ML19262A066
| ML19262A066 | |
| Person / Time | |
|---|---|
| Issue date: | 10/17/1979 |
| From: | Ross D NRC - TMI-2 BULLETINS & ORDERS TASK FORCE |
| To: | Keenan T GENERAL ELECTRIC OPERATING PLANT OWNERS GROUP, VERMONT YANKEE NUCLEAR POWER CORP. |
| References | |
| NUDOCS 7910260299 | |
| Download: ML19262A066 (6) | |
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UNITED STATES
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g NUCLEAR REGULATORY COMMISSION e
wacMiNGTon.o.c.20sss OQ-OCT 1 7N Mr. Thomas D. Keenan, Chairman General Electric Operating Plant Owners' Group Vermont Yankee Nuclear Power Seventy-Seven Grove Street Rutland, Vermont 05701
Dear Mr. Keenan:
SUBJFCT:
INFORMATION REQUIRED TO ADDRESS MICHELSON'S CONCERNS FOR BOILING WATP REACTORS As part of the staff's present review of small break behavior in LWR's, we are considering a number of concerns expressed by Mr. C. Michelson of TVA, who is presently a consultant to the ACRS. These concerns were originally developed in 1975 and 1977 as part of Mr. Michelson's review of CE System 80 and B&W 205 FA plants, respectively. A summary list of the concerns is provided in Enclosure A.
In addition, Mr. Michelson has more recently expressed a concern with regard to incorrect operator action leading to a break isolation. This latter concern is described in Enclosure B.
In order for the staff to assess these concerns as they relate to the three PWR vendors (with the exception of the Enclosure B item), we have asked all three PWR vendors to address each concern as it applies to their plants. This includes a discussicn of its applicability (or why it is not applicable) on both a specific and a more-generic basis as well as a resciution of the concern (An example of a specific issue that would be applicable on a generic basis would be the concern on pressurizer level as a corrtet indicator of system inventory. The sneric concern is vessel inventory measurement, and postulating conditions which would lead to falsc indicated level to the operators.).
We regtest that you review the two enclosures and determine the applicability of each concern to BWR's.
If the concern is not applicable, either on a specific or generic basis, a brief discussion of why it is not applicable should be pro-vided.
If it is determincd to be applicable, the resolution, including all of the necessary supporting analyses, should be provided.
Since these items have been discussed with General Electric and the Owners Group at the September 6,1979 meeting and based on our projected schedules for completing our review of small breaks for your reactor designs, we will need your complete responses to the Michelson concerns no later than October 31, 1979.
If you cannot meet this schedule or require clarification of the information 1215 003 7 910260 cN7 Q
Thomas D. Keenan OCT 1 7 B79 requested, please contact Cecil 0. Thomas, at (301) 492-7745.
Sincerely,
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D. F. Ross, Jr., Director Bulletins and Orders Task Force Office of Nuclear Reactor Regulation Enclosures-.
As stated cc: See attach ' lists 1215 009
Enclosure A TVA (C. Michelson) Concerns 1.
Pressurizer level is an incorrect measure of primary coolant inventory.
2.
The isolation of small breaks (e.g., letdown line; PORV) not addressed or analyzed.
3.
Pressure boundary damage due to loadings from a) bubble collapse in subcoo?ad liquid and 2) injection of ECC water in steam-filled pipes.
4.
In daterm iing need for steam generators to remove decay heat, consider that bret flow enthalpy is not core exit enthalpy.
. G.
Are sources of auxiliary feedwater adequate in the event of a delay in cooldown subsequent to a small LOCA?
g 6.
Is the recirculation mode of operation of the HPSI pumps n established design requirement?
7.
Are the HPSI pumps and RHR pumps run simultaneously? Do they share cormon piping?/ suction? If so, is the system properly designed to accomodate this mode of operation (i.e., are any NPSH requirements violated, etc...?)
8.
Mechanical effects of slug flow on steam generator tubes needs to be addressed.
