CA1134960A - Determination of can fracture characteristics - Google Patents
Determination of can fracture characteristicsInfo
- Publication number
- CA1134960A CA1134960A CA000340103A CA340103A CA1134960A CA 1134960 A CA1134960 A CA 1134960A CA 000340103 A CA000340103 A CA 000340103A CA 340103 A CA340103 A CA 340103A CA 1134960 A CA1134960 A CA 1134960A
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- Prior art keywords
- nuclides
- nuclide
- ratios
- group
- nomogram
- Prior art date
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Classifications
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C17/00—Monitoring; Testing ; Maintaining
- G21C17/02—Devices or arrangements for monitoring coolant or moderator
- G21C17/04—Detecting burst slugs
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- General Engineering & Computer Science (AREA)
- High Energy & Nuclear Physics (AREA)
- Monitoring And Testing Of Nuclear Reactors (AREA)
- Measuring Or Testing Involving Enzymes Or Micro-Organisms (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention relates to a method for detecting and determining the charac-teristics of breaks or fractures of cans for nuclear reactor fuel elements which makes it possible, after carrying out the detection of any can fracture occurring in one of the rod assemblies of the core, to determine the average number thereof, the extent of the fracture and possibly the position thereof by employing simple means.
The present invention relates to a method for detecting and determining the charac-teristics of breaks or fractures of cans for nuclear reactor fuel elements which makes it possible, after carrying out the detection of any can fracture occurring in one of the rod assemblies of the core, to determine the average number thereof, the extent of the fracture and possibly the position thereof by employing simple means.
Description
BACKGROUN~ OF T~ INVEN ION
The present invention relates to the detection and determination of the characterlstics of breakages which can occur to cans in nuclear reactors. It more specifically applies to heavy or light water reactors, but also has lnteresting ~pplications in the field o~ liquid metal-cooled reactors.
In the remainder of the text an~ in order not to make the description unduly long reference wlll almost exclusively be made to light water-cooled, moderated reactors, but it is obvious that this is not to be con-sidered as a limitation to the scope of t~le prese~t invent-ion.
In the hitherto kno~ PWR or BWR light water moderated reactors~ the fuel is generally uranium oxide U02, jacketed by zircaloy sheaths, the fueI being distri-buted into a certain number of autonomous assemblies, each having a large number of fuel rods. As an example and to give an idea of the orders of magnitude a PWR reactor with an electric power of 900 MW has approximately 40,000 fuel rods of length ~.60 m, subdivided into 15~ assemblies, ,j each of 264 rods.
These fuel elements, which co~stitute the core of the reactorJ are directly immersed in the moderating water~ which also constitutes the primary coolant of the reactor. In the case where one or more fuel rod cans sufrers from cracking or breakage, the radioactive rission 3~
products, which are normally trapped wlthin the can are spread outside the latter into the primary coolant and from there carl contamina~e the reactor vessel and a cer-tain number o~ components, such as pumps and primary exchangers. It is thererore very lmportant to monitor, during the operation of such a nuclear reactor, the appear ance and the possible spread o~ cracks or breaks in the cans constituting the ~uel element rods.
Hitherto no completel~ satis~actory method has been developed to meet this requirement and it has been necessary to make do with more or lèss empirical methods of monitoring the overall activity o~ the pr~nary coollng water ~or ~ission products.
BRIEF SUMMARY_OF_THE_INVENTION
The present invention relates to a method for detecting and determining the characteristics ofbreaks or ~ractures o~ cans ~or nuclear reactor ~uel elements which makes i~ possible, a~ter carrying out the detection o~ any can fracture occurring in one of the rod assemblies of the core, to determine the a~erage number thereof~ the extent of the fracture and possibly the position thereo~ by employing simple means. -In ~eneral terms it is only possible to monitor any ~ractures or breaks ko cans by using as the i~ormation source the relative ackivities either of gaseous ~lssion products or of solid ~ission products, whlch are ~oluble in the primary ~luid of the operating reactor. The most common and most intere~ting o~ the nuclides which can be used are in the case o.t` gaseous products,rare gases, kryptons and xenons and in the case of solid products iodines and cesiums. The ro:Llowing Table lis~s the various nuclides accompanied by their period, which can vary very widely from a ~ew mlnutes to several years.
NUCLID~ PERXOD
85m Kr 4.48 hours 87 Kr 76.3 minutes 88 Kr 2.8 hours 89 Kr 3.18 minutes 134 Cs 2.06 years 1~7 Cs 30.1 years 138 Cs 32.2 m~nutes 133 Xe 5.29 days 133m Xe 2.2 days 135 Xe 9.17 hours 137 Xe 3.83 minutes 138 Xe 14.1 minutes 131 I 8.o4 days 132 T 2.38 hours 133 I ~0.8 hours 1~4 I 52 minutes 135 I 6.59 hours N.B.: In the Table m means metastable.
As a ~irst approximation the fission product . activity o~ the primary water of a pressurised water-cooled 3Lls3~t;() ~5~
nuclear reactor is only dependent on three parame~ers, namely:
the number n o~ breaks in the cans;
the temperature ~ of the ~uel rod or rods~
which has been rractured;
the slze o~ the break or breaks, which can be translated by the leakage ~actor ~g~
As the in~ormation coll.ected on the a¢kivity o~
the water or the primary circuit is overall in~ormation and there is no possibility o~ "sectorizing" the inrormation source the temperature de~ined can only be the mean temper-ature o~ the temperatures o~ the dif~erent points o~ ~uel rods which have become cracked, so that the number n o~
~ractures exceeds 1. In the same way the concept o~
the size Or the ~racture can only represent the mean value for existing raulty surfaces~ These observations are important ~or the remainder o~ the description in which : re~erence must always be made to this reature whenever it is a questlon of the temperature of the cracks or the siz Or the fractures. For this latter ractor a more pre-cise definition can be given to it ln the case o~ a single break, as ~ollows: :
~g = D/~ x s/V
In this rormula:
D is the coe~ricient of dl~fusion o~ the fission product determined in cm /s;
e is the path in centimetres taken by the ~ission ~ ~ .
~..
~1~34~
product, l.e. with minor di~erences the thick-ness o~ the can;
s is the fault sur~ace or crack in cm ;
V is in practice the volume o~ the expansion chamber between the ~uel and i~s can, expressed in cm3.
Xt is therefore readily apparent that the coef~icient ~g characterlses the proportion o~ the total activity present in the expa~sion chamber3 which passes through the cracked can in each second. It thererore characterises ~he gravity of a break and is eæpressed by a number havlng the dimensions of the inverse o~ a time.
