ML20133D783
| ML20133D783 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 10/22/1996 |
| From: | PUBLIC SERVICE CO. OF COLORADO |
| To: | |
| Shared Package | |
| ML20133D772 | List: |
| References | |
| NUDOCS 9701100070 | |
| Download: ML20133D783 (10) | |
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PRELIMINARY REPORT J
ORISE SUPPORT OF NRC LICENSE INSPECTION 1
AT FORT ST. VRAIN ON SEPTEMBER 30 TO OCTOBER 3,1996 (DOCKET NO. 50-267, RFTA #96-5)
INTRODUCTION The Public Service Company of Colorado (PSC) operated a 330 MWe High Temperature Gas Cooled Reactor (HTGR) from July 1979 until August 1989. The plant, designated as the Fort St.
Vrain Nuclear Station (FSV), was authorized for construction on September 17,1968 when the U.S. Nuclear Regulatory Commission (NRC) issued a provisional construction permit.
3 Construction was completed in December 1973 and a facility operating license, License No.
DPR-34, Docket No. 50-267, was granted on December 21, 1973.
Initial fuel loading commenced on December 26,1973 and initial criticality was achieved January 31,1974. After i
a prolonged period of startup testing, low-power operation and plant modifications, the plant was committed for commercial operation on July 1,1979. Full power was achieved November 6, 1981 (PSC 1995a).
In the nuclear steam supply system for FSV, heat was produced by fission in the HTGR utilizing a uranium-thorium fuel cycle. Graphite was used for the moderator, core structure, and reflector.
High temperature helium was used as the primary coolant to produce superheated and reheated steam at a temperature of 1,000 F to match conventional thermal station conditions. The entire nuclear steam supply system, including the reactor core, graphite moderator and reflector, steam generators and helium circulators, was contained within a Prestressed Concrete Reactor Vessel (PCRV).
During the operational period, FSV operated for approximately 890 effective full-power days; FSV was shut down on August 18, 1989. The PSC Board of Directors reviewed and confirmed the Executive Management decision that FSV would not be restarted, and that PSC would pursue decommissioning of FSV. The decision to permanently shut down and decommission FSV was based on related technical and financial considerations. Problems were identified with the control Fort St. Vrain (621) October 22,1996 h \\essapireports%vrain\\st._vrain.002 9701100070 961022 PDR ADOCK 05000267 G
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,i rod drive assemblies and the steam generator steam ring headers that presented significant l
technical obstacles which could be overcome, but at a significant monetarv cost and time to PSC.
In addition, due to the uniqueness of the HTGR fuel cycle, the cost to purchase new fuel was prohibitive. This, in conjunction with low plant availability and correspondingly high operating costs, made continued operation of FSV impractical.
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PSC's objective is the dismantlement and decommissioning of FSV to release all site areas for unrestricted use. To accomplish this, a portion of the PCRV structure and the radioactive balance-of-plant equipment that exceed the limits for unrestricted use will be decontaminated or removed as described in the Fort St. Vrain Decommissioning Plan. In May 1991, the NRC granted a 10 CFR 50 Possession Only License. On November 23,1992, the NRC issued the Order to Authorize Decommissioning of Fort St. Vrain and Amendment No. 85 to Possession Only License No. DPR-34 (PSC 1995b).
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The FSV facility will be largely left intact following decommissioning; dismantlement of structures will be confined to the PCRV, and portions of the Reactor Building, Turbine Building, i
and Liquid Waste System. Removal will be for purposes of removing contaminated structures and to provide paths for removal of contaminated piping and equipment.
Following defueling, the PCRV contained the majority of the remaining radioactive material inventory. Portions of the PCRV concrete are activated due to direct irradiation from the reactor j
core, and concrete exceeding unrestricted use limits will be removed prior to final survey and i
disposed of as radioactive waste at a licensed radioactive waste disposal facility. Thus, the radioactive source term at FSV is primarily a result of neutron activation of both metallic and 4
concrete components of the PCRV and neutron activation of impurities contained in graphite i
components of the PCRV. These activation products include beta-gamma emitters such as Co-60, l
Eu-152, and Eu-154, and low-energy beta and x-ray emitters such as H-3, C-14, and Fe-55. It should be noted that H-3 and Fe-55 are the largest contributors to the total radionuclide inventory (PSC 1995a).
a Fort St. Vrain (621) October 22. Im 2
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FSV's final survey will include all pertinent structures, surfaces, systems and components, 4
j concentrating on those previously identified as contaminated or potentially contaminated during the dismantlement / decommissioning phases. The FSV final survey will include:
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Sampling outside the restricted area of PSC property, soil, pavement, water, and liquid 4
effluent ditch and pond sediment for radioisotopic analysis and measurement of gamma i
exposure rate, i
J Sampling inside the restricted area of PSC property, soil, basin sediment, pavement and water for radioisotopic analysis and measurement of gamma exposure rate, I
- Radiological surveys of the PCRV and Reactor Building, and i
1 Radiological surveys of the Turbine Building, Radwaste Compactor Building, New Fuel-Storage Building, Radiochemistry 1.aboratory, Helium Transfer and Storage System, and i
Liquid Radwaste System.