(transitioning from solid natural circulation to reflux boiling and back to solid natural circulation may cause slug flos in the hot leg pipes).
9.
Is there minimum ficw protection for the HPSI pumps during the recirculating mode of operation?
- 10. The effect of the accumulators dumping during small break LOCAs is not taken into account.
- 11. What is the impact of continued running of the RC pumps during a small LOCA?
- 12. During a s:nall bre!. LOCA in which offsite power is lost, the possibility and impact of pump seal damage and leakage has not been evaluated or analy:ed.
- 13. Dur1.3 transitioning from solid natural circulation to reflux boiling and back again, the vessel level will be unknown to the opert. ors, and emergency proc 2dures and operator training may be inadequate. This needs to be addressed and evaluated.
- 14. The effect of non-condensible gas accumulation in the steam generators and its possible disruption of decay heat rer:nval by natural circulation needs to be addressed.
- 15. Delayed cooldown following a smil break LOCA could raise the containment pressure and activate the containment spray system.
Impact and consequences need addressing.
Note: Items 1 through 4 are from Michelson report on B&W 205-FA plants; Items 5-15 are from Michelson draft report on CE system 80 plant.
All concerns considered potentially applicable to W plants.
P00R ORGEL
Enclosure B
/p* *scoq'o, UNITED ST A7E:
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1.,,,g g NUCLEAR REGULA TORY COMt.ilSSION 7,. -
M.' e ADVISORY COMMITTEE ON REACTCR sAFEGUAR0c o,
a wasectoN. o. c. 2osss 3 ~u j
3 June 4,1979 PDCRBRIGINn MC40 TO: Dr. D. Okrent p f, p FROM:
C. Michelson, ACRS Consultant
SUBJECT:
POSSIBLE D' CORRECT OPERATOR ACTION SUCH AS PIPE BREAX ISOL At our May 30 - June 1,1979 Subco. mittee neeting on T.'11 implications, I used the SUR pipe break isolation concern as an example of a possible incorrect operator action which needs to he identi: ad in emergency ocerating instruc-tions for all SWR plants.
I am.iriting this note to be sure that the example was fully understood and that its implications for P"R plants are also appreciated.
This concern relates to the possibility that an operator may be inclined and perhaps even trained to isolate, where pc,sible, a pipe break LOCA without realizing that it might be an unsafe actien leading to high pressure, and.
short-term core bakeout.
For example, if a SUR should experience a LOCA from valve for either reactor recirculation punp, it would be possible for t operator to close these valves following tha reactor bicwdcwn to low pressure and thereby isolate the break, stop the blowawn, and repressurize the reactor coolant system.
Before such isolation should be permitted, it is first neces-sary to show by an appropriate analysis that the high pressure ECCS is adequate to reflood the uncovered core without assistance fron the icw pressure ECCS which can no longer deMyer flow because of the. repressurization.
Otherwise, such isolation action should be explicitly forbidden in the emergency operating instructions.
Similar concern exists for PWR plants which have loop isolation valves and for either EWR or PUR pt nts using large diaceter extension of the primary pressare boundary which may contain no:cally open, remotely operable valves which are capable of blowdown interuption.
Ther is a real possibility that such a misunderstanding concerning isolation of RL breaks for BWR plants did exist as evidenced by LER 77-15 for Dresden 2 (ca.itrolnumberOlpl4,4/2/77). The HRC computer printout of this event reads, "while isolating G recirculation loop to replace a leaking test flange, the torque switch on the limitorque operator for the recirculation pumo suction valve opened and prevented the valve from closing.
A piping failure between tne suction and discharge valve of the recirculation pump would not have been isolated."
would appear prudent that the NRC should check the full LER r.epert to see how it It really read.
If the misunderstanding concerning break isolation did exist, would be of interest to know the extent of regional at headquarters review it this LER and to what corrective action might have been taken since then.
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0WNERS GROUP REPRESENTATIVES A. Meyer Jack 5. Bitel awa Electric Light & Power Commonwealth Edison Co.
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