ML20140H531
| ML20140H531 | |
| Person / Time | |
|---|---|
| Site: | 05000231 |
| Issue date: | 12/22/1970 |
| From: | GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20140G249 | List:
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| References | |
| FOIA-97-34 NUDOCS 9705130174 | |
| Download: ML20140H531 (13) | |
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REVISION NO. 2 0F
' PROPOSED CilANGE NO. 4
.... .../].72-70
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FOR Tile ,
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SOUTHWEST EXPERIMENTAL FAST OXIDE REACTOR RE: LICENSE DR-15 DOCKET NO. 50-231 i
GENERAL ELECTRIC COMPANY 310 DeGuigne Drive
,Sunnyvale, Calif.
' 94086 9705130174 970505 PDR FOIA VARADY97-34 PDR
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( Revision No. 2 of .
i Proposed Change No. 4 i ,
for the
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. SEFOR Technical Specifications
- 1. Introduction l Revision 1 of Proposed Change No. 4 was submitted by letter dated December 11, 1970, with the notation that additional information concerning the criteria for continued operation with failed fuel would be provided later. This document con-tains that additional information.
- 2. Proposed Changes Pursuant to the provisions-of 10 CFR 50.59, General Electric requests that the SEPOR Technical- Specifications be changed by adding pages 3.13-1 through 3.13-7 in Attachment A of this document to the current Technical Specifications. These pages replace those previously submitted as Revision 1, changes hav-ing been made to those parts related to cover gas activity and criteria for operation with failed fuel.
- 3. Purpose of the Proposed Change Specification 3.10.E of the present SEFOR Technical Specifica-tions requires that certain additional specifications be approved and incorporated into the Technical Specifications prior to ,
initial operation at 20 MWt. These specifications are submitted l
j herewith, based on experience gained in* operating SEFOR up to and including the 10 MWt power level, to satisfy the requirements of Specifications 3.10.E and 6.6.B.3.
- 4. Discussion 4.1 General The basic fuel failure detection system in SEFOR is the Gross Cover Gas Monitor (GOGM). Information obtained from the GCGM I is supplemented by isotopic analysis of the fission products in l
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i cover gas and sodium . samples and by examination of fuel rods in the~ refueling cell. The GCGM provides a continuous indication of the gross gamma activity in th'e reactor vessel cover gas.
3 Iso' topic analysis of the fission products in the cover gas and
. fuel rod examinations are performed on a routine basis as speci-fled in 4.4.P and 4.3 of the Technical Specifications. Proposed Specification 3.13.A.1 provides a specific change in level for the GCGM reading that will be treated as anomalous fuel behavior. ,
Proposed Specification 3.13.B provides a limiting condition for operation that assures that the CCGM is always capable of detect- )
ing an anomaly as defined by proposed Specification 3.13.A.1. .)
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Specification 4.9.B.1 outlines specific steps to be taken in the l event of a cover gas anomaly as defined by proposed Specification 3.13.A.1. Cover gas samples will be taken for isotopic analysis i as part of the diagnosis of a cover gas anomaly. (Specification l 4.4.P) If the results of this analysis give positive indication i
that cladding failure has occurred (as indicated by a significant increase in short half-lived [less than three hours) isotopes in i the cover gas as discussed below), Specification 4.9.B.3 and
, 4.9.B.4 require that the reactor be shut down for examination of !
all fuel rods which are accessible under the through-head ports and that at least two sodium samples be obtained from the reactor vessel. Section 4.9.B also specifies the conditions under which reactor operation may be resumed. In this regard, it should be noted that a decision to resume steady state operations may be .
made with an indication of failed fuel as well as leakers in the core. However, excursion tests with an indication of failed fuel would be prohibited by Specification 3.12.B.10.
The technical bases for the proposed specification covering opera-
. tion in the presence of a known loss of clad integrity is given in i the following discussion and in the bases for proposed Specifica-l tion 3.13.A.1 and 3.13.B.
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!' ~4.2 Technical Bases:
Thefeactorcovergasmonitoringfunctionincludes: (1) a con-tinuous gross gamma activity detection capability and (2) specific e
provisions for isotopic analyses at routine intervals or follow-ing detection of anomalous conditions. Taken together, these two functions provide an effective method of detecting anomalous fuel behavior and characterizing the natt re of such behavior.
The GCCM' responds to four decades (1 mr/hr to 10 R/hr) of activity, ranging well above and below the normal reading of 50 to 100 mr/hr during reactor operation. Its response to activity release events (43 min) is approximately equivalent to that of a delayed neutron monitor (N1 min). ,
A significant increase in delayed neutrons in the primary sodium is regarded as indicative of a significant cladding failure, since the short-lived delayed neutron precursors are not released to the sodium unless some fuel surface is exposed to flowing coolant.
l Requirements for cover gas analysis at SEFOR provide a similar cladding failure detection capability. Rather than detecting the presence of short-lived species by delayed neutron release, their noble gas daughters which are released to the cover gas, are detected by gamma emissions and are measured by means of gamma ray spectroscopy of cover gas samples. It should be noted, how-ever, that of the two methods, detection of delayed neutrons is related more conclusively to exposure of fuel material to flowing sodium, while detection of the noble gas daughters (which, compare'd to neutrons, possess significantly long ba.lf-lives) may also indi-cate the release (from a leaking fuel rod) of the low equilibrium levels of these species which are normally held within the clad-ding. However, through determination of the isotopic ratios of l
l various fission products, including these short half-life noble gas daughters, it is possible to distinged.sh between exposure of a fuel to flowing sodium and leakage of gases through small defects.
