LIllTERIM REPORT

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Accession No.Pgl@h2fSA M!

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Contract Program or Project Title: RAMONA Code Modification and Evaluation

Subject of this Document: December Monthly Highlight' Letter

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Type of Document:Monthly Highlights

Author (s): M. M. LevineDepartment of Nuclear EnergyBrookhaven National LaboratoryUpton, New York 11973

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Date of Document:,

.December 1979

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Responsible NRC Individual Dr. Stanislav Fabic, Chiefand NRC Office or Division: Analyses Development Branch

React;or Safety Research Div.U. S. Nuclear Regulatory Commission

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Washington, D. C. 20555_

This document was prepared primarily for preliminary or internalIt has not received full review and approval. Since thereuse.

may be substantive changes, this document should not be consideredfinal .

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Brookhaven National LaboratoryUpton, NY 11973

Associated Universities, Inc.for the

U.S. Department of Energy

Prepared forU.S. Nuclear Regulatory Commission

Washington, D. C. 20555Under Interagency Agreement EY-76-C-02-0016 80 022 20 Nb

NRC FIN No. A-3014

INTERIM RRW Researc1 anc "ec anical

Assistance Report -

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Thermal Reactor Safety Code Development

Highlights

for

D.ecember 1979*

Subtask A: RAMONA Code Modification and EvaluationSubtask B:

IRT and RETRAN Code Modification and Evaluation

M. M. Levine, Principal It.vestigator

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Thernal Reactor Safety DivisionThermal-Hydraulic Development Division

Department of Nuclear EnergyBROOKHAVEN taTIONAL IABORATORY

Upton, New York 11973

XRC Research anc .ecam'ca\.. t

Assistance Report

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Work carried out under the auspices of the United States Nuclear RegulatoryCommission

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A.RAMONA-III Code Modification and EvaluationA.1 Jet Pump Recirculation Loop Model

Work continued with the BNL jet pump recirculation loop model in order tohave the jet pump M ratio (suction leg mass flow divided by drive line massflow) as a given input number.

Two approaches to this problem are beingtried.

there is no freedom to fix the jet pump pressure drop.In one the loss coefficients are specified along with the M ratio andthe jet pump pressure drop and M ratio are fixed and the loss coefficientIn the other approachhave to be adjusted. s

model were received.The Scandpower (ScP) jet pump recirculation loop model and stecn separatorwhich will now be appliced to the BNL version and tested.The package included documentation and RAMONA updates

A.2 Plant Protection Sys tem

Nineteen different trips have now been implemented. A memo describingeach of the signals that cause a trip and what the trip activates has beenwritten.

A.3 Code Assessment

Calculations of Turbine Trip Test No. 3 (TT3) show that RAMONA-III under-predicts the rise in power that was observed.The cause for this seems to bea combination of deficiencies in the hydraulics modelling and the neutronics

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input data.In order to isolate and identify the source of these deficiencies

a small sinusoidal pressure peturbation was imposed rather than the TT3 steam-dome pressure. All other input was held constant. The systen variables suchas void, relative power, average flux, etc. were observed and noted to exhibitsinusiodal behavior.proximate transfer functions. Amplitudes and phases were noted and used to compute ap-

Of special interest were those of pressure-voidand void power.While realizing all the limitations of using such analysis on

non-linear systems, these approximate numbers were conpared to similar numbersextracted from BNL-TWIGL for TT3.the void power transfer function. Preliminary results Indicate agreement in

Other relationships noted such as a phaselag between relative power and average flux are to await further study

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The sensitivity of RAMONA to the slip formulation was explored.placement of the slip model with the nodel of Henry-Fauske was attaapted but

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led to difficulty in successfully relaxing to a steady state.by modifying the parameters in the Bankof f-Malnes correlation and allowing the

Removing " slip"

stagnation vapor velocity to approach zero void worked successf ully.increased the relative power peak by 10%. It

the core was explored.The sensitivity of relative power peak to the steady state avercge void inflow through the core thereby obtaining a variety of mean core voids.Different steady states were obtained by varying theBNL-IWICL value for mean core void was lower than the RAMONA value (0.28 as

Theopposed to .34).

