ML20056C506
| ML20056C506 | |
| Person / Time | |
|---|---|
| Issue date: | 10/06/1992 |
| From: | Dhir V NRC |
| To: | Catton I Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-2049, NUDOCS 9306240315 | |
| Download: ML20056C506 (2) | |
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31e-20s-2302 UCLA N E 522 F02 OCT 06 '92 16:21 j
cT-aow PDE le/m/93 To:
Dr. Ivan Catton October 6,1992 Chair, ACRS i
Subcommittee on Thermal Hydraulic Phenohiena Via:
Paul Boehnert, Senior Staff Engineer From:
V.K. Dhir gjg
Subject:
ACRS Joint Thermal Hydraulic Phenomena / Core Performance Subcommittee Meeting Sept. 17,1992.
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Below I give my comments on BWR Stability Issues and on the ATWS Rule Relative to BWR Thermal Hydraulic Stability.
BWR Stability I.
I generally agree with the solutions recommended in the Oakridge report ORNIJNRC/LTR-92115 for the stability problem in BWRs:
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Immediate Protection action (SRI or SCRAM) upon entrance in exclusion g
region.
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2.
Rely on quadrant based APRM (Average Power Range Monitor) to suppress 953 oscillations before safety margins are compromised.
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Rely on signal from several LPRMS (Local Power Range Monitors) to
@@C suppress oscillations before safety margins are compromised.
/f I find solution 3 to be the most preferable in reactors which have LPRMS.
l Use of this solution will require development of a correlation for change in critical power ratio as a result of neutron power oscillations. Utilities should gg l
be encouraged to develop this option, since online computing is not a h
S concem t ese days.
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I II.
The instability exclusion region is influenced by the reloading procedures. With the g
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experience G.E. has acemnulated over the years, one would expect G.E. to have developed M
l by now standardized reloading procedures.
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N$g' a l'p877L ATWS Rule Relative to BWR Thermal Hydraulic Stability
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1.
TRACG code is being used to determine the magnitude of power oscillations and
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the subsequent fuel damage. I am not familiar with TRACG, however, according to the Technical Audit Report, the code has not been validated with sufficient data after its augmentation.
II.
Calculation of fuel enthalpy rise during power oscillations may not have been done correctly. The enthalpy rise of 250 cal /gm calculated in the Audit Report is significantly larger than G.E.'s original value. Also, this value is not far from the critical value of 280 cal /gm. I believe that these calculations should be critically reviewed.
III.
It has been concluded that some fuel damage will occur. The damage will be limited to less than 0.5% of the core. The resulting radioactive release is also calculated to be below the maximum allowed for ATWS. This may be true, but because of large uncertainty in'the magnitude of the power peaks and the heat losses, (e.g in film and transition boiling) an uncertainty band should be placed on the calculated fuel damage limit.
IV.
Finally,.I suggest that before a conclusion is made that no change in ATWS rule is needed or is appropriate, a cross-check on the fidelity of the calculations with respect to energy that,is deposited into the fuel during oscillations and the extent to which fuel damage is possible, should be made.
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