ML20236D145
| ML20236D145 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 03/10/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20236D141 | List: |
| References | |
| NUDOCS 8903220483 | |
| Download: ML20236D145 (5) | |
Text
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0 UNITED STATES g
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.g NUCLEAR REGULATORY COMMISSION
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ENCLOSURE 2-q xm" 3
SAFETY EVALUATION BY THE OFFICF. OF NUCLEAR REACTOR REGULATION SUPPORTING AMEN 0 MENT NO. 95 TO FACILITY OPERATING LICENSE NO. OPR-79 TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT, UNIT 2 DOCKET NO. 50-328
1.0 INTRODUCTION
l The Tennessee Valley Authority (TVA), by submittal dated December 2, 1988, proposed to modify the Sequoyah Nuclear Plant (SQN) Unit 2 Technical Specifi-revise the upper head injection (VHI) accumulator level switch setpoint}(1 cations (TS).
This is TVA's TS change number 88-33.
The changes would
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tolerance band of Surveillance Requirement (SR) 4.5.1.2.c.1, and (2)
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l heat flux hot channel factor (FQ(z)) of the Limiting Condition for Operati 4
(LCO) 3.2.2 and SR 4.2.2.2 from 2.237 to 2.15.
The proposed Unit 2 UHI setpoint and tolerance change is consistent with the UHI setpoint and tolerance changes recently approved by the. staff for Unit 1.
The Unit I change (TS 88-20) was ap~ proved by letter dated October 14.-1988.
Similarly, the proposed Unit 2 FQ(z) change is consistent with the Unit 1 FQ(z) change (TS 88-28) approved by letter dated January 23, 1989.. The conclusions
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drawn herein supporting the proposed Unit 2 changes are the same as those drawn for TS changes 88-20 and 88-28 for Unit 1.
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2.0 DISCUSSION TVA Condition Adverse to Quality Report (CAQR) SQP871644 documents that the level switches and setpoints *M t were previously used could allow more than the analytical limit of 1,130.5 cubic feet of UHI water to be injected into the l
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reactor coolant system (RCS) during a postulated accident.
TVA has stated that two changes ia the design and configuration of the UHI system were pursued to correctthisiproblem. First, the minimum delivered UHI water volume was reduced from 900 cubic. feet to 850 cubic feet.
Second, a new model of level switch is being installed in'the UHI system in the current Unit 2 Cycle 3 refueling outage.
The new. switches are essentially the same as those presently used, except for their s, pan.
Because of the span differences, the switches have different accuracy characteristics.
The Demonstrated Accuracy Calculation 1-LS-87-21, provided by TVA submittal dated August 15,'1988, determined a new setpoint and tolerances based on the new instrument characteristics.
These new values are proposed by TVA to be incorporated into SR 4.5.1.2.c.1 to ensure that the delivered UHI water volumes are bounded by the volumes assumed in the 8903220483 890310 DR ADOCK 0500 0
fJ 1 $5 large-breaku 1Nsofcoolantaccident(LOCA) analyses. This would in turn ensure that the'offsite doses from a postulated LOCA are bounded by the analyses of Section 15.5 of the Sequoyah Final Safety Analysis Report (FSAR).
The proposed change in~ the delivered UHI water volume band described above is supported by Westinghouse Electric Corporation (WEC) evaluations. These calculations indicate that the potential decrease in delivered water volume to the core would result in increased peak clad temperatures (PCTs); but in all cases, the calculated PCT remains below the 2,200'F limit of 10 CFR 50.46. The worst caso postulated LOCA scenario resulted in a calculated PCT of 2198'F, providing little margin for calculational or modeling error. The staff has previously indicated to TVA that operation of Units 1 and 2 could be supported by sensitivity studies provided an exemption to certain administrative requirements of 10 CFR 50.46(a)(1) was obtair.ed and, that operational restrictions be imposed to provide at least 100*F of margin between the
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calculated PCT and the 10 CFR 50.46 limit.
By letter dated January 26, 1989, i
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the staff issued to TVA an exemption to certain requirements of 10 CFR 50.46(a)(1) for operatiing Cycle 4.
Specifically, TVA's Sequoyah Plant has been exempted i from having the Emergency Core Cooling System (ECCS) cooling performance based-on plant operating conditions and calculated in accordance with an acceptabl UHI evaluation model until the end of operating Cycle 4 for Units 1 and 2.
e exemption was issued with conditions for additional operating restrictions including the limit of FQ(z) not to exceed 2.15.. The other operational restriction is on the number of steam generator tubes plugged in the Unit 2 i
steam generators. TVA proposed in TS change 88-33 an FQ(z) limit of 2.15 for Unit 2.
Unit 2 is currently in its Cycle 3 refueling outage. The schedule is for it to.
j restart from this outage and enter operating Cycle 4 on or about March 31, i
1989.
In its letter dated November 3, 1988 TVA stated that the UHI system will be removed in the Cycle 4 refueling outage and a 10 CFR 50.46 ECCS analysis without UHI will be submitted before Unit 2 restarts from the Cycle 4 refueling outage.
