ML12076A142

Meeting Topics - Suggested Discussion Items Regarding Large Break Loss-of-Coolant Accident Submittal - Shearon Harris Nuclear Power Plant, Unit 1

ML12076A142
Person / Time
Site:	Harris
Issue date:	01/11/2012
From:	Billoch-Colon A Plant Licensing Branch II
To:
Billoch-Colon, Araceli
Shared Package
ML12076A140	List: ML12076A141 ML12076A142 ML12076A165
References
TAC ME6999
Download: ML12076A142 (2)

Text

SUGGESTED DISCUSSION ITEMS LARGE BREAK LOSS-OF-COOLANT-ACCIDENT SUBMITTAL SHEARON HARRIS NUCLEAR POWER PLANT, UNIT NO. 1 PROGRESS ENERGY DOCKET NO. 50-400

1. For droplet break up model, show the drop sizes produced by the model for several low reflood rate data. Present the clad, vapor temperature and total heat transfer coefficient versus time at the measured axial locations. Show the heat transfer coefficient for all of the components comprising the dispersed flow film boiling (DFFB) heat transfer, including the interfacial heat transfer coefficient.

2. Since RELAP5 is one-dimensional the vapor temperature and droplets are distributed evenly across the hot channel. The code computed cross-section average quantities appears to fail to properly capture the very high temperature gradient in the vapor phase boundary layer near the wall so that the distribution of the evaporating water droplets play a fundamental role in the heat transfer process. In particular, interfacial heat transfer is over predicted. This appears to be a major limitation for all one-dimensional codes. Test data shows that the channel is three-dimensional with accumulation of drops in the central region and a highly superheated region near the walls. Modeling this multi-dimensional behavior leads to a substantial reduction in the interfacial heat transfer and limiting of the droplet de-superheating to the central core and not the highly superheated layer near the walls.

Explain what adjustments are made to the DFFB model components to overcome this major discrepancy. That is, the sink temperature is not the average channel temperature for computing single phase heat transfer, an interfacial heat transfer between the drops and the vapor is control by the lower vapor temperature in the central core where the drops reside.

3. Due to the simplified one-dimensional averaging of thermodynamic quantities in RELAP5 and the limited data, it is difficult to quantify all of the component contributions to DFFB.

a. Address how the magnitude of the droplet contribution is verified in the RELAP5 model.

b. Without detailed knowledge of the magnitude of all of the components to DFFB, validation of this model against reflood data may result in including other phenomena/effects that are not pertinent to the heat transfer benefits from the droplet break up model. Explain and justify the magnitude of the impact on DFFB heat transfer with this new model.

c. Describe the interfacial heat transfer model and the impact on interfacial heat transfer coefficient with the new droplet model. In comparing the DFFB against data with the new droplet model, show all of the contributions to the total heat transfer coefficient versus time at the peak clad temperature (PCT) location.

4. The packing fraction of 50 percent does not appear to capture all of the test data.

Packing fraction as a function of burst strain varies in the range 52 to 80 percent based on data from Broughton, J. M, 1981, [Power Burst Facility] PBF [loss-of-coolant accident] LOCA Test Series, Test LOC-3 and LOC-5 Fuel Behavior Report, NUREG/CR-2073. The Nuclear Energy Agency (NEA) Organization for Economic and Co-operation and Development (OECD) Nuclear Fuel Behaviour in Loss-of-coolant Accident (LOCA) Conditions State-of-the-art Report identifies 55.5 and 61.5 percent fill fraction for the FR2 reactor test E2. Values for the high burnup fuel in IFA-650.4 are expected to be higher than 70 percent, consistent with the bounds for PBF/LOCA gamma scanning and micrographies and FR-2. (See Grandjean, C IRSN Calculation of the IFA-650.4 and .5 LOCA Tests ISRN, Cadadache, Fr. EHPG Meeting, Storefjell, March 12-15, 2007 meeting).

Show the impact on PCT for fill fractions up to and including 80 percent. Please also describe how the fill fraction is sampled.

5. Address whether the use of a nominal decay heat curve has ever been applied to decay heat test data over the range of applicability to show that this approach captures all decay heat conditions. The discussion should also address the uncertainty in generating this nominal curve and demonstrate that use of the nominal curve does not capture the decay heat for the first two seconds. Provide a multiplier which appropriate captures the decay heat behavior during this first two seconds of the curve.