Experimental Fast Reactor JOYO MK-III Function Test In-Vessel Coolant Flow Distribution and Primary System Pressure Drop Measurement

Ishida, Koichi; Ariyoshi, Masahiko; Fukami, Akihiro*; Sugaya, Kazushi*; Kuroha, Takaya*

JNC TN9410 2004-018, 91 Pages, 2004/05

JNC-TN9410-2004-018.pdf:4.31MB

This paper describes the results of following 2 tests, which were examined as a part of JOYO MK-III function test.1) In-Vessel Coolant Flow Distribution Measurement Test2) Primary System Pressure Drop Measurement Test

Evaluation of core bowing reactivity of Joyo MK-III performance tests core

Takamatsu, Misao; Kuroha, Takaya*; Yoshida, Akihiro

JNC TN9400 2003-012, 38 Pages, 2003/03

JNC-TN9400-2003-012.pdf:2.03MB

A study of passive safety test using Joyo has been carried out to demonstrate the inherent safety of sodium cooled fast reactor. In this study, emphasis was placed on the improvement on feedback reactivity calculation accuracy. Especially, the core bowing reactivity has been one of the main targets of this study because it can be designed to provide negative reactivity in the event of power excursion. The core bowing reactivity was calculated by "MERBA" (MEchanical behavior and Reactivity shift caused by core Bowing Analysis code system for Joyo)" which had been developed for Joyo MK-II core. Through the operation of MK-II core, measured power reactivity coefficient shows a power dependency on reactor thermal power, which is considered to be caused by core bowing effect. In order to investigate the mechanism of this phenomenon, the measured power dependency on power reactivity coefficient were compared with the calculation by "MERBA". It was confirmed that the power dependency on the power reactivity coefficient of the MK-II core could be explained by a core bowing reactivity. In the upgraded MK-III core, neutron flux, the coolant temperature difference between reactor inlet and outlet, etc. will be changed and these may effect on the core bowing reactivity. Therefore, the core bowing reactivity of MK-III performance tests core was evaluated using "MERBA" which was modified to analyze MK-III core. As a result of "MERBA" calculation, the core bowing behavior of MK-III performance tests core was almost similar to MK-II core; the fuel subassembly was initially bent toward the core center at zero power, because the middle spacer pad of fuel subassembly was suppressed by reflectors which have rather large permanent distortion. During the thermal power increase, the fuel subassembly was bent to outward and the negative reactivity was inserted by the fuel movement to outward.

Joyo ATWS test analysis by Mimir-N2

; *

JNC TN9400 2001-051, 38 Pages, 2001/03

JNC-TN9400-2001-051.pdf:3.46MB

The study on the passive safety test by using the Experimental Fast Reactor Joyo was performed to demonstrate the inherent safety of fast breeder reactors. An analysis code: Mimir-N2, which has been developed to analyze Joyo plant kinetics, was selected as a standard code for this study. In order to increase the reliability of the calculation, Mimir-N2 code was adjusted based on the data obtained through several plant characteristics tests carried out in Joyo. Throughout an operational data obtained in Joyo, it is supposed that the burn-up dependency observed on the power reactivity coefficient might be coming fiom the reactivity shift caused by a depression of a thermal expansion of fuel pellet. Based on the relationship between the measured power reactivity coefficient and the core averaged burn-up, the burn-up dependency mentioned above was estimated and introduced to Mimir-N2. As a result, calculated core and plant dynamics during the step reactivity response test, such as the response of the power range neutron monitor and the coolant temperature at the core inlet / outlet, corresponded with the measured value, Especially, it was confirmed that Mimir-N2 can simulate the perturbation caused by the thermal expansion of the core support plate. In addition, Mimir-N2 was modified to be enable to take into account for the core bowing reactivity, which is calculated by the core bowing reactivity analysis system developed for Joyo. The preliminary analysis of the plant dynamics during the ATWS events in MK-III core were carried out by using modified Mimir-N2. As a result, it was confirmed that the core bowing reactivity should not be neglected because it sometimes shows positive feedback characteristics.

Studies of passive safety tests by using the experimental fast reactor Joyo; Verification of Joyo plant dynamics analysis code Mimir-N2

Takamatsu, Misao; Kuroha, Takaya*; Aoyama, Takafumi

no journal, , 

Studies for passive safety tests to be conducted by using Joyo have been carried out to demonstrate the inherent safety of LMFBR. In these studies, emphasis has been placed on the improvement of the calculation accuracy of the feedback reactivity. Therefore, in the passive safety tests, the feedback reactivity measurement is planned under the condition simulating ATWS event. The Mimir-N2 which has been developed to analyze Joyo plant dynamic is used for predicting plant behavior during transients. In order to determine the passive safety tests plan, the improvement of the accuracy of Mimir-N2 was required. In this study, transient tests including manual reactor shutdown test, loss of power supply test and preliminary transient over power test were conducted to verify the updated model of the Joyo MK-III core and the heat transport system of Mimir-N2. As a result, a good agreement was obtained between calculated and measured sodium temperatures.