ML20024D151
| ML20024D151 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 07/29/1983 |
| From: | Woolever E DUQUESNE LIGHT CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 2NRC-3-058, 2NRC-3-58, NUDOCS 8308030218 | |
| Download: ML20024D151 (10) | |
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2NRC-3-058 (412) 787 - 5141 Telecopy Nuclear Construction Division July 29, 1983 Robinson Plaza, Building 2, Suite 210 Pittsburgh, PA 15205 United States Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Mr. Harold R. Denton Of fice of Nuclear Reactor Regulations
SUBJECT:
Beaver Valley Power Station - Unit No. 2 Docket No. 50-412 Turbine Missile Analysis Gentlemen:
At t ached for your review and consideration is a copy of the worst case de t erminis t ic ini.pect ion interval report for the Beaver Valley Power Station Unit 2 turbine.
It was our int ent ion originally to submit this repo rt to satis fy the turbine missile analysis requirements.
We feel that the worst case deterministic analysis is both an acceptable and a conservative approach to turbine missile analysis.
Howeve r, as a result of Mr.
G. W. Knigh ton's letter dated April 28, 1983, concerning the acceptability of utilizing this type of analysis, and subs equent conve rs ations with the NRC s t af f, this report is being submit ted fo r information purposes only.
Ac cording ly, although the text is written in the FSAR format, it is not our int ent ion to amend the FSAR to include this information.
For the development of a final Beaver Valley Power Station, Unit 2, turbine maintenance and inspection program, it is DLC's intention to imple-ment the results of the NRC's review of the Westinghouse generic repo rt e and any subsequent Westinghouse evaluation.
DUQUESNE LIGHT COMPANY By E. 3/. Woolever Vice President
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l At tachment SUBSCRIBED ANDJWf)RN TO BEFORE ME ON THIS 8 4 DAY OF. A e. 2 c,
, 1983.
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Notary Public ELVA G. LESONDAK, NOTARY PUBLIC RGBINSON TOWNSHIP, ALLEGHENYCOUNTY hb MY CO1W!SSION EXPIRES OCTOBER 20,1986 D
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I United States Nuclear Regulatory Commission Mr. Harold R. Denton Page 2 COMMONWEALTH OF PENNSYLVANIA )
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COUNTY OF ALLEGHENY
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, befo re me,
On thi
' day'of for[said [ommonwealth and County, pe rs onally a Notary Public in and appeared E. J.
Woolever, who being duly sworn, deposed and said that (1) he is Vice President of Duquesne Light, (2) he is duly authorized to exe-cute and file the foregoing Submi t t al on behalf of said Company, and (3)
. the statements set forth in the Submittal are true and correct to the best of his knowledge.
W
' Not ary Public ELVA G. LESONDAK, ilOTARY PUBUC ROBINSON TOWNSHIP, ALLEGHENYCOUN MY COMMISSION EXPIRES OCTOBER 2 a
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BVPS-2 FSAR 3.5.1.3 Turbine Missiles Advancements. in turbine technology, reliability of protection
- systems, and a conservative in-service inspection program are utilized to prevent the potential hazard of turbine missiles. The partial integral rotors manufactured by Westinghouse Electric Corporation (Westinghouse) have significantly reduced the traditional concern of stress-corrosion cracking, as discussed in Section 3.5.1.3.4.
The redundant overspeed protection system and turbine valve testing program are explained in Sections 3.5.1.3.2 and 3.5.1.3.3, respectively.
The deterministic analysis method, establishing turbine in-service inspection intervals meeting Nuclear Regulatory Commission (NRC) criterion, is presented in Section 3.5.1.3.1.
To provide still additional assurance of public safety, inspection intervals determined in Section 3.5.1.3.1 are further reduced by a factor of five.
3.5.1.3.1 Deterministic Inspection Interval The stress-corrosion crack growth rate and the critical crack size for the partial integral rotor has been calculated by Westinghouse.
The analysis is based on the worst case material properties as defined by the manufacturing specification (Westinghouse 1982) and listed in Section 3.5.1.3.4.
