ML20056B801

Forwards Rept Re Application of Final D3 Scanning Results to Plant

ML20056B801
Person / Time
Site:	Monticello
Issue date:	06/29/1971
From:	Ducanson R NORTHERN STATES POWER CO.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9102110361
Download: ML20056B801 (11)

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NORTHERN 5TATES POWER COMPANY MIN N E A POLIS. M B N N E SOTA 3 540t 6

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DocETED l June 29, 1971 me y g .

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oocer can Jul6 IEIIb Dr. Peter A. Morris, Director 8 -

Division of Reactor Licensing 1 y g4$$$[jasr United States Atomic Energy Comission Washington, D C 20$h5 2_ 9 d'[g8" g g

Dear Dr. Morris:

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MONTICELLO NUCLEAR GENERiTING PIANT E-5979 Docket No. $0-263 License No. DPR-22 '

Fuel Pellet Mixup Manufacturing errors involving inclusion of isolated pellets of incorrect enrichment in fuel rod loads occurred at the GE-Wilmington facility in 1970.

Tests to determine which groups of fuel production could have been affected have indicated that fuel assemblies for Monticello are included in the sus-i pected block of production. This matter was discussed with raembers of your

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staff and with Mr. C. D. Feierabend, Compliance Division Inspector. Six h n

copics of the attached report are forwarded to augment these discussions.

The report includes results based on enrichment scan results of D-3 fuel as of May 2,1971 and on final scan results of that fuel. The interium re-sults as of May 2 have been reviewed by the Monticello Operations and Safety Audit Committees. At that tirae the Committees concluded that, based on the information provided, the fuel enrichment deviation does not present a safety 1 l

hazard. The final scan results of the D-3 fuel do not change the net effect i

l 9102110361 710629 g059 CF o l ADOCK 0 % 263 l>-

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NO ERN CTATED POWER C((,4PANY  %

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Dr. Peter A. Morris June 29, 1971 i

4 of the deviations and the Safety Audit Connittee reconnended that information presented to the AEC include an analysis based on the complete D-3 fuel scanning.

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Yours very truly,

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- C Jul6 ,t 7 I R. O. Duncanson, Jr., P.E.

Gen. Supt. of Power Plants-Mechanical 55'h[fj,st [ sv8 ROD /RLS/bjr cn >.

Attachment 5

3059

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O O so-n a j June 17, 1971

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APPLICATION OF FINAL D3 SCANNING RESULTS TO MONTICELLO god w,ttr Datad Si'N Enrichment scanning of the Dresden 3 fuel has been completed and the results are summarized below.

At Wilmington, 1833 of the 1.20% fuel rods were scanned.

29 enrichment deviations were detected of which 24 were positive deviations (high enrichment) .

9,776 of the 1.69% fuel rods were scanned giving 145 enrich-ment deviating rods, 141 of which were in the positive u.rection. .

At the Dresden site 336 of the 1.20% fuel rods were scanned.

7 enrichment deviating rods were detected with 2 of these in the positive direction. 1792 of the 1.69% rods were scanned. 42 deviating rods were detected of which 27 were positive deviations.

The positive deviations are listed in Table 1 according to the magnitude of the deviation TABLE 1 Summary of D3 Positive Deviations Magnitude of Deviation Wilmington Site Total 1.20% 10-45% 14 1 15 45-60% 6 0 6 100% 4 1 5 l 1.69% 10-45% 116 20 136 45-60% 25 7 32 i

Applying these results to the Monticello fuel leads to

the probable number of deviating rods in the Monticello core. These are tabulated in Table 2 based on 255 of the 1.13% and 1238 of the 1.91% fuel rods loaded after March 1, 1970.

I TEM 2

) Probable Deviations in Monticello Core

% Deviation No. of Rods Contair .ng Deviations 1.13% 1.91% Total 10-45% 1.8 14.3 137T-l 45-60% .7 3.4' 4.1 100% .6 0 .6 i

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In terms of number of rods exceeding given KW/ft valves, the application of D3 results to the Monticello core yields the values in Table 3.

