ML19254E258

Forwards C Michelson Summary List of Concerns Re Small Break Behavior in LWRs & Concern Re Incorrect Operator Action Leading to Break Isolation.Requests Review & Determination of Applicability of Each Concern to BWRs by 791031

ML19254E258
Person / Time
Issue date:	10/17/1979
From:	Ross D NRC - TMI-2 UNRESOLVED SAFETY ISSUES TASK FORCE
To:	Keeman T GENERAL ELECTRIC OPERATING PLANT OWNERS GROUP
References
NUDOCS 7910310388
Download: ML19254E258 (5)

Text

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UNITED STATES y

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NUCLEAR REGULATORY COMMISSION p

WASHINGTON. D. C. 20555

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acT 1 7 879 Mr. Thomas D. Keenan, Chairman General Electric Operating Plants Owners' Group Vermont Yankee Nuclear Power Seven*.y-Seven Grove Street Rutla.1d, Vermont 05701

SUBJECT:

INFORMATION REQUIRED TO A[ORESS MICHELSON'S CONCERNS FOR B0ILING WATER 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 Sy cem 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 tnree PWR vendors (with the exceptien of the EnclJsure B item), we have asked all three PWR vendors to address each concern as it applies to their plants. This includes a discussion of its applicability (or why it is not applicable) on both a specific and a more-generic basis as well as a resolution 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 correct indicator of system inventory. The generic concern is vessel inventory measurement, and postulating conditions which would lead to false indicated level to the operators.).

We request 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 determined 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 7910310 4

!7'4 070 C.

Thomas D. Keenan OCT 17 279 requested, please contact Cecil 0. Thomas, at (301) 492-7745.

Sincerely,

'l C c,1j.

D. F. Ross, Jr., Director Bulletins and Orders Task Force Office of Nuclear Reactor Regulation

Enclosures:

As stated cc: See attached lists 1F 4 071

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Enclosure A TVA (C. Michelson) Concerns 1.

Pressurizar level is an incornet 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 stean-filled pipes.

4.

In datennining need for steam generators to renove decay heat, consider that break flow enthalpy is not core exit enthalpy.

. 5.

Are sources of auxiliary feedwater adequate in the event of a delay in cooldown subsequent to a small LOCA?

6.

Is the recirculation mode of operation of the HPSI pumps an established design roquirernent?

7.

Are the HPSI pumps and RHR pumps run simultaneously? Do they share cocinon piping?/suctica? If so, is the system properly designed to accocinodate this mode of operation (i.e., are any NPSH requirements violated, etc...?)

8.

Nechanical 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 flow 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 small break LOCA in which offsite power is lost, the possibility and impact 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 ::.ay be inadequate. This neecs to be addressed and avaluated.

14. The effect of non-condensible gas accumulation in the steam generators and its possible disruption of decay heat renoval by natural circulatien needs to be addressed.

15. Delayed cooldown following a small break LOCA could raise the containant pressure and activate trie containment spray system.

Impact and consequences need addressir.g.

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 30 plant.

All concerns considered potentially applicable to W plants.

l4 072

Enclosure B

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ADVisCRY COMMITTEE OfJ REACTCR sAFEGUAROc

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MEMO TO: Dr. D. Okrent p f. ' Q FROM:

C. Michelson, ACRS Consultant

SUBJECT:

POSSIBLE INCORRECT OPEPATOR ACTION SUCH AS PIPE SREAX ISCLAT At our.May 30 - June 1,1979 Subconmittee neeting on T'il implications, I used the BUR pipe break isolation concern as an example of a possible incorrect operator action which needs to be identi: 2d in emergency coerating instruc-tions for all EWR plants.

I am writing this note to be sure that the examole was fully understood and that its implications for PUR piants are also apprecia ted.

This concern relates to the possibility that an operator may be inclined 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 short-tem core bakeout.

For example, if a SUR should experience a LOCA fro-valve for either reactor recirculation punp, it would be possible for the operator to close these valves folicwing the reactor blowdcan to low pressure and thereby isolate the break, stop the blowdown, and repressurize the reactor coolant systen.

Before such isolation should be pemitted, 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 from the low pressure ECCS which can no longer deMver flow because of the. repressurization.

Otherwise, such isolation action should be explicitly forbidden in the emergency operating instructions.

Similar concern exists for P','R plants which have loop isolation valves and for either BWR or PUR plants using large diaceter extension of the primary pressure boundary which may contain nomally open, remotely operable valves which are capable of blowdown in'. eruption.

There is a real possibility that such a misunderstanding concerning isolation of RCS breaks for BWR plants did exist as evidenced by LER 77-16 for Dresden 2 (controinumber01p14,4/2/77). The NRC computer printout of this event reads, "while isolating G recirculation loop to replace a leaking test flange switch on the limitorque operator for the recirculation pumo suction valve opened

, the torque and prevented the valve from closing.

A piping failure between the suction and discharge valve of the recirculation pump would not have been isolated."

It would appear prudent that the N3,C should check the full LER r.eport to see how it really read.

If the misunderstanding concerning becak isolation cid exist, would be of interest to know the extent of regional anc headquarters revie, of it this '.ER and to what corrective action might have been taken since then.

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