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i Minute quantities of such fission products, apparently due to the 1 presence of tramp fissile material in the sodium or plated on surfaces in the vicinity of the core, have been identified at SEFOR; these are listed in Table I and afis. cussed below.
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41 23 .
.-- The background effects of A and Ne have afso been measured E 41 ?
at-10 MWt operation. 'A , at a level of 0.016 pCi/cc, produces a res,ponse of 4 mr/hr on the GCGM. Ne 23 activity was determined
, to be 0.88 pC1/ce, producing a response of 22 mr/hr.
A previous submittal (1) indicated that the GCCM response was due 41 to A . However, improved analytical techniques detected the- ]
23 1 38 sec Ne and determined that its contribution to cover gas j 41 '
activity was significantly greater than that of A . The dominant influence of the 38 sec Ne on' the GCGM reading causes a larger variation in the reading of the GCGM than originally anticipated due to small flow variations in the system. For this reason, the anomaly limit on the GCGM reading has been expressed in terms of l an incremental change rather than a multiple of the background .
I reading proposed in Reference 1.
I Provision has been made in the SEFOR design for accommodation of
[ . the fission-gas which might realistically be released from a large number of leaking fuel rods. ( ) Complete depressurization of a 1 l
1 fuel rod would yic1d a small fraction 1of this' amount. However, )
!. such a release level could also accompany the occurrence of a-more serious cladding defect and has been used to determine the incremental release which necessitates special diagnostic activ-ities. The response of the GCGM to the principal noble gases released from an average ~ rod following three days' irradiation at the 20 MWt level is given in Table II. The 1610 mr/hr increase is more than three times the proposed anomaly limit of 500 mr/hr.
The fractional release-to-birth ratios of Reference 3 have been
- l. adopted for this estimate.
Diagnosis of cladding failure characteristics on the basis of isotopic analysis of the cover gas has the potential of higher
- resolution than diagnosis by delayed neutrons because of favor-able branching ratios. Thus, fuel condition diagnosis by
$ radiometric assay of cover gas samples is practical due to the abundance of released gamma activity and the relatively high 3- efficiency of gamma-counting equipment. The fractional decay chains of the longest-lived precursor isotopes are given in i Table'III.
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. It is pertinent to note in this connection that the trip setting l above background of tlie FERD* system at EBR-II has been related t
to ap exposed fuel surface area. The relation was made on the
, basis of measured incremental count rates due to the deliberate
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introduction of a known (recoil surface) fission product source ,
in the reactor. (4,5) This bare fuel exper1 ment detemined that the full power background count rates can be correlated with approximately 11 cm surface of the unclad fuel. Since trip levels are set at twice background (on two-out-of-three channels),
automatic protective action is taken if the delayed neutron signal increases by an amount equivalent to that produced by the 11 cm sourCc.
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4 More generally, this trip-increment source is computed to corres-10 pond to the effect of 5.8 x 10 fissions /second (determined from 10 fission fragment range data) or 1.6 x 10 fissions /second (based 135 on Xe production observed during the bare fuel experiment). The i latter value is adopted as a more conservative estimate.
l l Exposure of SEFOR fuel to sodium would produce a weaker source per unit area than the EBR-II bare fuel, smaller by a factor of 15, l since the source is proportional to the fission density (and the-effective recoil skin depth). Thus, 11 cm of exposed SEFOR fuel surface would contribute approximately 10 fissions /second, Radiometric assay of reactor cover gas samples at SEFOR has shown
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a fission product activity of approximately 1 x 10"4 pCi/cc for short (<3 hrs) half-life isotopes and 2 x 10- pCi/cc for the longer-lived isotopes. Computations show that this activity would 8
be produced by a source level of approximately 10 fissions /second.
This level therefore corresponds to an effective recoil surface area of 1.1 cm at an average flux position, or a total in-core i
surface contamination level of 0.22 mg fissile (the corresponding j tramp level in EBR-II is 8.0 mg fissile).
- Fuel Element Rupture Detector, based upon detection of delayed neutrons.
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. Replacement Page
- December 31, 1970 i
Consequently, the technique of cover gas analysis to detect and measu,rc the short-lived fission products, as demonstrated at SEFOR, can effectively determine the condition of the fuel and can detect
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, significant changes which may occur as a result of operation with
. known loss of clad integrity.
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i Replacement Page December 31, 1970
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]' 'It is pertinent to note in this connection that the trip setting
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'\ above background of the FERD* system at EBR-11 may be related to an exposed fuel surface area. The' relation is made on the basis of measured incremental count rates due to the deliberate intro-
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s duction of a known (recoil surface) fission product source in the reactor.
