ML20154C138

Revised Safety Evaluation Accepting Continued Use of Hafnium Hybrid Control Blade & Proposed Surveillance Program

ML20154C138
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	09/07/1988
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20154C132	List: ML20154C128 ML20154C138
References
NUDOCS 8809140247
Download: ML20154C138 (2)

Text

_ - _ _ _ _ _ _ _ _ _ _ - _ _ _ _____-__ ________ ______ _______ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - _ . _ _ _ _

• • ' Weic

. o UNITED 8TATES g

4e$!" e NUCLEAR REGULATORY COMMISSION

.l W ASMOTON. D. C. M66

\,*****/ l SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO HAFNIUM HYBRIO CONTROL BLADE SURVEILLANCE CONSUMERS POWER COMPANY BIG ROCK POINT PLANT  !

l DOCKET NO. 50-155 l l

(REVISED) l

1.0 INTRODUCTION

> By letter dated April 28, 1988, the Consumers Power Company, the licensee for l the Big Rock Point nuclear power plant, submitted information regarding the post-Cycle 22 control blade inspection results (Ref. 1). The object of this inspection were six control assemblies, manufactured by NUCOM and approved for use in Amendment 88 (Ref. 2). The control blades in these control elements

] have the upper 17 inches of the absorbing rods made of solid hafnium. The remaining length (52 inches) consists of stainless steel tubing filled with 1 B,C. Six hybrid absorber rod blades were inserted in the reactor at the beginning of Cycle 22. The NRC staff required that the results of visual -

inspection and physics tests at the end and during Cycle 22 be submitted to the NRC for review and approval for Cycle 23 operation. In addition the staff  ;

requiredthatasurveillanceprogramforfuturecyclesbeestab1Ishedand ,

submitted for review and approval. Review and evaluation of both topics i follows.

4 2.0 EVALUATION 2.1 Results of Cycle 22 Surveillance l i

)'

The parameters which were to be verified through the surveillance program were those which affect Technical Specifications and define the proper operation of the control rods. These parameters are scram time and control blade worth.

Scram time is a function of blade weight, and the hafnium hybrid blades are  ;

, about 2 lbs lighter than the GE IIA blades they replaced, thus they are

favorably affected. Tests performed during Cycle 22 verified that all times j fell within Technical Specification acceptance criteria. The other factor ,

j which could affect scram times is the condition of the blade surface. A visual  !

examination was conducted to determine the condition of the surface and the I general structural condition of the blade. Each side of the blade was i i irspected (using a television camera) for the presence of wear, erosion, l cracks, the presence of debris and loose or broken parts. This inspection i j included the spot welds, the upper handle and lower connectors, the latch l mechanism and the blade wings. The results showed r.o visual signs of wear, l i cracking, deformation or (spot weld) undercuttings. In general, the blades i

! were found to be free from any physical defect. This is in agreement with the l l expectation for hafnium not to deform during irradiation. [

k 8809140247 880907 '

PDR ADOCK 05000155 P FDC .

4 i  :.

\,

Physics tests conducted during Cycle 22 verified that the reactivity worth of the NUC04 control blades was within the Technical Specification requirements.

Shutdown margin measurements at the beginning and the middle of the cycle met the Technical Specification requirements. In addition, calculated axial flux profiles and rod notch reactivity worths were compared to the corresponding measured values and found to agree with the predicted profiles and values.

Considering the results of the Cycle 22 surveillance, we conclude that the hafnium hybrid control rods are performing well and should be allowed to be used for Cycle 23 including the proposed two new control blades 2.2 Continued Surveillance Program The proposed survoillance program is essentially the same as the previous program; i.e., it includes visual inspection of the blades and physics testing of the scram times, blade reactivity worths and shutdown margin -

and comparison to calculated values. This program will be continued throughout the control blade design lifecime.

We conclude that the surveillence program outlined above will assure the control blades' reactivity worth and their mechanical integrity; thus it is acceptable.

3.0

SUMMARY

AND CONCLUSIONS We have reviewed the results of the Cycle 22 inspection of the nafnium hybrid control blades inserted in the Big Rock Point reactor for Cycle 22. The results indicated that the new control blades were free from physical defects, and their reactivity worth was within the required limits. The licensee proposed to continue the same surveillance program for the design iifetime of the blades. We conclude that the continued use of the blades and tne proposed surveillance program are acceptable.

4.0 REFERENCES

1. Letter from R. R. Frisch, Consumers Power Company, to USNRC, "Big Rock Point, Request for Approval for Continued Use of NUCOM Hafnium Hybrid Control Bladek," dated April 28, 1988.

2. Letter from R. Auluck, NRC, to K. W. Berry, Consumers Power Company, "Proposed License Amendment, Approval of Control Rod Portion of Technical Specification Change Request for Operating Cycle 22," dated February 17, 1987, Principal Contributor: L. Lois Date: July 29, 1988 (Revised)