The standard values for the coefficient ~g are between 10 2/s and.10 6/s on average ~or a reac~or o~ the type indicated hereinbefore, The acti~ity o~ a nuclide fission produck in the primary circuit Or a pressurized water reactor can there-~ore be represented by an expression of the formo Ai = F(n, T, ~g) For a can fracture or fractures having identical : characteriskics the ratio of the acti~ikies o~ two nuclldes~
4i and Aj is independent o~ the number o~ fractures5 gi~-ing;
R - Ai/Aj = F'~T~ ~g) The dekermination o~ the temperature and size o~
the can frackure or fractures in a reactor core can there-~ore easily be carried out by studying the nuclide activi~y ., :
. ... . . .
ratios on knowing both the functions F' (T3 ~g) and the value of one o* the parameters T or ~g. In the general case this is not so, but the Applicant has ~ound, this constituting an unexpected and interestin~ result, that by especially choosing the pairs of nuclides used for ~orming the activity ratios it was possible to determine in this way pairs, whose ac~ivity ratlos (which can easily be measured) are more particularly dependent on ~g or the temperature.
As the functions F' (T, ~g) can now be cal- ~;
culated by computer using special known programmes it is merely a question o~ solving equations with a single unknownJ making it posslble to successively calculate the parameters T, ~g and n.
This novel and ~ery important finding has made it possible to develop a method ~or the determination o~
the characteristics of the breaks or fractures of cans for - fuel elements of nuclear reactors, which is characterised by the following succession of operations:
by calculating for given characteristics o~ the reactor core and for the burn-up o~ its fuel elements lt is possible to determine:
a) a series of first nomograms ~iving~ ~or a certain ~umber of nuclides, their total activity in the prim-ary coolant as a function o~ the average temperature of the cracked fuel element for a ~racture state of the cans . ~
. arbitrarily defined by a single ~racture~ each nomogram of ' ' said series bein~ es~ablished ~or a particular value o*
the coe~ficient ~g;
b) a second nomogram giving, for dif~er~nt values Or the coe~icient ~g and as a ~unction Or the average temperature o~ khe cracked fuel element~ the act-ivity ratios o~ the differen~ nuclides taken in pairs in such a way as to show two groups of ratios, namely ratio.s of a ~irst group whichJ ln a ~irst approximation, are independent o~ the temperature and ratios o~ a second group, which vary in an increasing manner as a ~unction o~ khe temperature;
c) a third nomogram, derived ~rom activity ratios Or the first group, giving for said sarae ratios of the first group the variations o~ the coer~lcient ~ g as a ~unction o~ khe actual activity ratio;
from the values o~ the activity ratios o~
nuclides o~ the first ~roup measured in ~he primary coolant o~ the reactor and tr2nsrerred to the third nomo~ram i'c ls possible to determine a mean value of the ¢oefficient ~g, from the values of the activity ratios o~ nuclides o~ the second group measured in the primary coolant o~ the reactor and transferred at the same time as the previously found value of coef~icient ~ g to the second nomogram it is possible to determine a mean value o~ the cracked ~uel element temperature;
~ rom the measured activities for a certain number of nuclides present in the primar~ coolant and trans~erred .
~ ' ' ,, 'I
. - . - . - . . . . . . .
~3~
_g_ at the same time as the above mentioned temperature to the nomogram of the first series corresponding to ~he coe~icient ~g obtained it is possible to determine the true number of cracks.
The Applicant has been able to demonstrate that certain activity ratios of nuclicle rission products con-tained in the primary cooling water o~ a nuclear reactor essentially onl~ depend on one parameter, namely the value of ~g representing the average gravity o~ the cracks. As it is now standard practice to be able to determine by cal-culation using existing programmes the nomograms represent-ing the ~unctions R = F'(T, ~g)~ when said ~unction is dependent on more than only a single yariablQ it is readily apparent that it is possible to determine this variable by moving the values read on the theoretically established nomograms closer to the values ef~ectively determined by spectrometric measurement on the reactor coolant. Such programmes make it possible to simulate b~ a co.~puter the appearance in the reactor coolant fluid of a ~ission prod-uct activity ~ollowin~ a can fracture and are more partic-ularly known under the name PROFIP ~ and have been covered by the ~ollowing publication : Third cycle thesis, University o~ Parls, Faculty o~ Sciences~ Orsay (Paris XI), June 1978 "Study o~ the contamination o~ the primary circuit o~ pressurized water reactors" by J. M. GOMIT.
It is there~ore apparent that the realisation of the method according to the invention calls ~or the prior ,'~
!~
3~3~ iO
calculation o~ three dir~erent nomograms by means o~ a programme simulating the migration phenomena of fissio~
products resulting ~rom the fracture of cans in the coolant o~ the nuclear reactor, as well E~S the experimental measure-ment by per se known gamma spectrometric methods o~ acertain number o~ activtty ratios o~ nuclides present in the primary coolan~ as a result of can fractureJ
Thus, ~he realisatlon of the me~hod according to the invention leads to the step by step determinatlon of the average value of coe~ficient ~g~ the average value T
of the temperature of the rods at the location of the cracks and of the probable number n of actual cracks. At this stage it is pointed out that the di~erent values deter-mined are only in actual fact mean values, because the measurements are made on khe primary coolant ~rom all the rods of the reactor core and it is necessary to interpret the signl~icance in t'ne manner indicated hereinafter.
The mean value o~ the coefficient ~g is charact-eristic of the average gravityof cracks in cans throughou~
the presently considered reackor core. This coefficlent approximately represents the total surface area of cracks existing in the core divided by the numher thereo~. The means temperature o~ the cracks must be considered as the ~-mean value of the true temperatures in the axis of each of the different rods which have suffered from cracking.
The average number of cracks n which is finally obtained is derived from the mean value o~ a certain number o~
' :.. . .
' ~.34~;0 activity ratlos compared with a nomogram calculated in the hypothesis of one crack. The number n obtained in this way represents the probable number Or true cracks, taking account of the hypothesis of the identity Or gravity of the various cracks, said hypothesis leading to a part-icular value of the coe~icient ~ g.
The final determination o~ the three character-istics ~)g, T and n can be carried out, hS desired, either manually, or ~ithin the scope o~ the complete automation o~
the method, using computers and thus permitting the oontin-uous monitoring of the reactor, According to the invention two di~ferent categor-ies of nuclide pairs are used ~or carrying out the measure-ments. The first group of nuclide pairs gives activity ratios which are substantially independent o~ the temper-ature o~ the cracks and is obtained by associating the nuclides in pairs in a ~raction, whose first term cor-responds to a nuclide, whose period is below ten hours and whose second term corresponds to a nuclide, whose period is between three minutes and the period o~ the nuclide o~
the first term. Preferably the best results are obtained when the two nuclides o~ the ~irst group have a maximum period variation. On referring ~o the above-mentioned Table of the main ~ission products and their periods it can he seen that a large number o~ nuclide pairs can be used ~or constituting pairs o~ the first group. However, it is advantageous to use in the , :
:, denominator o~ the ~raction 135 xenon, whose period is 9.17 hours, associated with in the numerakor one o~ ~he nuclides chosen from among 138 xenon (14.1 minutes), 87 krypton (76.3 minutes) and 138 cesium (~2.2 minutes). It is also possible to use 89 krypton (3.18 minutes) or 137 xenon (3.83 minutes) ~or the numerator o~ the frackion, which would be in accordance with the definition. For a chosen pair of nuclides it is obviously possible to use inverses of the above ratios, by lnverting the numerator and the denominator.
