ML20206E142
| ML20206E142 | |
| Person / Time | |
|---|---|
| Issue date: | 02/11/1985 |
| From: | Ross D NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Bernero R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20204G644 | List: |
| References | |
| RTR-NUREG-1150 NUDOCS 8704130529 | |
| Download: ML20206E142 (3) | |
Text
f e s 3. 6 i UNITED STATES 8
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FEB 11 1985 fiEtiORANDUM FOR: Robert M. Bernero, Director Division of Systems Integration, NRR FROM: Denwood F. Ross, Deputy Director Office of Nuclear Regulatory Research
SUBJECT:
RES RESPONSE TO NRR NEED FOR MULTI-DIMENSIONAL MODELING OF RCS BEHAVIOR UNDER SEVERE ACCIDENT CONDITIONS
REFERENCES:
- 1. August 30, 1984 Vemo from Robert M. Bernero to Denwood F. Ross, "Need for Multi-Dimensional Modeling of RCS Behavior in Support of Severe Accident Investigations."
- 2. Denny, V., "The CORMLT Code," SAI-361-83-PA, (April 9,1984).
- 3. Denny, V. and Sehgal, B. R. , "PWR Primary System Temperatures During Postulated Severe Accidents,"
Trans. of ANS, Vol. 47, 317-319 (November 1984).
- 4. Ransom, V. H. et al., "Use of RELAPS Thermal-Hydraulic Models in the Severe Core Damage Accident Analysis Package," INEL Position Paper (March 1984).
l This is in response to your memo in which you addressed the need for multi-dimensional modeling of the reactor coolant system (RCS) behavior under severe accident conditions. Our response was necessarily. delayed by the recent uncertainties in the FY 1986 budget picture. We agree with you that multi-dimensional flow in the RCS can be important for severe accident investiga-tions and therefore should be modeled. We also appreciate your endorsement of our research efforts in this area.
To meet the NRR need, we currently have in FY 1985 the following research programs to address the multi-dimensional flow in the RCS for severe accident investigations. However, the completion of these programs is contingent on the assumptions in the President's Budget for FY 1986.
CONTACT: J. Han, x74460
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R. M. Bernero s
- 1. Under the MELPROG program at SNL and LANL, two-dimensional (axial and radial) fluid dynamics for degraded core modeling has been developed from TRAC methodology. In addition to the two fluid fields for water and gas as in TRAC, two more fluid fields are added to MELPROG to model the movement of liquid corium and solid corium respectively. Two-dimensional degraded core calculations will be performed by November 1985 to study the in-vessel natural convection flow under TMLB' sequence from core uncovery up to vessel2 failure. Results will be used to compare with EPRI-sponsored calculations by December 1985.
- 2. A program has been initiated at ANL to use the existing COMMIX code to model single-phase multi-dimensional natural convection flow in the entire RCS of a PWR. The purpose is to investigate flow patterns and temperature distributions along the piping and steam generator tubes. Results will be used to assess the RCS structural integrity (based on temperature and pressure) under TMLB' sequence for the conditions of (1) no pump seal Comparisons with EPRI calcula-failuge and (2) with pump seal failure.
tions will be made by December 1985.
- 3. Under the SCDAP program at INEL, the SCDAP code has been linked with RELAPS, Multi-dimensional flow in the vessel can be approximated by the multi-region core model in RELAPS provided the fluid speed is low (say, By Mach number less than 0.2)4; however, the model needs to be assessed.
September 1985, a preliminary version of the integrated SCDAP/RELAPS/
TRAP-MELT system code will be available to simulate RCS behavior for TMI-2 type of severe accidents and to predict fission product and hydrogen release to the containment.
- 4. Limited assessment of these severe accident analysis codes is being performed. This issue is being' addressed separately under the Severe AccidentResearchProgram(SARP). However, it should be noted that assessment requirements for severe accident analysis codes are broader in scope but less stringent for accuracy than those for design-basis analysis codes. This is because the core geometry and composition are time-dependent during severe accidents and as a result more physical processes and larger modeling uncertainties are involved. compared to design-basis accidents.
In summary, we currently have research programs to address the multi-By December dimensional flow in the RCS under severe gcjdent conditions.
1985, we will start to assess EPRI claims that because of the multi-dimensional flow the RCS structural boundary may fail and the system may depressurize before the failure of the vessel. Our staff has been working i
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i R. M. Bernero 3 FEB 111985 closely with your staff to try to resolve this issue by mid-1986, consistent with the planning of SARP Phase II studies.
Denwood F. Ross, Deputy Director
_0ffice of Nuclear Regulatory Research cc (w/o references):
G. Marino, RES R. Curtis, RES B. Agrawal, RES i
W. Lyon, NRR T. Spets, NRR L. Hulman, NRR A. Thadani, NRR
{, Z. Rosztoczy, NRR J F. Rowsome, NRR
- F. Schroeder, NRR s.
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