ML19312E966

Responds to NRC 800515 Ltr Requesting Info Re Possibility of Cracking in Low Pressure Turbine Discs.Site Specific Generic Info,Nominal Water Chemistry & Steam Generator Chemistry Is Provided

ML19312E966
Person / Time
Site:	Calvert Cliffs
Issue date:	06/16/1980
From:	Lundvall A BALTIMORE GAS & ELECTRIC CO.
To:	Clark R Office of Nuclear Reactor Regulation
References
NUDOCS 8006180260
Download: ML19312E966 (8)

Text

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BALTIMORE GAS AND ELECTRIC COMPANY P. O. B OX 1475 BALTIMORE M ARYLAN D 21203 AnTHUR E.LUNDVALL.JR.

v cc e c.ioc" Sup*Lv June 16, 1980 Office of Huclear Reactor Regulation U. S. Nuclear Regulatory Ccenissien Washingten, D. C. 20555 Attn: Mr. Robert A. Clark, Chief Operating Reactors Branch #3 Division of Licensira

Subject:

Culvert Cliffs Nuclear Power Plant Unit No. 1, Docket Ho. 50-317 Low Pressure Turtine Discs

Reference:

NRC letter dated 5/15/80 from R. A. Clark to A. E. Lundvall, Jr. , came subject.

Gentlemen:

The referenced letter recuested certain infonnation on the Calvert Cliffs Unit No.1 low pressure tur'oines with respect to the possibility of cracking in the d'ses. Attachment (1) to this letter provides the site specific portion of the information, and Attach'.ent (2) contains the generic infonnatien.

BALTIMORE GAS AND ELECTRIC CO.

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BY: / 3 s- A. E. Lundvall, Jr.

Vice President, Supply ,

Note: See next page for notarial statement O

f- 8006180 i

Mr. R. A. C19rk June 16, 1980 STATE OF MARYLAND:

TO WIT:

CITY OF'EALTIMORE:

Arthur E. Lundvall, Jr. being duly sworn states that he is Vice President of the Baltirore Gas and Electric Ccepany, e corporation of the State of Msryland; that he executed the foregoing response for the purposes therein set forth; that the statements made in said response are true and correct to the best of his knowledge, information and belief; and that he eration.

wasauthorizedtoexecutetheresponseenbehalfofsaidcerp/

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WITNESS My Hand and Notarial Seal: .

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G. F. Tro.: bridge, Escuire

.W. E. L. Conner, Jr.

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' ANSWERS'RELATED TO CALVERT CLIFFS U-l TURBINE DISCS SITE SPECIFIC ~ GENERAL I.' A. Subject unit is a tandem - compound, sextuple flow, 1800 rpm

! steam turbine-generator, nominally rated at 883 Mv.

! B. LP turbines A and C have'34,086 hours9.953704e-4 days <br />0.0239 hours <br />1.421958e-4 weeks <br />3.2723e-5 months <br /> each of parallel operation as of April 30, 1980. LP turbine B has 32,300 hours0.00347 days <br />0.0833 hours <br />4.960317e-4 weeks <br />1.1415e-4 months <br /> of parallel operation as of January 31, 1980. Projected hours of additional parallel operation until October 18, 1980 equals 3391 hours0.0392 days <br />0.942 hours <br />0.00561 weeks <br />0.00129 months <br /> I

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each for LP-A and LP-C turbines and 5177 hours0.0599 days <br />1.438 hours <br />0.00856 weeks <br />0.00197 months <br /> for LP-B turbine.

l C. This unit has been subjected to four (4) intentional overspeed trip tests and no unintentional overspeeds.

l D. Answers to these questions involve data which are proprietary to the General Electric Company. Information was provided directl'y to the NRC during a meet'ng between General Electric and NRC representatives on April 21, 1980. The NRC has informed General Electric that this information is an acceptable reply to this question.

II. As of this writing, the LP-A and the LP-C rotors have received neither disc bore nor disc keyway inspections (other than during manufacturing). LP-B rotor received an ultrasonic wheel bore l

l inspection in January of 1980. This procedure, developed by General l

I: Electric, revealed no radial-axial crack like indications in the I

vicinity of the wheel bore and keyway surfaces.

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'III. . The following parameters and. values represent the nominal water chemistry of Calvert Cliffs U-l and are considered representative of the LP turbine environment:

PARAMETER NOMINAL VALUE

1. Sodium (Na+) 1 ppb ["

2 '. pH (-log (H 0+)) 8.5-9 0 3

3 Cation Conductivity (.10 .15) mmhos/cm

4. Specific Conductivity (2.0-2.5) mmhos/cm 5 Silica 10 ppb

6. Chloride 10 ppb Significant changes in secondary water chemistry are subject to control as described below in " Table of Operational Steam Generator Chemistry". Deviations in normal values are promptly examined /

evaluated so that necessary corrective action can be taken to preclude significant disturbances to the LP turbine chemical environment. ,

TABLE OF OPERATIONAL STEAM GENERATOR CHEMISTRY

. 1 ANALYSIS NORMAL ABNORMAL FREQUENCY (1)

PROCEDURES / METHOD SPECIFICATION (2) LIMITS (3)

1. Specific' Conductivity /901 4 15 1/24 hrs.

(mmhos/cm. max) l

.2. pH @ 25 C/902 8.2 - 9 2 7.5 - 8.2(4) 1/24 hrs.