For the purpose of determining the nuclides which can be associated in pairs for constituting activity ratios o~ the second groupJ i.e. incPeasing the temperature, it is necessary to associate the nuclides in pairs in a fraction, whose ~irst term corresponds to a nuclide having a period below 10 hours and whose second term corresponds to a nuclide havin~ a period above 24 hours. As an example 1~5 xenon (9.17 hours) is frequently used in the denominator o~ the fraction o~ the activity ratio and 133 xenon (5.29 days) or for example 1~3 m ~enon (2.2 days) or 131 iodine (8.o4 days) in the numerator. Obviously these combinations are given in an in~ormative and in no wa~ limitative manner~ the optimum conditions being defined in the manner described hereinbe~ore. As previously stated with regard to the first group it is possible to use inverses o~ the above ratios~ by inverting the numerator and the denominator.
.~ " .
3 ~
Finally the present lnvention relates to a method for the determinatlon o~ characteristics Or fract-ures o~ cans ~or fuel elements o~ nuclear reactors by means of values o~ the ratio R/B for a certain number o~
nuclides present in the cooling ~luid and in which:
R is the number o~ atoms Or such a nuclide released every second into the primary ~luid by the operating reactor core;
B is the calculated number o~ atoms o~ the same nuclide which are theoretically produced every second, wherein ~or detecting the appearance o~ a crack the differ-ent values of the ra~io R/B determined in this way are placed on a ~raph in cartesian coordinates as a function of the decay constant ~ o~ each nuclide represented in the abscissa and wherein the satisfactory alignment on a single horizontal line of the different points obtained in this way is monitored, any discontinuance o~ said alignment being characteristic of the appearance o~ at least one crack.
Th`e method is particularly simple because it is merely necessary to take into consideration a small number o~ nuclides, for e~ample ten, in order to be able to obtain a graphically satis~actory result and to determine the true ack~vit~ released every second into the prlmary cooling ~luid.
By forming the ratio R/B of said number o~ atoms .
.
. . , , .' ' ''' . ' ' " ~ ' ' ' ' ,' ~,~.. ' ' . ' . : ~' ~ '. ' ' ` ~34~t;0 released per second with the number o~ atoms produced per second and theoretically calculated for the same nuclide, obviously taking account of the reactor operating power, a certain number of points theoretically shown to be located on the same horizontal l:lne when there is no can fracture is obtained on a graph as a function o~ ~ . It is therefore merely necessary to periodically trace this graph and check the alignment of the various points, allowing for measuring errors, whereby the discontinuance o~ this alignment is characteristic of the appearance of a ~ault. I~ this first part of the diagnosis proves positive and such a fault is in fact detected, the method according to the invention then makes it possible to check the ~raature revealed in the ~ollowing manner.
BRIEF DESCRIPTION OF THE DRAWINGS -The invention will be better understood from the ~ollowing description of a number of examples o~ the detection and determinatlon of characteris~ics o~ fractures in cans for fuel elements of a PWR-type nuclear reactor, said description being provided in an illustrative and non-limitative manner, with reference to the attached drawings:
Fig. 1 which illustrates the method ~or the detection of can ~racturesJ shows for a certain number o~
nuclides the activity ratio R/B as a function of the decay constant ~ o~ each of these expressed in seconds~l.
- ~34~60 Fig. 2 shows an example Or the calculation o~ the rir~t nomogram giving, for. a gi.ve~ coefficient ~g and as a ~unction o~ the temperature, the total activity in curies/konne o~ primary cooling water o~ a reactor ~or dif~erent radioactive ~isq~on products resulting ~rom a single can ~racture.
Fig. 3 shows an example of a second nomogram on which the ratio of the ac~ivities o~ nuclides o~ the ~irst and second groups is plotted as a ~unckion o~ the temperature in C ~or di~erent values o~
coer~icient ~g.
Fig. 4 shows an example o~ a third nomogram plotted for three particular activity ratios o~ the ~irs~
group of Fig. ~ and giving values of Vg as a ~unction o~ the activity ratio.
DETAILED DESCRIPTION OF THE_P~EFE M ED EMBODIMEMTS
. Fig.- 1 relates to the Fes~enheim reactor 1, which at the tlme when the ourve was plotted was operating at a 20 power of 2650 MW thermal. The ratio R/B, defined as .
hereinbe~ore by the ratio of the number Or atoms of each fission nuclide released per second i~to the liquid, rel-ative to the calculated number o~ akoms of the same nuclide theore~ically produced per second, is plotted in logarithmic scale on the ordina~e as a ~unction o~ the radioactive decay constant ~ expressed in second 1 and ~ . plotted in logarithmic s¢ale on the abscissa. Twelve .
: ~ .
, ' ~ ' ' ' ., r ~ ~ :
~L~3~
radioactive ~ission nuclldes were examined and were used ~or determining the twelve corresponding points on the curve. In the order o~ rising abscissas it ls possible to see iodine 131, xenon 1~3, 135 m xenon, iodine 133, xenon 1~5~ iodine 135~ 85 m kr~ptonJ 88 krypton, iodine 132 87 krypton, iodine 1~4 and xenon 138. As can be seen from the ~raph the dif~erent points, naturally allowing ~or measuring errors~ are distributed over two curves 1 and 2 which are separate and therefore dir~er ~rom a single horiæontal line. This simple ~indin~ gives the cextainty that at this time there is already at least one crack in the rods constituting the reactor core. For the purpose o~ additional explanakion the portion of the horizontal line correspondlng to the contamination level prior to can ~racture is plotted in dotted lines under the re~erence 2a.
With reference to Figs. 2 to 4 we will now des-cribe in a complete manner a study o~ the can ~ractures, in - the manner in which it was carried out in practice on the pressurized water reactor o~ the Tihan~e nuclear power station in 197g.
Fig. 2 shows a first nomogram (with the meaning given to this term in the present text) calculated on the computer by means o~ the PROFIP ~ programme on the basis of the following hypotheses: the leakage factor ~ g o~
the cracked cans was fixed at 10 2/s in the case o~ a sin~le can ~racture. Moreover the calculation was made on the basis Or a fuel element specific burn-up o~
.
, ~
' . ` " . ~ ' . . , ,,~' ' . ;. '.' ' ' , . ' ,, ,,, ', , ' :
' ';
~ 3 ~3 12,000 M~IJ/T .
Thus, the activity in curie/konne of water was calculated in the prlmary water of the reactor ror seven fission product nuclldes, namely the three xenons 133, 135 and 138, three kryptons 85 m, 87 and 88 and cesium 138, as a ~unction of the de~ec~i~e rod temperature in C. The ordinates are in logarithmic scale and ~he abscissas ln linear scale.
