ML20137W881

Safety Evaluation Granting Relief from Radiographic & Visual Insp of Reactor Coolant Pump Casings

ML20137W881
Person / Time
Site:	Calvert Cliffs
Issue date:	09/18/1985
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20137W859	List: ML20137W853 ML20137W881
References
NUDOCS 8510040412
Download: ML20137W881 (6)

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UNITED STATES y e g NUCLEAR REGULATORY COMMISSION

j WASHINGTON, D. C. 20555

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO REQUEST FOR RELIEF FROM RADIOGRAPHIC AND VISUAL IN5PECTION OF REACTOR COOLANT PUMP CA5ING5 BALTIMORE GA5 AND ELECTRIC COMPANY CALVERT CLIFF 5 NUCLEAR POWER PLANT, UNIT NOS. 1 AND 2 DOCKET N05. 50-317 AND 50-318 Backoround Section XI of the ASME Code requires examinations of reactor coolant pumps during each 10-year interval of plant operation. By letter dated February 4, 1985, Baltimore Gas and Electric Company submitted requests for relief from the requirements for Calvert Cliffs Units 1 and 2 and provided infomation in support of the requests. Pursuant to 10 CFR 50.55a(g)(6)(1), this information, together with supplemental infomation in BG&E's letters dated May 31, 1985 and June 24, 1985, was evaluated to determine if the requirement is impractical to perfom on the component and if the necessary findings can be made to grant relief as requested.

Relief Reouest ASME Code Section XI 1974 Edition with Addenda through Sumer 1975

examination categories B-L-1 i.nd B-L-2 require 100% volumetric examination of casing welds and visual examination of the internal pressure boundary surfaces of one pump casing in each of the pump groups perfoming similar system functions each inspection interval. The licensee has found this

requirement to be impractical and has requested relief. Alternative

! examinations have been proposed.

Code Class Current ISI Class: Class 1.

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i Function Each Calvert Cliffs,pnit has four reactor coolant pumps which are welded i

to the 30" recirculation loop. These pumps function during normal reactor

operation to provide forced recirculation through the core. All pumps are identical in design and function and are Byron-Jackson Type DFSS.

Licensee Basis for Relief Recuest A. The design configuration of the pump corresponds to a Type E pump

illustrated in Figure NS-3442.5-1 (1977 Edition, ASME Code Section III).

1 No practical technique currently exists to perform Inservice Inspection j Radiographic Examination (RT) or Ultrasonic Examination (UT) of this pump type, i

B. The presence of the diffuser vanes precludes conventional RT. The vanes j prevent placement of the RT film cassettes inside the pump (as does the l radiation field in terms of radiographic film and personnel radiation exposure). Placement of the film on the outside of the pump is feasible, i

but there is no radiographic source suitable for placement inside the pump. Standard isotopic radiation sources are too weak to penetrate the thick casting and background radiation from the inside surface of

! the pump would diminish sensitivity. Special strong isotopic sources would be impractical to handle and position inside the pump due to personnel radiological exposure from the radiographic source itself.  !

The recently developed Miniature Linear Accelerator (MINAC) was con-

) sidered, but the Type E pump design precludes positioning of the accelerator inside the pump. Double wall radiography utilizing the

MINAC has also been considered with some hope of attaining meaningful  !

radiographs of a portion of the casing welds. This technique has.not

, been qualified to date and appears to be some time off, if at all j possible. l i

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3-C. The coarse grain structure inherent in thick stainless steel castings precludes the use of conventional UT. Future developments in. ultra-sonic techniques may provide a method to examine thick stainless steel casting and.if developed,this would be preferred over the dif ficulties and dangers of thick wall radiography. We are hopeful that the Ultrasonic Data Recording and Processing System (UDRPS) technology may provide some breakthrough in stainless steel casting UT.

D. The pump casing is fabricated from cast stainless steel (ASTM A351, Grade CF8M). The material is essentially a cast-type 316 stainless steel. This material is widely used in the nuclear industry and no industry failures of this type material in reactor coolant pumps have been noted. The presence of delta ferrite (typically 15% or more) imparts increased resistance to intergranular stress corrosion cracking (IG5CC). The delta ferrite also improves resistance to pitting corrosion.

