ML20148F088
| ML20148F088 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 09/18/1975 |
| From: | Purple R Office of Nuclear Reactor Regulation |
| To: | Andognini G YANKEE ATOMIC ELECTRIC CO. |
| References | |
| NUDOCS 8011030760 | |
| Download: ML20148F088 (5) | |
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DRMlCH TECl!NICAL POSITION CPB 4.3-1 11ESTINGl!DUSE CONSTANT AXIAL OFFSET CONTROL,(CACC)
BACKGR9UND in connection tzith the staff review of 1l CAP-8185 (17x17), we reviewed and.
accepted a schemo developed by 11cstinghouse for operating reactors in such a fashion that throughout the core cycle including during the most Jimiting pouer maneuvers the total peaking factor, F, will not exceed '.hc value Q
consistent with the LOCA or other limiting accident analysis.
This operating scheuc called constant axial offset control (CAOC), involves naintaining the axial flux difference within a narrow tolerance band ercund : turnup-dependent target in an attempt to mininize the variation of the axial dis-I tribution of xenon during plant maneuvers.
Originally (carly '7:1), the maximum allowable Fq (for 1.0CA) was 2.5 or greater.
Later (late '74), when needed changes ucrc nade to the CCCS ovaluation modc),
b'estinghouse, in order to meet physics analysis commitments to all its cus-tomers at virtua51y the same time, did a generic analysis (one designed to suit a spectru$ of operating and soon-to-be-operating reactors) and showed that most plants could meet the requirements of Appendix K and CPR 50.46 (i.e., 22000F peak clad temperature) if Pq 1 2.32.
Also, 1lcstinghouse showed that CAOC procedures employing a + 5*6 target band would limit peak FQ for cach of these reactors to less than 2.32.
h'c recognized at that time, however, that not all plants needed to maintain Fq be4ow -2.32 to meet FAC, or, needed to operate within a + 5% band to achieve Fq 1 2.32.
In fact, Point Beach was allowed to operate with a vider band because the h'isconsin Elcetric Power Company demonstrated to our satisfaction that the reactors could be manctivered within a wider band (+6,-94) and still hold Fq below 2.32.
h'c fully expected that in time most plants would have individual CAOC analyses and procedures tailored to the requirements of their
"" '+ -specific ECCS analyses.
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Thereforc, when we accepted CAOC it was not just Fq = 2.32 and a + 54 band width wo vere approving, but the CAOC nothodology.
This is analogous to our review and approval of ECCS and fuel performance evaluation nodels.
7
.g The CAOC notho'dology, which is described in I? CAP-8385 (Ref.1), entails (1) establishing an envelope of allowed power shapes and power densitics, (2) devising an operating strategy for the cycle which maxini cs plant flexibility (maneuvering) and minini:cs axial power shape changes, (3) dran-strating'that this strategy will not result in core conditions that viole.tc the envelope of permissihlc core power characteristics, and (4) de:wnst: c tir.
that this poyer distribution control scheme can be effectively supervisef ei, out -o f-coro dc.t ectors.
liestinghouse argues that point 3, abpve, is achieved by calculating all of the load follow uaneuvers planned for the proposed evc]c and showing ths.
j the naximum power densities expected are within liuits.
These calculnti"ns are performed with a radial /nxial synthesis method,which has been shown te predict conservaiive power densitics when conpaved to experiment.
Thile te have accepted CAOC on the basis of these analyses, we have also required tha power distributions be neasured throughout a number of representative (fre-quently, limiting) mannuvers early in cycle life to confirm that peaking factors are no greater than predicted.
Additionally, we are sponsoring a series of calculations at DNL to check aspects of the liestinghouse analysis.
7 The power distribution measurement tests described above will, of course,
. automatically relate incore and excore detector responses, and thereby validate that power distribution control can be nanaged with excore detectors.
BRANCll TECIIXICAL POSITION hhenever an applicant or licensco proposes CAOC for other than Fq = 2.32 rnd AI = +5's he is c: aerted to }.
/ide:
1.
Analyses of Fq x power fraction showing the maximum Fq( ) at power Icycls up to 100'h and DNB performance with allowed axial shapes relative to the design bases for overpower and loss of flow transients.
The envelope of L
those analyses must be shown to be valid for all normal operating trodes and anticipated reactor conditions.
(See Tabic 1 of Reference 2 for the cases which must be analy:cd to forn such an envelope.)
2.
A description of tne codes used, how cross-sections for cycle were deter-mined, and what F values were used.
xy 3.
A con:aittent to perform load-follow tests wherein Fq is determined by takilig incore caps during the transient (NOTE h'estinghouse has outline:'
for both the NRC staff and the ACRS on augmented startup test progran I
designed to confi ra expe-inantally the predict ed power shap; s.
'lhe det'..
of this prograu will be disclosed in a soon-to-be-i.ssued
'.l CAP report.
The tests will be carried out at several representat ire - both 15x]5 and l
j 17x17 - reactors.
rlc have endorsed these tests as has the ACRS in its June 12, 1975 Diablo letter.
In addition, for the near tern, we plan to require that those licensees who propose to depart from the previously approved peaking factor and t arget band width perform sinila: tests, precisely which ones to be deternined on a case-by-case basis, to broaden our confid0nce in analytical methods by extending the comparison of prediction with 'neasurement to include nore and nore burnup histories.)
REFERENCE 1.
T. Morita, et cl., " Power Distribution Centrol and Load Following Procedures," tl CAP-8403, llcstinghouse Electric Corporation, Septcmber 197'..
(Ed. Note - rl CAP-8403 and -8385 are the non-proprietary and proprietary versions of the sana document.)
2.
C. Eichc1dinger, tlcstinghouse Electric Corporation, letter to D.
B.
Vassallo, U.S. Nuclear Regulatory Cor."nission, July 16, 1975.
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