ML19351E118
| ML19351E118 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 05/25/1968 |
| From: | YANKEE ATOMIC ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML19351E114 | List: |
| References | |
| NUDOCS 8011250623 | |
| Download: ML19351E118 (13) | |
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YANKEE NUCLEAR PCWER STATION OPERATION REPORT NO. 88 For the month of APRIL 1968 l
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Subuitted by YANKEE ATOMIC ELECTRIC COMPANY Boston Massachusetts May 25, 1968 801125 0 hd
f This report covers the operation of the Yankee Atonic Electric Ccmpany plant at Rowe, Massachusetts, for the month of April,196d.
During this report period the plant was shutdown for the Core s"
VI-VII refueling and maintenance outage.
At the beginning of the period preparations has been completed for removing the reactor vessel head.
However, test runs with the recently modified spent fuel chute transfer carriage indicated that difficulties etill existed.
Since the proper operation of this equipment is vital during core ecmponent removal, the spent fuel pit was emptied and additional modifications were made to the carriage system.
On April h, the reactor vessel head was removed; the control rod mechanisms were flushed prior to placing the head on the flatbed storage car. The shield tank cavity and spent fuel pit were filled and the necessary reactor vessel internals were removed to provide access to the reactor core.
During the initial filling of the cavity, a capacity test was performed with the safety injection pumps. All pumps performed satisfactorily.
On April 6, the unloading of core ccmponents commenced; seventy six fuel assemblies and eight shim rods were removed to the spent fuel pit.
Selected control rods were inspected and all 2h control rods were rotated 0
90 clockwise, as part of the rod wear equalization program.
The core barrel was removed from the vessel on April 9 to allcw inspection of vessel internals and repairs that were made to the thernal shield during the Core IV-V refueling outage.
These inspections were completed on April 12 and the core barrel was returned to the reactor vessel.
9 Loading of core components was started on April 13; new unitized chim rods, recycle fuel and new fuel including four Zircaloy test assemblies were inserted.
The refueling operation was completed on April 15.
Remain-ing reavtor vessel internals were installed and the shield tank cavity borated water was returned to the safety injection tank follcwing filtration.
On April ld, the reactor head was placed on the vessel and exposed shield tank cavity areas were decontaminated.
Considerable difficulty was encountered removing reactor vessel studs during that phase of the refueling (see Operation Report No, 67 b One of the fifty two closure studs experienced significant galling of the threaded portion in both the stud and the reactor vessel flange.
The damaged stud hole was rebored and a threaded sleeve, machined to accept a stud of h 3/h inch diameter, was installed in the vessel stud hole.
In order to effect these repairs, it was necessary to remove the reactor head and place temporary shielding around the damaged stud hole.
Following the incertion of the stud hole sleeve on April 22, the head was again placed en the reactor vessel-Tensioning of the fifty two head closure bolts inctading the newly fabricated reduced diameter stud was completed en Apri' 2$.
When system pressurizer water level was increased in preparation for system hydrostatic testing, it was observed that the mechanical seal in the north in-core ins trumentation thimble was leaking.
The mechanical g
seal was renade and seal welded as a precautionary measure.
. The main coolant system including the charging and bleed lines were hydrostatic tested at over 2h00 pai. Plant heatup commenced and the Core VII reactor care was brought critical on April 30 at Oh30 hours At the end of the report period the physics startup test program was in progress.
Core VI-VII Major Work Items During routine vibration testing of the four main coolant pumps prior to the outage, it was observed that t:.e high frequency vibrations from the No.1 pump upper bearing were significtmtly different from the other pumps. The pump was removed from the volute and disassembled for inspection.
Generally, the punp was in excellent condition, A chaffed surface on the thrust runner and nut were cleaned by machining.
The gasket area between the pump and guide vane was lapped. Pins in the thrust shoes were slightly worn; they were interchanged with the upper set of pins that experience The only condition observed that could have caused the high no wear.
frequency vibration was a slightly loose (6-7 mils) thrust collar locking nut. The pump was assembled and installed in the volute.
Vibration measurements of the pump upper bearing were made during plant heatup; only normal vibrations were detected.
A significant increase in the incidence of main condenser tube leaks was experienced during Core VI operation. In all instances tube leaks occurred just below the condenser non-condensable gas offtake section.
A substantial area in the suspect region was retubed in both water boxes.
A combination of $7 stainless steel and 12h Admiralty tubes were inserted in the east water box tube sheet; 1h3 stainless steel and 17 A.tmiralty tubes were installed in the west water box tube sheet.
Several defected G
tubes are currently undergoing metallurgical examination to determine the cause of failure.
During the outage, the low pressure turbine was disassembled for inspection. The first six stages of blades and spindle, the first three stages in the top half of blade ring and the gland casings were sandblasted.
