ML19221A940

Reg Guide 1.126,Revision 1, Acceptable Model & Related Statistical Methods for Analysis of Fuel Densification

ML19221A940
Person / Time
Issue date:	03/31/1978
From:	NRC OFFICE OF STANDARDS DEVELOPMENT
To:
References
REGGD-01.126, REGGD-1.126, NUDOCS 7907110144
Download: ML19221A940 (5)

Text

Revision 1

1. p g%

U.S. NUCLEAR REGULATORY COMMISSION March 1978 8

C, M,w RELATORY CDE 4

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OFFICE OF STANDARDS DCVELOPMENT REGULATORY GUIDE 1.126 AN ACCEPTABLE MODEL AND RELATED STATISTICAL METHODS FOR THE ANALYSIS OF FUEL DENSIFICATION A. INTRODUCTION nons must be taken mto account m apply mg analy t-Appendix K.

I CCS la atuation blodels, to lo CH4 Pait 50 1.icensing of Production and l'tili/a-tion I acihties.

requires that the steady ^ tate tem-The NRC statt has resiewed the as ailable inf orma-perature dotribution and stored energy in the f uel be-tion concermng f uel densification, and the technical tore a hy pothetical low-of-coolant accident 11.0C.\\i basis tor the regulatory position of :his guide is

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be calculated. taking f uel densiticanon mto consid-gis en m Ref erence I t he model presented in Sec-eration ~ Ibis guide pros ides an analy tical unidel and tions C. I and C 2 of this guide is not intended to f elJIed awuluptitins anJ prisedures that are accept-supersede N RC,ipprin ed s endir nadels able to the NRC statt for predithng the ettetts of' tuel densification m light-water-cooled nuclear power reactors. t he guide also describes statistical methods l he statishcal methoJs ISecnon C.31 measure-

% I t i' 41 I. and iMd!6ip) anulup-rClated 141 product sampling that w ill pros ide anur.

tuch ISettion C.51 are tionpatible w ith most s endor anCe that this and other approsed analytical nuidels will adequa!Cl) describe the cltects of dens lljCation m'dcl ThCICt OIC SCCIiOU' (' 3 b JUd b b Cou!d be appliCd to dCnsificahon models thJI ditler f rom the lor Cat h Intllal core and reload l'uel quJntH) pro.

duced.

one presented in Sectnins l' 1.ind ('.2.

The \\ds nor y Comnnttee on Reactor Safeguards has been tonsulted concermng this guide and has C. REGULATORY POSITION concurred in the regulatery posmon.

B. DISCUSSION

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The density of a tuel pellett in the reat tor in-In-reastor denutication (shrmkages of oxide tuel creases with burnup and achieses a inaxiinum salue pellets a tects f uel temperatures in ses cral way s (le relain ely low burnup f eencrally 10.000 at a cap c.mductance may be reduced because of the de-bl U.d t) I51r analy tiCJ1 purposes, this in a x i m u m crease in pellet diameter; i2i the linear heat genera-density nunus the imtial density. i.e.

the mamnum tion rate is increased because of the decrease in pellet dernit) thange. Is awumed to be the sanic as the den-length; and (3) the pellet-length decreases may cause uty t hange Av that w ould oct ur outside the reac-

-caps in the f uel column and m. > produce local power tor in the same pellet during resintering at I T O (.for spikes and iht potennal f or claJdmg collapse Ih-

,.A hours mensional chances in pellets in the reactor do not ap-i pear to be notropic, so axial and radial pellet dimen-4 sion chances will be treateJ dit terentis. I ur-W here the evreactor resinterine results m a ne.ca 7

thermore. it. nn ( 1) and 121 ahos e are single-pellet tise denuty -change (i.e swellingi. /cro in reactor g

ettects. w hereas item ( Ti n the result of sunultane<>us denutication should he awumed.

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2. Densitication Kinetics population or a group of material populations. A "ma-l'or pellers that hase a resintering density change terial population is defined as a group of pellets man-ap,mr of less than 4', of theoretical density (I DL the utactured f rom a single powder source under the same rance of tabricatine conditions in such a manner that the m-reactor density change Ap as a f unction of burnup MMMM i bhin IW hw lil' may be 'aken as -

subset s taken f rom material populations that exhibit consistent resintering behasior, the sample data f rom Ap 0

(la) the matenal population taken as a whole may be used to (f or ilU ' 20 N1Wd it characterize the densification behasior of the subsets.

