ML20248D591

SER Accepting Util 881130,890411,27 & 0523 Submittals Re Seismic Qualification of Byron Deep Wells

ML20248D591
Person / Time
Site:	Byron
Issue date:	08/07/1989
From:	NRC
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ML20248D552	List: ML20248D547 ML20248D591
References
NUDOCS 8908110085
Download: ML20248D591 (5)

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O 4 SAFETYEVALUATIONREP0g FOR SEISMIC QUALIFICATION OF BYRON DEEP WELLS BYRON UNITS 1 AND 2 DOCKET N05. 50-454 AND 50-455 1.0 Introduction Byron Station, Units 1 and 2, utilizes the Rock River as a source of cooling water make-up for the Ultimate Heat Sink (UHS). A minimum River Rock water level of 670.6 feet Mean Sea Level (MSL) is specified in the limiting condition requirements of Technical Specification 3/4.7.5, Ultimate Heat Sink. In order _to relieve.or mitigate these.operationa1 restrictions,'an exainination of the deep well's seismic response has been completed in support of changes to be made to the technical specifications.  ;

By letter of November 30, 1988 and subsequent submittals dated April 11, April 27 and May 23, 1989, the licensee (Commonwealth Edison Company) prov1eed information for qualifying the deepwells and pumps. This Safety Evaluation is based on the review of the submitted information in the area of mechanical engineering and structural engineering /geosciences.

The scope and their of review supports includes subjected to a the seismicSafe postulated adequacy of Earthquake Shutdown piping, motor, ISSEpump, )

of 0.2g Regulatory Buide (RG) 1.60 spectra; and the geologic, hydrologic and seismologic environment as well as the structural analysis of the entire well system. Furthermore, the operability surveillance testing of the deep well puinps was also briefly discussed.

2.0 Evaluation The Byron deep well system consists of a 1500 ft. deep borehole through competent dolomites and sandstones with a 16-inch diameter and 700 ft.

deep steel casing cement grouted into a segment of total rock depth. An 8-inch diameter and 425 ft. long discharge pipe hangs within the casing and supports the pump and the motor at its lower end. At the top of the weH, the vertical discharge pipe runs into a joint that changes the direction of the flow toward a horizontal discharge pipe. The horizontal discharge pipe, also of 8-inch diameter, is buried 5 ft. under the ground surface, i

The top of the well is covered by a reinforced concrete pump shelter structure designed for tornado loads. The finished grade elevations of deep wells Nos. 1 and 2 are 873 ft. - 7 in, and 868 ft. - 4 in.,

respectively. The top of casing is about 6 feet below the ground surface.

About 4 ft. of tbc reinforced concrete pump shelter structures are exposed above ground surface. No other structure is built near these deep wells; therefore, they will not suffer any damage during an earthquake due to collapse of neighboring non-safety related structures.

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ells Nos. I and 2 from the UHS, i.e. the Essential The Service distances of deep w(ESCT), are approximately 250 ft. and 750 ft.

Cooling Tower respectively. The finished grade elevation at the ESCT building is 874 ft. which is about the same as those of the deep wells. It can be assumed that the groundwater levels at these 1> cations are the same when the deep well pumps are not in operation. The top of the deep well casing is considered to be at depth 0 ft. while the end of casing is at a depth of 700 ft. and the bottom of well at a depth of 1500 ft. The pump operates at a depth of 445 ft.

The qualification data for Byron deep well system consist of two parts:

(1) A literature review of the past ex>erience of wells, pumps, and pipeline installations in areas of hig1 seismicity; and (2) an analytical examination of the seismic response of the Byron deep well/ pump system subjected to a Byron SSE event.

2.1 Literature Review

a. A comparison was made of seismic environments with several world wide earthquakes with magnitudes greater than the Byron SSE.

The following earthquakes were selected:

San Fernando Valley Ms = 6.6 Coalinga Ms = 6.2 Morgan Hill Ms = 6.2 Chile . Ms = 7.8 San Salvador Ms = 6.0 Edgecumbe Hs = 6.3 Two additional earthquakes were reviewed to demonstrate the response of wells to earthquake motion:

Tangshan Ms = 7.8 Alaska Ms = 8.4 '

Wells of construction similar to or less than the Byron wells were found to remain functional following the earthquakes which had larger magnitudes, higher accelerations, and longer duration motion created during multiple events,

b. Comparison of an earthquake on groundwater wells depends on many factors i such as the earthquake mechanism, wave propagation, geologic setting, characteristics of soil and rock, aquifer systems and well construction.

Three wells in the city of Byron, two in the city of Oregon, four in the city of Rochelle, and one in the Village of Stilman Valley have been investigated. All these wells are within 100 miles of the Byron site and i are still in service.

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s Earthquakes with an epicentral location within 100 miles of the Byron site -

were included.in the study. They are:

Beloit,1909,' Intensity VII N. .E. Illinois,1912, Intensity VI Rock Island,1934,' Intensity VI N. Illinois,1972, Intensity VI

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All wells have records of depths, date dug, and flow rate. There has been no known damage or impairment of pumpage of municipal groundwater wells in the-Byron area as a result of any earthquake during the past 90 years or more,

c. A comparison was made of the construction standards for wells in areas of high seismicity with those for the Byron wells. .

