ML19340A109
| ML19340A109 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 04/13/1979 |
| From: | Knighton G Office of Nuclear Reactor Regulation |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7905140445 | |
| Download: ML19340A109 (10) | |
Text
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M APR I 3 7979
!!Et:0RANDUli FOR:
D. Zienann, Chief, Operating Reactors Branch #2, DDR
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FROM:
G. Knighton, Chief, Environnental Evaluation Branch,
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SUBJECT:
YANKEE R0WE - SECOND, THIRD AND FOURTH PHASE OF PER-
!W'ENT MODIFICATIONS TO SPEllT FUEL PIT (TAC 11428)
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PLANT NAME: Yankee Nuclear Power Station DOCKET N0.: 50-29 RESPONSIBLE BRANCH: ORB #2 PROJECT !% NAGER:
A. Burger REVIEW STATUS: EEB - Complete By letters dated February 7 and March 5, 1979, the Yankee Atonic Electric p"
Company (the licensee) requested changes to Specification 3.9.7, Refuel-ing Operations, of the Technical Specifications for Yankee Nuclear Power Station (Yankee Roue). The licensee requested that a temporary gate and shielding panels be listed in Specification 3.9.7 as exceptions to the requirenent that loads greater than 900 pounds are not allowed over the h
spent fuel pit. These two exceptions will allou the licensee to continue i;
U to upgrade the spent fuel pit at Yankee Rowe.
I The letter dated February 7,1979, is Supplenent No. 3 to the letter of i.
July 13, 1978, in which the licensee proposed extensive permanent inprove-nents to the pit at Yankee P. owe. The first phase of these irgrovements was evaluated in our nenorandun fron G. Knighton to D. Zienann dated n
October 17, 1978. The final three phases of these improvenents, install-ing a pit liner and division wall with gate in the pit and nodifying the the pit cooling systen, are discussed in detail in the licensee's letter dated February 7,1979.
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'!e have completed our review and evaluation of the proposed technical spe--
cification change.
The proposed changes to Specification 3.9.7 of the Yankee Roue Technical Specifications to permit the installation of the ten-s He conclude
? porary gate and shielding panels are acceptable as written.that carrying loads
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kpitisinconformancewithSpecification3.9.7(i.e.,theseloadsdonot
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have to be listed as exceptions to this specification) because spent fuel F
and water are not stored in this part of the pit. 1:e have also conclu@f that no additional restrictions are needed for the safe storage of spent p'
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fuel in the pit and that the occupational exposure to 60 all the construc-
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tion work to install the liner and division wall in the pit is as low as n
is reasonably achievable.
L l-Enclosed is a safety evaluation and environmental deteraination suitaole i
for inclusion in the Safety Evaluation.
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Driginal signed by lI GecrceW. Knighten George !!. Knighton, Chief i
Environmental Evaluation Branch p
8" Division of Operating Reactors
Enclosures:
As stated cc:
V. Stello B. Grimes ii R. Vollmer i
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74 NUCLEAR REGULATORY COMMISSION s..fg -j ; j.
WASHINGTON, D. C. 20555 gk I
j rga SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGijLATION SUPPORTING AMENDMENT NO.
TO LICENSE NC.
YANKEE ATOMIC ELECTRIC COMPANY YANKEE NUCLEAR POWER STATION DOCKET r40. 50-29 Introduction
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By letters dated February 7 and March 5,1979, the Yankee Atomic Electric Company (the licensee) requested changes to Specification 3.9.7, Refuel-
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ing Operations, of the Technical Specification for Yankee Nuclear Power
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Station (Yankee Rowe).
The licensee requested that a temporary gate and
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shielding panels be listed in Specification 3.9.7 as exceptions to the gg requirement that loads greater than 900 pounds are not allowed over the 1:i' spent fuel pit. These two exceptions to Specification 3.9.7 will allow
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the licensee to continue to upgrade his spent fuel pit at Yankee Rowe.
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The letter dated February 7,1979, is Supplement No. 3 tp the letter from the licensee, dated July 13, 1978, in which the licensee proposed permanent g
extensive improvements to the spent fuel pit at Yankee Rowe. The initial modifications which were evaluated in the Safety Evaluation dated October 6; 1978 have been completed by the licensee. The final three phases of these improvements to the spent fuel storage pit are aiscussed in detail in the letter dated February 7,1979.
Discussion In his letter cated February 7,1979, the licensee provided cetaileo in-formation on the proposed (1) installation of a stainless steel liner in the spent fuel pit, (2) installation of a full-width division wall with
!1 gate across the north end of the pit, (3) installation of spent fuel rack support fixtures on the bottom of the pit, (4) modification to enlarge the r
enclosed area of the Spent Fuel Pit Building, and (5) modification of the
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spent fuel pit cooling system. The following information is given in the licensee's letter dated February 7,1979.