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At the request of the NRC's Division of Waste Management, the Environmental Survey and Site i
Assessment Program (ESSAP) of the Oak Ridge Institute for Science and Education (ORISE) performed independent confirmatory surveys activities at the Fort St. Vrain site in Platteville, Colorado. During the period September 30 through October 3,19%, ESSAP performed 2
independent confirmatory survey activities-including surface scans, direct measurements of surface activity, and exposure rate measurements-and a review of the licensee's hard-to-detect nuclide (HTDN) assessment program.
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SITE DESCRIPTION i
The FSV facility is located approximately 56 kilometers (35 miles) north of Denver and 5.6 kilometers (3.5 miles) northwest of the town of Platteville, in Weld County, Colorado. The site is located in an agricultural area with gently rolling hills. Grade elevation at the plant is 1,460 meters (4,790 feet) above sea level. The site consists of 1130 hectares (2800 acres) owned by i
3 n:w ps,,po,i.wi_vr.inut_vr.in.co2 Fort St. Vrain (621) - October 22. 1996
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PSC, identified as the Owner-Controlled Area, of which approximately 260 hectares was designated as the exclusion area during plant operation.
The station is located approximately 3 kilometers south of the confluence of the South Platte River and the St. Vrain Creek. Neither of these two streams are considered navigable. Cooling for the
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plant is provided by mechanical draft cooling towers. Make-up water to the cooling towers is obtained from the two streams, and is supplemented by shallow well water. Nineteen shallow monitoring wells are located on the site. The licensee also owns surface water rights in four irrigation ditches which traverse portions of the site.
The major structures within the Restricted Area include the Reactor Building which contains the PCRV, Turbine Building, Radwaste Compactor Building, New Fuel Storage Building, Technical Support Building which contains the Radiochemistry Laboratory, Mechanical Draft Cooling Towers, Warehouse and Construction Workshops, Evaporation Ponds, and the Electrical Switchyard. The ground surface covering within the Restricted Area is composed primarily of gravel and vegetation, with smaller portions devoted to concrete or asphalt roadv ays and laydown areas.
OBJECTIVES The objectives of the confirmatory survey activities were to provide NRC inspection support, including independent contractor reviews of decommissioning program elements and confirmatory survey data for use by the NRC in evaluating the adequacy and accuracy of the licensee's procedures and final status survey results.
PROCEDURES During the period September 30 through October 3,1996, ESSAP performed independent confirmatory survey activities at the Fort St. Vrain site in Platteville, Colorado. This technical assistance was provided to assist the NRC in their inspection of licensee decommissioning-related activities. Technical assistance activities included a review of the licensee's hard-to-detect nuclide Fort St. Vrain (621). October 22.1996 4
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program and independent confirmatory surface scans and surface activity measurements. These activities were performed in accordance with a survey plan dated September 16,1996 (ORISE 1
1996). This report summarizes the procedures and results of the technical assistance activities.
a REVIEW OF LICENSEE'S HARD-TO DETECT NUCLIDE PROGRAM ESSAP participated in a meeting on October 2,19% with NRC and licensee staff to discuss the FSV decommissioning project's hard-to-detect nuclide (HTDN) program. The pertinent technical i
basis document (TBD-201), " Site Specific Guideline Values" was referenced during the meeting.
t TBD-201 presents the results of sample analyses used to derive the site-specific guideline of 4,000 2
dpm/100 cm. This site-specific guideline incorporates the fraction of residual radioactivity comprised of H-3 and Fe-55. The initial sample analyses used to derive this guideline were performed in 1993 and 1994. Then in 1996 a sample of PCRV dust was collected and analyzed j
and the sample results confirmed the appropriateness of the site-specific guideline. Therefore, 2
compliance with the 4,000 dpm/100 cm surface activity guideline also ensures that the guidelines for HTDNs are satisfied.
While the licensee stated that periodic analyses for HTDNs should continue, as necessary, to verify the site-specific guideline values, a specific frequency for evaluating the HTDN levels has not been established. Instead, the frequency of HTDN sampling is based on engineering
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judgement and the location, such as plant systems that are expected to have tritium contamination.
i The record review performed by ESSAP indicated that additional docunientation may be needed 4
to fully characterize plant areas to ensure that the ratios in the TBD are appropriate. Locations within the plant may exhibit depositions of tritium contamination from nuclear power operations.
