ML19254E923
| ML19254E923 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 06/04/1979 |
| From: | Michelson C Advisory Committee on Reactor Safeguards |
| To: | Okrent D Advisory Committee on Reactor Safeguards |
| Shared Package | |
| ML19254E915 | List: |
| References | |
| NUDOCS 7911050067 | |
| Download: ML19254E923 (2) | |
Text
e EHCL.o Su s2 E C UNITED 5 ?.75:
o, NUCLEAR f EGULATORY COMMISSION
!V,., 7 - g ADVtsORY COV' aTTEE ON REACTCR sAFEGUARC"
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4HING7aN. D. C. 20555 T '" * * /
June 4,1979 i
mci 0 TO: Dr. D. Okrent g4'p FROM:
C. Hichelson, ACRS Consultant POSSIBLE It: CORRECT OPERATOR ACTION SUCH AS PIPE BREAK ISO
SUBJECT:
At our May 30 - June 1,1979 Subconmittee neeting on T!il implications, I used the Bl.'R pipe break isolation concern as an example of possible incorrect operator action which needs to be identified in emergency operating instruc-tions for all BWR plants.
was fully understood and that its implications for PWR plants are also appreciated.
This concern relates to the possibility that an operator may be 'ncli..ed and perhaps even trained to isolate, where possible, a pipe break LOCA without realizing that it might be an unsafe action leading to high pressure, and For example, if a SUR should experience a LOCA from short-tem core bakeout.
a pressure boundary failure somewhere between the pump suction and discharge valve for either reactor recirculation pump, it would be possible for the opers. tor to close these valves following the reactor blowdown to lo Before such isolation should be permitted, it is first neces-coolant systen.
sary to show by an appropriate analysis that the high pressure E Otherwise, such can no longer deltver flow because of the repressurization.
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 BWR or PilR plants using large diaceter extension of the primary pressure boundary which may contain nomally open, remctely operable valves which are capable of blowdown interuption.
There is a real possibility that such a misunderstanding coacerring isolation of RCS breaks for SWR plants did exist as evidenced by LER 77-16 for Dresden 2 (control number 01 3 14, 4/2/77). The NRC computer printout of this event reads, "while isolating 0 recirculation loop to replace a leaking test flange, the torque switch on the limitorque operator' for the' recirculation pump suction valve opened and prevented the valve from closing. A piping failure between the suction and It discharge valve of the recirculation pump would not have been isolated."
would ap; ear prudent that the NRC should check the full LER r.eport to see how it If the misunderstanding concerning break isolation did exist, it would be of interest to know the extent of regional and headquarters review of really read.
this LER and to what corrective action might have been taken since then, C. Mich A -r Li;inski P. O'2.--'
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TVA (C. Michelsen) 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 col!nse in subcoo?ad liquid and 2) injection of ECC water in sma-filled pipes.
4.
In datermining need for steam generators to remove decay heat, consider that break flow enthalpy is not core exit enthalpy.
. 5.
Are sources af auxiliary *:aedwater adequate in the event of a delay in cooldown subsequent to a smil LOCA?
6.
Is the recirculation mode of operation of the HPSI pumps an 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 frem solid natural circulation to reflux coiling and back to solid natural circulation may cause slug flow in the hot leg pipes).
9.
Is there minimum flow pt.cection for the HPSI pumps during the recirculating made of operation?
- 10. The effect of the accumulators duging 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 small break LOCA in which offsite power is lost, the possibility and igact of pump seal damage and leakage has not been evaluated or analyzed.
- 13. During transitioning from solid natural circulation to reflux boiling and back again, the vessel level will be unknown to the operators, and emergency procedures 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 receval by natural circulation needs to be addressed.
- 15. Delayed cooldown following a small break LOCA could raise the containment pressure and activate the containment spray system. Imp- " and cons w ances need addressing.
Note: Items 1 through 4 are fre,Michelson report on B&W 205-FA plants;
'tems 5-15 are from Michelson draft report on CE system 80 plant.
All concerns considered potentially applicable to W plants.
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