ML19309F977
| ML19309F977 | |
| Person / Time | |
|---|---|
| Issue date: | 05/16/1979 |
| From: | Levine S NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | |
| References | |
| SECY-79-333, NUDOCS 8005020084 | |
| Download: ML19309F977 (7) | |
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%lM C UNITED STATES 7Y 5020 May 16,1979 NUCLEAR R EGU LA*OR Y COP'MISslot3ECy.79 333 INFORMATION REPORT For:
The Commissioners From:
Saul Levine, Director Office of Nuclear Regulatory Research Thru:
Executive Director for Operations
[
Subject:
LOFT L2-2 CALCULATIONS
Purpose:
The purpose of this report is to inform the Commission of the status of the analyses of the first nuclear loss-of-coolant experiment, L2-2, performed at LOFT.
Discussion:
As discussed with the Commission on December 21, 1978, two predictions were performed prior to the L2-2 test.
The first was done with the one-dimensional computer code combination RELAP4/FRAP-T, and the second was done with the three-dimensional computer code TRAC.
Although a large number of thermal-hydraulic parameters were calculated for this test (such as core flow rates, 'vstem pressure, liquid level in the vessel, etc.) the pea;, fuel cladding temperature is generally of most interest.
The peak cladding temperature during the blowdown period predicted by RELAP4 was 1305'F compared with 1089*F predicted by TRAC.
The measured peak cladding temperature during the blowdown period was 957'F, considerably lower than either of the predictions made before the test.
Subsequent to the test, calculations were made.which included the following changes and corrections:
(1)
The actual measured initial conditions of the test were used in place of the assumed initial conditions; (2)
Errors in the codes and in the input data were corrected; and O
Contact:
G. D. McPherson, RSR 42-74437 l
The Comissioners 4 (3) Several miscellaneous changes were made to the codes and to the input data on the judgmental basis that these changes reflected the current best estimation predictive capability of the codes.
After making these changes and corrections, the calculated peak cladding temperatures were about 1026*F for RELAP4/FRAP and about 1035'F for TRAC.
The post-test calculations are in better agreement with the value of 957*F measured during blowdown, fleither code has done well in predicting the magnitude of the quench which occurred in blowdown nor in predicting the repeated dryout-rewet phenomena which LOFT experienced during reflood, as shown in Figure 1.
Changes in Computer Code Calculations A.
Initial Conditions The changes made in the initial conditions input to RELAP4 and TRAC are listed in Table 1.
These changes are due to operation within the tolerance bands allowed by the Experiment Operating Specifications.
Table 1 1
Initial Conditions Changed RELAP Parameter Changed Pretest Pos t-tes t Primary coolant sy(stemlb/s)
Code calculated 428.1 mass flow rate l
cold leg temp. (F)
Specified to give 544.5 hot leg temp. (F) correct core AT 585.3 Broken Loop hot leg temp. (F) near vessel 598.3 550.8 near break 598.3 517.8 cold leg (F) l near vessel 555.4 539.6 near break 555.4 509.5
4 The Commissioners Table 1 (Cont'd)
TRAC Parameter Chanced Pretes t Pos t-tes t Intact loop hot leg temp. (F) 608.0 586.0 cold leg temp. (F) 559.4 546.8 mass flow rate (lb/s) 411.4 456.6 Pump a P (psia) 11.3 13.3 Sti.am generator secondary pressure (psia) 914 899 Steam generator heat transfer area - corrected to give measured hot leg temperature.
B.
Input and Code Errors RELAP4 (1)
Examination of the computer output revealed an erroneous multiplier was being used with both the subcooled and saturated break flow models.
A value of 1.0 was used instead of the intended multiplier of 0.848 which is supported by the Semiscale S-06-5 test data, vena contracted calculations, and now by the L2-2 data.
(2) An independent check of the LOFT system model input data compared with the as-built drawings indicated that the volume specified for the reactor vessel upper plenum was in error.
The specified volume of 20 cu. ft. has been changed to the actual volu.ne of 33 cu. ft.
TRAC (1) The input to TRAC had erroneously specified a linear heat generation rate of 8.8 hv/ft instead of the intended value of 8.0 Kw/ft.
(2) A correction was made in the mathematical function used in TRAC to calculate thermodynamic parameters such as fluid internal energy.
.' ~
q The Commissioners C.
Miscellaneous Changes RELAp4 Numerous changes based on judgment and additional information pertaining to the performance of the LOFT system have been made in the post-test L2-2 analyses.
The changes are discussed briefly below.
(1) The subcooled to saturated transition quality upper limit is reduced from 2 percent to 0.25 percent.
The change gives a more accurate prediction of thermal hydraulic conditions immediately upstream of the break.
(2) The film boiling correlation :pecification has been changed from the Groeneveld correlation to the Tong-Young transition boiling correlation with the Condie-Bengston film boiling correlation.
The change is based on code assessment results and gives a
)
more accurate prediction of cladding temperature i
during blowdown and reflood.
(3) The intact loop hydraulic resistance has been corrected to account for data obtained during power range testing.
(4) A multiplier has been applied to the fuel rod gap conductance model to make the RELAP4 and FRAP fuel rod results consistent.
(5) To correct coupling problems between the system model and hot pin model, the incompressible form of the momentum equation at the core inlet and outlet of the system model is now being specified.
TRAC The containment pressure response (blowdown suppression tank pressure) was changed to the time dependent function measured in L2-2.
l The Commissioners Parameter studies are underway on the effects due to the j
gap conductance coefficient, rewet correlation, and heat slabs in the upper plenum. These studies are preliminary i
and have not produced reportable results at this time.
Status of LOFT Calculations The results of the LOFT L2-2 post-test calculations reported above are still preliminary.
Reporting of the final results has been delayed by the high priority given to work on Three Mile Island-2 calculations.
A detailed post-test calculation report will be issued when the completed results are available.
f
. wa Saul Levine, Director Office of Nuclear Regulatory Research
Enclosure:
As stated DISTRIBUTION l
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