ML20237A062
| ML20237A062 | |
| Person / Time | |
|---|---|
| Issue date: | 08/07/1998 |
| From: | Lainas G NRC (Affiliation Not Assigned) |
| To: | Larkins J Advisory Committee on Reactor Safeguards |
| References | |
| RTR-NUREG-1570 ACRS-GENERAL, FACA, NUDOCS 9808130055 | |
| Download: ML20237A062 (4) | |
Text
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i August 7, 1998 1
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MEMORANDUM TO:
John Larkins, Executive Director Advisory Committee on Reactor Safeguards bus C. Lainas, Acting Director FROM:
Division of Engineering Office of Nuclear Reactor Regulation
SUBJECT:
JAERI ANALYSIS OF FISSION PRODUCT HEATING OF STEAM GENERATOR TUBES This memorandum is to inform the Advisory Committee on Reactor Safeguards (ACRS) of the results of the staff's evaluation of information contained on Cooperative Severe Accident
' Research Program (CSARP) viewgraphs forwarded to the ACRS in a memorandum from J.
Hopenfeld to J. Larkins dated May 20,1998. The analysis supporting the slides was performed by the Japan Atomic Energy Research Institute (JAERI), and addressed, in part, the additional
' heating of steam generator (SG) tubes, during a station blackout sequence, caused by the j
deposition of fission products en the inner surface of SG tubes.
Although the JAERl analysis predicted that the SG tubes would survive the transient, with a small margin, it also predicted substantial fission product heating of the tubes due to deposited fission products. This is in contradiction to the NRC conclusion that the effect of deposited fission products in tube heating is trivial.
Attached is a description of the JAERI analysis and the staff's evaluation of its appropriateness.
This evaluation was prepared by RES and it concludes that the JAERI analysis applied incorrect boundary conditions which influenced the prediction of fission product deposition and heating.
Because of the thermal hydraulic assumptions and analytical treatment, we conclude that the finding of the JAERI analysis, relative to the significance of fission product heating, is not relevant to staff's evaluation of the matter. As a result, the staff's previous conclusions regarding the severe accident risk implications of degraded steam generator tubes documented in NUREG-1570 remain unchanged.
Attachment:
As stated i
CONTACT: Timothy Reed, NRR/DE l
415-1462 I
DISTRIBUTION:
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MEMORANDUM TO:
John Larkins, Executive Director Advisory Committee on Reactor Safeguards FROM:
Gus C. Lainas, Acting Director Division of Engineering
' Office of Nuclear Reactor Regulation
SUBJECT:
JAERI ANALYSIS OF FISSION PRODUCT HEATING OF STEAM GENERATOR TUBES This memorandum is to inform the Advisory Committee on Reactor Safeguards (ACRS) of the results of the staff's evaluation of information contained on Cooperative Severe Accident Research Program (CSARP) viewgraphs forwarded to the ACRS in a memorandum from J.
Hopenfeld to J. Larkins dated May 20,1998. The analysis supporting the slides was performed by the Japan Atomic Energy Research Institute (JAERI), and addressed, in part, the additional heating of steam generator (SG) tubes, during a station blackout sequence, caused by the deposition of fission products on the inner surface of SG tubes.
i Although the JAERI analysis predicted that the SG tubes would survive the transient, with a -
small margin, it also predicted substantial fission product heating of the tubes due to deposited fission products. This is in contradiction to the NRC conclusion that the effect ci deposited fission products in tube heating is trivial.
Attached is a description of the JAERI analysis and the staff's evaluation of its appropriateness.
The staff concludes that the JAERI analysis applied incorrect boundary conditions which influenced the prediction of fission product deposition and heating. Because of the thermal hydraulic assumptions and analytical treatment, we conclude that the finding of the JAERI analysis, relative to the significance of fission product heating, is not relevant to staff's evaluation of the matter. As a result, the staff's previous conclusions regarding the severe accident risk implications of degraded steam generator tubes documented in NUREG-1570 remain unchanged.