3p m log (Ill') +b (Ibi (tor 20 Ill' 2000 N1WJtt

a. MngMcHet WWh and 3p 3p,m, (Ici (f or IlU - 2000 N1Wd t t Analy se s of the etteet of densification on stored where the cocilicients m and b ue gnen by energy and hnear heat generation rate must account for pellets that h ne the greatest propensity for den-O m lop 4 20) +b d ation. To momplish this with a resintermg-based and Av

,r m log ( 20(H h + b.

model such as that des ribed in Sections C.I and C.2, a s ahle 3 Mr that consers a-resintering densit) thangC

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tnely bounds 95', of the population lpor salues with 1:or peHets exhiNting a resmtering density change in 95'; confidence shoulJ be used. The population of ana-ewess of 4',

'l D, the in-reactor density change as a

1 tical mterest is the initul core loading or reload quan-3 f unction burnup may be taken a' of f uel for which the sately analysis, and hence the densification analy sis, is being performed, and this 3p O

(2a) population may be composed of subsets trom a number (f or llU 551Wdtt of material populations. Once the matenal populations 3p m logtH U) +b (2b) and their respectise contributions ti e.

subse t s ) to the llor 3 Ill.

N_ N) N1%.d t i, population of analyllCal Interest are determined, random sampline procedures m.n be used to characteri/e the and Ap Ap.mr

<2c) resulting population. When random sampling of the re-Ifor Bl' - 5tM) N1WJ ti.

sultmp population n not leasible, a consers atis e charac-teri/athan ma) be t>btained by using the largest of the where the coetticients m and b are gnen by charieterizations of the contributing subsetsjt o

m logt 5 )

b and Apor m log (5(W h + b.

If the distribution of 3p,mr s alues of a population is normal, methods of es aluating normally distributed data mas be used,11 the

'W' test or D' test (when in applications of I quations I and 2, Ap-r w ill 50 or ulore data points are used) (Ret 2) demon-h.n e the s alue Aggr or a :mr, which will be de-v strates nonnormahts at the i,, lesel of...

scribed in Section C.3 T he burnup unit N1%.d t m the uenificance, nonparametne statistical methods should be used un-abus e expressions a megawa!t day s per meine ton of less I hen y metal t uramum or uranium plus plutonium m a dif f erent functh nal torm can be satisf actorily i

I mixed-oxide f uels) justified to describe the distribution of the Ap-r s al-Eus A p 3 is the upper one-sided 95 95 toler-ance limit for the density changes and can be ob-

3. Statistic.d N!cthods f ained hom the sampk s alues udng one of the methods outlined below.

Ta apply the abose model or any densification model that depends on an ex-reactor resinterine densits change, a random sample of the pellet popIdation ot

. i li Aormal Diuribution. In this case, 3pMr l interest shouhl be resintered Resintering the pellets in n gnen by the sample will iew't in a set of densii, t hanges 3pm,.

Sescral characterist.cs of these salues are needed to

---Spsmr

+C bp..

complete the densification analysn.

wr where ab, is the mean of the sample data, s a the l

Tne population of analytical mierest may be com-standard desiation of the sample data, and c' is gnen posed of subse's of pellets f rom either a smgle matenal in Table 1 (trom Ret 3).

tt It a mt orret t to prorate the c harm 'eotauons of the con-t M mbok are det med m the I nt of M mboh at the bask of thn inhutme whsets by somrutin g w eichtcJ as erages m er the sub-guide se t s 142 065

" 2'2

TABl.E I T A B l.li 2 val.UES TO BE USED FOR c' VAllES TO BE USED FOR m TO DETERN11NE TO DETERNtlNE Ap:A, Ap*A, WITil NONNORNI Al. DISTRIBUTION WITil NORNI AI. DIS IRIBUTION Number of Number of Obsers ations m

Obsers ations c'

50 4

5.15 ss 5

4.20 U

1 6

3.71 65 1

7 3.40 70 I

s 3.19 75 I

9 3 03 go i

10 2.91 g5 I

II 232 90 1

12 2.74 95 2

15 2.57 loo 2

20 1.40 11o 2

25 2.29 120 2

30 2.22 130 3

40 2.13 140 3

60 2.02 150 3

100 1.93 170 4

200

!.M 200 5

500 1 76 30()

9 x

1.64 ano 13 (2) Vonnormal Diursunon. In this case 5'U 17

AptA, is pisen by 6ho 21

Apre, ap 3,!

700 26 SOO 10 w here Ap,VJ i, the m"' largest Apm, s alue m a rank-900 35 ing of the obsersed s alues of Apua, from the sample.

lo00 39 The integer in depends on the sample si/c according to Table 2 (from Ref. 4 L w here Mn,, is the mean of the sample data trom the selected matenal population, s' is the standard desia-Note that a nanimum of 60 obsers anons is required tion of the sample data from the selected material to produce a meaningf ul result by this method.

population, and e is gisen in Table 3 if rom Ret. 3i

4. N1easurement Niethods

b. N1ultiple-Pellet Ef fects To measure the density change Ap,, durine resin-Fuel-column-length changes, w hhh can result in terine. either ceometric or true densities may be asial gaps in the pellet stack, are determined by as er-used.'so long as the same method n used beforc and age pellet behasior. In this case, how eser, the popu-af ter resintering. Techniques such as s acuum lation to be e onsidered is not the core or reload quan-mpregnanon w ater immersion, n ercury immersion, tity characterized abos e, but rather the material popu-gamma-ray absorption, and mensuration are accept-lation (or subset thereot) within that quantity that able. It is also acceptable to inter the density change exhibits the largest mean of the Apo, s alues t rom from a diameter chance. usine the isotropic relation the sample. The distribution of Apour salues for the Apsp - 3 AI),,. D w here ADm, is the diameter l selected material population may be awumed to be change esperienced during resintering.

normal.