92-95 3 . Sodium /908 (ppm, max) 0.1 -

7/W

4. Suspended. Solids /911 1.0 10.0 2/-

-- 5 SiO /916 (ppm, max) 1.0 10 1/W 2

6. C1/906 (ppm, max) 0.1 -

7/W

.N.S = Not.specified. ,

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(1) Frequency noted is minimum. These may be adjusted upward if conditions warrant. If normal specs are exceeded, the out-of-spec pe- ;ter(s) must be analyzed at least daily. If ab-normal limf ' 2 are exceeded, the out-of-spec parameter (s) must be ar9' 'ed at least once per shift. If blowdown is secured, a Crab sample must be drawn and analyzed for spec, cond, and pH at least 1/24 hours.

(2) Normal specifications are those which should be maintaine2 during proper operation of secondary systems.

(3) Abnormal limits indicate a fault condition exists and plant shutdown should be commenced if abnormal limits are exceeded

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for four (4) hours.

(4) The unit should be immediately sinit down when pH exceeds 10 5 "UK. Experience of Stress Corosion Cracking in Steam Turbine Discs"; J.M. Hodge; I.L. Mooford, I Mech E 1979 This paper concludes there appears to be no presently known correlation between disc cracking and secondary water chemistry.

IV. It is our intention to perform a full UT inspection on the LP-A and LP-C rotors during the planned outage commencing on or about 12:01 a.m. October 18, 1980. Plans are currently being drawn  ;

. i which include both keyway and disc bore inspections as per General Electric recommendations. Inspection is subject to availability of qualified General Electric inspection teams.

V. Not applicable O

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4 VI. An analysis and evaluation of the effects of turbine generated missiles has been perfomed and is documented in section 14.8 of the FSAR.

This analysis shows that the Unit No. 1 turbine v$ll accelerate to 169% of its normal operating speed during turbine run-9vay, at which speed' failure (sf the lest stage turbine wheel and/or disintegration of the generator will prevent further acceleration.

Under these conditions the missiles having the greatest potential for damage were postulated to penetrate the missile barriers to the depths shewn in table 14.8.2 of the FSAR. Using the most conservative assumptions, namely that no loss of kinetic energ'/ occurs during penetration of the turbine casing the missile barriers are shown to withstand the effects of both the lo,: and high trajectory miss'les.

Since the missile barriers will withstand penetration by the most

- energetic fragment during 169% overspeed incident, it will obviously withstand the o:islought of a turbine generated missile if it were to result frcm a 120% overspeed incident. For this reason it is clear that the current concerns with pc ential disc failures will have no deleterious effects on plant safety.

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Attachment P l

l GENERIC QUESTIONS

.I. After,the rough ma.nined wheel / disk forging has been tempered, material is removed from surface locations to measure mechanical properties. The forging is them subjected to a 100% volumetric ,

ultrasonic inspection. .If the test results meet stringent accep-tance standards, the forging is released for final machining.

During final machining, attention'is continually paid to the finish, contour and dimensions of every surface. For instance, the keyway depth, vidth, location, radii, and surface finish for 'every wheel is checked for conformance to drawings. Quality control personnel assure that tolerances are maintained. Any deviation from accepted tolerances are reported to engineering for disposition.

Only coolants and lubricants approved by Engineering are used in the manufacturing and assembly process. These coolants and lubri-cants have undergone extensive laboratory corrosion testing to

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ensure their acceptability prior to their approval for use in manufacturing'. Periodic sampling is done on all such fluids to verify that their chemistry is within acepetable limits. If re-quired, corrective actions are taken to maintain the chemistry within limits.

After finish machining, each wheel is thoroughly cleaned and given a magnetic particle inspection of all surfaces. If acceptable, the buckets are assembled and the wheel is static balanced. After assembly on-the shaft, each wheel is inspected and measurements are made to assure its proper location. The assembled rotor is then spun to 20% overspeed 'following a high speed balance. Finally, after a magnetic particle inspection of the buckets, the rotor is cleaned to prepare for shipment. ,

II. Stress corrosion cracks have not been observed to date in nuclear wheels manufacture 0 by General Electric, and we do not anticipate that removal or replacement of wheels will be requ' ired because of this phenomenor.. The water erosion which has been observed in the keyways of wheels on several non-reheat machines is being studied intensively. We currently believe that the erosion process is self-limiting and should not require the replacement of any wheels.

III. fio immediate actions are required to minimize water erosion because of the apparent self-limiting nature of the phenomenon. However, if future inspections show an unexpected progression of the water erosion, appropriate operating restrictions and/or modifications vill be recommended.

IV. The wheel / disk forgings are heat treated in the rough machined con-dition. The heat treatment consists of soaking at a temperature above the upper critical temperature with the time and temperature sufficient to ensure complete austenitization throughout the forging, followed by a quench in cold, vigorously circulated water for a sufficient time to ensure complete transformation throughout the section. The forgings are heated uniformly to a tempering tempera-ture below the lower critical temperature and held for a sufficient time to soften to the desired tensile range. After tempering, the forgings are still-air cooled to room temperature.

• After final machining, the wheels (di'sks) are uniformly heated in an electric furance to a temperature below the embrittling range, but sufficiently high to increase the wheel diameter enough to assemble on the shaft with the req'uired shrink fit.

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