ML19339B633
| ML19339B633 | |
| Person / Time | |
|---|---|
| Site: | 07106698 |
| Issue date: | 09/30/1980 |
| From: | Clay Johnson NAC INTERNATIONAL INC. (FORMERLY NUCLEAR ASSURANCE |
| To: | Macdonald C NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| Shared Package | |
| ML19339B620 | List: |
| References | |
| 17575, CRJ-80-151-ETS, NUDOCS 8011070355 | |
| Download: ML19339B633 (6) | |
Text
O Nucteer Assurance Cttporett:n 24 Secutive Asrx West Attar ta. Gecrga 30329 i4c41325-4200 Teiex:549567.542703 Tr$ ~:rt:n onve 3ran: knc:::n. Carcrac: 315:'
13C2I 245-4220
.v t 9:c9295324 Serr:er22:rasse 9 3CC1 : r cn. Sa:eranc cn ace u 7e en $7275 September 30, 1980 CRJ/80/151/ETS Mr. Charl.2 E. MacLunald, Chief Transportation Certification Branch Division of Fuel Cycle and Material Safety United States Nuclear Regulatory Commission Washington, D.C.
20555 Re:
Occket No. 71-6698 Cear Mr. MacDonald:
As we discussed last week, we will appreciate your informal review and verbal comments on the following draft of language we will propose to replace paragraph 14 of Docket No. 71-6698, Certificate of Compliance No. 6698.
"14. Before inactive casks are returned to service and for active casks at ncminal intervals of six (6) months but no later than seven (7) months following the first shipment of irradiated fuel under Revi-sian 9 and later revisions to Certificate of Compliance No. 6698, the licensee shall perform physical measurements of the inner shell of each cask at comparable locations to those documented in Appen-dix C to NAC letter dated June 8, 1979. These measurements are to be comnired with the Reference dimensions of each cask as deter-mined by the average of at least three measurement replications, without intervening use of the cask, using separate equipment set-ups for each replication.
The measured values for cavity dimensions shall agree within a 95/95 confidence interval with the Reference dimensions and any deviations from the Reference dimensions shall be random.
Addi-tional replications of cavity measurements may be made providing values from each replication are used to compute average dimen-sions for comparison with Reference dimensions and to verify randomness of deviations.
To verify that individual measurements differing frem the Reference dimensions are part of the inherent variability of the ineasuring system and do not represent localized dimensional changes in the cavity, a ' chi-squared test' as described in the attached appendix shall be performed. This shall consist of comparing the frequency of individual changes in measured values in each of five axial segments of the cask with the frequency of individual changes in measured values observed between the sets of measurements used to yo no70355
Mr. C. E. MacDonald Page Two establish the Reference dimensions of the cask.
The probability quan-tity p resulting from the chi-squared test shall lie between 0.1 and 0.9.
Should the probability quantity p lie outside of this range, the cask shall be removed from service."
Results of the chi-squared test on the measurements in 1979 and 1980 in the O cask cavity are enclosed. The chi-square bounds are taken from the.cigure plot of p as a function of chi-square and degrees of freedom.
Sincerely, NUCLEAR.ASSURAi Q CORPORATION
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(h-lesR.Jonn, son t-,. ti.
K.
Cha Vice President Engineering & Transportation Services CRJ:cnr Attachment o
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THE CHf-SQUARED TEST FOR DIMEtiSICNAL CHAtiGES IN CASK CA'/ITIES In establishing Reference dimensions of the inner cavities of the NAC-1 casks, at least three (3) replications of measurements as documented in Aopencix C to NAC's letter to ;4RC dated June 8,1979 shall be made with-out intervening use of the cask.
The purpose of the replications is twofold:
first to provide values from which average dimensions can be established and, second, to provide data frem which the variance inner-ent in the measuring system can be determined.
A normal distribution of differences between individual measurements at comparable locations shculd result if there is no change or bias in the measuring system.
Differences in measured values frem comparable locations after the cask has seen service will represent a change in the cavity dimensions unless they can be shown to be a part of the same population as that established by the replicated measuremees used for the Reference dimensions.
Local differences in cavity dimensions might still be masked by a general statistical comparison of measured values.
For this reason, the chi-squared test shall be performed over five axial segments of the cask.
The test consists of comparing the distribution of the frequency of occurrence of diametral changes of 0.001 inch that occurred between the three replicated measurements used to establish the Reference dimensions.
In equation form, the test is expressed as:
2*
If(*i' 0*) - P(*i' 0*)I X
i=1 p(x, ax) g wnere X is the chi-square value f(x, ax) is the number of diametral differences g
in the rance between x$ and x$ + ax p(x, ax) is the number of diametral differences j
in the range between x and x + ax predicted by the ncaa distrlbution representing the dirferences noted in establishing the Reference dimensions.
n is the nutoer of measurement locations l
a The acceptance of the results of the chi-square test is based upon the determination of a quantity p which is defined as 'the probability ;."at, on receating the series of measurements, larger deviations from the expected values would be observed." Reference 1 also states that if p lies between 0.1 and 0.9, "the assumed distribution very probably I
corresponds to the observed one, while if p is less than 0.02 or greater than 0.98, the assumed distribution is extremely unlikely and is to be questiched seriously."
4 Figure 2.1 on page 776 of Reference 1 (attached) presents p as a function e
of x and F.
F is the number of degrees of freedom which in this case is two less than the number of different values of the diametral differ-ences. Thus, the cceeptable chi-square must result in a probability between 0.9 and 0.1 for the diametral differences to be considered as measurement error and not real dimensional changes.
Satisfaction of I
this criteria provides confidence that there are no diametral changes wnich could reflect a change in the cavity configuration.
References 1.
Evans, Robley D., The Atomic Nucleus, McGraw-Hill Book Company, Inc.,
1955.
2.
Parratt, Lyman G., Probability and Excerimental Errors in Science, Dover Publicaticni, Inc., 1961.
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