Fig. 3 shows a second nomogram also calculated for a speci~ic burn-up of 12,000 MWJ/T. It shows the evolution of the activlky ratios of fission product nuclides plotted on the ordinate in logarithmic scale, as a ~unction o~ khe average temperature o~ the cracked rods plokted in linear scale on the abscissa. These ratios were made for a certain number of values o~ coe~icien~ ~g varying from 10 2/s ko 10 6/s. The value of Fi~. ~ is that ik clearly shows the two groups o~ nuclide pairs, namely in the lowe~ part of Fig. 3 the ratios of the rirst g-roup ~Jhich are substantially independent of the temperature and in the upper part t~e activity ratios o~ the second group (in solid lines), which signi~icantly and rapidly rise as a function o~ the same temperature. In the example o~
Fig. 3 the rakios o~ the nuclides o~ the ~irst group are three in allg namely 87 ~rypton/135 xenon, 138 xenon/135 xenon and 138 cesium/1~5 xenon. Only one pair was studied in the second group, namely the ratio o~ 13~ xenon/
1~5 xenon.
t ~''"" .
34~60 Fig. 4 g~ves khe results o~ pairs of nuclldes o~ the first group o~ Fig. 3, in the form of a di~erenk presentation~ corresponding to a nomogram o~ the third type described hereinbe~ore. The value o~ the coe~fici-ent ~g in second 1 is plotted in logarithmic scale on theordina~e and the ratio of the activities o~ each pair of nuclides is plotted in logarikhmic scale on khe abscissa.
In Fig. 4 the temperature is absent, because by de~inition it has no action on the activi~g rakios of nuclides of the ~ st group.
In practice ~or monitorlng ~ractures o~ cans the third nomogram is used ~irst and ~he activity ratios o~
nuclides belonging to khe rirst group are measured. It is then easy to deduce the average value ~g characteristlc o~ the state o~ ~ractures Or cans in the core at the given time, i.e. in practice khe ratio of the kotal sur~ace area o~ the cracks to the number of cracks.
In the particular case of the calculation car-ried ouk on the Tihange reactor a ~g oP the order of 10 2/s was found as the mean value through using this third nomogram.
By then trans~erring this mean ~alue ~g to ratios o~ ac~ivities o~ nuclides o~ the second group on the second nomogram (Fig. 3) and by approximaking it to the activity ratio measured by spectrometry in the primary . .
water o~ the core for ~he ratio o~ nuclides 13~ xenon/135 xenon it is possible to determine the mean temperature o~
-: ~
:
., i, .' . '. ', i : , ' ' ' ' ~ ' 113~0 ~-19- ' the cracked cans. ~his mean temperature was found to be 1560 C in the case o~ the Tihange reackor.
By transferring the latter temperature value to the ~irst nomogram of Fig. 2~ corresponding to a coe~ici-ent Yg of 10 2/s and a single can fracture and a specificburn-up o~ 12~000 ~J/T it is possible to determine the real number of can fractures by comparison wi~h the measured value of the tokal activity in primary water for each o~ the seven fission products on the first nomo~ram.
After taking account o~ the dif~erent possible errors this determination led to an average number of cracks n = 2.7 + 0.5.
The accura~e resul~s measured for the activity of each nuclide appear in the att~ched Table corresponding to measurements carried out during January 1978 in the Tihange nuclear power station.
~ = 10-2 T = 1550 Nuclides Measured activiky PROF~P calc~lat- Galculated (Ci/t3 lon for a single number of can fracture fractures 133 Xe(7.52 + 2.04) 10 ~2.50 10~1 7.0 + o.8 173mXe(1.87 + 0.38j 10~16.78 10-3 2.8 + o.6 135 Xe(1.61 + O.l9j 10 15.77 1o~2 2.8 + 0.3 85mKr(3.o8 + 0.4~j 10-21.18 10-2 2.6 + 0.4 2587 Kr~.12 + 0.40j 10 21.87 10 2 2.2 + 0.2 88 Kr(6.04 + 0.76) 10-21.85 10 2 3.3 ~ o.4 At the end of the test cycle the reactor was shutdown and the core was discharged and examined. It ~ ' ' ~1~3~
was round that three fuel rods were damaged and one hand in ~act lost its plug. The three rods were operating at temperatures of about 1560 C, i.e. above the average core temperature, taken in the axls of the rods~ where it was about 1300 C.
., , . "
:
The present invention relates to the detection and determination of the characterlstics of breakages which can occur to cans in nuclear reactors. It more specifically applies to heavy or light water reactors, but also has lnteresting ~pplications in the field o~ liquid metal-cooled reactors.
In the remainder of the text an~ in order not to make the description unduly long reference wlll almost exclusively be made to light water-cooled, moderated reactors, but it is obvious that this is not to be con-sidered as a limitation to the scope of t~le prese~t invent-ion.
In the hitherto kno~ PWR or BWR light water moderated reactors~ the fuel is generally uranium oxide U02, jacketed by zircaloy sheaths, the fueI being distri-buted into a certain number of autonomous assemblies, each having a large number of fuel rods. As an example and to give an idea of the orders of magnitude a PWR reactor with an electric power of 900 MW has approximately 40,000 fuel rods of length ~.60 m, subdivided into 15~ assemblies, ,j each of 264 rods.
These fuel elements, which co~stitute the core of the reactorJ are directly immersed in the moderating water~ which also constitutes the primary coolant of the reactor. In the case where one or more fuel rod cans sufrers from cracking or breakage, the radioactive rission 3~
products, which are normally trapped wlthin the can are spread outside the latter into the primary coolant and from there carl contamina~e the reactor vessel and a cer-tain number o~ components, such as pumps and primary exchangers. It is thererore very lmportant to monitor, during the operation of such a nuclear reactor, the appear ance and the possible spread o~ cracks or breaks in the cans constituting the ~uel element rods.
Hitherto no completel~ satis~actory method has been developed to meet this requirement and it has been necessary to make do with more or lèss empirical methods of monitoring the overall activity o~ the pr~nary coollng water ~or ~ission products.
BRIEF SUMMARY_OF_THE_INVENTION
The present invention relates to a method for detecting and determining the characteristics ofbreaks or ~ractures o~ cans ~or nuclear reactor ~uel elements which makes i~ possible, a~ter carrying out the detection o~ any can fracture occurring in one of the rod assemblies of the core, to determine the a~erage number thereof~ the extent of the fracture and possibly the position thereo~ by employing simple means. -In ~eneral terms it is only possible to monitor any ~ractures or breaks ko cans by using as the i~ormation source the relative ackivities either of gaseous ~lssion products or of solid ~ission products, whlch are ~oluble in the primary ~luid of the operating reactor. The most common and most intere~ting o~ the nuclides which can be used are in the case o.t` gaseous products,rare gases, kryptons and xenons and in the case of solid products iodines and cesiums. The ro:Llowing Table lis~s the various nuclides accompanied by their period, which can vary very widely from a ~ew mlnutes to several years.
NUCLID~ PERXOD
85m Kr 4.48 hours 87 Kr 76.3 minutes 88 Kr 2.8 hours 89 Kr 3.18 minutes 134 Cs 2.06 years 1~7 Cs 30.1 years 138 Cs 32.2 m~nutes 133 Xe 5.29 days 133m Xe 2.2 days 135 Xe 9.17 hours 137 Xe 3.83 minutes 138 Xe 14.1 minutes 131 I 8.o4 days 132 T 2.38 hours 133 I ~0.8 hours 1~4 I 52 minutes 135 I 6.59 hours N.B.: In the Table m means metastable.
