ML20154H405

Safety Evaluation Supporting Continued Use of Present Six Nucom Rods,Insertion of Two Similar Rods for Cycle 23 & Use of Surveillance Program

ML20154H405
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	05/17/1988
From:	Office of Nuclear Reactor Regulation
To:
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ML20154H383	List: ML20154H379 ML20154H405
References
NUDOCS 8805250326
Download: ML20154H405 (2)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO HAFNIUM HYBRIO CONTROL BLADE SURVEILLANCE CONSUMERS POWER COMPANY BIG ROCK POINT PLANT DOCKET NO. 50-155

1.0 INTRODUCTION

By letter dated April 28, 1988, the Consumers Power Company, the licensee for 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 83C. Six hybrid absorcer 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 required that a surveillance program for future cycles be established and sebmitted for review and approval. Review and evaluation of both topics follows.

2.0 EVALUATION 2.1 Results of Cycle 22 Surveillance 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 fell within Technical Specification acceptance criteria. The other factor 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 eneral structural condition of the blade. Each side of the blade was nspected (using a television camera) for the presence of wear, erosion cracks, the presence of debris and loose or broken parts. ThisinspectIon included the spot welds, the upper handle and lower connectors, the latch mechanism and the blade wings. The results showed no visual signs of wear, cracking, deformation or (spot weld) undercuttings. In general, the blades were found to be free from any physical defect. This is in agreement with the  !

expectation for hafnium not to deform during irradiation, y ,

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! PhysicstestsconluctedduringCycle22verifiedthatthereactivityworthof the NUCOM control blades was within the Technical Specification requirements, i Shutdown margin measurements at the beginning and the middle of the cycle met  :

the Technical Specification requirements. In addition, calculated axial flux 4 profiles and rod notch reactivity worths were compared to the corresponding

, measured values and found to agree with the predicted profiles and values.  !

I Considering the results of the Cycle 22 surveillance, we conclude that the t l 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 surveillance program is essentially the same as the previous, program i.e., includes visual inspection of the blades and physics testing of i l the scram times, blade reactivity worths and shutdown margin and comparison to

calculated values, The control blades are also weighed to identify possible corrosion or dimensional changes. This program will be continued throughout the control blade design lifetime.

j We conclude that the surveillance 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 hafnium 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 lifetime of  ;

, the blades. We conclude that the continued use of the blades and the

, proposed surveillance program are acceptable. .

4.0 REFERENCES

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1. Letter from R. R. Frisch, Consumers Power Company, to USNRC, "Big Rock ,

j Point, Request for Approval for Continued Use of NUCOM Hafnium Hybrid i Control Blades," dated April 28, 1988.

i 2. Letter from R. Auluck, NRC, to K. W. Berry, Consumers Power Company, ,

! "Proposed License Amendment, Approval of Control Rod Portion of Technical l Specification Change Request for Operating Cycle 22," dated February 17, 1981. .

j Principal Contributor: L. Lois  ;

4 Date: May 17, 1988 i >

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