The degree of corrosion in the seventh and ninth row of blades was measured.
The undercutting problem of the gland seals on the shaft has not reached a condition requiring i.cnediate repair. The total time required for the disassembly, inspection and assembly ofthe low pressure turbine was 2h days.
As a part of the plant inspection program, the welds of the safety injection line 5 inch transition section which is attached to each main coolant loop were radiographically tested.
It was observed that the internal weld of the No. 2 loop safety injection line that attaches the thermal sleeve to the transition piece had developed a crack.
The upper section of this transition piece containing the thermal sleeve was removed and a newly fabricated section of improved welded thermal sleeve design was installed. This area is in a non-stressed region of the main coolant system.
Design Chang 2s 1.
Modification of Bleed Line Orifice System G
The 75 gpm bleed line orifice was replaced with a 0-100 gpm variable orifice valve.
This substitution orovides a more flexible system than the previous arrangement and service requirements on the downstream valves are reduced.
2.
Core VII Core VII was loaded in the same general regional pattern that was V'
used in the previous cores.
Four assemblies that were originally h.9h%
enriched, which were cycled in Cores V and VI were placed in the central region. Thirty six assemblies, also originally h.9h% enriched which were cylced in Core VI were placed in the intermediate region. T.:irty two new, h.9h% enriched assemblics and four new 3. $% enriched Zircaloy test assemblies were located in the peripheral region.
3.
Modifications to Safety Injection and Charging and Volume Control Systems The automatic safety injection circuit was duplicated so that the system will function in the event of a signal from either of two pressure detectors.
A new two inch check valve was installed in the charging line upstream from the isolation valve.
If the isolation valve fails to close in the event of a charging line failure upstream from the check valve, this modification reduces the liklihood of a loss of main coolant.
A complete functional test of the modified safety injection system under simulated low pressure conditions was performed; all components operated as required.
h.
Feedwater Line Modifications G
U-tube loop seal connections were installed in the eight inch feedwater piping to both No, 1 and No. 2 steam generaters.
This modi-fication reduces the watsr hammer condition which occurs during periods of low feed flow to the steam generators.
A similar installation was made to the No. 3 and No. h stema generator feedwater lines during the Core V-VI refueling period.
"lili :atien of a Reduced Diameter Reactor Head Closure Stud One of the $2 reactor vessel flange stud holes was bored and tapped, A threaded sleeve that would accept a h 3/h inch stud was inserted into the rebored stud hole. The new reduced diameter stud was fabricated from ASTM-A320-Gr.Lh3 material.
Inspec ti ons Following is a list of major inspections performed during the period.
Inspoetion techniques included; visual, underwater television, boroscope and binoculars.
1.
All the bolting joining the core barrel to the lower core support barrel was in place and no separation of the flange was cbserved.
2.
The belts joining the core barrel to the lower core support plate were in place; there was no detectable separation of the joint.
3.
Eolta joining the upper core support plate to the bottom of the upper core support barrel were in place.
_4_
h.
The outermost bolts joining the top of the shroud tubes to the bottom 7 -
of the lower core support plate were in place and no separation of the joint was observed.
5 All the bolts joining the shroud tube tie assembly to the bottom of the shroud tubes Vere in place.
6.
The bolts attaching the lateral supports to the bottom of the lower core support plate were in place. A tack weld to the centering pin on all four lateral supports was corroded. Apparently the wrong ma+erial was used in making the weld. The pins were in proper position.
7 No abnormal conditions were found in the thermal shield bolting, the seam clamp assemblies or the secondary core support assemblies.
8.
Accessible reactor vessel clad areas including the worn area in the bottom of the vessel were inspected.
Impressions and underwater television pictures indicated that no pitting or undercutting had occurred; only normal penetration due to general corrosion was observed.
All other clad areas appeared normal; however, it was noted that overlay weld pads were provided in the areas where the thermal shield radial support pins could contact the vessel wall. These pads are not indicated on the prints and could not be seen without the use of the ur.derwater television.
9 Three control rod drive shafts were inspected; no abnormal conditions S
were found.
10.
Visual, dye penetrant and ultrasonic tests were performed on the core barrel flange and gussets. Conditions were unchanged since the previous inspection.
11.
The welds of the safety injection line 5 inch transition section which is attached to each main coolant loop were radiographed and dye penetrant tested; similar welds on the 2 inch charging line were tested in the same manner. The internal weld of the No. 2 loop safety injection line that attaches the thermal sleeve to the transition piece was cracked.
No other abnormal conditions were detected. All welds associated with the transition section and the new charging line check valve were radiographed and dye penetrant tested following installation.
12.
The reactor vessel head clad behind stud No. 3h was Zyglo tested; no abnormal condition was observed.
13.
Two control rods were inspected; only minimum wear was found in the guide block area.
