ML19345A367
| ML19345A367 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 05/11/1976 |
| From: | YANKEE ATOMIC ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML19345A366 | List: |
| References | |
| NUDOCS 8011210095 | |
| Download: ML19345A367 (7) | |
Text
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O SAFETY EVALUATIO::
OF Tile ACCLE LATOR PRESSURE SETPOI!T FOR Tile YA:IEE NUCLEAR PCUER STATIO!;
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Yankee Atonic Electric Company 20 Turnpike Road Westborough, Massachusetts 01581 I
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1.
INTRODUCTION AD SU'01ARY The Yankee Nuclear Power Station is currently li=ited to less than 100 percent power due to the results of the =ost recent LOCA analysis approved by the NRC (Reference 1).
As a result, YAEC is currently engaged in a review of the ECCS design and performance capability in an atte=pt to provide i= prove =ents.
During this review, it has been determined that the flow capability of the LPSI accumulator as tested at the plant is slightlygreater than that assu=ed in the approved LOCA analysis (Reference 1) and in the = ore recent LOCA analysis currently being reviewed by the NRC (Reference 2).
This difference would nor= ally be conservative because higher ECCS flow rates vould ter=inate the transient more rapidly and thus provide greater cargin to the limits of 10CFR50.46.
However, the accu =ulator represents a li=ited supply of coolant and all ECCS coolant injected during the bypass phase of the transient must be discarded as required by Appendix K to 10CFR50. Thus, with a larger accu =ulator flow rate, a larger fraction of its inventory must be discarded and it vill e=pty sooner.
It is seen in the Reference 1 and 2 analyses that the accu =ulator e=pties shortly after EOCREC during the reflood phase of the transient.
A significant reduction in this accu =ulator e=pty ti=e would yield a peak clad te=perature beyond the li=its of 10CFR50.46.
One solution to this dile==a vould be to re-analyze the LOCA at the higher accu =ulator flev rate and seek the eaxi=u= allovable LHGR which would produce results within the linits of 10CFR50.46. This approach is unacceptable because it vould require a large expenditure of capital and =an-hours and would produce results which would lic2-plant operation.
The solutien proposed by YAEC and described in the following sections is to adjust the accu =ulator pressure.at the plant so that its flow capability would agree with the Reference 1 and 2 analyses.
This approach would =aintain the validity of the LOCA analysis. currently before the NRC and would allow a = ore prompt resolution of the proble=.
2.
ACCUMULATOR FLO'4 TEST OBJECT: To confir= =ini=u= ECCS flow rate by a preoperational-accu =ulator flov test.
PLANT CONDITION: This test was performed during refueling with a 30 ft. head of water above the core.
The accu =ulator' nitrogen overpressure was 382 psig.
MOV-1, the accu =ulator isolation valve (see~ Reference 3), was initially closed. A visicorder was used to assure that accurate
~
time determinations could be obtained. Accu =ulator level changes were recorded fro = the accu =ulator 1evel instru=entation.
In
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addition, the flow to each loop.vas =onitored.
The test was initiated by opening MOV-1.
=.
RESULTS:
A:
The sum of the flow rates.from the individual flow.
indicators was 5375 gpa.
B:
Eased on ceasured accumulator-level and recorded time, the average flou rate uhile !!OV-1 was fully open was 5390 gpm.
CONCLUSION: The flow from the accumulator is 5375 gpm based on A and E above.
3.
SIMULATION OF EXPERI:: ENTAL DATA A simulation of the enperimental anta was conducted using RELAP4-EM.-
The nodtl diagram of the simulction appears in Figure 1; it is ceu1 valent to the nodal representation which was ceployed for.the ECCS in the Core XII LOCA submittal. The pressures in the accumulator and the two -
cold legs (ona representing the broken loop and the other the'three intact loops) vare set to the experimental values above.. The hydraulic friction factors for the junctions in the podel were adjusted so that the calculated accumulator flou rate catched the experimentally determined flow.
This revised nodal representation of ECCS was used to calculate the flow into the reacter vessel'during the worst break LOCA as'previously determined in Referen 2.
