ML20024G594
| ML20024G594 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 03/02/1973 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Ziemann D US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9102130443 | |
| Download: ML20024G594 (5) | |
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Re NSF NORl'HERN STATES POWER COMPANY M I N N IE A PO LI S. M I N N E S OT A 59401
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h RECULATCRY Mr. D L Ziemann MAIL SECTION A,
Operating Reactors Branch 2 DOCKET CllAX ' (6
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Dear Mr. Ziemann:
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MONTICELLO NUCLEAR GENERATING PLANT co io Docket No. 50-263 License No. DPR-22 l
Answers to December 21, 1972 Questions Concerning the Rod Drop Accident Analycis We are writing in response to your December 21, 1972 letter requesting addi-tional information pertaining to our Supplement No. 1 to Change Request No. 3 of our Technical Specificatione. We would like to preface our answers to l
your questions with the following commento on the Control Rod Drop Accident (RDA).
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The bases for the RDA postulate a single active component failure an doec the Loss-of-Coolant Accident (LOCA) and the Steam Line Break Accident (SLBA).
Unlike the LOCA or the SLEA analysec, the RDA further allows for a single op-
,b erator error.
The active component failure in the case of the RDA ic accused i
to be the separation of the control rod blade from the rod drive, the hangup l
of the blade and the subcequent drop of the blade out of the core.
This sequence in itself can be debated to be a combination of unlikely events "W
!R constituting multiple active component failures having a very low probability
{I of occurring in thic combination, therefore, making the RDA very unlikely.
lC The single operator error is assumed to be the vithdrawal of an out-of-cequence l vn rod having a large reactivity worth.
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l When at power, the RDA involving an out-of-sequence rod can be tolerated as
,#j9 diccusced in the FSAR and in Topical Report NEDO-10527 The RDA involving
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an out-of-sequence rod cannot be Mlerated during heatup; therefore our
,k Technical Specifications require that either the Rod Worth Minimizer (R44) or a second independent operator monitor the rod withdrawal cequence. Allow-ing for a cingle component failure simultaneous with a single operator error, tj pp y
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the IdA vill not occur at low power since one muct either acct.me a recond active component failure in that the IN!4 fails to block the erroneouc control rod with-drawal, or a second operatur error in that the independent operator obccrying the rod withdrawal procedure fails to obcerve the erroneouc rod celection by the console operator.
A IHA involving an in-sequence rod can be tolemted at any power level. hece guidelinec for analyzing the lilA are no different than thore uced in the FCt.R.
There are two calculations that muct be performed.
Firot, one muct celect the power level above which the RIA can be tole rated accuming an operator error cimultaneous with a component failure, allocing the JM!4 to be bypacced.
Figure 3-9 of lied 0-10527 above very dromatically why the INM can be bypacced at power and also why it is required daring hot ctandby.
The cecond calculation, the one in quection at thic time, is needed to celect a limit for the worth of in-coquence control rode which vill allow operating flexibility without a rick to the health and cafety of the ceneral public in the unlikely event of a PJA in-volving an in cequence rod.
Ilote that a RDA involving an in-cequence control rou can be postulated to occur with only a cingle active cosponent failure.
Ib operator error muct be accumed and the KdM will not cupply a block to the vitbdrawal of an in-cequence rod.
There fore, the limit ectabliched for the worth of, each in-cequence rod ic cuch thet in the unlikely event of a FlA, the concequencec are tolerable.
Section 14.6.2 of the FCAIl states that a RDA involving a 0.025 delta k eod can be tol-eroted while the vorth of the ctuch (in-cequence) rod io limited to about 0.01 delta k.
Le latter fact is reinforced by Figure 3-3-h which also chawc thnt the maxi. mum worth of an out-of-cequence rod vac found to be well in excece of 0.03 delta k and could, therefore, not be tc.Lerated in a IdA.
!bre recent analycer chov that while in-cequence rodc have approximately the came vorth as previoucly analyzed and that while out-of-cequence red worthe remain above that level where they are tolerable for the FIA, the threshold of rod vorthe belov vhich the RIA ic tolerable 1a clightly below that previoucly analyzed.
Since thic threchold ic the technical bacis for the limit of in-cequence rod worthc, we have requected that the allavable limit cpecified in our Technical Specificationc be reduced from 0.025 delta k to 0.015 delta k.
With thic in mind we answer each of your fotr quections ac follovc:
1.
The General Electric Topical Report referenced c.pja c to beginning of life conditione for curtained corec.
While the Ibnticello core ic within the ccope of this report, it precently han an averace burnup of approximately 7000 MJD/STU.
Calculations do not exist for thic exact censition.
Of more in.portance is the bound for the moct criti-ce.1 ctage in che life of the Ibnticello-type core.
