ML19308C320
| ML19308C320 | |
| Person / Time | |
|---|---|
| Site: | Millstone, Monticello, Pilgrim, Crane  |
| Issue date: | 10/25/1977 |
| From: | Stello V Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19308C302 | List: |
| References | |
| TASK-15-19, TASK-RR, TASK-TF, TASK-TMR NUDOCS 8001220715 | |
| Download: ML19308C320 (2) | |
Text
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MEMORANDU!i FOR:
Division Directors, Office of liuclear Raactor,
Regulation FROM:
Victor Stello, Jr., Director Division of Operating Reactors l
SUBJECT:
IrlFORIGTION l'EMORANDUM NO. 8 LOW FLOW EFFECTS ON BUR LOCA A"ALYSES While performing an ECCS analysis for a BWR-3 plant Gencrcl Electric determined that under reduced core flow conditions the calculated peak clad temperature (PCT) could exceed the limit of 2200"F.
Further l
evaluation indicated that this problem existed for all E.WR-3's with reactor vessel inner dieneters (lD) of less than 250 inches, and for c
BWR-4's with reactor vessel ID's of IE,3 or 213 inches which dn not
' l have the LPCI modification to eliminate the locp sensing locic.
Genera l Electric submitted their evaluation of this problem to NRC (Z. Roszto::y) on August 24 and Nover.ber 4, 1976.
Conservative LOCA calculations for jet rumo BUR's predicteo thet nu:leate
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boiling will be maintained for several seconds following a LOCA.
11ucleate boiling removes sufficient stored enercy to preclude exceeding the 220D*F PCT.
Ho'.tever, for certain SWR's operqtina at icss than ID of rated core flow, LOCA calculations in the p"iod irr.ediately follo.>ing the bred initittion predict a transient core iiow reduction for which nucleate t' oiling cannot be sustained.
This early departure from nucleate boiling was not fully considered in BWR-LOCA analyses for plant operation below rated flows and the resulting MAPLHGR limits for several plants were established in a non-conservative manner.
DDR has accepted restrictions on MAPLl'GR limits at reduced flow proposed by GE.
Chances to the technical specifications of affe:ted facilities:
Pilgrin 1, tiilistone 1, and Monticello, have been made.
These are E'.'R-3 units with reactor vessel ID less than 250 inches.
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Divi., ion Dir ectors, flRR i l
l DDR recommends that the effects of reduced core flow on LOCA analyses
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l, be addressed during the revita of all new BWR's.
The effect of recently approved ECCS-LDCf. model changes on previously perforned studies re-(i garding low flo.! cffects should also be considered.
Certain of the rodel changes resulted in a change of the cost limiting break size, which I
could increase the raagnitude of the necessary penalty in !%PLHGR to account
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for the effect of lower initial core flows.
p The Safety Evaluation Report is available from the Project fianager.
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't' Victor Stello, Jr., Director "L
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DDR CO.'; TACTS:
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2 S. Hanauer Deputy Directors, flRR I
Assistant Directors, l;RR DDR Branch Chiefs DDR Section Leaders g.
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