By using worst case material properties, the inspection interval developed is more conservative than an interval based on actual material properties. Using this data and the NRC criterion limiting crack growth to half the critical
- length, inspection intervals were determined for each of the non integral discs as follows:
Step 1: Determine the inherent material toughness, KIC K
= [5 o
(.85 CVN - o
)]t/2 IC YS YS (3.5-1) 20 where:
l o
l y
= Minimum yield strength at upper shelf temperature, ksi CVN = Charpy V-n>tch energy at upper shelf temperature, ft-lb Step 2: Determine the critical Crack size, A (inches)
Q
( 1.2KIC-) 2 (3.5-2)
A
=
CR 1.21 x eBore l
Q = Flaw shape (2.30 for bore, 1.35 for keyway) l o
= Bore stress at overspeed, ksi Bore i
= Toughness (Step 1) 3.5-6 l
I t
BVPS-2 FSAR Step 3: Determine the Crack Growth Rate, R (in/hr) 73+ Constant (3.5-3) in R = -7302
+ 0.0278 o T + 460 where:
T = Metal temperature, 'F Constant = -4.205 for keyway
= -3.531 for bore c-YS = Maximum yield strength at upper shelf temperature, ksi 2
Step 4: Establish Reinspection interval for A /
Reinspection interval T=
[A
- p] (years)
(3.5-4)
CR where:
8760R A
= Critical Crack Size (Step 2)
P = Keyway radius for keyway
= Zero for Bore R = Average crack growth rate (Step 3)
The results of the above analysis using the assumptions listed below are reported in Table 3.5-5.
1.
No inspection of the central integral portion (first three discs) is required since it does not have keyways and the bore will not be exposed to steam (no stress-corrosion cracking is expected to occur).
2.
The inspection interval is controlled by disc 4 or.5.
3.
The inspection interval is calculated using the alternate method discussed in Westinghouse memorandum report No.
MSTG-1-P (Westinghouse 1982) approved by the NRC.
4.
Crack growth rate is determined for the expected bore / keyway temperatures in the BVPS-2 discs.
5.
Yield strength is assumed to be the maximum permitted by the Westinghouse materials specifications (Westinghouse 1982) for the BVPS-2 discs (this gives the higher crack growth rate).
6.
Charpy impact values are assumed to be the minimum acceptable by the Westinghouse materials specifications for the BVPS-2 discs.
3.5-7
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EVPS-2 FSAR 7.
The NC is computed using the minimum impact energy determined in Item 6 above and minimum yield strength (this gives the minimum toughness).
- 8. - The critical ' crack size is calculated using the bore stress at 120 percent of running speed for discs 4_ and 5 of the BVPS-2 rotors.
i Note: The yield strength is assumed to be.the highest permissible by the specification for calculating the crack growth rate, while the lowest required by the specification for computing the K-IC Despite the conservative approach used-in determining the above intervals, the importance of public safety is acknowledged by still further reductions.
The LP rotors will be ultrasonically inspected during the refueling outage which most nearly coincides with 5 years of operation since the last inspection.
In no case will the inspection interval exceed 6 years of operation.
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3.S.1.3.2 Turbine Overspeed Protection i'
The turbine _ speed control system has adequate redundancy to ensure that the turbine does not attain destructive _overspeed. The standard Westinghouse analog -electro-hydraulic control (EHC) system and electromechanical-trip system-includes three separate speed sensors mounted on -the turbine stub shaft located in the turbine front pedestal. These sensors are:
1.
Hechanical overspeed trip weight-(spring-loaded bolt),
2.
Electromagnetic pickup for main speed governing channel, and 3.
Electromagnetic pickup for the overspeed protection control channel. This pickup uses the same toothed wheel as item 2.
An overspeed protection ' controller is provided and is activated in the event turbine speed exceeds 103 percent of rated speed (1,800 rpm), or the measured electrical output of the generator as compared to the low pressure turbine inlet pressure indicates a power mismatch.
(load ' impulse pressure feedback).
The low pressure turbine inlet pressure represents the energy input to the turbine generator.
If a mismatch occurs, one of the following actions is initiated:
I 1.
During a -partial load drop, the interceptor valves are closed and then reopened after a set time delay, or L
l.
2.-
During a full load drop, both the governor and the
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interceptor valves close. The governor valves remain closed until the speed is decreased to rated speed (1,800 rpm).
The interceptor valves are modulated and reopen when speed decreases to below 103-percent of rated speed to remove i
l 3.5-8 I
BVPS-2 FSAR entrapped steam-in the reheat system.
If speed again increases above 103 percent, they reclose and continue to modulate until speed remains below 103 percent of 1,800 rpm.
The overspeed protection controller is the first line of overspeed protection and is designed to prevent the turbine from reaching the overspeed trip point.
Should the turbine exceed approximately 110 percent of rated speed, the throttle (stop), governor, reheat stop, and intercept valves will all be tripped closed by both the mechanical overspeed bolt and the backup electrical trip. Thus, the turbine is tripped by redundant trip systems from independent speed sensors to assure utmost safety.
