Effective void fraction for a BWR assembly with boiling in the bypass region
Galperin, A; Segev, M [Ben-Gurion Univ. of the Negev, Beersheba (Israel)]; Knoglinger, E [Paul Scherrer Inst. (PSI), Villigen (Switzerland)]
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; BWR TYPE REACTORS; VOID FRACTION; BYPASSES; BOILING; EIGENVALUES; PRESERVATION; CROSS SECTIONS; DANCOFF CORRECTION; FUEL ASSEMBLIES; MATHEMATICAL MODELS; THEORETICAL DATA; TRANSIENTS; 210100; POWER REACTORS, NONBREEDING, LIGHT-WATER MODERATED, BOILING WATER COOLED
Average BWR assembly cross-sections for nominal conditions, namely for zero bypass void, can be utilised in the analysis of transient conditions with boiling in the bypass. A model is developed to yield an effective channel void for such conditions. The use of this void in conjunction with the `nominal conditions` cross section library approximately preserves the assembly K-infinity corresponding to the true channel and bypass voids. The effective void is an augmentation of the actual channel void. The augment is proportional to the bypass-to-channel volume ratio, to the bypass void, and to a weight W which is introduced to quantify the fact that a water molecule in the bypass has a different assembly criticality worth than one in the channel. The formula developed is superior to the practice of choosing W=1, namely a simple, non-weighted, transfer of water from channel to bypass. The use of this approximate effective channel void reproduces actual K-infinity values of assemblies to better than 5 mk, whereas the use of a simple model sometimes misspredicts the assembly K-infinity by 40 mK. The effective void model cannot handle cases in which both channel and bypass void value are high, simply because then the effective void {alpha}{sub ch}{sup eff} becomes meaningless. A method to treat the {alpha}{sup eff}>1 domain is developed by which corrections to cross sections are provided. Such corrections are synthesised as functions of the assembly parameters. (author) figs., tabs., refs.
Paul Scherrer Inst. (PSI), Villigen (Switzerland)
OSTI; NTIS (US Sales Only); INIS
Switzerland
1991-09-01
English
Technical Report
Numerical Data
Other Information: PBD: Sep 1991
Medium: X; Size: 90 p.
ON: DE92613804
PSI-108; STARS-5.
Other: ON: DE92613804; TRN: CH9100672011953
CHN; SCA: 210100; PA: AIX-23:011953; SN: 92000638077
2008-02-12
10111431