ML19207B009
| ML19207B009 | |
| Person / Time | |
|---|---|
| Issue date: | 07/24/1979 |
| From: | Lainas G Office of Nuclear Reactor Regulation |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| REF-GTECI-A-10, REF-GTECI-CR, TASK-A-10, TASK-OR NUDOCS 7908230193 | |
| Download: ML19207B009 (4) | |
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UNITED STATES NUC' EAR REGULATORY COMMISSION
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WASHINGTON, D. C. 20555 W,
N.5....f JUL 241979 MEMCRANDUM FOR:
D. Crutchfield, Chiaf, Systematic Evaluation Program Branch, Division of Cperating Reactors FRCM:
G'. Lainas, Chief, Plant Systems Branch, Division of Operating Reactors
SUBJECT:
CONTROL RCD CRIVE SYSTEM MODIFICATIONS TAXEN TO MITIGATE RETURN LINE N0ZILE CRACKING - GENERIC TASK A-10 BWR N0ZZLE CRACKING (TAC 7006)
The Plant Systems Branch has reviewed the folicwing infornation provided by General Electric Ccmpany, as they relate to the generic concern of reliability of the Control Rod Drive System (CRD) following modifications:
a.
Service Information Letter (SIL) 200 dated October 29, 1976; b.
SIL 200 Supplement 1 dated March 25, 1977; c.
SIL 200 Supplement 2 dated November 18, 1977; d.
Submittal dated January 27, 1978; e.
Minutes of Staff Meeting held with General Electric May 17, 1978; f.
Submittal dated March 14, 1979; g.
Submittal dated April 9, 1979; h.
Submittal dated May 1, 1979;
- i. Submittal dated May 22,1979 (re: corrosion);
- j. Submittal dated May 22, 1979 (rt:
return line changes).
We find that a response to the attachtd request for additional information is needed in order for the Plant Syste is Branch to ccmolete our generic review of this issue.
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, G. Lainas, Chief
' Plant Systems Sranch Divisicn of Cperating Reactors
Contact:
F. Clemensen, X27110 7 r, q 7 9 08 2301 cO,
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Attachment:
Request for Additional Information cc w/ enclosure:
D. Eisenhut R. Vollmer B. Grimes R. Reid T. Ippolito A. Schwencer D. Ziemann G. Lainas E. Adensam R. P. Snaider F. Clemenson
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ATTACHMENT
,.g REQUr.ST FOR ADDITIONAL INFORMATICN GENERIC REY:EW 0F SWR CR0 MCDIFICATICNS 1.
In reference to the May 22, 1979 submittal on CRD Hydraulic Centrol System Return Line Mcdifications Fce Operating Plants, provide the following:
a.
Should a licensee choose to retain the ex!r.ing carben steel piping rather than replacing it with stainless steel, describe and discuss the circumstances under which it would be acceptable to permit power operation without installing the 50 micron particulate filters in the cooling water line?
b.
Assuming the above mentioned 50 micron filters are installed, describe and discuss the recorrmended method and frequency of cleaning the carbon steel pipes.
c.
Explain why the 50 micron carticulate filters are not shown on Figure 2 of the modified CRD hydraulic system.
d.
Provide the circumstances or reasons, implied in the May 22, 1979 cover letter, why a utility could consider makir.g modifications to the CRD hydraulic system without submitting a request to NRC.
The response should address the staff's concern that corrosion products may collect between the check ball and it's cage to such an extent as to jara the ball.
e.
The need for LRD system modifications were initia.'y addressed in Service Information latter (SIL) 200 dated Octocer 29, 1976.
Considering that the concern is not fully resolved to date quantify and supply the supporting information for the term " interim" in the folicwing sentence:
" Operation with che present return line closed is only an interim solution to the cracking problem, since the line is still susceptiale to stress corrosion."
2.
Item 3 of Attachment C to the January 27, 1978 submittal indicata; that the recommended equalizing valves prevent a high pressure differential between the cooling water header and exhaust header.
- Carther, this potentially high pressure differential may result in an excessive iritial control rad withdrawal speed. Describe and discuss the folicwing:
a.
The maximum potential magnitude of tnis pressure differential.
b.
The various modes of reactor operation that lead to high pressure differentials and the estimated frequency of their occurrence.
c.
The maximum initial control rod withdrawal speed and its potential impact en reactor safety if the ecualizing valves are not installed or should become inoperative.
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d.
The method available to verify proper operation c; the equalizer valves and the reccamended frequency of these verifications.
3.
Paragraph 3.2.3 of the May 22, 1979 submittal, dealing with corrosion products acknowledges that it is possible for corrosien products to settle in the annular clearance between the check ball and its cage.
Further, if corrosion products accumlate in this space there is no available way to detect its presenc or verify that the control rods will scram other than scraming when che reactor is at an appreciable pressure.
Provide a discussion, plus succorting theoretical and experimental inform 1ation, to support the statement:
"There is sufficient clearance around the check ball and its cage so that corrosion products would offer little resistance relative to the large upward force exerted on the ball following a scram at elevated reactor vessel pressure." The d:scussion should include all critical parameters such as the rate of crud deposition, the possibility and frequency of crud bursts, the range and distribution in sizes of crud particles, the clearance between the ball and its cage as well as the tenden y for the cmd to aggregate into a somewhat solid mass with time.
Further, the discussion should deal with the geometry of the surfaces which would have a tendency to further compress the aggregated crud as the ball mcves up and thereby wedging the ball.
4.
It has been indicated that the potential for centrol rods drifting will be increased as a result of implement;ag the recommended CRD system modifications. A recent operating plant monthly operating report indicated the cccurrence of a such an event. To overcome the drifting problem, they increased the drive pressure to 400 psid.
Describe and discuss the following:
a.
The acceptability of increasing the drive pressure differential as described above.
b.
The potential adverse consequences that may folicw from this procedures.
c.
The anticipated number of drifting centrol rods that will ccco '
throughout the life of the plant as a result of implementing the final recomended CRD system modifications.
The discussion should include the estimated repiacement intervals of the fuel channel boxes since the frictional forces between the channel boxr.s and centrol rods is a significant parameter in the tendency for the rods to drif t.
d.
What provisions are made to verify chat the control rod - channel box fricticn is not excessive and at what frequency should such checks be ace.
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