E. Report Numhae EP.P-05-102, Revision 0, August 1983, prepared for the Electric Power Research Institute by NUTECH Engineers, Incorporated, concludes that:

1. Based on the generic pump casing analysis, there is justification for the extension of the pump-casing examination up to 15 years.

2. Plant unique analysis will show greater margins of safety.

3. The tearing modulus analysis shows that large, final flaw sizes can be tolerated in the pump casing before fracture is pre-dicted.

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4. The recent 10 year Inservice Inspection of several pump casings (Type F) indicates no detectable flaw growth from base line inspections, which corroborates the above analytical conclusion.

F. Pump disassembly for the sole purpose of conducting a very limited

! visual examination of the interior pressure boundary surfaces of a reactor coolant pump is fruitless, particularly in light of the i

i manhours and radiation exposure that would be expended. The pump 1

has an as-cast surface texture for the most part.

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G. Over 1,000 manhours and over 50 person rem are estimated to disassemble, visually inspect, and reassemble one reactor coolant pump. The manhour estimate is based only on on-site outage work j performed by Maintenance, Operations, and Nondestructive Testing personnel. The estimate does not include engineering time or preoutagejobplanning. Additionally, manhours and person rem j will be expended by Radiation Protection personnel providing direct coverage. The time required to perform the disassembly and inspection

, would be approximately 2 weeks of critical path time. Most of the

{ work would be performed under full face mask conditions.

Alternate Examinations Proposed by Licensee 5

A. The pump interior will be inspected to the extent practical (in j recognition of the vanes therein) should the pump be disassembled for any other reason. _

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B. The reactor coolant pumps shall be hydrostatically tested per the

{ requirements of ASME Code Section XI. .

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i C. A surface examination of one RCP in each unit shall be performed on the exterior casing weld surface areas by the liquid penetrant i, method. Also, the pump selected shall receive a 100% visual examina-tion of the exterior pump case surfaces.

The proposed additional examinations will identify flaws that may have

, propagated or originated at the pump outer surface since preservice examination. Since the, Code acceptance standards for allowable sur-face flaw indication length is significantly less than that allowed for a subsurface flaw, the pump surfaces represent the more critical i

site for flaw location, i

L Staff Evaluation and Conclusion 5

The need for this relief was recognized during the initial Inservice Inspection program development. At that time the NRC Resident Inspector I

requested that the relief request submittal be delayed in hope that techniques might be developed and qualified by the end of the first j 10 year interval. It is now apparent that no such technique applicable

to the pumps will be available before the first interval concludes.

l j During operation, the condition of the pumps is monitored for abnormalities.

Each RCP has vibration monitoring instrumentation. The reactor coolant flow is monitored and displayed in the control room. When flow is reduced to 95%

of design, the reactor is automatically tripped. The Reactor Coolant System

is monitored for impact due to loose parts or foreign objects. In addition to the above, the reactor coolant pump's motor current is monitored. The RCP motors also have high vibration alarms.

Considering the pump design, materials of construction of the pump casing, and the radiation levels associated with performing the required examinatio..;,

I the staff finds the examinations impractical to perform. In lieu of the I

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4 volumetric examination of the pump casing weld and visual inspection of the internal surfaces, the licensee has comitted to perfom a surface examination of the welds. In addition to the surface examination, a visual inspection of the casing exterior surface will be performed during the hydrostatic test of the reactor coolant system. In the event that the pump has to be disassembled for operational or maintenance purposes, the required visual inspection of the internal surfaces will be performed.

We conclude that conducting a 100% volumetric examination of pump casing welds is impractical. Moreover, the alternate surface and visual examinations which will be perfomed on the pump casing will provide adequate assurance of its structural integrity and therefore relief from the

! volumetric examination of the casing weld and visual inspection of the internal surfaces may be granted.

i Therefore, in accordance with 10 CFR 50.55a(g)(6)(1), we find the relief requested may be granted. The relief is authorized by law and will not J

endanger life or property or the comon defense and security and is otherwise

! in the public interest giving due consideration to the burden upon the

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! licensee that could result if the requirements were imposed on the facility, i

Principal Contributor: '

! B. Turovlin, DE j D. Jaffe, DL i Date: September 18, 1985 i

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