In this situation, the site-specific guideline may not effectively account for the HTDNs present.
That is, if the HTDNs exist at ratios exceeding those identified from the TBD samples, direct measurements may not provide adequate confidence that HTDN levels are in compliance. To resolve this concern, the licensee subsequently reviewed results of characterization survey analyses relative to the removable tritium surface activity levels.
Fort it Vrain (620. October 22. Im 5
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j Results of previous sample analyses for tritium during 1992 and 1994 were provided to ESSAP i
j for review. Results indicated that levels of removable tritium contamination within plant systems 2
were as high as 156,000 dpm/100 cm. Most of the analyses indicated that H-3 was present, 3
without any detectable alpha or beta activity using conventional smear analysis techniques.
l Discussions with the licensee's contractor indicated that only two samples collected from structure surfaces had detectable tritium levels-both these samples indicated low levels of tritium activity.
I Thus for structure surfaces, the assessment of the detectable surface activity is an adequate surrogate for demonstrating compliance with the HTDN. The greatest potential for the presence of HTDN, without the benefit of a detectable nuclide fraction, is within plant systems. It is i
recommended that the licensee provide a summary of the procedures used for assessing HTDNs in plant systems and clarify how these procedures provide adequate documentation of the j
contamination status in the plant systems.
l When positive levels of HTDNs are identified, the results are first compared to the radionuclide j
mixture used to derive the site-specific guideline and to the individual guidelines for HTDNs. For j
example, if a smear sample identified 5,000 dpm/100 cm of HTDNs, compliance would be 2
j demonstrated by comparing the smear result to the HTDN removable guideline-and the total surface activity level would be independently compared to its limit ( 4,000 dpm/100 cm ),
2 a
INDEPENDENT MEASUREMENTS IN SELECTED SURVEY UNITS e
a Eight survey units were selected by the NRC with input from ESSAP for confirmatory survey activities. The selected survey units include (convention used survey group / survey unit):
A0007/BZ003, B0006/FZ001, B0012/FZ002, C0004/WZ001, C0009/BZ001, C0030/FZ001,
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C0031/SZ001, and D4800. Surface scans, surface activity measurements, and exposure rate j
measurements were performed in each survey unit. Data reduction was performed on the collected direct measurements to allow comparison to the licensee's data. ESSAP's average 4
surface activity level in each survey unit was less than the corresponding surface activity reported by the licensee, and therefore, also less than the surface activity guideline. Surface scans did not
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identify any locations of elevated direct radiation.
1 Fort 5t Vram (621) October 22,1W b
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ESSAP also performed confirmatory survey measurements on miscellaneous concrete, metal, and wood debris from the demolition of the New Fuel Storage Building and Building 28. This material was staged on the east side of the Fort St. Vrain site. Surface scans and 20 direct measurements were consistent with ambient background levels.
SURFACE SCANS AND COMPARISON TO LICENSEE SCAN RESULTS Confirmatory surface scans for alpha and beta activity were performed over accessible floor, lower wall, and equipment surfaces in survey units F0015, F0039, F0077, F0084 (and a portion of the adjacent F0ll5), F0126, and the refuel floor (Level 11 of the Reactor Building). These survey units were selected because characterization surveys indicated contamination above guideline levels prior to remediation. Scans were performed using gas proportional detectors coupled to ratemeter-scalers with audible indicators; both a floor monitor with a 573 cm detector 2
2 and a hand-held 126 cm detector were used for scanning. Scans were also performed with GM detectors on wall surfaces and difficult-to-access areas. Surface activity levels were determined from locations of elevated direct radiation as identified by scans.
F0015-steam / water dump tank room-is an affected area located on Level 1 of the Reactor Building. Floor drains in this area had been grouted in prior to the scan survey. One hundred percent of both floor and lower wall surfaces were scanned. The scan range on the floor was 1,800 to 2,400 cpm-consistent with background levels. No elevated direct radiation was detected on any of the wall surfaces; scan ranges were 300 to 550 cpm.
F0039, located on Level 3 of the Reactor Building, consisted of surfaces that were largely inaccessible. Scan surveys were performed over a limited area of one wall and on pipes, valves, and ledges. No areas of elevated direct radiation were detected in the scanned areas. Scan ranges were consistent with background levels-400 to 600 cpm and 40 to 65 cpm for the gas proportional and GM detectors, respectively.
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j F0077 is an affected area located on Level 5 of the Reactor Building. One hundred percent of both floor and wall surfaces to 4 meters were scanned. One location of elevated direct radiation was identified with the GM detector in a relatively inaccessible area behind an electrical raceway.