3.0 EVALUATION TVA implemented two corrective actions to resolve the above mentioned CAQR.. As discussed above, the first change is a proposed actual reduction in the total amountofwaterigjectedbytheUHIsystemfromthecurrentrequirementof 3
900 ft to 850 ft ; thereby, decreasing the probability of over injecting water from the UHI tank. Supporting WEC evaluations were provided by TVA in of the December 2, 1988 submittal. The second CAQR corrective action is the replacement of the level switches with a new model.. The new level switches are different only in the span of response.
Only the switch accuracy calculations, therefore, are different. As justification for Unit 2 TVA has referenced the same calculations submitted to the staff by. letter dated August 15, 1988 supporting TS change 88-20 for the setpoint and.setpoint tolerances changes made for Unit 1.
Also in support of the proposed TS change for the UHI level switch setpoint.
TVA has imposed certain operating restrictions for upcoming operating Cycle 4 i
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! L of Unit 2 to hovide at least 100*F margin between the calculated PCT and the regulatory limit of 2200*F established by 10 CFR 50.46(b).
TVA stated that at least-100*F PCT margin can be obtained by administratively limitin generator tube plugging (SGTP) to 5 percent and by reducing FQ(z) g the steam from 2.237 to 2.15.
As defined in FSAR Section 4.3.2.2.1, FQ(z) is the maximum local heat flux on the surface of a fuel rod divided by the average fuel rod heat flux.
Limiting this ratio minimizes the magnitude of localized " hot spots" along the fuel cladding surface.
This in turn helps ensure that the PCT will remain below 2,200 F during a postulated LOCA.
3.1 UHI Injected Water Volume As documented in FSAR Section 6.3.2, the UHI System is designed to passively provide additional water inventory to the reactor core during the blowdown phase of a postulated LOCA.
The limiting case break, as documented in Emergency Core Cooling System (ECCS) Analysis, (FSAR, Section 15.4.1.1.4),is the double-ended, cold-leg guillotine (DECLG) break using a discharge coefficient, Cn = 0.6 with the imperfect mixing of UHI water assumed in the 2
watervolumeat900ft'jsanalysisestablishedthelowerboundvaluegfinjected vessel upper hMad, Th TVA proposed to lower this value to 850 ft and has; provided a WEC analysis to support the conclusion that the increase in s
calculated fuel PCT remains below the 10 CFR 50.46 regulatory requirement of" 2200*F.
The reduction in the UHI water volume increased the PCT by 53 F and when PCT penalties for potential guide tube flexure failure and instrument guide tube filling during reflood are added, the limiting PCT reached 2198*F.
This is less than the maximum acceptance criterion (2200*F) in 10 CFR 50.46.
3.2 Level Switch Setpoint Calculation Level switches are used to automatically isolate the UHI System accumulators from the RCS after the UHI System has injected the borated water. The level switch setpoints are selected to ensure that the quantity of UHI water delivered is within the limits calculated for the large break LOCA ?nalysis.
TVA has performed an accuracy calculation (1-LS-87-21) to demonstrate that level switch setpoint and tolerances will be within the bounds of the accident analysis.
The TVA calculation is based on Static-0-Ring test report. 8601-042, using the sum of the squares method for all independent variables that affect accuracy. The bi-directional and uni-directional errors are combined in such a manner that the negative uni-directional error is added to the negative portion of the bi-directional error and the positive uni-directional error is added to the positive portion of the bi-directional error.
The result is a corrective number for the instrumen,t accuracy.
The staff has reviewed the subject calculation, as is docuniented by letter to TVA on TS 88-20 for Unit 1 dated October 14, 1988, and the proposed TS for the level switch setpoint and tolerances (92.0+2.6/-5.8) and finds that the TS are acceptable because the accuracy calculation has been conducted in a manner which predicts the worst-case accuracy.
TVA has established the level switch setpoint based on the above accuracy calculation.
However, the calculation was also based on the assumption that
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s the UHI systesFaccumulator room temperature will be between 70 F and 85"F.
UHI room temperature is monitored via Surveillance Instruction SI606 which requires that UHI room temperature be maintained between 75*F and 85"F.
Since the margin between the safety limit and the instrument operating band was and still remains very small (.01" of water column), the staff conclusion remains that, anytime the temperature of the UHI room is not between -70*F and 85*F, the level switches should be declared inoperable.
TVA comitted in its letter to the NRC staff, dated September 21, 1988, to revise the balance-of-plant t
temperature monitoring procedure to indicate that the UHI level switches are inoperable if the ambient temperature in the area of the switches exceeds the values used in Demonstrated Accuracy Calculation 1-LS-87-21 to determine temperature-induced reference water-leg error. These values are the.
temperature values discussed above. This'should be included in the next scheduled updato of the FSAR.
3.3 PCT Margin and FQ(z) Change To provide additional assurance that tne PCT is below the 2200*F acceptance criterion, the following operational restrictions are imposed by TVA on
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Sequoyah, Unit 2:
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The steam generator tubes plugged (SGTP) limit will be administrative 1y lowered from 10 percent to five percent.
