ML20002D597
| ML20002D597 | |
| Person / Time | |
|---|---|
| Site: | Clinch River |
| Issue date: | 11/21/1980 |
| From: | Curtis R, Guppy J BROOKHAVEN NATIONAL LABORATORY, NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | |
| References | |
| BNL-NUREG-28045, NUDOCS 8101210537 | |
| Download: ML20002D597 (6) | |
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APPLICATI0tl 0F SSC-L s
TO INVESTIGATE NATURAL CONVECTION Itt DAtiAGED LtiFBR CORES By James G. Guppy, Brookhaven flational Laboratory and Robert T. Curtis, U.S. fluelear Regulatory Commission Submitted to ANS/ ENS /AIE 'nternational Conference Washington, D.C., November 17-21, 1980
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SUMMARY
APPLICATION OF SSC-L TO IilVESTIGATE*
flATURAL C0flVECTION Ifl DAriAGED LMFBR CORFS James G. Guppy (BNL), Robert T. Curtis (USflRC)
The loop version of the Super System Code (SSC-L)l 2 is utilized to study the response of a system representation of the CRBRP to various degrees of assumed damage postulated to occyr in single fuel assemblies and groups of fuel assemblies under coast down to natural convection operation. The damage imposed is measured in terms of instantaneous increases to the fuel assembly nominal pressure drop (AP ).
Damage factors for APA of 1.0, 1.88, 3.0 and A
4.0 were applied to average fuel channels in groups of one, seven and forty-two assemblies.
Using the SSC-L code, damage to fuel assemblies can be assumed to occur in various ways: '(1) blockages at the assembly inlet orifice zone, (2) blockages through the heated zone via fuel swelling, bowing, etc.; or (3) blockages at the assembly outlet. The detailed responses of the flow rates and tempera-tures of the affected assemblies to these blockages do depend on the actual blockage l'acation, but these influences of blockage location on the peak core assembly temperatures attained will be shown to be minor and can be considered as second-order effects.
For the purposes here, the postulated blockages are assumed to occur with-in the heated zone of-the fuel assemblies. Both the extent of the blockage within an individual assembly and the number of fueled assemblies damaged within the core are investigated. To provide a normalized method of compari-son, the extent of damage to an assembly is quantified by the amount of damage required to instantaneously raise the total assembly pressure drop (AP ) by A
- Work performed under the auspices of the U.S. fluclear Regulatory Commission
s flo. of Assemblies Peak Tempera _ture (K)
Damaged APA x 1.0 APA x 1.88 APA x 3.0 APA x 4.0 1
912 1010 1115 1184 7
912 1009 1113 1181 42 912 100R 1103 1167 Table 1.
Peak Coolant Temperatures Attained in Damaged Fuel Assemblies During L0EP Event assembly flow rates. Typical of this type of natural convection trans'ent, the lower flow rate produces not only higher temperatures, but also delays the time at which the second peak occurs (from 160 seconds for no damage case, out to 300 seconds for APA x 4.0 case).
The transient system response for the other damage cases studied (groups of I damaged assembly and 42 damaged assemblies) are quite shnilar. The peak maximum temperatures attained are summarized in Table 1.
As noted, even for cases where the assumed damage caused the initial APA to be increased by a factor of 4.0, the sodium in the affected average fuel channel did not reach saturation temperature.
Table 1 also indicates another interesting result. For cases where the assumed damage to the individual assemblies is identical, the peak temperature attained decreases as more assemblies are involved. This would not be entire-ly obvious at first glance since competing factors influence this response.
flamely:
(1) increasing the number of assemblies assumed damaged leads to higher overall resistance and consequently lower loop and total vessel flow available; (2) as si,Ure assemblies are damaged, a higher percentage of the core
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1300 1
.!!o DAMAGE 25 2 - APg x 1.83 y
3 - APA x 3.00 l
II-APg x 4.00 p4 E
J" 1100 e
8 o
s 2
5y 900 1
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700 0
80 160 240 320 TIME (S)
FIGURE 1 IlESPONSE OF IIAxlMUM COOLANT TEMPERATURE IN AVERAGE FUEL CHANNEL (CLUSTER OF SEVEN ASSEMBLIES) TO AN L0EP EVENT WITH ASSUMED DAMAGE
N will be at elevated temperatures, which means, due to bouyancy driven flow redistribution effects, that more flow will redistribute in a relative sense to the damaged assemblies; and (3) since all assemblies are forced by design to have identical pressure drops, momentum and continuity relationships dictate that involving more assemblies in the damage will lead those assem-blies to obtain a higher percentage of the total flow available. The re-sults of this study show for the cases analyzed, that the combined effect of the second and third influences dominate over the first, such that the peak temperature attained Acreases when the number of identical assemblies assumed damaged is increased. These results also emphasize the fact that the use of an analytical tool such as SSC-L, which can simultaneously account for the complex inter-coupling of the many competing physical phenomena modeled is es-sential to properly calculate transients of this nature In summary, damage factors for APA of 1.0,1.88, 3.0 and 4.0 were ap-plied to average fuel channels in groups of one, seven and forty-two as-semblies. A factor for APA for an average fuel assembly of greater than four was found necessary to cause sodium boiling under coast down to natural convection conditions. Due to the inter-coupling of several physical phe-nomena properly modeled within the SSC-L code, increasing the number of aver-age fuel assemblies assumed to be damaged led to a decreasing peak maximum coolant temperature attained. For the cases analyzed here, SSC-L typically computed the simulated transient on a CDC 7600 in a machine time faster than 4
real time.
89-REFERENCES 1.
A. K. Agrawal, et al., "An Advanced Thermohydraulic Simulation Code for Transients in LMFBRs (SSC-L Code)," Brookhaven National Laboratory, BNL-NUREG-50773 (February 1978).
2.
A. K. Agrawal, et al., " User's Manual for the SSC-L Code," Brookhaven National Laboratory, NUREG/CR-0452 (October 1978).
3.
Clinch River Breeder Reactor Plant Preliminary Safety Analysis Report, with Amendments through 51, Project Management Corporation (1975-1979).
4.
J. G. Guppy, " Application of Multiple Timestep Integration Method in SSC-L", Trans. Am. Nucl. Soc., 33, 340, 1979.
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