ML20059E976
| ML20059E976 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 08/27/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20059E973 | List: |
| References | |
| NUDOCS 9009110045 | |
| Download: ML20059E976 (8) | |
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UNITED STATES -
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eg-NUCLEAR REGULATORY COMMISSION-e.
5 WASHINGTON, D. C. 20555
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jVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PORTING AMENDMENT NOS; 113 AND 94 TO FACILITY OPERATING LICENSE-NOS.-DPR-70 AND DPR-75 PUBLIC SERYlCE ELECTRIC & GAS COMPANY-PHILADELPHIA ELECTRIC COMPANY
'0ELPARVA POWER AND. LIGHT COMPANY ATLANTIC ClTY. ELECTRIC' COMPANY-SALEM GENERATING STATION. UNIT NOS! 1-AND.2>
001CKET N05. 50-272 AND 50-311-1.0 1HTRODUCT10N By letter dated February 22,1990(Ref.~1)and' supplemented.byletterdated May 29, 1990 (Ref. 2),'Public Service Electric and Gas Company (PSE8G) requested an amendment to Facility Operating License Nos. DPR-70 and.DPR-75 for the Salem Generating Station, Unit Mos. I and 2.
The proposed amendments would change the Technical Specifications (TSs) by modifying (1) the most negativemoderatortemperaturecoefficient(KTC)limitingconditionfor operation (LCO), (2) the associated surveillance requirement (SR),-ar.d 13) the affected basis. The May 29, 1990 supplemental letter-did not increase the' scope of the original amendment request and did not' affect;the staff's original no significant hazards determination. The supplement provided additional information on the safety analysis assumotions used in the licensee's original amendment request.
2.0 EVALUATION
2.1 Background
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The purpose of the MTC LCO and MTC SR is to ensure that the most negative MTC at end-of-cycle (EOC) remains within the bounds of the safety analysis in particular, for those transients and accidents that assume a constant value of the moderator density coefficient (MDC) of 0.43 delta-K per gm/cc. The SR involves an MTC measurement at any thernal power within 7 effectiv; full power days (EFPDs) after reaching an-equilibrium primary coolant boron cuantration of 300 ppm. - After corrections are made, the measured value is comparec to the all reds out (ARO), hot full power (HFP) core condition SR limit.
In the event that the measured MTC is more negative than the SR limit, then the MTC must be remeasured and compared with the E0C MTC LCO value at least once per every 14 EFPDs during the remainder of the cycle. 'The LCO and SR volun for the most negative MTC are conservative (less negative) with respect to the value of the MTC (actually moderator density coefficient (MDC) which is simply related to the MTC) which is used in the safety analysis.
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For the high discharge burnup cores used for Salem Units.1 and 2, PSE&G 1
anticipates that the measured value of the MTC near EOC will result.in.an MTC L
that will be more negative than the SR-limit.
This will then require PSE&G to j
make MTC measurements once every 14 EFDDs until the EOC.
Failure to meet the SR MTC does not necessarily mean that.either the most negative MTC that occurs i
near EOC would be exceeded or that the safety analysis MTC would be exceeded.
The additional-MTC measurements, if needed to comply with the SR,;would be an undue burden for the Salem plants.
PSE&G proposes to change the Salem Unit 1 LCO -(3.1.1.4(b)) most negative MTC; value from -38 pcm/*F to -44 pcm/ F and the. Salem Unit 2 LCO (3.1.1.3(b)) most negative MTC valug from -40 pcm/*F to -44 'pcm/*F, where a pcm is equal to's reactivity of 10 The SR for Salem Unit 1 (4.1.1.4(b)) would be changed from
-29 pcm/*F to -37 pcm/ F;.the SR for Salem Unit 2 (4.1.1.3(b)) would be changed from -31 pcm/ F'to -37 pcm/*F. '-These changes would change the differenco
.between the SR and the E0C LCO MTC values by about 2 pcm/*F.
The SR and'E0C LC0 MTC values would still be bounded-by the Salem Units 1 snd 2 safety analysis vali'e of the MTC of -52.6 pcm/ F, which is used for maximum negative reactivity feedback analyses.
These changes apply to the-current and future reload cycles for Salem Units 1 and 2 and are supported by an evaluation provided in a Westinghouse report (Ref. 3) submitted by Reference 1.
The staff's review of these proposed changes to the most negative MTC LCO, SR, and associated basis follows.
2.2 Methodology The current method used to determine the most negative MTC is described in the Westinghouse Standard Technical specifications (STS) 'in Basis.Section 3/4.1.1.3 (Ref.-4).
The method is based on incrementally correcting the conservatin MDC used in the safety analysis to obtain the most negative MTC. value or, I -
equivalently, the most positive MDC at nominal HFP core conditions.
