ML19317E506
| ML19317E506 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 08/01/1975 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19317E502 | List: |
| References | |
| NUDOCS 7912180743 | |
| Download: ML19317E506 (5) | |
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PARTIAL LOOP ECCS ANALYSIS 791218o 7 7 3
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partial Loop ECCS Analysis This etudy shows that in the event of a LOCA during partial loop operation, peak cladding temperatures and metal-water reactions are significantly lower than those during 4-pump operation. The partial loop analysis was performed 2
assuming the worst case break (8.55ft DE,Cp=1) reported in BAW-10103 and the maximum kW/ft limit shown in Figure 2.2 of BAW-10103. The maximum cladding temperature for the partial loop LOCA analysis is 1766F, which is 3130F less than the same break at full power and full flow conditions.
There are 5 possible break configurations at the pump discharge for partial loop operation:
1.
3-pump operation a.
break in inactive cold leg (cold leg with idle pump),
partially idle-loop (loop with idle pump) b.
break in active cold leg, partially idle loop c.
break in active cold leg, full: active loop 2.
2-pump operation, one pump active in each loop a.
break in inactive cold leg b.
break in active cold leg Analysis of the 3-pump operation instead of 2-pump operation was chosen for the following reasons.
First, 3-pump operation is the more probable partial loop operational mode.
Second, the rated power level 21 3-pump operation is 77% of full power rating compared to 51% of full powzt rating for 2-pump operation. The reflooding rate will be lower for higher core power, thus a greater cladding temperature rise after the end-of-blowdown (E0B) is ex-pected for 3-pump operation.
Due to the nature of core flow which results during a cold leg break, two break locations for 3-pump operation were examined. Typically, core flow remains highly positive during the initial phase of the blowdown transient.
As the head of the RC pumps degrades, due to 2-phase effects, the magnitude of the positive core flow diminishes.
Core flow then becomes negative _for the remainder of the blowdown transient.
The two phases of core flow, posi-tive and negative, are effected by the choice of break location.
Placement of the break at the pump discharge of the idle pump will induce a greater driving force from the intact cold legs.
This will yield high positive flows and low negative flows.
2 j
A break at the pump discharge of the active cold leg in the pnrtially idle loop will cause a loss in positive flow during the first half of the transient.
Analyzing both break locations will ensure that the most conservative assump-tions effecting core flow during the blowdown transient have been considered.
The paramerars used in the partial loop CRAFT and THETA models are consistent with the spectrum analysis reported in section 6 of BAW-10103, except for the following:
1.
The core power for both cases analyzed is reduced to 77% of rated power for 3-pump operation.
The peak linear heat rate for the hot bundle is the maximum kW/ft LOCA limit shown in Figure 2.2 of BAW-10103 at the 6 ft. elevation for this mode of operation.
2.
Since there is a power imbalance between the loop with 2 RC pumps running and the loop with 1 RC pump running, the load ratio between the steam generators is changed to 2.27:1 by control in the feed-water flow to each steam generator.
3.
The flow and pressure distribution was modeled to reflect the im-balance caused by the idle pump and the reduction in the RC flow to 75% of normal 4 pump operation. At steady stcte conditions the idle pump is locked in position because flow is reversed in that cold leg.
The flow proceeds from the idle pump to the lower plenum of the steam generator where it mixes and proceeds back to the reactor vessel through the RC pump in the inactive cold leg.
About 14% of the RC flow, from the downcomer plenum is directed back in the cold leg.
If the flow reverses to the positive direction during the transient the idle pump would act as a free spinning rotor with no power.
Table 1 summaries the results of the partial loop analysis and compares those results to the worst 'utcak reported in BAW-10103.
Figures 1 and 2 show respectively the hotspot and rupture node cJadding temperature anc the core flow for 3-pump operation with the break located at the active cold leg of partially idle loop. The maximum cladding temperature is 1766F at 98.5 seconds.
Figures 3 and 4 show respectively the hot spot and ruptured node cladding temperature and the core flow for 3-pump operation with the break located in the inactive cold leg of the partially idle loop. The maxi-mum cladding temperature is 17510F at 91 seconds.
Examination of the core
3 flow for both cases reveals a distinct difference in the flow transient.
With the break at the idle pump, core flow is similar to the 4-pump operation shown in Figure 6-2 of BAW-10103.
When the break is placed at the pump discharge of the active cold leg of the partially idle loop, the positive phase of the core flow is sharply reduced and the transition from positive to negative flow occurs earlier, approximately 11 seconds compared to approxi-mately 14 seconds for the 4-pump cr'e.
The negative flow is increased due to the decrease from 3 to 2 active pumps tryira to force the flow into the vessel. The flooding rates calculated using the faTLOOD code are slightly higher than those predicted for the 4 pump operation case because of the lower average core power.
The hot pin cladding temperature response calcu-lated with the THETA code are shown in Figures 1 and 3 for the two cases examined.
Rupture for both cases occurs just af ter the E0B.
The ruptured node cladding temperature decreases rapidly after rupture because of the reduced gap heat transfer from the fuel to the cladding and the increase in the surface area for cooling.
The reflooding heat transfer coefficients are high enough to prevent a rise in the ruptured cladding temperature after rupture.
The containment building pressure calculated by the CONTEMPT code is similar to the worst case shown in Figure 6-10 of BAW-10103.
The low temperatures experienced for the partial loop cases analyzed are considerably lower than those for 4-pump operation reported in BAW-10103.
The maximum cladding temperature for the partial loop LOCA analysis is only 1766F compared to 2079F for the worst 4 pump operation break as reported in Section 6 of BAW-10103.
The Technical Specifications for 3-and 2-pump operations previously submitted to the staff (7/9/75) for the operating Category 1 plants are calculated in a manner consistent with these results and remain applicable.
TABLE 1 Comparison of 8.55-ft2 DE break at pump discharge, Cp m 1.0, with 4 and 3 pump operating.
3-pumps, break in 3-pumps, break in active leg, parti-inactive leg, parti-4-pump (BAW-10103) ally idle loop a,11y idle loop Case Number FC 112(IL)
PP102(Yl)
PP101(1B)
Percent Power 102 77 77 (100% Power = 2772)
Peak Cladding Temp 2079/61.5 1766/98.5 1751/91.0 unrupt/ time, F/s Peak Cladding Temp 1916/43.5 1674.4/11.5 1569/42.0 rupt/ttme, F/s Cont Pressure at Peak 36.4 35.37 35.48 Cladding Temp, psia Rupture Time / blockage 13.8/63.14 25.39/65.04 25.9/64.78 S/:
CFT cetuation time, s 16.7 16.6 17.2 End of bypass, s 24.4 24.8 25.2 End of Blowdown, s 24.4 24.8 25.2 End of adiabatic heatup, 35.4 35.8 36.4 s
Water mass in reactor at 1532.0 1824 1623.0 end of blowdown, ibm Local metal-water reac-4.2923 2.86 2.738 tion, %
Full-power seconds at 1.949 1.874 1.959 end of blowdown
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