14.
The north source vane was inspected and found to be in good condition.
15 Three Core VI fuel elements were inspected. A light crud film was observed over the entire area of the assembliee; no mechanical abnormalities were detected.
. Plant Maintenance
)
In addition to the major work items performed by the plant staff
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during the month of April,1968 ; the following pertinent maintenance was completed during the period.
1.
The secondary side of No's 1 and 3 steam generators were inspected and found in good condition.
2.
The No. 1 steam generator feedwater check valve was inspected. The disc and sect were in good condition; there was no wear on the pin.
Repairs were unnecessary.
3.
The No. 1 condensate pump was disassembled for inspection and maintenance. The shaft was stainless steel metal sprayed in the packing area; the first staga impeller was built up with bronze and ground smooth. All bearings were replaced.
h.
The No. 2 boiler feed pump was disassembled for inspection and maintenance. Both inboard and outboard shaft sleeves were replaced.
The bearing J iners were renewed at both ends. Pump motor windings were retied and one connection was retaped. Rotor and stator were spray painted; new oil seals and gaskets were installed.
5 A general inspection of the moisture separators was performed; in addition, the left and right cone assembly, strut supparts and directional change deflectors were tested using the magnetic particle l
h technique. A crack in a vane of the L.H. separator was ground and welded. At the next refueling shutdown it would be advisable to replace three guide vanes and two water deflector plates.
6.
The pressuriner low and high set safety valves were disassembled.
The low set valve had been leaking. The seat was built up with stainless steel and machined to specification; a new disc was installed and lapped to the seat.
A new disc was also installed and lapped to the seat of the high set valve. ' lev springs veie installed on both valves.
It now will be possible to evaluate the performance of a stainless steel seat (low set valve) with that of a stellite seat (high set valve).
Instrumentation and Control The following is a list of pertinent instrumentation and control maintenance items performed by the plant staff during the month of April,1966, 1.
All primary plant instrumentation channels and feedwater system controls were recalibrated.
2.
New coaxial cables were installed between loop No. 2 pull box and neutron detector thimbles No's 2 and 3.
(l l 3.
Vapor container trip valves were tested at simulated high vapor container pressure; all valves operated normally.
. h.
The in-core instrumentation rack was inspected for flux wire tube damage; no abnormal conditions we e detected.
5 Temporary coaxial cable and control wiring were installed for the experimental fission chambers inserted in the flux wire thimbles.
Reactor Plant Performance Spent Fuel Pit Monitoring The spent h.9h% enriched assemblien were monitored durirg loading into the Boral spent fuel rack.
Elements were placed in every other storage position. During loading of the 36 assemblies into the rack, the shutdown was measured at 80 % AK/K, Core Loading Core loading was completed in approximately 35 hours4.050926e-4 days <br />0.00972 hours <br />5.787037e-5 weeks <br />1.33175e-5 months <br />. Followirg loading the measured shutdown margin was 7.8% AK/K; the coolant boron concentration was 2855 ppm.
Core VII Startup Physics Test Program This program commenced on April 29, at 1715 hours0.0198 days <br />0.476 hours <br />0.00284 weeks <br />6.525575e-4 months <br /> and was completed in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Test results were es follows:
Rod Worth l
g Group A:
1.0h%
Group C:
1.60%
Group B:
2.h7%
Group D:
4.72%
Groups C & D:
6.20%
Temperature Coefficient (1655 ppm boron): -1.35 x lo-AK/K/ F Boron Worth (1655 ppm boron): 8.5% AK/K A problem developed with Group C during cold rod exercises. At the 27 inch level during rod insertion, the primary indicating light showed that the group had dropped into the core without a scram breaker trip. This condition could not be repeated with further exercising of the group. It is possible that low voltage on the stationary gripper coil allowed the group to drop. Voltage adjustments to all the stationary gripper coils were made to prevent this occurrence.
During the cold rod exercises, three control rods stuck at the 6 inch primary indicating position. The rods dropped to zero without difficulty by operating the trip breakers.
This problem had been experienced during previous plant operation and is associated with the compression of the dashpot spri"g during the last six inches of rod travel.
In all instances full insertion of the rod was achieved by either operating the trip breakers or energizing the pull down coil.
-T-l Chemistry
^
During this shutdown the water in the shield tat'- cavity was exceptionally clear. This clarity is attributed to the newly installed j
adjustable stardpipe which can take suction at various levels thus preventing stratification of the shield tank cavity water. Water drawn through this
}
standpipe at '25 gpm passed through a 1-3 p filter and then into the low pressure surge tank where it joined the shutdown cooling flow of ' 25 gpm j
coming from # h loop hot leg.
Water taken from the low pressure surge tank pasged through the normal purification system consisting of a mixed bed B0 5) demineralizer and a 1-3 p filter before it was returned to the (H
3 l
reactor vessel through # h cold leg.