TABLE 3 Number of Rods with KW/ft X X Number of Rods 17.5 1.9 20 .8 25 .1 Comparison of these results with those of the previous analysis (May 6, 1971) indicates that the frequency of occurence of enrichment deviations is somewhat higher in the D3 analysis than was found during the audit. Mcrever, the magnitude of the deviations tended to be less. The net result is that the effect of these deviations in the Monticello core remains the same as previously reported as can be seen by comparing the values in Table 3 with those in the May 6 report.

The conclusions reached on the basis of the audit data are confirmed by the D3 data and the effects on accidents and transients are unchanged by the new data.

- O W

, P.me 2 May 6, 1971 .

t fuel ro 's whre beinq loadre; .as n. wr more than 2 and the number of separm e cr.richmente in "rocena was a]wayn less than 10 and within the capabili ty of c: sting facilities for maintaining  ;

separation. Between February 20 and March 13, 1970, 3 additional enrichments had been introduced, and by March 22 there were four  !

separate projectn undergoing rod loading. This was the largest number of enrichner 's and the largest number of projects und r-going l od loading any single previous month of production at i Wilminqton. Althcm a records show that shop vclume had been steadily increasing since December 1969, the total number of fuel rods loaded during March 1970 was higher than any previous month of Wilmingtr.n production. Subsequ -nt to the beginning of March l

1970, the increased volume ud increased number of enrichments apparently resulted in some reduction in the effectiveness of the adminictrative enrichment controls. The effects of the in-creased number of enric' nents on tba enrichment control pro-cedures was first evidenced on March 1, 1970, with the introduction of Dresden 3 pe!'ets, uhen it became nscessary to store more tb :n one enrictent in a sincie 5 D et storcs;e cabinct. Prior to t: is time each nellet sternge enb:.tet contained on'y one e aici.uant, i This chanue coupled with the increased volume and number of en-richments greatly increased the possibility for undetected "ellet mixups which could result in incorrcet icading of .somo pellots.

As a consequence, fuel rods loaded af te.r N cch 1, 1970, ana before

'tnuary 1, 1971, are believed to be subject to e. Tregrency of en-l richment deviations rcughly consistent with that obtn'.wd in the j extensive gamma scan audit performed 6aring th. pericd fr o Se:-

I terber through i nconber 1970. The subject production, m c fi ca l l; involves selected rods in 92 Monticello fuel c.s-v"':.>s, <J l Ecclenor assoublics, and all of Dresden 3, and a~ , m : al) of the Cuud Cities 1, Pilgrim, and Vermont Ynchcc fu '

ai c=hlacs produced after March 1, 1970, ant prior to January 1, 1971, i excepting the fuel scanned during the 1970 audit. The fuel for the Millstone and Fukushima-1 anf the first 392 Monticelle fuel assemblics were produced daring a period of relatively low pro-duction and lower number of enrichments when no equipment capa-city proble"s vere encountered which required any deviation from previous y >cedures. As a consequence this earlier Wilmington production is expected to be as free from pellet enrichment de-viations as the fuel produced at San Jose for which extensive examination has uncovered no enrichment errors.

l As part of a continuing program to evaluate and improve gus2ity l information techniques and equipment, facilitics were devclopcd during 1970 for continuous ganmc :. canning of full length fuel l

rods for pellet enrichment deviations. Initial use of this equipacnt was begun in the last week of July 1970. From this time through the first week in September 1970, full length garma scanning was performed on random]y selected fuel rods from Dresden 3 and OC-1. During this period of September '970, the first fuel rods with pellet enrichment mixup were detected by the full length scanning equipment. At this time it was decided to perform an in-depth audiu f rod enrichr at control effectiveness by scan-ning an many fuel a.?c as possible. The audit involved scanning of fuel rods from all init2.' core projects in the shop, with the largest samp]c of rods takes. from the Pilgrim project which

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I I. Introduction Manufacturing errors involving inclusion of isolated pellets of incorrect enrichrmnt in fuel rod loads occurred in 1970.