The surface activity level at this location, as measured by the GM detector, was 19,600 dpm/100 l'
cm. Scan ranges in the remaining surveyed areas were consistent with background levels-1,800 2
l to 2,200 cpm, 200 to 950 cpm,40 to 60 cpm for the floor monitor, gas proportional and GM 1
j detector, respectively.
1 Survey unit F0084 is an affected area on Level 7 of the Reactor Building. One location of clevated direct radiation was identified with the GM detector on the exterior wall of the PCRV.
It was subsequently determined by the licensee that this location of elevated direct radiation was actually within F0ll5, the survey unit immediately adjacent to and above survey unit F0084. The licensee had also identified this elevated area with their scan survey and assessed the surface.
2 activity level-and reported 8,716 dpm/100 cm. The surface activity level measured by ESSAP 2
at this location-determined to be less than 100 cm as measured by the GM detector-was 19,100 2
2 dpm/100 cm. Subsequent measurement of this location with a 126-cm gas proportional detector 2
resulted in 9,210 dpm/100 cm. Scan ranges in the remaining surveyed areas were consistent with background levels-168 to 600 cpm and 40 to 78 cpm for the gas proportional and GM
- detector, respectively.
F0126, survey unit for the regenerator heater equipment room, is located on Level 11 of the Reactor Building. Fifty percent (50%) of the floor and one hundred percent of wall surfaces to 2.5 meters were scanned. No areas of elevated direct radiation were detected in the scanned areas. -Scan ranges were consistent with background levels-600 to 850 cpm and 40 to 75 cpm for the gas proportional and GM detectors, respectively. Additionally, seventy-five percent (75%)
of the refuel floor was scanned with a floor monitor. Scan ranges were consistent with background levels-1,800 to 3,100 cpm.
I Comparisons of the ESSAP scan results to the licensee scan results documented in their survey packages were performed for survey units where ESSAP identified locations of elevated direct j
radiation: survey areas F0077 and F0115. For survey unit F0077, the licensee did identify an I
area of elevated activity that was subsequently remediated. ESSAP identified one location of Fort St. Vrain (621)- October 22.1996 8
h:\\casap\\ reports st_vrain\\st_vrain.002 1
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elevated activity (19,600 dpm/100 cm ) located behind an electrical raceway that the licensee did not detect. In survey unit F0115, both ESSAP and the licensee identified the same location of elevated direct radiation by surface scans. ESSAP measured 9,210 dpm/100 cm at this 2
location-while the licensee reported 8,716 dpm/100 cm. In other survey units scanned by 2
ESSAP the licensee identified locations of elevated direct radiation that ESSAP did not identify, j
due to ESSAP's limited scan coverage. In general, the scan results were consistent between ESSAP and the licensee in these survey units, indicating that the licensee's program for performing scan surveys is successfully identifying significant areas of contamination.
SUMMARY
During the period September 30 through October 3,1996, the Environmental Survey and Site Assessment Program of ORISE performed confirmatory survey activities at the Fort St. Vrain site in Platteville, Colorado. Survey activities included technical review of the hard-to-detect nuclide program and independent confirmatory survey activities, including surface scans, surface activity measurements, and exposure rate measurements.
Review of the hard-to-detect nuclide program identified that the greatest potential for the presence of HTDN, without the benefit of a detectable nuclide fraction, is within plant systems.
It is recommended that the licensee provide a summary of the procedures used for assessing HTDNs in plant systems and clarify how these procedures provide adequate documentation of the contamination status in the plant systems.
Confirmatory survey activities in eight survey units identified no locations of elevated direct radiation. Surface activity levels were below those reported by the licensee and therefore, demonstrated compliance with the surface activity guidelines.
Comparison of scan results from the five survey units evaluated showed general agreement between the licensee and ESSAP.
9 b:\\essap\\reporu\\st vrain\\styrain.002 Fort SL Vrain (62t). October 22. Im
I REFERENCES Oak Ridge Institute for Science and Education (ORISE). Confirmatory Survey Plan for the Fort St. Vrain Nuclear Station, Public Service Company of Colorado, Platteville, Colorado (Docket No. 50-267, RFTA %-5). Oak Ridge, TN; September 16, 1996.
l Public Service Company of Colorado (PSC 1995a). Final Survey Plan for Site Release (revision
- 1) Fort St. Vrain Nuclear Station Decommissioning Project. May 25,1995.
Public Service Company of Colorado (PSC 1995b). Final Survey Report for Release of Repower Area. Fort St. Vrain Nuclear Station Decommissioning Project. March 2,1995.
Fort SL Vrain (621). October 22, tm 10 6:1, ps,,po,i.s.i_vr. ins.i_vr.in.co2