ML20140H317
| ML20140H317 | |
| Person / Time | |
|---|---|
| Site: | 05000231 |
| Issue date: | 07/08/1970 |
| From: | GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20140G249 | List:
|
| References | |
| FOIA-97-34 NUDOCS 9705130066 | |
| Download: ML20140H317 (9) | |
Text
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~]b PROPOSED CHANGE NO. 3 FOR THE SOUTHWEST EXPERIMENTAL FAST OXIDE REACTOR' l
Re: LICENSE DR-15 DOCKET 50-231 9
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GENERAL ELECTRIC COMPANY 310 DeGuigne Drive Sunnyvale, California 94086 1
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l 9705130066 970505 ADY 34 PDR y
Proposed Change No. 3 for the Southwest Experimental Fast Oxide Reactor I.
Int'roduction Under the authority of License DR-15, General Electric operates the Southwest Experimental Fast Oxide Reactor at a site near Strickler, Arkansas.
A revision of the current Technical Specifications is desired as described herein.
The applicable revised pages of the Technical j
Specifications are also included as Attachment A.
II.
Proposed Changes Pursuant to the provisions of 10 CFR 50.59, General Electric lequests that the Technical Specifications be changed by substi-tuting the pages, numbered 3.3-1, 3.3-5, 3.10-3, 4.3-1 and 4.3-2 in Attachment A of this document, for corresponding pages of the current Technical Specifications. The proposed changes to the current Technical Specifications are indicated by brackets in the margin on the enclosed pages.
III.
Purpose of the Proposed Change The present Technical Specifications require removal of guinea pig fuel rods located under the three innermost refueling ports during steady state reactor operations above 17.5 MWt.
The purpose of the proposed change is to provide additional information to confirm the margin of safety for standard fuel rods by utilizing the guinea pig principle over the full operating range of the reactor.
This change will also provide deta on the thermal performance of mixed oxide fuel in a f ast neutron environment.
These data may demonstrate that the currently used lower error band on fuel l l t
thermal conductivity is. unnecessarily conservative and would, as a minimum, increase the confidence in the fuel design of the LMFBR Bemonstration Plant.
. Tests ronducted during the SEFOR pre-operational R&D Program have demonstrated that the guinea pig fuel rods will exhibit safe per-formance at the 20 Wt power level, and fuel rod inspections, utilizing procedures called for in the Technical Specifications, will be used to verify the condition of the guinea pig rods af ter operation at 20 Wt.
IV.
Reason for the Proposed Change Guinea pig fuel rods under the innermost refueling ports operate at a peak linear power density which is 15% higher than that of a standard fuel rod nearest the center of the core.
This relation-ship was used to establish the last three power levels in the approach to power, namely, 15, 17.5 and 20 Wt.
Thus, examination of guinea pig fuel rods, which is required by the current Technical Specifications after operation at 15 and 17.5 Wt, will provide information which will verify the safety.of operating the standard fuel rods at the next power level.- By using this method, a maximum of six guinea pig fuel rods are exposed to operation at power genera-tion rates previously untested in this reactor.
If the guinea pig principle were not used, 90 to 100 standard fuel rods would be subjected to such exposure at each step in the approach to power.(1)
The present plan, calling for removal of the innermost guinea pig rods for operation at power levels above 17.5 We, provides advance information for standard fuel rods only up to the nominal reactor 1
power level of 20 W t.
It does not verify the capability of the fuel rods at the LSSS (21 Wt) or at the safety limit (22 Wt).
The pre-operational R&D Program has demonstrated that SEFOR fuel I
rods can be operated at power generation rates well above the rates
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corresponding to these reactor power levels without damage.(2,3)
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t Furthermore, they have shown that operation at significantly higher power levels does not result in loss of cladding integrity, although local "diametral changes after such operation might exceed the amount allowed in Paragraph 3.3.K of the Technical Specifications.
In sunmary then, the proposal that the guinea pig fuel rods under
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the innermost refueling ports be left in the reactor during opera-tion at 20 MWt is based on the following arguments:
1.
Such operation will provide additional confirmation that the hottest standard fuel rods can operate safely at power genera-tion rates corresponding to the reactor power safety limit of 22 MWt.
2.
Tests conducted during the pre-operational R&D Program have demonstrated that fuel rods can operate safely at the maximum linear power densities which might be experienced by guinea pig rods under the innermost ports at the reactor safety limit
)
of 22 MWt.
3.
The guinea pig fuel rods will be examined af ter completion of initial tests at 20 MWt and must meet the requirements of Paragraph 3.3.K of the Technical Specifications.
4.
The limits for fuel rod damage, as presently specified in 3.3.'K of the Technical Specifications,are well below values which would result in a loss of cladding integrity.
V.
Discussion l
i l
A.
General Description l
i The guinea pig fuel rods (4,5) contain mixed oxide fuel enriched to 25% fissile Pu0 rather than 18.7% as used for the standard fuel 2
rods.
Two of these rods may be located under each of six refueling 4
ports, although some of these positions will contain standard fuel rods for comparison purposes.
The three innermost ports are located _
such that the guinea pig ro,ds under them operate at 15% greater l-power level than do standard rods located nearest the center of t
the core. The three outermost ports are located such that the guinea pig rod power level is the same as that of standard rods nearest the center of the core.
B.