As a ~irst approximation the fission product . activity o~ the primary water of a pressurised water-cooled 3Lls3~t;() ~5~
nuclear reactor is only dependent on three parame~ers, namely:
the number n o~ breaks in the cans;
the temperature ~ of the ~uel rod or rods~
which has been rractured;
the slze o~ the break or breaks, which can be translated by the leakage ~actor ~g~
As the in~ormation coll.ected on the a¢kivity o~
the water or the primary circuit is overall in~ormation and there is no possibility o~ "sectorizing" the inrormation source the temperature de~ined can only be the mean temper-ature o~ the temperatures o~ the dif~erent points o~ ~uel rods which have become cracked, so that the number n o~
~ractures exceeds 1. In the same way the concept o~
the size Or the ~racture can only represent the mean value for existing raulty surfaces~ These observations are important ~or the remainder o~ the description in which : re~erence must always be made to this reature whenever it is a questlon of the temperature of the cracks or the siz Or the fractures. For this latter ractor a more pre-cise definition can be given to it ln the case o~ a single break, as ~ollows: :
~g = D/~ x s/V
In this rormula:
D is the coe~ricient of dl~fusion o~ the fission product determined in cm /s;
e is the path in centimetres taken by the ~ission ~ ~ .
~..
~1~34~
product, l.e. with minor di~erences the thick-ness o~ the can;
s is the fault sur~ace or crack in cm ;
V is in practice the volume o~ the expansion chamber between the ~uel and i~s can, expressed in cm3.
Xt is therefore readily apparent that the coef~icient ~g characterlses the proportion o~ the total activity present in the expa~sion chamber3 which passes through the cracked can in each second. It thererore characterises ~he gravity of a break and is eæpressed by a number havlng the dimensions of the inverse o~ a time.
The standard values for the coefficient ~g are between 10 2/s and.10 6/s on average ~or a reac~or o~ the type indicated hereinbefore, The acti~ity o~ a nuclide fission produck in the primary circuit Or a pressurized water reactor can there-~ore be represented by an expression of the formo Ai = F(n, T, ~g) For a can fracture or fractures having identical : characteriskics the ratio of the acti~ikies o~ two nuclldes~
4i and Aj is independent o~ the number o~ fractures5 gi~-ing;
R - Ai/Aj = F'~T~ ~g) The dekermination o~ the temperature and size o~
the can frackure or fractures in a reactor core can there-~ore easily be carried out by studying the nuclide activi~y ., :
. ... . . .
ratios on knowing both the functions F' (T3 ~g) and the value of one o* the parameters T or ~g. In the general case this is not so, but the Applicant has ~ound, this constituting an unexpected and interestin~ result, that by especially choosing the pairs of nuclides used for ~orming the activity ratios it was possible to determine in this way pairs, whose ac~ivity ratlos (which can easily be measured) are more particularly dependent on ~g or the temperature.
As the functions F' (T, ~g) can now be cal- ~;
culated by computer using special known programmes it is merely a question o~ solving equations with a single unknownJ making it posslble to successively calculate the parameters T, ~g and n.
This novel and ~ery important finding has made it possible to develop a method ~or the determination o~
the characteristics of the breaks or fractures of cans for - fuel elements of nuclear reactors, which is characterised by the following succession of operations:
by calculating for given characteristics o~ the reactor core and for the burn-up o~ its fuel elements lt is possible to determine:
a) a series of first nomograms ~iving~ ~or a certain ~umber of nuclides, their total activity in the prim-ary coolant as a function o~ the average temperature of the cracked fuel element for a ~racture state of the cans . ~
. arbitrarily defined by a single ~racture~ each nomogram of ' ' said series bein~ es~ablished ~or a particular value o*
the coe~ficient ~g;
b) a second nomogram giving, for dif~er~nt values Or the coe~icient ~g and as a ~unction Or the average temperature o~ khe cracked fuel element~ the act-ivity ratios o~ the differen~ nuclides taken in pairs in such a way as to show two groups of ratios, namely ratio.s of a ~irst group whichJ ln a ~irst approximation, are independent o~ the temperature and ratios o~ a second group, which vary in an increasing manner as a ~unction o~ khe temperature;
c) a third nomogram, derived ~rom activity ratios Or the first group, giving for said sarae ratios of the first group the variations o~ the coer~lcient ~ g as a ~unction o~ khe actual activity ratio;
from the values o~ the activity ratios o~
nuclides o~ the first ~roup measured in ~he primary coolant o~ the reactor and tr2nsrerred to the third nomo~ram i'c ls possible to determine a mean value of the ¢oefficient ~g, from the values of the activity ratios o~ nuclides o~ the second group measured in the primary coolant o~ the reactor and transferred at the same time as the previously found value of coef~icient ~ g to the second nomogram it is possible to determine a mean value o~ the cracked ~uel element temperature;
~ rom the measured activities for a certain number of nuclides present in the primar~ coolant and trans~erred .
~ ' ' ,, 'I
. - . - . - . . . . . . .
~3~
_g_ at the same time as the above mentioned temperature to the nomogram of the first series corresponding to ~he coe~icient ~g obtained it is possible to determine the true number of cracks.
The Applicant has been able to demonstrate that certain activity ratios of nuclicle rission products con-tained in the primary cooling water o~ a nuclear reactor essentially onl~ depend on one parameter, namely the value of ~g representing the average gravity o~ the cracks. As it is now standard practice to be able to determine by cal-culation using existing programmes the nomograms represent-ing the ~unctions R = F'(T, ~g)~ when said ~unction is dependent on more than only a single yariablQ it is readily apparent that it is possible to determine this variable by moving the values read on the theoretically established nomograms closer to the values ef~ectively determined by spectrometric measurement on the reactor coolant. Such programmes make it possible to simulate b~ a co.~puter the appearance in the reactor coolant fluid of a ~ission prod-uct activity ~ollowin~ a can fracture and are more partic-ularly known under the name PROFIP ~ and have been covered by the ~ollowing publication : Third cycle thesis, University o~ Parls, Faculty o~ Sciences~ Orsay (Paris XI), June 1978 "Study o~ the contamination o~ the primary circuit o~ pressurized water reactors" by J. M. GOMIT.
It is there~ore apparent that the realisation of the method according to the invention calls ~or the prior ,'~
!~
3~3~ iO
calculation o~ three dir~erent nomograms by means o~ a programme simulating the migration phenomena of fissio~
products resulting ~rom the fracture of cans in the coolant o~ the nuclear reactor, as well E~S the experimental measure-ment by per se known gamma spectrometric methods o~ acertain number o~ activtty ratios o~ nuclides present in the primary coolan~ as a result of can fractureJ
Thus, ~he realisatlon of the me~hod according to the invention leads to the step by step determinatlon of the average value of coe~ficient ~g~ the average value T
of the temperature of the rods at the location of the cracks and of the probable number n of actual cracks. At this stage it is pointed out that the di~erent values deter-mined are only in actual fact mean values, because the measurements are made on khe primary coolant ~rom all the rods of the reactor core and it is necessary to interpret the signl~icance in t'ne manner indicated hereinafter.