.l.o anals /c ettects related to column-lencth Resmtermg should be pertonned in a furnace with a tempaatum Wstnbution in k woWng m changes. redintering-based densification models

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should use a densits chance s alue Ap",,u, that bounds

-cion.

emperatures during resintering should be measu us ng ei a nuoc ou p s or ca W atM l the selected materUl population mean with 95'l con-the upper oneaided 95'<.

optical methods with established blackbody condi-tidence. Thus Ap:n,, is contiJence limit on the mean densits chance and can tions. Furnace temperatures should be so maintained be obtained f rom the sample salues using the espres-Out spMmen tempaatun s am no lowa Wan the de-

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sired test temperature (1700 L, in the model abose) g atter ternperature mea,urernent errors hase been Aptni, - Rn, + cs' taken into account.

142 066 u 2sa

TABLE 3 asoiJing temperatures in excess of ~ lHHFC.

VALUES TO BE USED FOR c

5. Isotrophy Awumptions TO DETERN11NE ApL, Number of in orderi predicted density changes in a cal-culation of th tiects of in-reactor densification, it is Obsers ations e

necessary to n.ake some assumption about the iso-4

,yg tropy of fuel densification For changes in pellet

'5 6

OM diameter D, isotropic densitication may be assumed, 7

N so that AD'D = Ap'3p. For changes in pellet or fuel 3

g column length I., anisotropic densification is assumed such that AUI Ap '2p.

9 g

10 0.5x i1 0.55 D. IMPLEMENTATION 12 0.52 15 0.45 The purpose of this section is to proside informa-20 0.39 tion to applicants ar.d licensees regarding the NRC 25 0 34 staff's plans for using this regulatory guide.

30 0.31 40 3.27 This guide reflects a refinement in NRC practice 60 0.22 anJ supersedes the presiously accepted assumption 100 0.17 that all fuels densify to a maumum density of 96.5'i 209 o i2 of their theoretical density as measured geometri-500 0.07 cally. Except in those cases in which the applicant x

o proposes an acceptable alternatise method for com-plying with specified portions of the Commission's regulations, the method desetibed herein should be used in submittals for construction permit, operating license, Fuel stoichiometry (0 N1 ~ 2.00) should be main-and reload applicatians until this guide is revised as a tained. This may be accomplished by using dry tank result of suggestions from the public or additional staff l@

hydrogen or dry gas mixtures (e.g., NrH,) and reuew.

O 1.126-4 142 067

REFERENCES

1. R. O N1ey er.

'Ibe Analy sis of f uel Densitica.

3. (i J llahn.

Statistical Inters als f or a Normal 9

tion. ' USNRC Report Nt' REG 0085. July 197n Population. P.ut 1. Tables, lisamples and Applica-tions. ' J. Quahty Technol

2. I 15 t 1970).

2.

'Amencan National Standard Assessment ot' the

4. P N. Somersille

' l'a b l e s f or Obtaining Non-Assumption of Normality tiimploying Indnidual Oh-Parametric Tolerance 1.imit s.

Ann Nlath. Stat.

sers ed Value 4).

ANSI Standard N I 5.15-1974.

29. 599 a 195S).

LIST OF SYMBOLS

~l he major sy mbols used in Sections C. I through 31.

In-reactor pellet length thange s tanction of C 5 are identified below:

burnup), t m A/>

In-reactor pe!!et density thange it' unction of 1

IlU llurnup. N1Wd t.

hurnup) g clH 3 > oar Nleasured density change ot' a pellet due to

/

D Nominal initial pellet diameter cm ex-reactor resintering. g em' l.

Nominal initial pellet length, cm 3 >:mr One-sided 95', upper confidence linut en the

/

inean ot' the 3 > ear s alues f rom the selected

/

i TD Theoretical densits. e cm

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material population. g'cm' AD in-reactor pellet diameter change (tunction a;>;a, One-sided 95 95 upper tolerance limit f or the ot' burnup). em.

total population of 3/> cur salues, gcm 3Dua, Nicasured diameter change ot' a pellet due to coreactor resintering, cm.

/>

Nominal initial pellet density. g cm' O

142 068 1.1 % 5

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