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corrections involve subtracting the incremental change in the MDC, which is associated with a core condition of all rods inserted (ARI), to an ARO core condition.
The MTC is then equal to the MDC times the rate ofcchange of l
moderator density with temperature at rated' thermal power conditions. This l
STS method of determining the most negative MTC.LCO value results;in an ARO MTC which is significantly less negative than the MTC'used in the safety analysis and may even be less negative that' the ~best estimate E0C ARO MTC for-extended burnup reload cores.
This has the potential for requiring the-plant j
to be placed in a hot shutdown condition by Technical specification 3.1.14 for Salem Unit 1 and 3.1.1.3 for Salem Unit 2, enn though substantial margin to.
the safety analysis MOC exists. This problem with the current STS method is caused'by adjusting the MDC from a HFP ARI to a HFP ARO condition in defining the most negative MTC. -The HFP ARI condition is not allowed by TSs on control.
rod positions for allowable power operation in which the shutdown banks are completely withdrawn from the core e.nd the control banks must meet rod l
insertion limits (RIL).
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In Reference 3 Westinghouse p ovides an alternative' method for adjusting the-
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safety analysis MDC to obtain a most negative MTC.
This method is termed the Most Negative Feasible (MNF) MTC.
The MNF MTC me+ hod seeks to determine the conditions for which a core will exhibit the most negative MTC value that;is consistent with operation' allowed by the T5s.
For example,- the MNF MTC method.
would rM require the conversion assumption of the ARI H5P condition but would require ;he conversion assumption that all control rod beaks are inserted the-i maximum amount permitted by thc TSs.
Westinghouse uses the MNF MTC method-to-determine EOC MTC sensitivities to those design and operational parameters that.
1 directly impact the MTC in such a way that the sensitivity to one parameter is independent of the assumed values for the other parameters.
The parameters-considered with this MNF MTC method clude::
(1) soluble boron concentration in the coolant (2) moderator temperature and pressure i
(3) control rod insertion (4) axial power shape (5) transient xenon concentration-The MNF MTC approach uses this sensitivity.information to derive an EOC ARO 3
HFP MTC LCO value based on the safety analysis value of'the MDC.
This MNF MTC method has, according to Westinghouse,.a number of' advantages over the previous method for determining the most negative MTC LCO value.
The MNF MTC will be sufficiently negative so_that repeated MTC measurements from a 300 ppm core condition to EOC would not be required.
The.MNF MTC method does not change the safety analysis. moderator feedback assumption. The safety acalysis value of MDC is unchanged.
The MNF MTC method is a conservative und reasonable basis to assume for an HTC value of a reload core and is' consistent with plant operation defined by other TSs.
Finally, the MNF MTC method retains the SR on MTC at~ the 300 ppm core condition to verify that the core 'is operating within the bounds of the safety analysis.
l Westinghouse determined the sensitivity of the above parameters on the EOC MTC for five different reload designs representative of future Salem Units l'and 2 reloads.
These reload designs included fuel designs,-discharge burnups, and cycle lengths, which are typical of those expected'.for Salem Units ~1 and 2.
The solwole boron concentration was not used in the sensitivity analysis because the E0C HFP ARO MTC TS value is assumed to be at 0 ppm of boron, the definition of E00, and because the most negative MTC occurs at 0 ppm of boron.
in the coolant.
The sensitivity study did not include the radial power distribution which can vary under normal operation and can affect the MTC.
The operational activities that affect the radial power distribution do so through the movement of control rods and activities that affect the. xenon concentration.
The allowed changes in the radial power distribution are. implicitly included in the MTC sensitivity to control rod insertion and xenon concentration.
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i In Reference 3 Westinghouse 'staes that the SR MTC value would b' obtained in.
e the,ame manner as currently described in the STS' Bases. The SR MTC value is l
obtained from the EOC HFP ARO M'C'valu1r by making corrections for bctnup and I
boron at a core condition of 300. ppm of boron.
iie staff has reviewed the assumptions and basis for'the MNF MTC method de:cribed above and concludes that they are ecceptable because they will.
l resuM. in conservative most negative MTC LCO and SR values that could resulte from a: lowed operation of Sale + Units 1 and 2 from ' nominal. conditions and beaus'., the MTC measurement at 300 ppm of boron core condition will. essure, using-the SR value of MTC, that the safety analysis.MDC wil'.not be exceeded.
i 2.3 Salem Units 1 and 2 Accid _ent Analysis MDC Assmoption 1
0 Westinghouse uses an MDC for performing accident antlyses.
For events sensitive to. maximum negative moderator feedback, a constant value of the' MOC J
of 0.43 delta K/gm/cc is. assumed throughout the analysis, for HFP?and full flow nominal-operating conditions, the temperature and prassure are. 57L 9'F and 2250 psia,' respectively.
