ML19296D107
| ML19296D107 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 07/13/1979 |
| From: | SIEMENS POWER CORP. (FORMERLY SIEMENS NUCLEAR POWER |
| To: | |
| Shared Package | |
| ML19296D077 | List: |
| References | |
| NUDOCS 8002290347 | |
| Download: ML19296D107 (7) | |
Text
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Exxon Nuclear Ccepany, Inc Report to Consumers Power Company July 13, 1979 e
t 8002290347
Effect of 45 Second Diesel Start Time On Big Rock Point LOCA-ECCS Analysis Results The effect of an increase in the start delay time of the diesel driven spray pumps from 20 to 45 seconds was determined for the Big Rock Point loss of coolant accident (LOCA). The results of the analysis show th't the diesel start delay affects only the large breaks in the LOCA-ECCS spectrum.
The Peak Cladding Temperature (PCT) resulting from the delayed diesel start for the worst large break case was calculated to be 2079 F which is well below the 2200 F 10CFR50.46 limit and the 2138 F calculated for the 0.375ft2 limiting break. Since the limiting break remains as previously calculated and is not affected by the start delay of the diesel pumps, the Maximum Average Planar Linear Heat Generation Rates (MAPLHGR's) calculated previously and reported in XN-NF-79-21 Rev. I remain applicable even if the diesel start time is increased from 20 seconds to 45 seconds.
A complete LOCA-ECCS break spectrum had previously been analyzed for Big Rock Point and the results of this analysis were reported in XN-NF-78-53.
Starting time of the diesel driven spray pumps affect the LOCA-ECCS analysis through the calculated time at which core spray flow is provided. The primary LOCA-ECCS results affected are time of core spray flow initiation and the time to reach rated core spray flow.
In the LOCA-ECCS analysis, three condi-tions must be met before spray flow can initiate:
(1 ) the diesel driven spray pumps must be at speed; (2) the battery powered spray valve must have begun to open; and (3) the system pressure must be below the spray system shutoff head.
Similarly, for rated spray flow conditions to be assured:
(1) the diesel driven spray pumps must be at speed; (2) the core spray valve must be fully open; and (3) the system pressure must be low enough to allow rated spray flow (292 gpm).
In the LOCA-ECCS analysis, the controlling trip to actuate the diesel pumps is calculated low steam drum level, and the controlling trip for valve opening is low reactor pressure.
The effects of delayed diesel start time on break spectrum event times can be anticipated from the table of break spectrum blowdown event times presented as Table 3.2 of XN-NF-78-53 and shown as attached Table 1.1.
From Table 1.1, the time to initiate spray flow is currently controlled by the diesel start (low steam drum level + 20 seconds) for all the large
guillotines and for the large 3.53 and 2.12ft2 split breaks. The time to reach rated spray flow is controlled by the opening time of the spray valve
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(low reactor pressure + 15 seconds) for the 0.375ft2 split break and all larger breaks.
Increasing the start delay time (by an additional 25 seconds) for the diesel pumps will delay initiation of spray flow for
' rft2 breaks and larger with the maximum delay being experienced for the h.
est breaks. Time to rated core spray flow will be increased for breaks of 1.0ft2 and larger with the maximum delay again being for the largest breaks. Thus, increasing the diesel start delay time will affect only the large breaks and not the limiting 0.375ft2 break, and the greatest delays will occur for the largest breaks. Delaying time to rated spray flow has the greatest effect on ECCS analysis results because the time duration of minimal core heat removal is increased.
Delaying spray flow initiation will have a lesser effect through calculated flow and heat transfer during the time when spray is being injected into the system, but has not reached rated flow magnitude.
Examining the break spectrum LOCA-ECCS results from XN-NF-78-53, (Table 1.1 and Figure 1.1) for breaks which will have a delayed time to rated spray flow (1.0f t2 and larger), shows that the affected break with highest 2
peak cladding temperature (PCT) is the largest (3.53ft ) split break.
Since the largest break also experiences the maximum effect of the delayed start time for the diesel pumps, a recalculation of the 3.53ft2 split break with the 45 second start delay will yield a worst case LOCA-ECCS analysis over the affected break size range.
A recalculation of the 3.53ft2 split break ':a made with diesel start assumed to occur 45 seconds after the calculated low level signal rather than the 20 seconds assumed previously. Other than the delayed diesel start time, input was identical to the previous spectrum calculation for the 3.53ft2 split break.
The calculated PCT for the 45 second delay case was 2079 F which is 171 F higher than the previously reported 20 second delay case.
Calculated event times and LOCA-ECCS results for the 45 second delay case are shown in Table 1.2 along with the comparable 20 second delay results.
The final HUXY heat up results are shown in Figure 1.1.
The calculated results for the worst affected break, even with the 45 second delayed diesel start, are well below the 10CFR50.46 limits and significantly below the previously identified limiting break (0.375ft2
split) results. Thus, the LOCA-ECCS Maximum Average Planar Linear h'at Generation Rates (MAP' HGR's) established previously for the limiting break (Xfi-flF-79-21 Rev.1) remain valid and applicable when the maximum allowed start time for the diesel driven spray pump is increased fror 20 seconds to 45 seconds for the Big Rock Point Reactor.
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TABLE 1.2 Big Rock Point Large 3.53ft2 Break LOCA ECCS Analysis Results BOL, Axial Times P3 dial Peaking = 1.79 MAPLHGR = 7.49 Type G-3 Fuel Event 20 Second Delay 45 Second Delay Break Initiation 0.0 0.0 Low Steam Drum Level 1.23 1.23 RDS on (3 out of 4 valves used) 121.2 121.2 Low Reactor Pressure 11.9 11.9 Spray Flow Starts 21.2 46.23 Core Spray > 292 gpm and valve full open 26.9 46.23 PCT ( F) 1908 2079 PCT-time (sec.)
310 285 PCT Rod No.
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