This purification process reduced the 8y activity levels in the shield tank cavity" from T.00 x 10 pc/ml to 2.06 x 10 pc/nl with an average of 4.81 x 10 pc/nl; tritium activity in the chi d tank cavity averaged 0.08 pc/ml during the shutdown.
Shield tank cavity boron concentration averaged 2830 ppm during and after ruel loading.
Commencing April 16, cavity water was drained through a 1-3u filter to the safety injection tank. On April 28 filling and venting of the main coolant system was completed and hydrazine was added to scavenge the residual oxygen.
Crud levels as high as 27.6 p7m were experienced during plant heatup after main coolant pumps were started.
Prior to this shutdown crud levels averaged 0.35 ppm.
On April 29 the main coolant boron concentration was decreased by dilution for physics testing and at the end of the period the concentration was 1991 ppm.
A crud sample collected from the shutdown cooling system on April 15 and corrected to the date of shutdown had the following radiochemical j
analyses: dpm/mg crud 1
I Cr-51 Hf-181 Mn-59 Fe-59 6
h S
5 1.2h x 10 3.41 x 10 8.46 x 10 3.39 x 10 1
l Co-58 Co-60 Ag-110M g l
6 6
h.Th x 10 1.03 x 10 1.02 x 10 Health and Safety During April the waste liquid releases totaled 100,713 gallons containing 164 pc of gross beta-gamma activity and 100.2 curies of tritium.
In addition to the above releases, 33h,608 gallons of water were discharged from the secondary plant. The total gross beta-gamma and tritium activities released from the secondary plant were 7.64 me and 54.37 me, respectively.
An additional 1.90 curies of tritium vapor was purged from the vapor container t'. trough the primary vent stack to the environment during the period.
_8_
Samples of vapor container atmosphere were collected from the shield tank cavity and the charging floor during reactor vessel head removal. No gaseous radionuclides were detected in these samples.
An attempt was made to reduce the radiation level around the reactor head area by flushing the control rod drive mechanisms. Curvey results indicate that the flush was ineffective; however, substantial crud vac removed from the housings.
Radiation curveys were performed on the reactor core barrel on April 10.
The measurements were taken with 3 feet and 6 feet of the barrel exposed above the vnter surface.
On April 12 a radiation survey was taken of the reactor veccel proper, with all internals removed. A similar survey was performed during the Core IV-V refueling.
One loose Charpy specimen was recovered from the lower support plate, and disposed of as vaste. The radiation level from the specimen was
'50 r/hr at h" in air.
Work area radiation levels for boring and tapping the reactor Vessel flange stud hole were reduced from 1.0 - 1.5 r/hr to 100-300 mr/hr through the use of a temporary shielding structure which was placed between the reactor vessel opening and the stud hole.
Radiation exposure doses icr Yankee personnel and N.E.P.S.Co.
lll personnel as measured by film badge, for the month of April, '968 vere:
Yankee Plant Pecconnel:
Average accumulated exposure dose 975 mrem Maximum accumulated exposure dose 2210 mrem N.E.P.S.Co. Personnel:
Average accumulated exposure dose 1320 crem Maximum accumulated exposure dose 2153 mrem.
l i
m YANKEE ATOMIC ELTTRIC COMPANY -- OPERATUiG
SUMMARY
APRIL 1"j68 RTFETRICAL P0 NTH IEAR TO DATE Gross Generation' WH 0
283,560,000 7,99h,hhh,600 Sta. Service (While Gen. Incl. Losses)
WH 0
19,751,333 532,h18,266 263,808,667 7, h 62,u 26,3 3!.
Net Output WH n
Station Service 0
6.9 "
6.66 Sta. Service (While Not Gen. Incl. Iosses)
WH 690,566 SS1,219 25,6S6,7h6 Ave. Gen. For ibnth 719.0 W
0 Ave. Gen. Running 0.0 W
0 PIANT PERFORMANCE Net Plant. Efficiency 0
27.88 28.37 Net Plant Heat Rate Bru/W H 12,2h1 12,029 Plant Operating Factor 0
Sh.32 72.61 Reactor Plant Availability 0
68.h6 82.72 NUCLEAR 10FTH CORE VI TOTAL Hours Critical HRS 1h.73 11,396 L" 55,122.15 Times Scrammed 0
3 5.3 Burnup Core Average ND/MPU 0
12,h18.76 Region Average ND/MPU A (DINER) 0 12,h93.537 29,266.08 B (MIDDLE) 0 1h,8ho.0h2 22,515.33 C (OtfrIR) 0 9,037.h32 9,oST.h3
t YANKEE ATOMIC RIC COMPANY DAILY AVERAGE IDAD for AFT)1L 1969 200 -
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