The mean value o~ the coefficient ~g is charact-eristic of the average gravityof cracks in cans throughou~
the presently considered reackor core. This coefficlent approximately represents the total surface area of cracks existing in the core divided by the numher thereo~. The means temperature o~ the cracks must be considered as the ~-mean value of the true temperatures in the axis of each of the different rods which have suffered from cracking.
The average number of cracks n which is finally obtained is derived from the mean value o~ a certain number o~
' :.. . .
' ~.34~;0 activity ratlos compared with a nomogram calculated in the hypothesis of one crack. The number n obtained in this way represents the probable number Or true cracks, taking account of the hypothesis of the identity Or gravity of the various cracks, said hypothesis leading to a part-icular value of the coe~icient ~ g.
The final determination o~ the three character-istics ~)g, T and n can be carried out, hS desired, either manually, or ~ithin the scope o~ the complete automation o~
the method, using computers and thus permitting the oontin-uous monitoring of the reactor, According to the invention two di~ferent categor-ies of nuclide pairs are used ~or carrying out the measure-ments. The first group of nuclide pairs gives activity ratios which are substantially independent o~ the temper-ature o~ the cracks and is obtained by associating the nuclides in pairs in a ~raction, whose first term cor-responds to a nuclide, whose period is below ten hours and whose second term corresponds to a nuclide, whose period is between three minutes and the period o~ the nuclide o~
the first term. Preferably the best results are obtained when the two nuclides o~ the ~irst group have a maximum period variation. On referring ~o the above-mentioned Table of the main ~ission products and their periods it can he seen that a large number o~ nuclide pairs can be used ~or constituting pairs o~ the first group. However, it is advantageous to use in the , :
:, denominator o~ the ~raction 135 xenon, whose period is 9.17 hours, associated with in the numerakor one o~ ~he nuclides chosen from among 138 xenon (14.1 minutes), 87 krypton (76.3 minutes) and 138 cesium (~2.2 minutes). It is also possible to use 89 krypton (3.18 minutes) or 137 xenon (3.83 minutes) ~or the numerator o~ the frackion, which would be in accordance with the definition. For a chosen pair of nuclides it is obviously possible to use inverses of the above ratios, by lnverting the numerator and the denominator.
For the purpose of determining the nuclides which can be associated in pairs for constituting activity ratios o~ the second groupJ i.e. incPeasing the temperature, it is necessary to associate the nuclides in pairs in a fraction, whose ~irst term corresponds to a nuclide having a period below 10 hours and whose second term corresponds to a nuclide havin~ a period above 24 hours. As an example 1~5 xenon (9.17 hours) is frequently used in the denominator o~ the fraction o~ the activity ratio and 133 xenon (5.29 days) or for example 1~3 m ~enon (2.2 days) or 131 iodine (8.o4 days) in the numerator. Obviously these combinations are given in an in~ormative and in no wa~ limitative manner~ the optimum conditions being defined in the manner described hereinbe~ore. As previously stated with regard to the first group it is possible to use inverses o~ the above ratios~ by inverting the numerator and the denominator.
.~ " .
3 ~
Finally the present lnvention relates to a method for the determinatlon o~ characteristics Or fract-ures o~ cans ~or fuel elements o~ nuclear reactors by means of values o~ the ratio R/B for a certain number o~
nuclides present in the cooling ~luid and in which:
R is the number o~ atoms Or such a nuclide released every second into the primary ~luid by the operating reactor core;
B is the calculated number o~ atoms o~ the same nuclide which are theoretically produced every second, wherein ~or detecting the appearance o~ a crack the differ-ent values of the ra~io R/B determined in this way are placed on a ~raph in cartesian coordinates as a function of the decay constant ~ o~ each nuclide represented in the abscissa and wherein the satisfactory alignment on a single horizontal line of the different points obtained in this way is monitored, any discontinuance o~ said alignment being characteristic of the appearance o~ at least one crack.
Th`e method is particularly simple because it is merely necessary to take into consideration a small number o~ nuclides, for e~ample ten, in order to be able to obtain a graphically satis~actory result and to determine the true ack~vit~ released every second into the prlmary cooling ~luid.
By forming the ratio R/B of said number o~ atoms .
.
. . , , .' ' ''' . ' ' " ~ ' ' ' ' ,' ~,~.. ' ' . ' . : ~' ~ '. ' ' ` ~34~t;0 released per second with the number o~ atoms produced per second and theoretically calculated for the same nuclide, obviously taking account of the reactor operating power, a certain number of points theoretically shown to be located on the same horizontal l:lne when there is no can fracture is obtained on a graph as a function o~ ~ . It is therefore merely necessary to periodically trace this graph and check the alignment of the various points, allowing for measuring errors, whereby the discontinuance o~ this alignment is characteristic of the appearance of a ~ault. I~ this first part of the diagnosis proves positive and such a fault is in fact detected, the method according to the invention then makes it possible to check the ~raature revealed in the ~ollowing manner.
BRIEF DESCRIPTION OF THE DRAWINGS -The invention will be better understood from the ~ollowing description of a number of examples o~ the detection and determinatlon of characteris~ics o~ fractures in cans for fuel elements of a PWR-type nuclear reactor, said description being provided in an illustrative and non-limitative manner, with reference to the attached drawings:
Fig. 1 which illustrates the method ~or the detection of can ~racturesJ shows for a certain number o~
nuclides the activity ratio R/B as a function of the decay constant ~ o~ each of these expressed in seconds~l.
- ~34~60 Fig. 2 shows an example Or the calculation o~ the rir~t nomogram giving, for. a gi.ve~ coefficient ~g and as a ~unction o~ the temperature, the total activity in curies/konne o~ primary cooling water o~ a reactor ~or dif~erent radioactive ~isq~on products resulting ~rom a single can ~racture.
Fig. 3 shows an example of a second nomogram on which the ratio of the ac~ivities o~ nuclides o~ the ~irst and second groups is plotted as a ~unckion o~ the temperature in C ~or di~erent values o~
coer~icient ~g.
Fig. 4 shows an example o~ a third nomogram plotted for three particular activity ratios o~ the ~irs~
group of Fig. ~ and giving values of Vg as a ~unction o~ the activity ratio.
DETAILED DESCRIPTION OF THE_P~EFE M ED EMBODIMEMTS
. Fig.- 1 relates to the Fes~enheim reactor 1, which at the tlme when the ourve was plotted was operating at a 20 power of 2650 MW thermal. The ratio R/B, defined as .
hereinbe~ore by the ratio of the number Or atoms of each fission nuclide released per second i~to the liquid, rel-ative to the calculated number o~ akoms of the same nuclide theore~ically produced per second, is plotted in logarithmic scale on the ordina~e as a ~unction o~ the radioactive decay constant ~ expressed in second 1 and ~ . plotted in logarithmic s¢ale on the abscissa. Twelve .
: ~ .