Baced on a para-metrin evaluation of PlA analycec, General Electric has recently n
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informed us that Figurec 2-1 and 2-2 of Cupplement 1 to NED0-lOS27 provide concervative boundo for all expocure conditionc.
(It chould be noted that Supplement 1 in its entirety applico to a core dec1gn different from that of Ibnticello. ) A topical report coon to be iccued will diccuco the analytical methode uced in evaluating the the exposed core raoponce to a 10%.
Ucing thic more recent '.nfor-mation, it ic concluded that the maximum tolerable worth for a rod involved in a IUA 10 0.015 delta k.
2 10 in no way chances our ini-tial A chnical Cpecification change requect cubmitted September 22, 1972.
2.
he bottom curve in Figure 3-9 of NED0-10527 chowc the worth of that increment of a control rod withdrawn in a nom 91 cequence.
In our i
normal withdrawal zequence the firct 50f; of the control rodo are taken from fully incerted to fully withdrawn an one otep in the ce-quence. After achieving thic co called black-white pattern, the remaining rodo have a maximum vorth approaching 0.W delta k.
Rece rodc are therefore banked out cuch that each increment of rod with-j drawn in no chown in the bottom curve. We cee no need to change our operating control rod withdrawal cequence in cuch a way that the worth of the withdrawn incremento of in-cequence rode witLlrawn vill exceed 0.01 delta k.
We are accured that the withdrawn incre-l mento of in-cequence rode vill not exceed 0.015 delta k.
We refrain from arbitrarily rectrictity ourcelvec to a limit cuch ac 0.01 delta k for un increment of a rod even though we can cenerally meci, tha+ eriteria now and in the forececable future.
Arbitrarily placing a limit that cloce to operating conditiom would require an unwarranted bulk of calculationc and loco of flexibility in ectablich-ing a control rod withdrawal cequence.
Itither we prefer to bace thic Technical Opecification on a concervative, cound technical calculation which allovn adequate flexibility while accuring the health and cafety of the general public through limite cet forth in 10 CFR 100. We feel that we have done thic in ectabliching the 0.015 delta k limit.
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philocophy remains to operate ac far as practicabic below cuch a limit.
3 Your quection, we accume, applies in particular to rol vortha at low power levels.
The worth of reactivity withdrawn as an increment of an in-cequence rod m1Cht be increated or decreaced by specifying dir-ferent increments of withdrawal in our withdrawal cequence.
The vorth of a full length out-of-sequence rod vould not be affected.
- Ecrefore, if the operator error is accumed to be fully withdrawing an out-of-i cequence rod, ao ic chovn by the middle curve of Figure 3-9 of the top -
j, ical report, the concequenceu of a RhA would not be affected by the cpecified rod withdrawal cequence.
If on the other hand, the oferator
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y. D L Ziemann error is accumed to be the erroneous selection of an out-of-cequence rod but the withdrawal to only the limit specified for the bank of in-sequence roda, the concequences would be much leco than represented by Figure 3-9 Both postulated errors, of cource, accume that either the INM fails to perform ito block function or the cecond independent person monitoring the withdrawal cequence fails to observa the error.
4.
The FEla analysic of the RDA chovo that in thic unlikely event 330 fuel pins vill exceed the threchold for fuel failure of 170 calorico per grcm; the pesk enthalpy was determined to be 250 calories per l
The reviced analysis chown that 600 fuel pine v121 exceed 170 calorico per gram with a peak enthalpy of up to 280 calories per gram.
f gram.
The corrected total doses for FCAR Table 14-6-2 for the most unfavor-I able meteorlogical conditions are 0.013 rem for the whole body and i
0.00062 rem for the thyroid.
Using conservative TID multiplication factero, the dosce from this unlikely event are still lecs than 0.2%
of the whole body doce limit and less than 10% of the thyroid doce limit specified in 10 CFR Part 100, i
Yours very truly, K O. '
L 0 m yer, P.E.
Director of Nuclear Support Servicec LOM/VJIV/br cc:
B H Grier M
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Minnesota Pollution Control Agency fi^
Attn. K D:ugan yys HEN a
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(TENORARY 70iv.)
C0;GROL tion 1540 -
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Northern States Power Company Minneapolis, Minn. 55401
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Mr. Ziemnn 1 aigned CIASS:
Q)JPROP I4T/0 IlGV2 NO CYS IGC'D DOC.ET liO:
50-263 hn DESCaIITIO;is E;iCL0 w aI S:
Ltr re our 12-21-72 ltr....... furnishing info re Suppl 1 to Change Request No. 3 to Tech Specc.......& coments on the Control Rcd Drop Accident (RD.i).
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