ML19309F944
| ML19309F944 | |
| Person / Time | |
|---|---|
| Issue date: | 08/02/1979 |
| From: | Levine S NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | |
| References | |
| SECY-79-469, NUDOCS 8005020046 | |
| Download: ML19309F944 (7) | |
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- Qgg 52 UNITED STATES Aucust 2,1979 NUCLEAR REGULATORY COMMISSION g j-79 469 WASHINGTON, D. C. 20555 INFORMATION REP 0lT._
Fo r:
The Commissioners From:
Saul Levine, Director Office of Nuclear Regulatory Research Thru:
Executive Director for Cperations /N b t
Subject:
LOFT NUCLEAR TESTS L2-2 AND L2-3 RESULTS
Purpose:
The purpose of this report is to inform the Commission of the results of the first two nuclear loss-of-coolant experiments performed at the LOFT facility.
Discussion:
Two nuclear loss-of-ccolant experiments have been performed to date at the LOFT facility.
Both tests have been double-ended cold leg breaks with cold-leg injection of the emergency core ccolant. Both tests have considered off-site power to be available to the emergency systems used to mitigate the con-sequences of the accident being simulated. 'The difference in the two tests is in the power at which the reactor was operating.
For the first test, designated L2-2, the maximum core power density was two-thirds the value corresponding to full power operation in comercial pressurized water reactors.
For the second test, designated L2-3, the maxi.nm core power density was equal to that for full power operation in commercial PWR's.
The first two nuclear loss-of-coolant experiments yielded results that were quite similar. Differences which occurred in the results were due to performing the L2-3 test at a core power 50% greater than that for the L2-2 test.
The increased core power resulted in an inc. ease in the coolant temperature rise in the core of 45"..
Since the hydraulic behavior during the test is dependen'. upon the coolant temperature rise in the core, the hydraulic events, though the same in both tests, occured earlie in the L2-3 test than in the L2-2 test.
Contact:
G. D. McPherson, RSR 42-74437 I
..The Comissioners.
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As had been predicted for both tests, the rupture caused the coolant flow to reverse until the hotter coolant from the core reached the break. At this time, the saturated coolant which created choked flow at the break plane due to coclant vaporizing caused the flow rate at the break plane to drop.
The drop in the flow rate out the break caused part of the coolant flowing from the intact loop to the reactor vessel to resume its initial flow direction and flow up through the core. The core flow can be deduced from the curves in Figure 1.
In the period from four to six seconds the difference between the upper curve (the flow from the intact loop cold leg) and the lower curve (the flow out the broken loop cold leg) is the amount of coolant flowing up through the core.
This coolant flowing up through the core causes a sudden quenching, or temperature reduction, of the fuel rods.
Figures 2 and 3 illustrate the quenching which occurred in both the L2-2 and L2-3 experiments.
The magnitude of the observed core quench was not predicted by the accepted computer codes, as illustrated in Figure 4 for the L2-3 tes t.
The reason for this is that the codes are not equipped with quench heat transfer correlations capable of predicting the temperature turn-around under the conditions of flow, clad temperature and pressure which prevailed during the LOFT blowdown. An experimental version of the TRAC code, which contains the Iloeje quench correlation, was used to predict the L2-3 experiment. It predicted a peak clad temperature within 15*F of the measured peak and a quench to the same temperature as measured. The conditions necessary for quench and the Iloeje correlation are currently under review by the Research staff.
The temperature response of the fuel in the first two nuclear loss-of-coolant experiments, combined with the post test core requalification, indicates that in neither test was there any fuel damage. Therefore, the present fuel is available for future tests, although the central assembly was removed for visual inspection.
Within the limited experience of nuclear operation of LOFT, the results provide confidence in our belief that future results will be of increasing value in estimating the margin of conservatism in today's nuclear reactor safety system.
A Saul Levine, Director Office of Nuclear Regulatory Research DISTRIBUTION
Enclosure:
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