, ' ~ ' ' ' ., r ~ ~ :
~L~3~
radioactive ~ission nuclldes were examined and were used ~or determining the twelve corresponding points on the curve. In the order o~ rising abscissas it ls possible to see iodine 131, xenon 1~3, 135 m xenon, iodine 133, xenon 1~5~ iodine 135~ 85 m kr~ptonJ 88 krypton, iodine 132 87 krypton, iodine 1~4 and xenon 138. As can be seen from the ~raph the dif~erent points, naturally allowing ~or measuring errors~ are distributed over two curves 1 and 2 which are separate and therefore dir~er ~rom a single horiæontal line. This simple ~indin~ gives the cextainty that at this time there is already at least one crack in the rods constituting the reactor core. For the purpose o~ additional explanakion the portion of the horizontal line correspondlng to the contamination level prior to can ~racture is plotted in dotted lines under the re~erence 2a.
With reference to Figs. 2 to 4 we will now des-cribe in a complete manner a study o~ the can ~ractures, in - the manner in which it was carried out in practice on the pressurized water reactor o~ the Tihan~e nuclear power station in 197g.
Fig. 2 shows a first nomogram (with the meaning given to this term in the present text) calculated on the computer by means o~ the PROFIP ~ programme on the basis of the following hypotheses: the leakage factor ~ g o~
the cracked cans was fixed at 10 2/s in the case o~ a sin~le can ~racture. Moreover the calculation was made on the basis Or a fuel element specific burn-up o~
.
, ~
' . ` " . ~ ' . . , ,,~' ' . ;. '.' ' ' , . ' ,, ,,, ', , ' :
' ';
~ 3 ~3 12,000 M~IJ/T .
Thus, the activity in curie/konne of water was calculated in the prlmary water of the reactor ror seven fission product nuclldes, namely the three xenons 133, 135 and 138, three kryptons 85 m, 87 and 88 and cesium 138, as a ~unction of the de~ec~i~e rod temperature in C. The ordinates are in logarithmic scale and ~he abscissas ln linear scale.
Fig. 3 shows a second nomogram also calculated for a speci~ic burn-up of 12,000 MWJ/T. It shows the evolution of the activlky ratios of fission product nuclides plotted on the ordinate in logarithmic scale, as a ~unction o~ khe average temperature o~ the cracked rods plokted in linear scale on the abscissa. These ratios were made for a certain number of values o~ coe~icien~ ~g varying from 10 2/s ko 10 6/s. The value of Fi~. ~ is that ik clearly shows the two groups o~ nuclide pairs, namely in the lowe~ part of Fig. 3 the ratios of the rirst g-roup ~Jhich are substantially independent of the temperature and in the upper part t~e activity ratios o~ the second group (in solid lines), which signi~icantly and rapidly rise as a function o~ the same temperature. In the example o~
Fig. 3 the rakios o~ the nuclides o~ the ~irst group are three in allg namely 87 ~rypton/135 xenon, 138 xenon/135 xenon and 138 cesium/1~5 xenon. Only one pair was studied in the second group, namely the ratio o~ 13~ xenon/
1~5 xenon.
t ~''"" .
34~60 Fig. 4 g~ves khe results o~ pairs of nuclldes o~ the first group o~ Fig. 3, in the form of a di~erenk presentation~ corresponding to a nomogram o~ the third type described hereinbe~ore. The value o~ the coe~fici-ent ~g in second 1 is plotted in logarithmic scale on theordina~e and the ratio of the activities o~ each pair of nuclides is plotted in logarikhmic scale on khe abscissa.
In Fig. 4 the temperature is absent, because by de~inition it has no action on the activi~g rakios of nuclides of the ~ st group.
In practice ~or monitorlng ~ractures o~ cans the third nomogram is used ~irst and ~he activity ratios o~
nuclides belonging to khe rirst group are measured. It is then easy to deduce the average value ~g characteristlc o~ the state o~ ~ractures Or cans in the core at the given time, i.e. in practice khe ratio of the kotal sur~ace area o~ the cracks to the number of cracks.
In the particular case of the calculation car-ried ouk on the Tihange reactor a ~g oP the order of 10 2/s was found as the mean value through using this third nomogram.
By then trans~erring this mean ~alue ~g to ratios o~ ac~ivities o~ nuclides o~ the second group on the second nomogram (Fig. 3) and by approximaking it to the activity ratio measured by spectrometry in the primary . .
water o~ the core for ~he ratio o~ nuclides 13~ xenon/135 xenon it is possible to determine the mean temperature o~
-: ~
:
., i, .' . '. ', i : , ' ' ' ' ~ ' 113~0 ~-19- ' the cracked cans. ~his mean temperature was found to be 1560 C in the case o~ the Tihange reackor.
By transferring the latter temperature value to the ~irst nomogram of Fig. 2~ corresponding to a coe~ici-ent Yg of 10 2/s and a single can fracture and a specificburn-up o~ 12~000 ~J/T it is possible to determine the real number of can fractures by comparison wi~h the measured value of the tokal activity in primary water for each o~ the seven fission products on the first nomo~ram.
After taking account o~ the dif~erent possible errors this determination led to an average number of cracks n = 2.7 + 0.5.
The accura~e resul~s measured for the activity of each nuclide appear in the att~ched Table corresponding to measurements carried out during January 1978 in the Tihange nuclear power station.
~ = 10-2 T = 1550 Nuclides Measured activiky PROF~P calc~lat- Galculated (Ci/t3 lon for a single number of can fracture fractures 133 Xe(7.52 + 2.04) 10 ~2.50 10~1 7.0 + o.8 173mXe(1.87 + 0.38j 10~16.78 10-3 2.8 + o.6 135 Xe(1.61 + O.l9j 10 15.77 1o~2 2.8 + 0.3 85mKr(3.o8 + 0.4~j 10-21.18 10-2 2.6 + 0.4 2587 Kr~.12 + 0.40j 10 21.87 10 2 2.2 + 0.2 88 Kr(6.04 + 0.76) 10-21.85 10 2 3.3 ~ o.4 At the end of the test cycle the reactor was shutdown and the core was discharged and examined. It ~ ' ' ~1~3~
was round that three fuel rods were damaged and one hand in ~act lost its plug. The three rods were operating at temperatures of about 1560 C, i.e. above the average core temperature, taken in the axls of the rods~ where it was about 1300 C.