The design basis for the Byron well site is based upon American Water WorksAssociation(AWWA) Standards,A100-66,governingtheinstallation of the water wells.. Used for comparison were the Water Well-Standards of State of California Bulletin 74-81 and the AWWA Standard for Water Wells, ANSI /AWWA, A 100-84 for seismic design criteria. The Byron well construction exceeds the requirements of the AWWA and California standards.

Three aquifer pumping tests had been perforired in 1974, 1978, and 1980.

These tests had demonstrated the ability of the station deep wells to provide the design basis quantity of water makeup to the essential

. service water system during the 30-day period for safe shutdown. The AWWA type of well construction, with the length of casing welded together and seated into the bedrock, provides the maximum strength for a groundwater weil.

2.2 Seismic Analysis and Stress Analysis Conventional methods of structural dynamics were used in seismic and stress analyses of the well system structures. Specifically, a nonlinear time history analysis was-performed for the well system where the L discharge pipe is modeled by elastic beam elements and the gaps between the discharge pipe and the casing are modeled by nonlinear gap elements.

Two percent damping for the pipe has been assumed.

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l The same acceleration time-history used for Byron Station corresponding to SSE of 0.2g horizontal is applied to the seismic analysis of the well system. The response spectrum generated from the time history envelops the corresponding design response spectrum of RG 1.60.

Two cases have been considered in the analysis:

(1) Earthquake when pump is r.ot operating, groundwater level at 250 ft.

below ground.

(ii) Earthquake when pung is operating, groundwater level at 375 ft.

below ground.

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The major components considered in the analysis are:

1) Uncased well cavity ii) 16" diameter steel pipe casing iii) 8" diameter steel discharge pipe i) Buried reinforced concrete duct v Pump shelter structure v) Motor and pump j

The design criteria are acceptable to the staff since ASME Code allowables and conventional allowable strength of rock and reinforced concrete were used. The results of the analyses show that, strain and stresses induced in the components during the SSE (including the other normal loads) are well within the acceptable allowables. Item (v),thepumpshelterstructure, was designed for tornado. loads.

l The staff has looked into the problem of aquifer rupture. This is a very rare event in North America, and it is reported that in general, earthqu'akes east of the Rocky Mountains do not rupture the earth's surface. Since the shallow dolomite aquifers at Byron are near the ground surface and no capable faulting is known to exist within 5 miles of the site, aquifer rupture will not occur at the Byron site.

The well pumping tests of 1974, 1978, and 1980 had demonstrated adequate capacities of water supply. Even during a drought season, the source of groundwater will not be affected because it came from over 100 miles to the plant site and the groundwater level at site does not influence nor relate with the source of groundwater supply.

2.3 Operability Surveillance Testing of the Deep Well Pumps In response to the NRC staff's questions, the licensee stated in the May 23, 1989 letter that there are two periodic surveillance that would he required to demonstrate the operability of the deep well pumps. The first surveillance is a monthly surveillance that required the pumps to be run and the current reading for the running pumps will be obtained.

These amp readings will be used for trending and to show the deterioration of pump performance over time, The second surveillance is on an 18-month frequency to show that the required 550 gpm flow rate for each pump is obtained. In the past, the licensee has been performing this second surveillance every six months instead of every 18 months. In these surveillance, the pump amp readings and flow rate measurements will be recorded and trended to detect pump degradation.

Furthermore, the licensee samples the well water to determine the quality of the station drinking water every year. The analyses performed on the drinking water would detect substantial groundwater leakage into the well.

Additionally, the licensee will physically examine the welded connection of the piping to the well head every two years to ensure early detection of deterioration of this connection.

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3.0 Conclusion The NRC staff has reviewed the licensee's submittals for the seismic qualification of the Byron station deep wells. At the request of the staff, the licensee also performed the detailed calculation on the threaded coupling connection of the pipe to the well head fitting under SSE loads. This connection was judged to be the weakest link in the anchorage of the discharge piping that supports the pump. The staff has reviewed this information and finds the stress margin acceptable.

The staff has also visited the plant site and its vicinity to review and

_ verify certain hydrologic and topographic features of the UHS systems.

The deep wells are close to the essential service water cooling towers and have approximately the same ground elevation.

The staff also briefly reviewed'the licensees operab'ility surveillance testing of the deep well pumps. Due to the practical restrictions to the installation of instrumentation, only monthly current readings and semi-annual flow rate measurements are to be recorded and trended to assure bpercbility of the pump and to detect pump degradation. To add more confidence in the operation of the deep wells during the critical summer season, at the staff's request, the licensee agreed to add a flow surveillance test in the summer. Thus, the flow rate surveillance testing shall be done three times (in spring, summer and fall) each year.

The staff, therefore, concludes that the Byron Station deep wells are seismically qualified and can be considered as part of the ultimate heat sink system in the event of an earthquake.

Principal Contributors: Pei Ying Chen, EMEB j Sai P. Chan, ESGB Dated: August 7, 1989 1

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