The ECCS Jeg connected to the broken loop was conservatively represented as spilling to the containment, which was maintained at a ecnstant pressure of 14.25 psia. LPSI pump flow ecs started at 25 seconds. The'results using the prescnt occumulctor pressure of 420 psia is co pared uith the Core XII LCCA submittal in Table 1.
Table 1
' Effective-Average Flow Accumulator E0BY During Refill
-BOCREC Empty Time (sec)
(Iba/s ee).
(sec)
(sec)
YR Core XII LOCA 40.3 534 102.49 114.79 submittal Reanalysis based on 40.3 580 97.60 100.43 cxperimentcl flow data The-revised calculation pre
-ted higher ficu rates into the intact loops, which results in a reduced EOCREC time and correspondingly lower clad terperatures at EOCRFC.
In the Ecferenec<2 LOCA analysic, a high~
reflood rate Insted for 12 : seconds af ter EOCREC. - At this point.. the -
accumulator emptied and.a lower reflood ' rate vas then _used.
In the revised analysis, the high'reflood. rate lasted for 3' seconds after BOCREC. at which time,-_the rato changed from 580 to 221 lb=/sec.
This R
9 ACCUMULATOR 3l INTACT LOOPS BROKEN LOOP Ib
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LPSI, llPSI PUMPS O v0tuxE C JUNCTION b
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ECCS flow rate produces very small flood rates after accumulator empty time, thereby increasing the calculated peak clad temperature and the time of its occurrence.
4.
EVALUATION OF REV7 SED ACCUMULATOR PRESSUPI The present 420 psia accueulator pressure results in ECCS flow values which are non-conservatively different then those used in Care XII LOCA submittal studies.
In order to re-establish the flow rates used in the LOCA submittal, a parametric study of ECCS flow versus accumulator pressure was performed over a range of pressures.
It was demonstrated that an accumulator pressure of 352 psia vill produce an ECCS flow rate in agreement with the YR Core XII LOCA submittal.
It was also demonstrated that a plus or minus range of 10 psi on this pressure would maintain acceptable BOCREC, reflood rates and accumulator empty times. These parameters versus accumulator pressuta are given in Table 2.
Table 2 Reflood Rates (lb/sec)
Accumulator Before After Effective Pressure EOCREC Accumulator Accumulator Accumulator (psia)
(sec)
Empty Empty Empty Time (sec)
YR Core XII 102.49 534.0 221 114.79 LOCA submittal 342 103.80 541.5 221 118.67 352 102.83 550.2 221 115.87 "62 102.50 558.7 221 113.88 5.
CONCLUSIONS Reducing the accumulator pressure to 352 psia makes the ECCS system performance conforn to the LOCA analysis submitted in Reference 2.
6.
REFERENCES (1) Amendment No. 21 to Facility Operating License No. DPR-3.
issued by NRC on December 4,-1975.
(2)
Supplement No. 8 to Proposed Change No. 125,_ submitted to the NRC on February'20, 1976.
(3) Yankee Nuclear Power Station FSAR Figure 6.3-1.
~;[ite r cHv *.05 v.s. Nuc Lt. AH HL GUL A 10 H Y ^ 'MMf 0rlON t>OC KE T NUM nt. H uaa gn_pq 1
NRC DISTrilBUTION ron PART 50 DOCKET' MATERIAL 10: USNRC FilOM: Iankee Atomic Elec. Co.
o^Tc Or oOcuutNT l
D Westborough, Mass.
5-11-76 D.E. Vandenburgh oATc ntetivto 5-13-76
' t.LTTtn C N OTo nlZ E D P fiOP BNPU T F O R'.1 N8eMDE R OF COPIES RECElvC o J
C O niO'N AL Ouse tA:sirit o Ocory 40 0-C O O RI P T IO N ENCLCSURE Ltr. re. Proposed Change # 138(May 11,1976)..
Safety Evaluation of the Accumulator Pressure trans the folicsing......
Setpoint.......
(3 Sigeed & 37 Carbon = 40 Cys. Received)
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