ML20149E922
| ML20149E922 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 02/18/1994 |
| From: | Hopenfield J NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Tim Reed Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9408080204 | |
| Download: ML20149E922 (3) | |
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UNITED STATES j.J fj NUCLEAR REGULATORY COMMISSION
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\\,..v p' g g l 3 }ggg MEMORANDUM FOR:
Timothy A. Reed Project Directorate 111-1 i
Division of Reactor Projects III/IV/V Office of Nuclear Reactor Regulation FROM:
Joram Hopenfield Engineering Issues Branch Division of Safety Issue Resolution Office of Nuclear Regulatory Research i
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SUBJECT:
CONCERNS REGARDING GENERIC LETTER ON VOLTAGE BASED REPAIR CRITERIA This is in response to Jack Strosniders' request, February 15, 1993, for documentation of concerns regarding the Farley 2 V IPC propasal and the resolution of public comments as discussed at the February meeting.
I a:n opposed to the following two changes:
a.
Allowing 2.0 Velt IPC limit instead 1.0 Volt limit.
b.
Allowing industry to propose plans for systematically pulling tubes instead of pulling tubes at each plant.
REASONS FOR CONCERNS The combination of undetected cracks and main steam line break, MSLB, can result in unacceptably high radioactivity releases to the eqvironment.
Present periodic in-servita inspections are not sufficiently reliable to predict tube degradation and therefore a conservative approach must be employed.
The proposed changes remove the conservatism which was in the NUREG BACKGROUND The above concern was raised in a DP0 dated 12/23/91, RES proposed a new Generic Issue to address the concern, however, no work has been initiated. A Task group was formed in early 1993 to address Voltage-Based Plugaing criteria including the above concern.
The conclusions of the task group was summarized in an agreed upon draft NUREG-1477. The proposed changes represent a substantially new and different NRC position.
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Timothy A. Reed ((g ] 8 ]9%
l REASONS FOR MY CONCURRENCE WITH THE DRAFT NUREG Following are my observation from the meeting which resulted in the NUREG:
1.
In general, there is no correlation between leakage and voltage.
For certain crack geometry, however, some statistical correlation may exist.
2.
A
' aging process continuous the appearance of complex networks of short longit jal cracks, closely spaced, partially through the wall will become more pronounced.
The worst leakage from such cracks under MSLB can not be determined.
3.
Historically, the statistical data indicates that crack growth is slow.
This does not preclude, however, high growth rates in the future.
4.
The history of new material problems in steam generators, such as at Palo Verde for example, clearly indicate.; that the learning curve has no yet matured.
Because of many uncertainties I have concluded that the IPC must be based on a conservative approach, the lowest possible voltage and an examination of pulled tubes at each plant.
It is not possible to conduct any meaningful cost benefit analysis regarding these parameters.
While the issue of containment by-pass due to degraded steam generator tubes during severe accidents will continue to be debated the issue of meeting 10 CFR PART 100 is easier to define.
The current design basis accident for SGTR assumes leakage of about 600 GPM for the purpose of calcula. ting dose releases.
Given a steam line break and degraded tubes it is difficult'to argue that licensing type calculations of primary / secondary leakage will lead to less than 600 GPM.
Best estimate models,however, could provide lower leakage rates.
I considered the group conrensus that the leakage will be much lower (5 to 20 gpm) as "the best estimate model."
REASONS FOR NON CONCURRENCE 1.
No new relevant data to justify 2 V instead 1 V has been presented.
2.
The focus on one single parameter, 1 V vs 2 V, instead of taking the NUREG in its entirety is not justified.
3.
Public comments on the NUREG did not produce an industry position which was not already known to NRC when the NUREG was issued, (no tube removal, use voltages higher than 1).
4.
Unlike Lne consensus which existed when the NUREG was issued, the February 7 meeting clearly indicated that there is no consensus on what the leakage should be under MSLB.
Timothy A. Reed g RECOMMENDATIONS
- 1. Issue the NUREG and the Generic Letter without the above changes REQUEST If the 2V and tube pull modifications are adopted in the Generic Letter please indicate in the final NUREG report that I have not concurred with the r.eport.
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