I
- The electromechanical trip system also trips the turbine generator on excessive thrust bearing wear, low bearing oil pressure, low condenser vacuum, and low control system fluid pressure.
The turbine is tripped by the durping of control system hydraulic fluid from all valve pistons, causing the heavy springs to close the throttle (stop), governor, reheat stop, and intercept valves in 0.15 second. Two valves in series in each steam entrance to the turbine are closed simultaneously upon a unit trip to provide redundant steam isolation to the turbine. The turbine operation, trip, and overspeed protection are discussed in more detail in Sections 10.2.2.1.1, 10.2.2.1.2, and 10.2.2.1.3.
The redundancy, component reliability, and test procedures of the turbine control system are detailed in Section 10.2.2.1.
3.5.1.3.3 Turbine Valve Testing i
- Throttle, governor, interceptor, and reheat stop valves of the turbine generator are tested periodically in the single valve mode while the EHC system is in operator automatic and load impulse pressure feedback is in service.
Throttle and governor valves are tested' individu:11y.
Upon completion of each test, the valve is returned to its original position before the next valve is tested. Interceptor sad reheat l
-stop valves are interlocked so that a pair of these valves in one crossover pipe are tested together. Each pair of valves is returned to the open position before the next pair is tested.
Reducing load when testing valves is not necessary since valves may be tested at any load.
The maximum load reduction during any valve test occurs when the unit is at full load.
Under these circumstances, a test of a governot valve results in a short-time l
load' reduction of about 4 percent of -full load. The test of a throttle valve or an interceptor-reheat stop valve pair at full load results in a load decrease of 1 to 3 percent of full load. When 3.5-9
BVPS-2 FSAR valve tests are made below full load, the control system acts to maintain load.
When governor valves are tested at full load, the pressure drops are those normally experienced at the 75 percent admission operating point (that is, 3 out of 4 governor valves open). When governor valves are tested at less than full load, the pressure drops are no different than those experienced in normal operation at reduced load.
3.5.1.3.4 Turbine Characteristics The partial integral rotor employed for BVPS-2 is illustrated in Figure 3.5-1.
The basic concept of the design of these rotors is to fabricate the shaft and first three discs on each side of the rotor's center as a single integral part. This eliminates the keyway which has been the source of stress corrosion cracking problems in previous rotor designs. The bore of the integral part is not exposed, while the exposed areas have lower stresses, which in turn allows the use of material less susceptible to cracking.
For the above reasons, j
there is no need to calculate the inspection interval for the i
integral part of the rotor.
The disc and keyway configuration of discs 4 and 5 is shown in Figure
)
3.5-2.
Because these discs are beyond the transition region from dry to wet steam where most cracks have occurred, the use of the equations of Section 3.5.1.3.1 is very conservative as these are developed from historical crack data.
The following material properties (Westinghouse 1982), bore stresses, and temperatures are used in calculating the values presented in Table 3.5-5.
Charpy V-notch energy at upper shelf temperature = 88 ft-lbs Yield strength at upper shelf temperature:
Minimum = 100 ksi Maximum = 110 ksi Disc 4 Disc 5 Bore stress at overspeed 78.2 ksi 73.5 ksi Metal temperature inlet 192'F 186'F Metal temperature outlet 182 F 192 F Keyway radius 0.375 in 0.375 in 3.5.1.3.5 References Westinghouse Electric Corporation, MSTG-1-P, Criteria for LP Nuclear Turbine Dise Inspections, June 1981.
Westinghouse Electric Corporation, Material Purchasing Department Specification 10325TC, June 1982.
3.5-10
BVPS-2 FSAR TABLE 3.5-5 INSPECTION REQUIREMENTS - DETERMINISTIC APPROACH
- Crack Critical Growth Potential Crack Rate Reinspection
' Disc Crack Size (inches /
Interval No.
Location (inches) year)
(years) 4 Bore (Inlet) 4.972 0.07468 33.28 4
Bore (Outlet)-
4.972 0.06273 39.630 4
Keyway 2.917 0.03197 39.756 I
5 Bore-(Inlet) 5.628 0.0673 41.812 5
Bore (Outlet) 5.628 0.07468 37.676 5
Keyway 3.3025 0.03806 38.459 i
NOTE:
- The required reinspection intervals for critical turbine locations based on a deterministic analysis (Section 3.5.1.3.1) are tabulated l
here.
This table demonstrates the conservatism inherent in the l
Imposed inspection interval limit of 6 years.
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BEAVER VALLEY POWER STATION - UNIT 2 FINAL SAFETY ANALYSIS REPORT
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FINAL SAFETY ANALYSIS REPORT 1
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