At these conditions the HTC, equivaltint to the.
i HOC of 0.43 delta K/gm/cc, is -52.6 pcm/*F. ;We will refer to this MTC as the.
safety analysis MTC.
Based on its review, the ' staff concludes that V.he l
evaluation of the MTC from the MDC is acceptable because it conforms W the
. relationship of MTC to HDC, that is, the MTC is equal to the MDC times the rate of change of density with temperature at ~the nominal pressure and~
temperature of the coolant at rated thermal power conditions.
l 2.4 Sensitivity Results Salee Units 1 and 2 TS 3.2.5 provide the LCO' values of the Departure from 1
Nucleate Boiling (DNB) parameters; reactor coolant system average temperature 2289)sia(2220psiaindicated)andamaximumallowableT**0 (T
and pressurizer pressure. The minimum allowable'pressuriter pressure is 5
p is 582.0'F.
These i
values of the minimum pressurizer pressure and maximust T"V9or Salem Units 1 and were also assumed for the safety analysis. The current nominal design T '
2 is 677.9*F.so that the safety analysis represents a UI'F maximum allowable increase in T nominal conditions.. The current nominal design pressure-is 2250 psia so net the safety analysis represents a'45 psi maximum allowable decrease from nominal pressurizer pressure.
Based on these maximum-allowed system variations, a maximum allowable limit is placed on the moderator density variation.
Using the sensitivity of the MTC to temperature.and pressure, derived from the analysis of the five reload designs, Westinghouse obtained for Salem Units 1 and 2 a bounding delta MTC (a proprietary value) associatea with these maximum allowable conlant temperature and pressure deviations from nominal conditions.
l Salem Unit 1 TS 3.1.1.4 and Salem Ura t 2 TS 3.1.1.3 require an ARO configuration in the evaluation of the MTC.
TS 3.1.3.4 requires that all shutdown banks be withdrawn from the core during normal power operation (that is, while in Modes 1 and 2).
TS 3.1.3.5.11mits control bank insertion by Rod Insertion L.imits (RIL) in Modes 1 and 2.
All control rods can be inserted at.
hot zero power (HZP) coincident with a' reactor' trip.
In general, greater l
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control rod insertion results in a more negative MTC. assuming that all other J
L parameters are held constant.- However, greater control rod insertion will L
also cause e reduction in core power and T which causes the MTC to become more positive.
ThiseffectismorepronouMdatlowerpowerwiththepositive change being more important than the negative change in the MTC.
Based on this' 1
line of reasoning, Westinghouse determined that the most negative MTC q
configuration will occur at HFP with control rods insertea to the RIL.
1 Westinghouse analyzed five reload core designs, using a bounding value of-Control Bank D insertion at HFP with no soluble boron in the coolant.
This analysis gave for Salem Units 1 and 2 a bounding delta MTC'(a proprietary value) associLed with the control bank inserted to the RIL.
The axial power shape produces changes in the MTC caused primarily by the rate-at which the moderator is heated as it flows up the core, with the MTC sensitivity to extremes of axial power shapes being small.
This effect can be correlated with the axial' flux difference (AFD), which is the difference in ;
the power in the top half of the core minus the power in the lower half of the -
core.
Salem Units 1 and 2 TSs include limits on the AFD. ~ Westinghouse-determined that the more negative the AFD the more negative the MTC.
Westinghouse analyzed four reload designs and determined the sensiti'!ity of the MTC to AFD.
This analysis gave for Salem. Units 1 and 2-a bounding delta MTC (a proprietary value) for an assumed bounding value of AFD.
Although no TSs limits exist on either the xenon' distribution and. concentration, the axial xenon distribution is effectively limited by TSs limits on the.AFD.
i The physics of the xenon buildup and decay process limits _ the xenon -
concentration. The effect of xenon axial distribution is quantified in:the effect of the axial power shape on-the MTC,'as discussed previously..The.
effect of the overall xenon concentration on the HTC needs to be evaluated separately.
Westinghouse determined that the MTC became more negative with no xenon in the core.
Therefore, Westinghouse analyzed the five reload core-designs at E0C HFP AR0 with no xenon present.
This analysis gave for Salem Units 1 and 2 a delta MTC (a proprietary value) for-the xenon concentration i
factor.
All of the delta MTCs described above are summed to provide a total delta MTC
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for-Salem Units 1 and 2 based on the allowed deviations of the various factors 4
from nominal values.
The staff has reviewed the discussion and anclysis of the primary factors of the MNF MTC method and concludes that the results obtained are acceptable because approved methods and conservative assumptions were used to generate the results.