Attachment:
As stated I
CONTACT: Timothy Reed, NRR/DE 415-1462-DISTRIBUTION:
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File Center EMCB RF JDonoghue CAder -
JMitchell JHopenfeld JSchaperow SLong CTinkler-h DOCUMENT NAME: G:\\
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August 7, 1998 MEMORANDUM TO: John Larkins, Executive Director Advisory Committee on Reactor Safeguards FROM:
Gus C. Lainas, Acting Director Division of Engineering Office of Nuclear Reactor Regulation
SUBJECT:
JAERI ANALYSIS OF FISSION PRODUCT HEATING OF STEAM GENERATOR TUBES This memorandum is to inform the Advisory Committee on Reactor Safeguards (ACRS) of the results of the staff's evaluation of information contained on Cooperative Severe Accident f
Research Program (CSARP) viewgraphs forwarded to the ACRS in a memorandum from J.
j Hopenfeld to J. Larkins dated May 20,1998. The analysis supporting the slides was performed by the Japan Atomic Energy Research Institute (JAERI), and addressed, in part, the additional heating of steam generator (SG) tubes, during a station blackout sequence, caused by the deposition of fission products on the inner surface of SG tubes.
Although the JAERI analysis predicted that the SG tubes would survive the transient, with a small margin, it also predicted substantial fission product heating of the tubes due to deposited fission products. This is in contradiction to the NRC conclusion that the effect of deposited i
fission products in tube heating is trivial.
Attached is a description of the JAERI analysis and the staff's evaluation of its appropriateness.
This evaluation was prepared by RES and it concludes that the JAERI analysis applied incorrect boundary conditions which influenced the prediction of fission product deposition and heating.
Because of the thermal hydraulic assumptions and analytical treatment, we conclude that the finding of the JAERI analysis, relative to the significance of fission product heating,is not relevant to staff's evaluation of the matter. As a result, the staff's previous conclusions regarding the severe accident risk implications of degraded steam generator tubes documented in NUREG-1570 remain unchanged.
Attachment-As stated CONTACT: Timothy Reed, NRR/DE 415-1462 I
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EVALUATION OF COOPERATIVE SEVERE ACCIDENT RESEARCH PROGRAM VIEWGRAPHS Recently, ACRS was provided a copy of a presentation made by a representative of the Japan Atomic Energy Research Institute (JAERI) at the May 1998 Cooperative Severe Accident Research Program meeting. This presentation provided the results of analysis of steam generator tube integrity during a TMLB' sequence with the secondary side of a steam generator depressurized. The analysis showed that the temperature of the steam generator tubes could be significantly affected by heat from deposited fission products which differed from previous analysis performed by NRC staff. Following the presentation, staff from the Accident Evaluation Branch, RES, hold discussions with the JAERI representative to better understand the basis of the analyses. As a result of these discussions, the following provides the staff's understanding of the analysis and an assessment of the relevance of the analysis to the issue of steam generator tube integrity.
The JAERI analysis was based, in part, on the ART code, a Japanese code for predicting fission product deposition in the reactor coolant system (RCS) given thermal hydraulic and fission product release boundary conditions. SCDAP/RELAPS and MELCOR results were modified to establish boundary conditions. The results presented showed significant fission product deposition in the first meter of the steam generator tubes as a result of thermophoresis.
However, a review of the JAERI analysis revealed several inconsistencies. First, it was leamed that JAERI analysis improperly assumed the temperature of the steam entering the tube bundle was equal to the temperature of the unmixed vapor in the steam generator inlet plenum (from the hot leg). Use of the temperature of the unmixed vapor in the steam generator inlet plenum l
as the temperature of the vapor in the tube apparently resulted in a temperature difference -
between the vapor and the steam generator tube wall of up to 250K inside the first section of the tube. It is this high temperature difference that is responsible for the fission product deposition in the ART calculation. It is unreasonable to assume such a large temperature difference in this region without water on the secondary side of the steam generator given the heat transfer across the thin tube wall. The NRC's SCDAP/RELAPS results showed a temperature difference of about 15K in this region, which results in minimal deposition by thermophoresis.
The NRC staff's VICTORIA analysis of this sequence showed that the dominant mechanism for deposition was settling inside of the steam generator u tubes onto the upward facing surfaces in the bends of the u-tubes. This is reasonable given the recirculatory flow pattems in the RCS and the lack of other driving forces for deposition other than settling. The JAERI analysis did not l
attempt to model settling on upward facing surfaces inside of the steam generator u tubes. The j
reason for this treatment is unclear.
Finally, in another apparent inconsistency, the JAERI analysis did not explicitly consider the primary source of heat (i.e., cladding oxidation) in their calculation of heat up of the steam generator tube wall. The relative importance of deposited fission product heating was determined by JAERI by comparison against the heat carried to the tubes by superheated steam heated only by decay heat in the core. Because of their thermal hydraulic assumptions and analytical treatment, the staff concludes that the finding of the JAERI analysis, relative to the significance of fission product heating, is not relevant to our evaluation of this matter.
ATTACHMENT 4
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