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The licensee stated that because these mocifications must be carried out while spent fuel is stored in the pool, a temporary gate must be used to divide the pool roughly in half and to pemit dewatering and construction on one side while spent fuel is stored in the other. The spent fuel will
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-r be stored in the south end of the pit, the temporary gate will be installed in its support bracket and the north end of the pit will be dewatered to
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permit construction work to be done in this end of the pit. After this con-struction work has been completed, the north end will be flooded, the tempo-rary gate will be removed from the pit, the spent fuel will be moved into the north end of the pit,.the temporary gate will again be installed in its support bracket and the south end of the pit will be dewatered to permit construction work to be done in this end of the pit. After this construc-tion work has been completed, the south end of the pit will be flooded and the temporary gate will be removed from the pit. After the temporary gate has been removed, a diver will complete the final part of the construction work in the pit which is in the vicinity of the temporary gate and its sup-port bracket and could not be done before this time.
The temporary gate consists of two pieces which, when joined, form a wall 34 feet high dividing the pit into two parts. The bottom section will be lifted with the yard crane and moved to the enclosure building central hatch without passing over stored spent fuel. Once in position, the piece will be lowered onto support beams which rest on the pit walls. With the first sec-tion supported on the beams, the second piece is lifted, transported to the center hatch without passing over the fuel, and lowered into position. With the crane still attached, the pieces are bolted together. Then the' full gate is raised off the beams and lowered to its final position. Removal is the reverse of these steps.
Each section of the gate weighs approximately 14.1 tons and will be lifted using the 15 ton auxiliary hook. When the piec s are joined, they will be lifted with the 75 ton main hook.
Sealing around the installed gate will be by redundant continuous inflatable seals mounted on the support bracket so that loss of plant compressed air or one of the seals will not cause overall gate seal failure. The horizontal joint between the gate sections has a compressible segl for watertightness.
Before shipment to the site, the gat.e sections will be pressurized to verify watertightness. There are two independent barriers to leakage between the bracket plate and the concrete.
It will be necessary to reduce the radiation levels in the work zone, the dry side of the temporary gate. First, the spent fuel will be positioned as far from the gate as possible and graded so the oldest fuel is closest to the gate. Second, as much shielding as possible will be placed between the fuel racks and the gate. Third, using a 10 element rack next to the north wall when the fuel is in the north end of the pit, the first row of the racks can be emptied, providing a significant reduction in radiation.
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- Measurements of radiation have been taken close to the spent fuel in the pit. The radiation on the dry side of the temporary gate is conservatively estimated to be 10 to 20 R/hr. The licensee stated that it is, therefore, necessary to provide three tenth-value layers of additional shielding be-tween the spent fuel and gate. The shielding will be steel cased lead pan-els providing 4.75 inches of lead. Each panel weighs approximately 9.5 tons and will be lifted using the 15 ton auxiliary hook.
g The licensee estimates that removing fuel from the first row, using the shielding panels, and floodin'g the core of the lower gate section will pro-vide enough shielding to lower the radiation to less than 20 mr/hr. Con-crete shield plugs, which weigh less than a spent fuel assembly, will also be placed in the empty first row cavities. A survey will be taken and ad-ditional shielding placed on the dry side as required to eliminate any
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zones higher than 20 mr/hr.
The final effort to reduce radiation is in the construction schedule. Tak-ing advantage of the progress prior to November,1978, the schedule has been shortened so as to complete all liner installation before the next refuel-
~c ing outage. This will reduce radiation levels because there will be 36 less fuel elements stored when the north end is dewatered.
A division wall with a gate will be erected across the full width of the pool in at the north end to allow future dewatering of the fuel transfer area without affecting the fuel storage area. This will allow access for repair of the fuel transfer equipment and fuel transfer chute and will pro-vide capability for cask handling.
Spent fuel rack support fixtures will be installed to transfer loads from the spent fuel racks through the liner into the concrete structure. They also provide capability for future expansion of spent fuel storage capacity.
In his safety analysis of the proposed modifications of the pit, the licen-see stated that the movement of the shielding panels and each temporary gate section directly over stored spent fuel is prohibited, that all handling will be in accordance with approved written procedures and that redundant slings-i and lifting eyes are to be used.
The licensee evaluated the off-site consequences of the rupture of spent H
fuel in the unlikely event of an accidental drop into the pit. Assuming j
all the fuel in the pit is damaged, the resultant thyroid dose calculated by the licensee is 0.34 rem and the resultant whole body gamma dose is 0.05 rem. The licensee stated that these values are much less than the 10 CFR Part 100 limits.
