCOR for crash analysis of KHRR reactor.
1. 1. RELAP/SCDAP
1. 1. 1. Thermal Hydraulic
RELAP5 computer program can be applied to an array of reactor designs and transient/incident conditions. Aside from certain reactivity-initiated occurrences, the code does apply to LOCAs; loss of flow injuries (LOFAs); lack of heat removal occurrences and anticipated transients without scram (ATWS).
Modelling of the subcooled boiling stream is important because an accurate knowledge of the void small fraction distribution in reactor cores must properly perform various safe practices analyses. Most available boiling models were developed for and examined at the high-pressure conditions of an vitality reactor. Many reactor safe practices analysis rules such as RELAP5, designed to use such models, cannot satisfactorily predict void small percentage distributions in low pressure subcooled boiling moves. It has limited the utilization of the RELAP5 code for low-pressure research reactor applications. It seems that the situation of fast reactivity transient will be influenced due to the importance of the models for the precise description of the complex occurrence of subcooled boiling and two phase flow occurring during the transient. With regards to the trustworthiness of the RELAP5 code for the evaluation of research reactor transients additional investigations related to the above issues are needed.
1. 1. 2. Core Melt Progression
Although developed for light normal water reactors (LWR), the code is a adaptable tool for computerized simulation as its procedure allows to models around needed of a specific thermal-hydraulic system, with use both for expected transients of nuclear power vegetation or of research reactors, and also for small range test facilities.
It is normally known that design peculiarities of HWR type reactors, especially the moderator separated from the coolant do not allow a straightforward software of the advanced primary degradation models existing in computer rules such as SCDAP/RELAP5, MELCOR, ICARE/CATHARE or ATHLET. But the examination of design basis mishaps and the modelling of tests in specially designed facilities can be effectively performed. Moreover, the early stage of the incident, including heatup scheduled to voiding and oxidation, as well as, to a certain extent, other particular phenomena from the lack of geometrical integrity in span of a LOCA type incident coincident with ECCS, can be successfully modeled.
Several code extensions (for Atucha specific features) were added in RELAP/SCDAPsim3. 6. These changes included: modeling of coolant route to coolant route radiation heat transfer, oxidation of the outside wall structure of the coolant channels, molten pool tendencies and relocation of a core with separated coolant channels, and heat transfer in a lower head that includes a filling up body (considerable steel structure take up most of the hemispherical volume level and causing relocated debris to truly have a extensive and thin-in-height form). As a supplementary argument in favor of the use of the code for KHRR, the lifestyle of the heavy normal water library in the discharge deals of RELAP/SCDAPSIM types can be brought up.
1. 2. MELCOR
1. 2. 1. Material Properties
Thermophysical properties for some sound materials should be added to the Materials Properties (MP) package deal database. They are really melting point, latent temperature of fusion, denseness, specific high temperature, thermal conductivity and enthalpy for Zr-1. 5%Nb, type 304 stainless. Beliefs for these materials properties can be acquired from an open literature or, because of lack of data for the alloys at high temperatures, can be estimated by Nause and Leonard.
In addition to properties of sturdy materials, the MP offer in MELCOR contains tabulated beliefs for thermal conductivity and Viscosity of light water (H2O) and heavy steam. Because of the occurrence of heavy water (D2O) in the KHRR reactor, an diagnosis was made concerning the variations between these properties and those befitting D2O. Nause and Leonard concluded that the differences between heavy and light normal water thermal conductivity, heavy and light steam viscosity, and heavy and light heavy steam thermal conductivity are negligible for the purpose and supposed applications of MELCOR. For these properties, MELCOR use the light drinking water data in the MELCOR databases to model heavy and light normal water in the KHRR reactor system.
The only thermophysical property of D2O witnessed to change from that of H2O by more than 10 % is viscosity. Viscosity of D2O is seen to change from that of H2O by so as 30 percent over substance, the temperature range of interest for the KHRR reactor. It is not known if variations in this solo property are large enough to cause noticeably different predictions of KHRR reactor cooling system hydrodynamic behavior. Awareness analyses will be performed in the future to examine this remaining uncertainty
The MP bundle in MELCOR includes tabulated values for the viscosity of hydrogen gas and the Noncondensible Gas (NCG) Formula of State deal contains worth for hydrogen heating capacity. Again, due to possible coexistence of hydrogen and deuterium gas in the KHRR reactor systems, a comparison of the viscosity and temperature capacity between your two gases was made. The difference between hydrogen and deuterium gas viscosity and high temperature capacity is concluded to be sufficiently large to warrant adding D2 to the noncondensible gas move field in MELCOR (D2 gas viscosity is roughly 40 percent greater than H2, and H2 heating capacity is roughly 50 percent higher than D2. ). Because of this, both properties have been included in their appropriate MELCOR repository locations
The H2O program in MELCOR signifies the formula of state for light normal water. Because heavy water is the primary coolant and moderator in the KHRR reactor system, a comparison of the thermodynamic properties of light and heavy water and heavy steam was made. It was found that the saturation pressure versus temperatures data for light and heavy normal water differ by less than six percent. The difference in enthalpy between light and heavy water for the saturated and subcooled liquid says is below five percent at all temperatures and stresses of matter. The distinctions between light and heavy heavy steam enthalpy are below eight percent over-all temperatures and stresses of concern. These dissimilarities in properties between light and heavy normal water and steam are tolerable with the objective and planned applications of MELCOR. Any change in properties related to the formula of status for light water in MELCOR would require that the changes be made in a manner that preserves the Maxwell relations. Therefore, simple modifications to the present H2O properties aren't useful. Either the properties within the H2O deal must be changed, or the existing properties must be used. It has been concluded that using light normal water transport properties to signify the coolant, moderator Crisis COOLANT SYSTEM (ECS), and confinement squirt essential fluids in the KHRR reactor system is an acceptable and pragmatic approximation to people for the real combined H2O/D2O system.
1. 2. 2. Core Melt Progression
Unique top features of KHRR do not allow a straightforward request of MELCOR for evaluation of primary melt progression in KHRR reactor, same as RELAP/SCDAP.
Coolant programs in KHRR reactor are located inside the moderator reservoir in a hexagonal pitch, so that it is expected that the habit of the main during meltdown will be relatively not the same as that of regular LWRs. As the coolant programs aren't in close contact with one another, molten materials from different programs most likely won't agglomerate to form a crust strong enough to support an in-core molten pool. So the most expected patterns is that molten materials is directly relocate to the bottom of the center.