Exictence of such errors was detected during an audit employ-ing a gamma scan technique recently deve'oped. Additional tests determined which group: of fuel production could have been affected. Fuel assemblies for Monticello are included in the affected b1cck of production.

II. Revi- of " a. n o .S. c t u r i i n Ascr;# s

"'? ini '-ial Nality Control. Plan for enrichment control at the

GL-Eilnine: ton facility wac. , utterned af ter the syste: used

a. the o] d Ci:-f:. '. Jos e cen.pl ex. The plan within the pcll"*-

handling area c.s administrative with a system of checke cach time a tray of nellets vas placed into or removed from tha pel-let sto. cage cabinets, and each tina a tray of pellets ua. placed on the rod loading station. The ;enults of periodic audits of enrichment control procedures demonstrate that such procedures effectively prevented the cross mixing of the various enriched pellets in fuel produced prior to March 1, 1970.

A measure of the effectiveness of these procedures is our exper-icnce with fuel made by then. Although the possibility of unde-tected enricP at deviations has always existed, detailed post-irradiation e::cmination of fuel made at San Jose, including gm.ma scanning of selected fuel rods and bundles from Dresden Unit 1, Big Rock Point, KRB, SDN, and more recently, some Dresden 2 and Truruga fuel, has never shoun evidence of an enrichment de-viation or the occurrence of a failure which could be attributed to one.

The effectivenccs of the adninistrative enrichment control pro-cedurc during the period prior to March 1970 uas enhanced by the small number of separate enrichments and the low volume producticn, which allowed more complete ccparation of enrichments during ,

manufacture through pellet loading into the fuel rods. Up to the last wuck in l'ebruary 1970, the number of projects for which

es

'. O r- 3 V nev 6, 1973 l

began rod 1.cading in Gc pb .er 1970.

i III. EnrichnenL Sc7n Pe mits

1. Resul;s of Scecial Audit- - 1970

-a The audit statistics cover two production periods, i.e.,

3733 fuel rods produced prior to PW 47 of 1970 (November 2

' 3 6 to 22) and 4924 fuel rods produced from FW 47 1970  ;

thrn :qh TN 1 of 1971. Tne nianificance of the separation into two paiodu o f prN- tion is that after TU 47 1970 a chenge in pellet. stor me p? c dures was ,introdur: J to reduce to frequency of h ighoct enric!.mont pell.ets in lower enrichment rods. All of the Menticello fuel van produced prior to P ; 4 7 of 1970 The results of tho audit can be smarrized as follo :

197 Aedit Statistics --  !

Numbe. of Pod: with Indicatw I or Great er n viatj on Magnitudo* 3733 Rodr "::nnined 49'4 RcCv E r M ned of Deviation Prior to TU 47 After "" 47 i

i 7 09 34 37 .

l 202 16 32 40S i 6 12  !

70t 5 --

i During this audit, and in subacquent sc:nning, no pell:. c enrichment deviation greater than 100t; in magnitud_ has  !

been detected. All the enrichment deviations detected in the 1970 audit which are summarized above were single 2

pellets of incorrect enrichment.

2. Recent Dresden-3 Results ,

As of May 2, 1971 a total of 8108 low enriched fuel rodt from the Dresden III plant including 1276 havina an enrici-- i ment of 1.20 w/o and 6912 with 1.69 u/o have been reanned for enrichment deviation. A total of 15 deviations have been '

observed in the 1.20 w/o and 76 deviations in the 1.69 w/o, h thus the incidence is essentially the same as r.reviously ll observed during the audit, g li. li The largent deviation obccrved during the current enrichacnt 61

'l scan is 60% deviction in which a 1.90 w/o pellet appearcd j{

in a 1.20 w/o fuel rod. All other deviations have been Icss

than 50t. l l

The current enrichment scan has shown several instanc's  !

where strings of pelletc having improper enrichment occurred.

