ML16340D025
| ML16340D025 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 12/07/1982 |
| From: | Fraley R Advisory Committee on Reactor Safeguards |
| To: | Harold Denton, Minogue R Office of Nuclear Reactor Regulation, NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| Shared Package | |
| ML16340D026 | List: |
| References | |
| NUDOCS 8212220448 | |
| Download: ML16340D025 (6) | |
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4y*y4 UNITEDSTATES NUCLEAR REGULATORY COMMISSION ADVISORYCOMMITTEE ON REACTOR SAFEGUARDS WASHINGTON, D. C. 20555 December 7, 1982 MEMORANDUM FOR:
Harold Denton, Director, NRR Robert Minogue, Dire to,
RES FROM:
Raymond F. Fra ey, ir c
SUBJECT:
FLOW BLOCKAGE BY STEAM DURING NATURAL CIRCULATION IN PWRs Mr. Etherington has asked that I provide you with copies of the attached
. supplement to his memorandum of September 7, 1982 which was forwarded to you under my memorandum of November 10, 1982.
Attachment:
Supplement to Memorandum by H. Etherington Steam During Natural Circulation in PWRs cc:
D.
G. Eisenhut, DL R.
H. Vollmer, DE H. L. Thompson, DHFS S.
~ C. Kelber, RES H. Sullivan, RES G. A. Arlotto, RES 0.
E. Bassett, RES K. R. Goller, RES R. Bernero, RES W. J. Dircks, EDO V. Stello, EDO J. Austin, OCM E. Abbott, OCM J. Milhoan, OCM D. Garner, OCM S. Chestnut, OCM
Subject:
Flow Blockage By
, dated September 7, 1982.
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UNITEDSTATES NUCLEAR REGULATORYCOMMISSION ADVISORYCOMMITTEE ON REACTOR SAFEGUARDS WASHINGTON, D. C. 20555 December 6, 1982 h
p MEMORANDUM FOR:
P.
G.
- Shewmon, Chairman ACRS Members FROM:
SUB13ECT:
K. Ethhr>ngton, em SUPPLEMENT TO MEMORANDUM "FLOW BLOCKAGE BY STEAM DURING NATURAL CIRCULATION IN PWRs,"
DATED SEPTEMBER 7, 1982 It has been found desirable to release the referenced internal memo as a
public document, and there is some indication that the memo mav have been interpreted as implying that a serious problem exists.
This was not the inteIItion, and is.hardly consistent with the conclusion (Item 17) that "The Committee may want to review the final disposition of this problem, and to be assured that the various possibilities are reflected in sufficiently flexible and understandable operating procedures."
It wak thought unnecessary to develop Item 14, and the misunderstanding probably arose from the wording of this item:
"The main concern is a
BKW System with a SBLOCA that is too small dp f~fffi1 f
fy 1
1 f
1 1
1 sure safety systems, yet too large to permit the inventory to be maintained by the high pressure pumps.
Loss of inventory leads to formation of steam voids at high spots, and the possibility of "degraded" modes of heat transfer as discussed in Sections 9 and 10."
This supplement is a discussion of the implications of Item 14.
A steam void blocking a candycane, can be eliminated either by in situ con-densation, or by transport of steam to the condensing surfaces of the steam generator.
The previous memo indicates that condensation by heat transfer processe's associated with repressurization may be too slow to be effective, and in situ condensation by other processes is somewhat conjectural.
It therefore appears necessary to review conditions that will induce bulk tr ans-port of steam from the candycane.
B8W and NRC have long recognized that some LOCAs are characterized by a stage in which natural circulation is interrupted by steam accumulation" at the top of the candycanes, but analyses of these LOCAs indicate that the 'condition is transien't, and that the flow of coolant (water or steam) is re-established without assuming in situ condensation at the top of the loop.
It is useful to distinguish between two cases of a void that completely blocks flow, i.e.,
that does not extend far enough down into the steam generator tubes to permit cooling in the boiler-condenser mode:
1.
system at saturation, 2.
system subcooled,
P.
G.
Shewmon ACRS Members 2
In the first case, continuing loss of inventory and generation of steam will
'ause the void to grow until it extends far enough into the s)earn generator tubes to sustain stable. cooling in the boiler-c~ denser mode.
The second case could develop from a loss of inventory followed by repres-surization with the reactor coolant pumps unavailable.
This condition was discussed in the attachment to Mr. Denton's letter of May 7, 1982, to Dr. Myers.
The temperature of the water will increase and, in the absence of automatic or manual corrective measures, the volume of the water inventory and the pressure will increase.
The result could be:
1.
Sufficient contraction of the void by compression to permit spillover from the hot leg would re-establish cooling in the single-phase natural circulation mode (once coolant flow is re-established by spillover it would cool and condense the bubble quickly) or 2.
Saturation will be reached, in which case boiling would occur in the system; if boiling extends to the hot legs, or if steam enters the hot legs, the void will become enlarged until it extends far enough into the steam generator tubes for cooling in the boiler-condenser mode to be established, or 3.
The pressure will reach the PORV or SV setting, without conditions (1) or (2) being established; loss of inventory and boil'ing will eventually lead to condition 2.
(Activation of high-pressure in-jection pumps would modify this course of events).
In all three cases natural circulation (single-phase or boiler-condenser) is established without assuming any in situ condensation.
Conclusions 1.
Accident analyses on which operating procedures are based give no credit for condensation by repressurization.
2.
To the degree that any condensation may occur, it is likely to be an effect that will change the time at which a transition 'from one mode of cooling to another will occur but not the basic mechanism by which it occurs.
The term "boiler-condenser mode" is used here to include the condition in which steam, rising in the hot leg, causes slug flow and massive carryover of water into the steam-generator tubes.
I have referred to the boiler-condenser mode as a '-'degraded" mode of cool,i ng.
I believe the NRC Staff does not dis-tinguish between the effectiveness of liquid-phase natural circulation and the boiler-- "denser mode.
I agree that the boiler-condenser mode is an effective mode of heat transfer.
P.
G.
Shewmon ACRS Members 3
3.
'Although no safety issue has been identified, operator action would
,be beneficial to expedite elimination of a steam block and curtail the transient,.
However, different conditions require different actions, and it would be necessary that the operator recognize the particular condition in order Co take appropriate action.
4.
My suggestion in 'Item '17 of the previous memo (quoted in the first para-qraph of this -memo) was probably unnecessary, because ACRS Subcommittees have been reviewing Technical Guidelines for Emergency Operating -Procedures (EOPs), including those by BSW, and the matter will be receiving additional Committee attention in its continuing 'review.
DcD-0/4 DISTRIBUTION FOR BOARD NOTIFICATION BN-82-125A TMI-1 5 Diablo Can on
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UNITED STATES UCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 I
SEC 0 S f983 MEMORANDUM FOR:
FROM:
SUBJECT:
V Chairman Palladino Commissioner Gilinsky Commissioner Ahearne Commissioner.
Roberts Commissioner Asselstine I<Darrell G. Eisenhut, Direc r
Division of Licensing Office of Nuclear Reacto Regulation BOARD NOTIFICATION 82-1 5A (TMI-1 and DIABLO CANYON)
RECENT ACRS EVALUATI CONCERNING PMR FLON BLOCKAGE In accordance with the procedures f Board Notification, the attached memorandum (Fraley to Denton/Minogue, dtd De ember',
1980) is being sent directly to the Commission..
This information s pplements the PMR Flow Blockage evaluation sent to the Commission on Board N
ification 82-125.
Enclosure:
As Stated cc:
ASLAB OPE SECY OGC Service List Division of Licensing