Method and apparatus for diagnosing breached fuel elements
AssigneeThe United States of America as represented by the United States Department of Energy
InventorsKenny C. Gross, John D. B. Lambert, Shigeo Nomura
Life of this patent
Estimating the term…
Abstract
The invention provides an apparatus and method for diagnosing breached fuel elements in a nuclear reactor. A detection system measures the activity of isotopes from the cover-gas in the reactor. A data acquisition and processing system monitors the detection system and corrects for the effects of the cover-gas clean up system on the measured activity and further calculates the derivative cure of the corrected activity as a function of time. A plotting system graphs the derivative curve, which represents the instantaneous release rate of fission gas from a breached fuel element.
Claims18
In a nuclear reactor having a core of a plurality of fuel elements, said elements having a cladding, and said reactor having a cover gas and a cover-gas clean up system for removing fission gas activity from said cover-gas said cover-gas clean up system comprising an argon gas purging system, an on-line breached fuel element diagnostic system comprising:
- (a) detector means responsive to fission gas isotope activity in said cover-gas;
- (b) means for measuring the argon purge rate of said argon gas purging system;
- (c) processing means responsive to the outputs of said detector and said argon purge rate measuring means and operable to calculate the corrected gas activity, C*.sub.j+1, and the derivative thereof from the solution of the equations:
- P.sub.j =dc/dt+C.sub.j (X.sub.i +X.sub.L +X.sub.p)
- dC*/dt=P.sub.j -C*j(X.sub.i +X.sub.L)
- C*.sub.j+1 =[P.sub.j -C*.sub.j (X.sub.i +X.sub.L)]dt+C*.sub.j
- where
- dt=Time interval between t.sub.i and T.sub.j+1 ;
- dc=Activity difference of fission gas isotope i at the interval dt=C.sub.j +1;
- C.sub.j =Activity at t.sub.g ;
- X.sub.i =decay constant of fission gas isotope i;
- X.sub.L =Cover-gas-leak-rate constant;
- X.sub.p =Cover-gas-purge-rate constant;
- dC*=Activity different at dt without cover gas clean up system operation=C*.sub.j+1 -C*.sub.j ;
- C.sub.j *=Activity at t.sub.j ;
- and;
- (d) display means responsive to the output of said data acquisition and processing means for displaying the curves of said corrected gas activity and said derivative of said corrected gas activity as a function of time, said derivative curve representing a curve of the instantaneous release rate of fission-gas from a breached fuel element.
The diagnostic system of claim 11 wherein said means for displaying is operable to superimpose said delayed-neutron signal vs. time curve on the log R/B vs. time axis of said three-dimensional plot.
In a nuclear reactor having a core of a plurality of fuel elements, said elements having a cladding, and said reactor having a cover gas and a cover-gas clean up system for removing fission gas activity from said cover-gas said cover-gas clean up system comprising an argon purging system, of diagnosing breached fuel elements comprising the steps of:
- (a) measuring the fission-gas activity in said cover gas;
- (b) measuring the argon purge rate of said argon gas purging system;
- (c) correcting the effects of the cover-gas-clean up system on the measured fission gas activity and calculating the corrected gas activity C*.sub.j+1 ;
- (d) calculating the derivative of said corrected gas activity as a function of time;
- and
- (e) plotting said corrected gas activity and derivative of said corrected gas activity as functions of time, said derivative curve representing a curve of the instantaneous release rate of fission gas from a breached fuel element, wherein the corrected gas activity, C*.sub.j +1 and the derivative thereof are calculated from the solution of the equations:
- P.sub.j =dc/dt +C.sub.j (X.sub.i +X.sub.L +X.sub.p)
- dC*/dt=P.sub.j -C*.sub.j (X.sub.i +X.sub.L)
- C*.sub.j+1 =[P.sub.j -C*.sub.j (X.sub.i +X.sub.L)]dt+C*.sub.j
- where
- dt=Time interval between t.sub.i and T.sub.j+1 ;
- dc=Activity difference of fission gas isotope i at the interval dt=C.sub.j+1 ;
- C.sub.j =Activity at t.sub.j ;
- X.sub.i =decay constant of fission gas isotope i;
- X.sub.L =Cover-gas-leak-rate constant;
- X.sub.p =Cover-gas-purge-rate constant;
- dC*=Activity difference at dt without cover gas clean up system operation=C*.sub.j+1 -C*.sub.j.
Dependencies are inferred from the claim text.