This is contrary to the results of the audit which chu ard '

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only individual pellet deviations.

ljl "Mannitude of Deviat. ion' in ('I'ned for purposcu of this pre tation as: ~

n-measured rcJnal X 100. )

"nc:.inal ij

] - ~ luge 4 May 6, 1971 t

! The rer.u]ts of tb- cur' se,n as of May 2 are suramar-j i :'e d below:

No. of Ro6- llavina Poci t ive Devi . t-i t.u i l

l I i Deviation 1.20 w/o 1.69 w/o Total 1 10 - 45 14 76 90 45 - 60 0 1

)

1 No. of Pellet. '

! in Strina  !!o . of Positive Deviation Strings I,

2-6 6 32 38 76 6 17 23 l All of the deviating strings were in error range 10 - 45%.

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IV. _7m_ o_l i__c a_ _t_ i. o_.n._t o_: :e n t_..i c_e_l l o

._. _ ._ l i It M s b ,c - cctahlished that 255 fuel rods having an enrich-

! ment of 1.13 u/o and 1238 coas of 1.91 w/o were lo.ded aftcr f I' rch 1, 197', and thus are considered to have possible en:- -h- l

. ment dcriotions. These rods are locat ' :n 92 of the Mon; _llo l

) f uel bu:'fles . Based on the evidence obtained from the en:. ' c;h:acnt

! scan data described above, the nurber of rods which coult. cont, tin 1

a enrichnent deviations .in ?enticello are as follows:

l t Dei ' tion No. of "ch, Con tainin a Nvi t f onc i

i 1.13 _/_o_

-- 1 . 9 1 _u _/ o_ Tctal j

- 20t .65 5.1 5.75

204 - 70t 2.15 3.8 5.J5 f  ; 70% .40 .40 i

i 1

Total 3.3 8.9 12.1

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i These valuc.s arc basca on the total results of the 1970 cudit l as representative of the best statistical data. Use of the l recently compiled D3 data does not appreciably effect these

! results.

l The effect of deviation in the 2.95 w/o fuel do not enter into j consideration. Positive c:2richment deviation in this fuel is

! not possible beenuse no higher enrichment was availab]e and 1 negative deviations vould prcduce only a very small perturbation.

Is t any particular time, only a s all fraction of the core vill be operating nec- the design limits, thus the probchilit;. of a deviating fuel rod being 1ccated in this region is ma] 1. In the following tab 2 cs the mcabers of fuel rods which could be operating in various linncr heat fl u:-: , and MCilFR ranges are listed.

No.~c" Rods w4th Kh7/FT ?X X N_o .

17.5 2.2 20 0.7 25 0.06

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May 6, 1971 l

Mo. of Fryp wi th, fir'HPR <X X No.

l 1.9 2.2 1.5 .55

.25 .13 1.00 0 i L

These values assume that the reactor is operating at full 1 power and would have a peak neat flux of 17.5 and MCHFR =

1.9 if no enrichment deviations existed.

It is seen that damage limits will not be exceeded by any rods and that only about 2 rods would exceed the design limits.

It may be noted that even if no enrichment deviations exist 1 l

I a feu rods could be over the nominal 17 1/2 KW/ft due to '

' in5t_ent uncertainties in determining the power distrjbution.

This n nber is estinctcd u plant. & 15 rods for the Monticello V. P.ffect_on Trafsic-'., and Accidents

1. Rod & ,n ?ccide-t i

j a. Eu"her of Fuel Rod Failu:cas 4

In the absence of enrichment deviations it has been computed that 300 fuel red fc tures could occur in the l worst case. The numt.er of expected deviations in the Montjuello core is only 12, and the number in the neighborhood of a "Crcpped rod" would be 41. Enrich-  ;

ment deviationc will have no effect on the number of 1 rod failures in this accident.