(') This bare fuel experiment determined that the full ,
power background count rates can be correlated with approximately 8 bgt exposed fuel surface. Since trip levels are set at twice back und (on two-out-of-three channels), automatic protective action taken if an additional effective source corresponding to.8 cm fuel surface should develop.
135 C,over gas ana ses at EBR-II established a fission product Xe 10 production rate f 1.1 x 10 atoms /second due to presence of the bare fuel pin.
( Assuming a fission chain yield of 0.06, the fis-sion rate is 1.8 x 1 fission /second. Since the fuel. surface area
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was 40 cm , exposure o 8 cm of fuel would provide a source of 10 3.6 x 10 fissions /secon Exposure of SEFOR fuel to so um would produce a weaker source per unit area, smaller by a factor f 30, since the source is proportional to the fission density (and the e ec,tive recoil skin depth). Thus, l
8 cm2 of exposed SEFOR fuel surface ould contribute approximately 10 fissions /second.
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! Radiometric assay of re'accor cover gas sam es at SEFOR have shown l a fission product activity of 1 x 10 pCi/cc or short (<3 hrs) half-life isotopes. Computations show that thi activity would be produced by a source level of 1 x 10 fissions /se nd. This level
- therefore corresponds to an effective recoil surfac area of only ;
-4 m 2, which provides a measure of the capabil ty of current 8 x 10 diagnostic methods at SEFOR to detect small changes in uel condition. I 4
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- Fuel Element R,upture Detecto", based upon detection of delaye neutrons.
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- \ A factor of 1000 increase in the present short-lived fission product x
background would be related to the presence of 0.8 cm of exposed
.\N fuel, if it were not accompanied by a corresponding increase in lon'g life isotopes. Consequent 1y', sensitive measuring capabilities
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\ are available at SEFOR to determine the condition of the fuel and N to detect any changes in the fuel which may occur as a result of operation with a known loss of clad integrity.
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i TABLE I I COVER CAS ISOTOPES DETECTED'IN SEFOR Principal y
' Isotope 11alf-Life E (Mev) Comment i
Ne 38.6 sec 0.440 Na + n + Ne +p+y 41 A
1.83 hr 1.29 A +n+A' +y Na 15.0 hr 1.37 Na + n + Na24 , ,
133 Xc 5.27 d 0.081 Fission Product 135 Xe 9.16 hr 0.250 Fission Product 135m Xe 15.7 m 0.527 Fission Product l
Xe 14.2 m* Cs 38 Detected by Cs 138
-Daughter E(y) = 0.46, 1.01, 1.426 Mev 85m Kr 4.4 hr 0.150 Fission Product 1
0 Kr 76 m* 0.196 Fission Product Kr 2.79 hr* 0.403 Fission Product
- Daughters of delayed neutron precursors, alternate branch. .
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.. . TABLE Il .
t:
' GCGM RESPONSE TO ROD DEPRESSURIZATION*
e- .
. r Isotopic Calculated Release / Birth (3} pCi/cc mr/hr ,
Isotope - R6d ' Activity Ratio (3 days) In Cover Gas GCGM Reading l
33 2 Xe 3.00 x 10 C1 3 x 10 -2 15.0 75 l
Xe 135 1.76 x 10 3 6 x 10
-3 17.6- 880 6 x 10 -3 85m 2 Kr 1.92 x 10 1.92 60 2 x 10 -3 2
Kr 3.91 x 10 1.30 505 Kr 3.22 x 10 2
1 x 10
-3 0.54 90 l ,
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Total GCGM Response = 1610
- Assumes 3 days operation at 20 MWt and no significant holdup (delay) within the cladding. Additional contributions from shorter-lived isotopes may increase the total response, if their release / birth ratios prove to be signifi-cant.
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TABLE III t
DELAYED NEUTRON PRECURSOR DECAY BRANCHING Precursor y - Emitting n - Emission Branch Isotope Half-Life Daughter (Fraction) Daughter (Fraction) 87 *-
Br 54.8 see Kr (0.97) Kr (0.03) 137 1 24'.4 sec Xe 137 (0.97) Xe 136 (0.03) ]
j' Br 16.3 sec Kr (0.94) Kr 87 (0.06) l 138
-I 6.3 sec Xe 138 (0.98) Xe 137 (0.02) l e
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References ,
,(1) Proposed. C$ange No. 4 to the SEFOR Technical Specifications,
. . Sept. 3, 1970-L -
- e. .
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'(2) SEFOR FDSAR,' Supplement 21, pages 32, 33. i 1 i
('3) A.W.ELongest (ORNL)' et.al. , " Fission' Gas Release Measurements f rom L
Fast Breeder (U, Pu)0 2 Fuel," Transactions of the American Nuclear j Society Winter Meeting, November 15-20, 1970, Washington, D.C. 1 (4) R.R. Smith, et.al. , " Exposed Fuel . Calibration Study in- EBR-II - )
i- Second Series," ANL-7558, EJanuary, 19 70. !
(5) G.G. Brunson, " Studies with the Reactor Cvoer Gas Monitor,"_ANL -
Reactor' Development-Program Progress Report, ANL-7679, March, 1970 .
p . 91. .,
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