., , . "
:
Claims (5)
1. A method for the determination of the characterist-ics of fractures of cans for fuel elements in nuclear reactors, wherein after detecting the appearance of such a fracture the following operations are successively performed:
by calculating for given characteristics of the reactor core and for the burn-up of its fuel elements it is possible to determine:
a) a series of first nomograms giving, for a cer-tain number of nuclides, their total activity in the primary coolant as a function of the average temperature of the cracked fuel element for a fracture state of the cans arbit-rarily defined by a single fracture, each nomogram of said series being established for a particular value of the coefficient ?g;
b) a second nomogram giving, for different values of the coefficient ?g and as a function of the average temp-erature of the cracked fuel element, the activity ratios of the different nuclides taken in pairs in such a way as to show two groups of ratios, namely ratios of a first group which, in a first approximation, are independent of the temp-erature and ratios of a second group, which vary in an increasing manner as a function of the temperature;
c) a third nomogram, derived from activity ratios of the first group, giving for said same ratios of the first group the variations of the coefficient ?g as a function of the actual activity ratio;
from the values of the activity ratios of nuclides of the first group measured in the primary coolant of the reactor and transferred to the third nomogram it is possible to determine a mean value of the coefficient ?g;
from the values of the activity ratios of nuclides of the second group measured in the primary coolant of the reactor and transferred at the same time as the previously found value of coefficient ?g to the second nomogram it is possible to determine a mean value of the cracked fuel element temperature;
from the measured activities for a certain number of nuclides present in the primary coolant and transferred at the same time as the above-mentioned temperature to the nomogram of the first series corresponding to the coefficient ? g obtained it is possible to determine the true number of cracks.
by calculating for given characteristics of the reactor core and for the burn-up of its fuel elements it is possible to determine:
a) a series of first nomograms giving, for a cer-tain number of nuclides, their total activity in the primary coolant as a function of the average temperature of the cracked fuel element for a fracture state of the cans arbit-rarily defined by a single fracture, each nomogram of said series being established for a particular value of the coefficient ?g;
b) a second nomogram giving, for different values of the coefficient ?g and as a function of the average temp-erature of the cracked fuel element, the activity ratios of the different nuclides taken in pairs in such a way as to show two groups of ratios, namely ratios of a first group which, in a first approximation, are independent of the temp-erature and ratios of a second group, which vary in an increasing manner as a function of the temperature;
c) a third nomogram, derived from activity ratios of the first group, giving for said same ratios of the first group the variations of the coefficient ?g as a function of the actual activity ratio;
from the values of the activity ratios of nuclides of the first group measured in the primary coolant of the reactor and transferred to the third nomogram it is possible to determine a mean value of the coefficient ?g;
from the values of the activity ratios of nuclides of the second group measured in the primary coolant of the reactor and transferred at the same time as the previously found value of coefficient ?g to the second nomogram it is possible to determine a mean value of the cracked fuel element temperature;
from the measured activities for a certain number of nuclides present in the primary coolant and transferred at the same time as the above-mentioned temperature to the nomogram of the first series corresponding to the coefficient ? g obtained it is possible to determine the true number of cracks.
2. A method for the determination of characteristics of fractures of fuel element cans according to claim 1, wherein pairs of nuclides are obtained giving activity ratios of the first group by associating the nuclides pairwise in a fraction, whose first term corresponds to a nuclide, whose period is below 10 hours and whose second term corresponds to a nuclide, whose period is between 3 minutes and the period of the nuclide of the first term, and wherein activity ratios of nuclides of the second group are obtained by associating the nuclides pairwise in a fraction, whose first term corres-ponds to a nuclide, whose period is below 10 hours and whose second term corresponds to a nuclide, whose period exceeds 24 hours.
3. A method for the determination of characteristics of fractures of fuel element cans according to claim 2, wherein the pairs of nuclides of the first group are formed by selecting two nuclides having a maximum variation between the periods.
4. A method for the determination of characteristics of fractures of fuel element rods in nuclear reactors, according to claim 1, wherein the nuclides used are chosen from kryptons, xenons, cesiums and iodines.
5. A method for the determination of characteristics of fractures of fuel element cans of nuclear reactors according to claim 1 by means of values of the ratio R/B for a certain number of nuclides present in the cooling fluid and in which:
R is the number of atoms of such a nuclide released every second into the primary fluid by the operat-ing reactore core;
B is the calculated number of atoms of the same nuclide which are theoretically produced every second, wherein for detecting the appearance of a crack the different values of the ratio R/B determined in this way are placed on a graph in cartesian coordinates as a function of the decay constant .lambda. of each nuclide represented in the abscissa and wherein the satisfactory alignment on a single horizontal line of the different points obtained in this way is monitored, any discontinuance of said alignment being characteristic of the appearance of at least one crack.
B 6567.3 AM
R is the number of atoms of such a nuclide released every second into the primary fluid by the operat-ing reactore core;
B is the calculated number of atoms of the same nuclide which are theoretically produced every second, wherein for detecting the appearance of a crack the different values of the ratio R/B determined in this way are placed on a graph in cartesian coordinates as a function of the decay constant .lambda. of each nuclide represented in the abscissa and wherein the satisfactory alignment on a single horizontal line of the different points obtained in this way is monitored, any discontinuance of said alignment being characteristic of the appearance of at least one crack.
B 6567.3 AM
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FREN7833266 | 1978-11-24 | ||
| FR7833266A FR2442492A1 (en) | 1978-11-24 | 1978-11-24 | METHOD FOR DETECTION AND MONITORING OF BREAKS IN THE GAINING OF NUCLEAR REACTOR COMBUSTIBLE ELEMENTS |
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|---|---|
| CA1134960A true CA1134960A (en) | 1982-11-02 |
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|---|---|---|---|
| CA000340103A Expired CA1134960A (en) | 1978-11-24 | 1979-11-19 | Determination of can fracture characteristics |
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| EP (1) | EP0012061B1 (en) |
| JP (1) | JPS5574495A (en) |
| CA (1) | CA1134960A (en) |
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| CN113191066B (en) * | 2021-04-30 | 2022-12-09 | 西安交通大学 | Nuclear reactor fuel element failure analysis method based on meshless method |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4080250A (en) * | 1973-11-20 | 1978-03-21 | The United States Of America As Represented By The United States Department Of Energy | Method of locating a leaking fuel element in a fast breeder power reactor |
| AT340543B (en) * | 1975-02-25 | 1977-12-27 | Interatom | PROCEDURE AND DEVICE FOR DETERMINING DEFECTIVE FUEL CANS AND / OR FUEL ELEMENTS OF NUCLEAR REACTORS |
| FR2356244A1 (en) * | 1976-06-23 | 1978-01-20 | Commissariat Energie Atomique | METHOD AND DEVICE FOR DETECTING AND PRELOCALING A SHEATH RUPTURE IN A FAST NEUTRON NUCLEAR REACTOR |
| FR2383454A1 (en) * | 1977-03-11 | 1978-10-06 | Commissariat Energie Atomique | Checking concn. of fission products in fluid - e.g. nuclear reactor coolant, by circulating through U=tube in by=pass unit incorporating measurement system and alarm |
-
1978
- 1978-11-24 FR FR7833266A patent/FR2442492A1/en active Granted
-
1979
- 1979-11-16 EP EP79400881A patent/EP0012061B1/en not_active Expired
- 1979-11-16 DE DE7979400881T patent/DE2964169D1/en not_active Expired
- 1979-11-19 CA CA000340103A patent/CA1134960A/en not_active Expired
- 1979-11-22 JP JP15081879A patent/JPS5574495A/en active Pending
- 1979-11-24 ES ES486704A patent/ES486704A0/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2442492A1 (en) | 1980-06-20 |
| EP0012061B1 (en) | 1982-12-01 |
| ES8100526A1 (en) | 1980-11-01 |
| DE2964169D1 (en) | 1983-01-05 |
| ES486704A0 (en) | 1980-11-01 |
| JPS5574495A (en) | 1980-06-05 |
| FR2442492B1 (en) | 1982-01-29 |
| EP0012061A1 (en) | 1980-06-11 |
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