Westinghouse has performed and I
i analysis which demonstrates that this restriction reduces the calculated PCT by 22*F.
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The FQ(z) limit will be lowered from 2.237 to 2.15 by rearranging the control rod positions during power operation.
This reduces the calculated PCT an additional 87 F for the limiting imperfect mixing case.
By its application dated December 2, 1988, TVA provided evaluations conducted by WEC which showed that a reduction in FQ(z) from 2.237 to 2.15 reduces the PCT by 87 F for the limiting imperfect mixing case and by 96 F for the limiting perfect mixing case. As sumarized on Page 4 of the WEC evaluation, this PCT reduction, combined with the reduction obtained by administrative 1y limiting SGTP to 5 percent, results in PCTs of 2,089*F for the limiting imperfect mixing case and 2,067"F for the limiting perfect mixing case.
These PCT values provide over 100 degrees of margin to the regulatory limit of 2200*F.
TVA has proposed that the FQ(z) limit for Unit 2 in LC0 3.2.2 and SR 4.2.2.2 shall be 2.15 instead of 2.237.
Since the reduction in FQ(2) discussed above provides additional margin to the PCT regulatory limit of 2200 F, and the 2.15 limit will remain in effect until an analysis for the p)reviously reviewedand accep NRC, the staff finds the proposed changes to the Unit 2 TS acceptable. The staff notes that, in accordance with 10 CFR 50.46, upon TVA submitting to NRC an analysis in conformance with 10 CFR S0.46 using plant operating conditions and showing)that a limit of 2.237 satisfies the requirements of 10 CFR 50.46(b),
the TS'FQ(z limit of 2.237 may be reinstated.
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.4 Staff Conclusions
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ased on the above, the staff concludes that the proposed changes to the Unit 2 l
S in TVA's application dated December 2, 1988 (TS 88-33) are acceptable.
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taff also concludes that the Static-0-Ring level switches for the UHI The ccumulator System are inoperable if the room temperature is not between 70*F nd 85'F.
TVA comitted in its letter dated September 21, 1988 to revise the q
alance-of-plant temperature monitoring procedure to indicate that the UHI evel switches are inoperable if the ambient temperature in the area of the witches exceeds these values.
ipdate of the FSAR.
This should be included in the next scheduled i
.0 ENVIRONMENT'. CONSIDERATION his amendment involves a change to a requirement with respect to the nsta11ation cr use of a facility component located within the restricted area i-s defined in 10 CFR Part 20 and changes to the surveillance requirements.
aff has determined that the amendment involves no significant increase in the The 91 eased offsite, and that there is no significant increase in individual o amulative occupational radiation exposure. The Comission has previously ssued a proposed finding that this amendment involves no significant hazardi3 ansideration and there has been no public coment on such finding.
E clusion set forth in 10 CFR 51.22(c)(9).cordingly, the amendment meets the eligi Pursuant to 10 CFR 51.22(b), no vironmental impact statement or environmental assessment need be prepared in nnection with the issuance of the amendment.
O CONCLUSION ie Comission made a proposed determination that the amendment involves no gnificant hazards consideration which was published in the _ Federal Register
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3 FR 53102) on December 30,, 1988 and consulted with the State of Tennessee!
public coments were recefved md the State of Tennessee did not have any nents.
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) there is reasonable assurance that the health and safet g
11 not be endangered by operation in the proposed manner,y of the public and (2 such ivities wi.11 be conducted in compliance with the Comission's re) security nor to the health and safety of the public.
ncipal Contributor:
,T. Rotella ed: March 10, 1989 m
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, jh 3.4 StaffConklisions l
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Based on the above, the staff concludes that the proposed changes to the Unit 2 TS in TVA's application dated December 2, 1988 (TS 88-33) are acceptable.
The staff also concludes that the Static-0-Ring level swidhes for the UHI accumulator System are inoperable if the room temperature is not between 70'F anc'sPT TVA comitted in its letter dated September 21, 1988 to revise the bal ece-et-plant temperature monitoring procedure to indicate that the UHI level etch (s are inoperable if the ambient temperature in the area of the switches exceeds these values.
This should be included in the next scheduled update of the FSAR.
4.0 ENVIRONMENTAL CONSIDERATION
This amendment involves a change to a requirement with respect to the installation 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 amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may bei released offsite, and that there is no significant increase in individual orj cumulative occupational radiation exposure.
The Comission has previously issued a proposed finding that this amendment involves no significant hazards 7
. consideration and there has been no public coment on such finding.
Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to'10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
5.0 CONCLUSION
The Comission made a proposed determination that the amendment involves no significant hazards consideration which was published in the Federal Register (53 FR 53102) on December 30, 1988 and consulted with the State of Tennessee.
No public coments were received and the State of Tennessee did not have any coments.
(1) there is reasonable assurance that the health and safety of the will not be endangered by operation in the proposed manner, and (2) public such activities will be conducted in compliance with the Comission's regulations, and the issuance of the amendments will not be inimical to the comon defense and security nor to the health and safety of the public.
Principal Contributor:
,T. Rotella Dated: March 10, 1989
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