Planned Use of Guinea Pig Rods While the guinea pig rods will perform a lead fuel function, it is not intended -to use them in a manner that may cause their f ailure or to intentionally jeopardize their safe performance at any time. Measures normally taken to protect-the hottest standard fuel rods have been applied to the operation of these rods. These measures include pre-operational full-scale testing at conditions j
of power and temperature exceeding the expected SEFOR test condi-tions.(6)
In addition, the Technical Specifications provide for suitable periodic inspection of fuel rod condition, and require that certain specified criteria be met before proceeding with the next step in the approach to power.
C.
Linear Power Density Ic is predicted that the hottest standard fuel rod in the core will i
operate at a peak linear power density of 21.8 KW/ft when the reac-tor power level is 20 MWt.
This value is based on the minimum allowable core loading of 600 fuel rods and assumes that all power generation is in, the fuel.
The present core loading is 636 fuel rods, although it may be necessary to increase (or decrease) this number by one or two rods, before reaching 20 MWt. Furthermore, physics data and calculations have established that only 94% of the energy defined as reactor power ( ) is actually generated in the fuel.
Thus, the linear power density actually experienced by j
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the fuel rods at 20 MWt will be less than the 21.8 KW/f t indicated l
l above, or about 19.4 KW/f t for the hottest standard fuel rod. The j
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gk effects of_using 630 fuel rods and 94% heat. generation for linear l-power density calculations are illuctrated in Figure 1.
The uncertainty in reactor heat balance data must also be considered.
l The effec't of the maximum expected error of +5% in heat balance data l
. is 'shown by the different scale f actors on the right side of Figure 1.
Thus, if the heat balance data are 5% high at an indicated reactor j
power of.20 MWt, the true linear power density for a given fusi rod will be 5% lower than the calculated value, and vice versa, i
l D.
Expected Operating Parameters Using the curve for 630 fuel rods and 94% heat generation, Figure 1 i
indicates that the guinea pig rods under the innermost ports at 20 MWt reactor power will operate at a linear power density of 22.6 KW/f t with nominal heat balance data, or at 23.7 KW/fe if the heat balance data contain the maximum expected error of 5% on the low side. These power densities are within the rafe operating region presently recognized by the Technical Specifications.
l l
Initial operation at 20 MWt will be for a lim.ited anoant of time i
j sufficient to obtain necessary heat balance and reactot coefficient data.
Immediately' following these tests, the reactor will-be shut l
down and fuel rods (both guinea pig and standard) will be examined.
l Additional fuel rod examinations are called for prior to the start of and during the transient test program.
l VI.
Safety Analysis A.
Operatina Conditions l
l l
l The proposed change to the Technical Specifications would permit 1
operation at 20 MWt with guinea pig rods under the innermost refuel-ing ports.
Operation at 20 MWt implies the possibility of reaching j
21 MWt before reactor scram occurs, and also implies the possibility
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of momentary power overshoot to a value below the safety limit of 22 MWt.
Consequently, the proposed-change must be evaluated in
. terms of reactor safety at the 22 MWt power level.
- f B.-
Fuel Melting l
l The present power limits in the Technical Specifications were chosen l
. to provide assurance that fuel melting would not occur in any of the i
fuel rods.
This assurance will remain in effect for all fuel rods t
in the core except those guinea pig rods (maximum of six) located under the innermost ports.
These guinea pig rods may experience some central fuel melting if the combination of parameters which l
determine this is unfavorable. However, operation with the expected core loading and with nominal values of calibration data and fuel l
parameters would not result in fuel melting at the reactor safety limit of 22 MWt. '(See Figure 1).
C.
R&D Test Results i
The pre-operational R&D tests have demonstrated that the fuel clad-ding will maintain its integrity under conditions much more severe than the conditions permitted under the Technical Specifications. (8)
These tests also showed that repeated cycles (2) to a linear power density of 28 KW/ft (above melting) did not result in cladding diameter changes beyond the allowable limits given in Paragraph 3.3.K of the Technical Specifications. Furthermore, capsule tests in which fuel pins experienced significant amount of fuel melting (3) showed maximum cladding diameter changes of 18 and 10 mils, as com-pared to. the 10 mil limit in the Technical Specifications, with no I
-loss of cladding integrity.(
These data indicate that the thres-hold for loss of cladding integrity at SEFOR operating conditions is significantly above the limits established in Paragraph 3.3.K of the Technical-Specifications.
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A D.
Summary Operation of the reactor at 20 MWt with up to six guinea pig fuel rods und,er the innermost ports will provide lead information to l,
confirm that the standard fuel rods will not be damaged by operation
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up to the saf ety 1 Lait of 22 MWt reactor power.
Fuel melting is not expected to occur in these guinea pig rods, although this cannot be assured when consideration is given to the worst combinations of l
factors which affect power density. However, even if fuel melting were to occur in the guinea pig fuel rods, the cladding would not
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be damaged,(8) and reactor safety would not be reduced.
)
I
References:
l 1.
SEFOR FDSAR, Supplement 10, Figures I-3, I-5, and II-1.
2.
SEFOR FDSAR, Supplement 3 Figure B-6, and Table 5-1.
i 3.
SEFOR FDSAR, Supplement 3, Figures B-13 to B-16, and Table 5-1.
j 4.
SEFOR FDSAR, Para. 4.2.2.2.
5.
SEFOR FDSAR, Supplement 10, Para.1.6.2..
6.
SEFOR FDSAR, Supplement 3, Page IN-1.
7.
Technical Specifications, Para. 1.5.
8.
SEFOR FDSAR, Supplement 3,Section III (conclusions).
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