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' During the construction work a pool cover will be placed over the storage area of the pool to prevent accidental entry of tools or debris into the wa-ter. All pieces making up the pool cover weigh under 900 pounds and will be installed following approved written procedures. This cover will be the same one used during installation of the center roof hatch.
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During the erection of the liner, rack supports and division wall, construc-tion materials weighing more than 900 pounds but less than 3000 pounds will be lifted into the pool. However, these loads will be lifted only over the de-watered portion of the pool, and an accidental drop will not affect the water h
volume on the other side of the temporary gate. These lifts will be made fol-lowing approved written procedures and only when the temporary gate is in place.
The temporary gate serves to retain cooling water around the spent fuel dur-1..
ing construction. The only active components are the pneumatic seals which
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are redundant.
If the smaller volume in the north end suddenly equalized
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over the full pool, the resultant water level would be 7 feet above the ac-tive fuel. This is sufficient to shield against radiation; and, since no fuel will be handled when the gate is in the pool, the consequences of a I,-
y fuel handling accident are not increased.
To provide cooling in the case of failure of the temporary gate during con-struction, pieces are to be installed in the cooling system suction piping ir to lower the inlet to 14 feet above the pool floor.
In the event of water equalization in the pit, the inlet will be 2 feet below the water surface and the pump will be throttled to 500 gpm to have sufficient net positive suction head. There are three water sources available as makeup to the pit.
The licensee addressed the effect of the installation work on the safety related function of the spent fuel pit. He concluded that there is no in-crease in the probability of an accident (or equipment malfunction) or of an accident of a different type which has not been analyzed, and the margins of safety which have been defined in the bases of the Technical Specifications have not been reduced. He also concluded that the new structures in the
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pool will represent a significant upgrade and increase in the margins of i
safety.
i By letter dated March 5, 1979, the licensee provided information on the oc-cupational exposure to install the liner, the rack support fixtures and the division wall in the pit. The licensee stated that the occupational ex-posure to do the work would be about 80 man-rem and that this exposure is as low as reasonably achievable. He states he plans to nove the spent fuel as far as possible from the areas of work in the pit with the fresh-est spent fuel being farthest o.ay.
He has added as many shield panels as possible between the spent fuel racks and the temporary gate. This is expected to lower the radiation level to that of the general area of the
m building. The walls of the pit will be cleaned and additional shielding may be used to cover hot spots. However, it is not practical to place enough shielding to lower the general area radiation level without interfer-ring with the construction work, increasing man-hours and, perhaps, posing a safety hazard to workers. The dose rate in the vicinity of the pool with only seven feet of water in the pool is estimated to be less than 10 mrem /
hour.
In addition, in this letter, the licensee explained that divers will be used in the final phase of upgrading the spent fuel pit to complete the in-stallation of the rack support structure in the pit. The diver will work in the vicinity of the temporary gate support bracket in the center of the pit for a few days. The licensee states that the spent fuel in the pit will be moved away from this area into both ends of the pit and shielding is not anticipated to be needed.
Evaluation We have reviewed and evaluated the licensee's proposals to (1) rearrange the existing spent fuel racks and spent fuel in the spent fuel pit, (2) install a temporary gate and shielding panels, (3) install a pit liner, (4). install a division wall with gate in the pit, (5) install a rack sup-port structure, and (6) modify and upgrade the pit cooling system. Only the licensee's proposal to install the temporary gate and shield panels in the pit involves proposed changes to the Yankee Rowe Technical Specifica-tions.
The spent fuel racks and spent fuel are being relocated in the pit to al-low the licensee to install the liner and the division wall in the pit with a minimum of occupational exposure. After the spent fuel racks and spent fuel have been relocated, a temporary gate will be installed in the pit and the part of the pit without fuel will be dewatered. The gate and the bracket it is in have redundant barriers to leakage into the dewatered part of the pit.
If this gate fails, the water level will equalize at a minimum of 7 feet above the fuel. The resulting dose rate in the vicinity of the pit is estimated to be about 10 mrem /hr. This dose rate is only about an order of magnitude greater than dose rates typical for the vicinity of the pit. There are at least three sources of water available as makeup to the pool to raise the water level and the pit cooling system would be able to operate, although at reduced flow, at the minimum water level. The spent fuel racks are those that have been reviewed and accepted by NRC in the spent fuel pit modification safety evaluation issued by NRC in Decem-ber 1976.
Based on the above, we conclude that no additional restrictions are needed for the safe storage of spent fuel in the pit.
The licensee has proposed to install a liner, a division wall with gate, and a rack support structure in the pit and to modify and upgrade the pit cooling system. These are improvements to the spent fuel pit at Yankee
. Rowe and do not affect the potential consequences of the postulated design basis accidents for the spent fuel pit and ere, therefore, acceptable. The licensee has not submitted an analysis for the cask drop accident to be re-viewed and approved by the staff. Until this is done, the licensee is pro-hibited from bringing a spent fuel shipping cask near the pit to preclude t
the cask from tipping or dropping onto spent fuel in the pit.