Such variation made less than 10% difference in the relativepower peak value,

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Specific problems related to using the code were investigated. Theseincluded problems in achieving the steady state, oscillations in the steam-load, and errors in the direct moderator energy deposition.

The RAMONA code has shown to be sensitive in attenpts to relax to steadystate. The steady state formulation will not entertain negative velocities.When negative velocities are encountered they lead to fatal errors. Duringthe relaxation process swings in values do occur which of ten prevent success-ful relaxation to steady state. One example of this sensitivity was in astudy in which the input da ta for the Solberg void correlation was varied.Small variations in these parameters led to an unsuccessf ul relaxation of thesteady state. This has also been 6bserved with changes in downccuer/recircu-lation loop input parameters.

The mass flow into the line, USL, was observed to oscillate. In TT3WSL of course changes magnit ude and sign consistent with acoustic waves in thelong steam line. In the version of RAMONA used, the value of USL was noted toswing in one time step from positive to negative its full value. In thisversion the steam doce pressure is Laposed from a data table. (A series ofordered pairs of pressure and time values.) The value of the deriva tive ofpressure with time is computed from the table and is discontinuous. In thisversion of the code the value of USL is computed from this derivative, thevolume of vapor in the vessel and its compressibility. Calculations with thispart of the code were modified and were not found to affect the power peak.This area of RAMONA will be modified when the BNL steamline model is incor-po ra ted .

Turbine _ trip test reeults have been found in the past to be sensitive to '

the amount of power directly deposited in the water of the reactor. RAMONAconsiders the inchannel water as " coolant" and the water in the bypass regionas " moderator." The bypass region includes water in the gaps between bundlesas well as in the reflector region. Direct neutronic feedback is only af-fected by the coolant conditions; the moderator temperature and density arenot used in that way. Nevertheless the overall system balance requires theproper coderator conditions.

Seven input numbers in RAMONA bear on the energydeposited outside the fuel. In examining how these were used it was dis-covered that the code did not deposit energy directly in the moderator asadve rtised . The only mechanism for energy deposition in the moderator was byconduction from the coolant region.

A.4 Steamline Model

Work has continued on the implementation of the steamline model inRAMONA-III and is now close to completion. With the additional code and stor-age required for the steamline nodel the BNL version of RAMONA-III is nowclose to the capacity of Small Core Memory on the BNL 7600. Before the imple-mentation of other changes and new models to the code it will be necesary tocreate an overlayed version of RAMONA-III.

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B.IRT and RETRAN Code Modification and EvaluationB.1

.' IRT Code Modification

B.l.l. IRT Once-Through Steam Generator Modeling

The downcomer equations in the Mark II version of the once-through steamgenerator model are being revised to remove instabilities that occurred duringthe testing of the model.

A quasi-steady momentum equation is being incorpo-rated and the solution of the downcomer and tube region equations is beingmodified such that all equations;are solved simultaneously.

The Mark I once-through steam generator model is currently being expandedto allow for the simulation of asymetric plant transients.

B.l.2 Once-Through Steam Generator Analyses

Further revisions to the reactor upper head region modeling have beenimplemented for the analysis of the overfeed transient for a typical B&W plant.

B.2 RETRAN Code Implementation4

The MOD 002 of the RETRAN code has been received at BNL and is currentlybeing implemented on the CDC-6600.The main difference between MOD 001 andMOD 002 are corrections in the non-equilibrium pressurizer model. The modifi-

cations improve the convergence of the calculation when the pressurizer isnearly solid or nearly empty.ity of'the non-equilibrium pressurizer model have been implemented.In addition, corrections to the restart capabil---

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Distribution

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S. Fabic, Chief - NRCW. Y. Kato11. J. C. KoutsT. Murley - !!RCF. Odar - HRC

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Z. Rosztoczy - NRC,

J. B. Spraggins-

L. S. Tong - flHC-

G. M. Vineyard11. Zuber - NRC

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RN40f!A personnel . .

RSP Division HeadsRSP Group Leaders

HRC Technical Information Div. (Bethesda) (2)

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