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- 2. 5 Salem Units 1 and 2 EOC MTC TS Value P
Using the total delta MTC obtained with the MNF MTC method, Westinghouse determined that the Salem Units I and'2 safety analysis MTC of -52.6 pcm/*F I
should be increased by the total: delta MTC plus'an additional amount'for:
conservatism.
The resulting EOC MFP ARO MTC for Salem Units l' and 2 is -44 pcm/*F.
This value replaces the current-TSs value'.
Thus, determination that-l an MTC for the E0C HFP ARO reload core is less negative than -44.pcm/*F 1
provides assurance that the safety analysis MTC remains bounding, t
Westinghouse also performed an analysis'tc determins! the SR value of the ARO reload core at 300 ppm of boron.
Analysis of reload cores sim.ilar to. Salem-Units 1 and 2 futu'.re reload designs-resulted in a-conservative'value.of 7 pcm/'F to bound the expected difference in MTCs between the 300 ppm of boron core condition to EOC.
Thus, the SR MTC'value is -37 pcm/'F compared to the present TSs values for Salem Units 1 and 2.
The staff has reviewed this determination of=the most negative MTC LC0 and SR.
and concludes that they are acceptable.
2.6 Safety Analysis-Impact of MNF MTC Approach
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Changes in the parameters discussed previously could take place.during'd transient to make the MTC more negative than allowed during normal operation.
The most adverse conditions sesn:in the affectedetransient events will not.
result in a reactivity insertion that would invalidate the conclusions of.the FSAR' accident = analyses.
Thus, the MDC used as a basis for the MNF MTC TS will-not change.
The reload safety analysis process will include-verification that the HDC safety analysis value remains valid.
The staff concludes that this verification process for the safety analysis MDC is acceptable.
l 2.7 Conclusions Based on the review discussed above, the staff concludes that the proposed changes to the most negative MTC Technical Specification, the Surveillance Requirement MTC value at or near a-300 ppm of boron core condition, and.
L associated basis for Salem Units 1 and 2 are acceptable-for the following reasons:
1.
The most negative feasible MTC method considered the important factors y
affecting the MTC and the limits on these factors.
2.
Approved computer codes and methods (in some cases updated versions) were used in the analysis.
3.
The MTC measurement at or near 300 ppm of boron will provide assurance-that the MTC at E0C HFP AR0 conditions will be less negative than the-safety analysis MTC.
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Future reloads for Salem Units 1 and 2 will'be analyzed to confirm the most negative MTC Technical Specification at EOC and the Surveillance Requirement on MTC at a core condition of 300: ppm of boron.
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Future reloads for Salem Units 1 and 2 will.be analyzed to confirm the.
I applicability of the safety. analysis value of the MDC.
2.8 R_e_ferences 1.
Letter (LCR-90-01) fqm S. LaBruna (PSE&G) to USNRC, dated February 22, 1990.
1 2.
Letter, additional information LCR-90-01) from S. LaBruna. (PSE&G) to USNRC, dated May_29, 1990.
3.
" Safety Evaluation Supporting a More Negative E0L Moderator Temperature' Coefficient Technical Specification for the Salem-Units.1 and 2,"
WCAP-12451 (proprietary), WCAP-12452. (nonproprietary),' November 1989.
4.
" Standard Tect.nical Specifications for Westinghouse Pressurized Water Reactors," NUREG-0452, Revision 4, issued Fall 1981, i
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3.0 ENVIRONMENTAL CONSIDERATION
These amendments involve a change to a requirement with respect to 'the installa-
-l tion or use of a facility component located within the restricted area as.
defined in 10 CFR Part 20 and changes to the. surveillance requirements...The staff has determined that the amendments involve no'significant-increase in the amounts, and no significant change in the types,: of any effluents.that may be released offsite'and that there is no significant increase 1 1n individual or l:
cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments-involve-no significant hazards
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consideration and there has been no public comment on such finding. Accordingly, l
the amendments meet the eli forth in 10 CFR 51.22(c)(9)gibility criteria for categorical exclusion set Pursuant to 10 CFR 51.22(b), no environmental' assessment need be prepared in connection with the issuance of the amendments.
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4.0 CONCLUSION
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L The Comission made a proposed determination that the amendments involve no significant hazards consideration which was published in the Federal Register (55 FR 21978) on May 30,'1990 and consulted with the State of New Jersey. - No public coments were received and the State of New Jersey did not have ar.y comments.
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The staff has concluded, bassd on the considerations discussed above, thet:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Comission's regulations and the issuance of the amendments will not be inimical to the conrnon defense and curity nor to the health and safety of the public, t
a Principal Contributor: Daniel Fieno Dated:
August 27, 1990 4
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