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b. Peak Fuel Enthalpy  !

a 2 Without deviations the peak fuel enthalpy is computed b to be 250 cal /gm if the rod worth is assumed to be

2 1/2% ok. To reach fuel vaporization point (425 cal /gm) an enrichment error of 70% or more would be j required which can only occur in the 1.13 w/o fuel rods. Based on 255 suspect fuel rods of this enrich-ment it is expcoted that only 2 or 3 would contain errors of any kind and only v 0.3 rods uould have cr-rors of sufficient magnitude to exceed 425 cal /gm. The probability of such a rod being located in the neighbor-hood of a dropped rod is less than .003. Coupled with the low probability of a rod drop occurring and the conservatism inherent in the analysis of this accident, f

) it is clear that enrichment deviations wil.1 have no offect on this accident. Even if such an unlikely i

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, .. -l' O Pn G Q May G, 1M j

combina ti on of event:. did occur, the energy injected l

into the moderator would Le no small that no vescel l dnnage could result. It is estimated that 50 1:q of

( U0 2 dispersed would Le required to cause vessel damage.

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c. Reactivity Effect The presence of high enrichment fuel in a low enrich-ment location will increace the worth of the control rod. It is estimated that the worth will increase by j

1- 0.25 tak if the enrichment error amounts to 100%

(i.e., a facter of 2) and a long-string of deviant j pellets occurs. As indicated above, this is very j

i un?ikely. Normal control rod sequc :cs yield manimum rod worths of -u lt bk and even this increase will I

j renult in a rod worth well bc]cw the 2 1/2t assumed in the accident.

I

! 2. Losn of Coolant Accident 1

t The effect of enlichment deviations is summarized ia the following table which li sts the fractional number of fuel j

I rods e::pected in various clad tcaperature rangec. Th e c c-

' valucc were calcu' ted with the came technicuas and models discussed in detcil in the FSAR and represent the worst cane LOCA.

CL7sD TEMPERTT'JRE EXPLCTED NO. OF RODS 4

f 71900 F 2,2

72000*F 0,7

'7 216 0

• F (,1 i

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i Notice that there is Icss than a 10% probability that even one rod would exceed current temperature limits and that l

even this rod would be uell belc.' melting temperature.

3. Othcr Transients

a. Two Pump Trip l

Without enrichment deviations it has been ecmputed that

{ the simultaneous trip of two recirculatory punrs while 1

operating at limiting conditions leads to an MCHFR value of 1.68. The expected nunber of rods experiencing MCHFR l

1 1 is estimated to be 0.1 with the expected number of pellet enrichment deviations. Thus it is unlikely that i

this transient will cause any fuel rods to vio] ate the i

defined damage limit of MCHFR = 1.

i a

b. Continuous Rod Withdrawal from Full Power l

i Erroneou: control rod withdrawal can lead to a.10L  :

increase in peak heat flux and a reduction in MCIIFR l

! to 1.3. With the probable number of enrichment de- I viations, the expected number of rods having a heat  !

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• v Page ? May 6, 1971 [

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't flux greater than 28 Pl/f t (defined dar'ge limit) is  !

' estimated to be less than 0.1, and the number experienc- )

ing MCl!FR i 1 is appro:.:imately 0. 5. )

I' VI. Conclusion  !

,' It ir our conclusion that it is safe and prudent to operate the Monticello plant as now constituted up to full power i (1670MN). This conclusion is based on the following consider- !

ations. i i

l

1. The expected numbe of fuel rods having enrichment de-  !

viations of a magnit ude to e::ceed the design limit is '

a very small fraction ci the core (2 out of 24,000) . '

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. 2. The prer" :ce of a small number of drtriating fuel rods li does not jeopardize reactor safety nor adversely effect  ;

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reac:.or performance. I i

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