To permit instabation of a temporary gate and shielding panels in the sup-port brackets which have been previously installed in the pit, the licensee has proposed changes to Specification 3.9.7 of the Yankee Rowe Technical Specifications. Because each weighs more than 900 pounds, the licensee pro-poses to include them in the list of excepted weights in Specification 3.9.7.
The temporary gate is needed to permit the dewatering of one half of the pit while the other half continues to store the spent fuel.
The shielding panels
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are needed to reduce the occupational exposure to the workers in the dry half of the pool to reasonable levels while they are installing the pit liner and division wall. Neither the temporary gate nor the shield panels will be al-lowed over spent fuel. They will be handled only in accordance with approved written procedures. Also, they will be lifted using a hook capable of lift-e ing them with redundant lifting. cables to protect against failure of a sling.
This should prevent the temporary gate and shielding panels frcm falling or tipping into the pit.
We have considered the potential consequences of the temporary gate and shielding panels falling or tipping into the part of the pit containing spent fuel. The temporary gate and shielding panels are in sections with heights about half the depth of the pit.
If they fall or tip into the pit while they are being placed in the temporary gate support brackets, they could damage all the spent fuel in the pit. The licensee has not presented an evaluation of the extent of damage to spent fuel in this accident.
If all the spent fuel in the pit has decayed at least 60 days, the potential consequences of dropping or tipping the temporary gate into the pit are well within the exposure guide-lines of 10 CFR Part 100 and are, therefore, acceptable.
This would also be true if 36 additional assemblies (a refueling) also with 60 days decay were added to the present number in the pit.
Because all the spent fuel in the pit has decayed 150 days since the last refueling (October 21,1979),the potential consequences of this accident are less than one percent of the exposure guidelines of 10 CFR Part 100.
Based on the abcve, we conclude that the proposed changes to Specification 3.9.7 of the Yankee Rowe Technical Specifications are acceptable as writ-ten. These changes do not affect the potential consequences of the postu-lated design basis accidents for the spent fuel pit.
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. There will be other loads greater than 900 pounds which will be carried over the spent fuel pit. These loads will only be carried over the de-watered part of the pit which will not have spent fuel in it.
Because of this fact, we conclude that these loads do not have to be listed in Spe-cification 3.9.7 as exceptions to the requirement that no loads over 900 pounds are allowed over the pit.
In other words, the spent fuel pit in Specification 3.9.7 refers only to that part of the pit containing water and spent fuel.
We have reviewed the licensee's plan for installation of a liner, a divi-sion wall with gate and the rack support structure in the spent fuel pit with respect to occupational exposure. The licensee estimates that the occupational exposure to do all the installation work in the pit is 80 man-rem. We consider this to be conservative and as low as is reasonably achievable as discussed below. The licensee is moving the spent fuel as
~~c far as possible from the work area with the freshest spent fuel at the greatest distance. He will clean the walls of the pit. The licensee will place as many lead shield panels as possible between the spent fuel racks and the temporary gate. The core of the lower section of the tempo-rary gate will be flooded.
Concrete shield plugs will be placed in the empty cavities in the spent fuel racks near the gate.
In addition, the' licensee is doing the construction work in the pit before the next refuel-ing outage when 36 fresh spent fuel assemblies will be added to the pit.
In the final phase of work, the licensee will use a diver in the pool after-the temporary gate in the pit has been removed. The diver will complete in a few days the installation of the rack support structure in the middle of the pit in the vicinity of the temporary gate and its support bracket.
This work cannot be done with the temporary gate in place. The spent fuel in the pit will be placed at both ends of the pit away from this work area.
The licensee has looked at additional shielding but does not anticipate that any will be needed. The licensee stated, by telephone, that the shielded work enclosure, which we reviewed in our previous Safety Evaluation dated October 6,1978, cannot be used because of the nature of the work to be done by the diver.
Based on this, we conclude that the licensee is doing every-thing reasonable to reduce occupational exposure during the construction work to upgrade the pit.
i-Environmental Considerations 1
We have determined that the amendment does not authorize a change in ef-J fluent types or an increase in total amounts of effluents nor an increase J
in power level and will not result in any significant environmental im-pact. Having made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and pursuant to 10 CFR Part 51.5(d)(4), that an e
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environmental statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of this amendment.
Conclusion We have concluded the proposed changes to Specification 3.9.7 of the Yankee Rowe Technical Specifications to permit installation of the temporary gate i
and shielding panels in the spent fuel pit are acceptable as written.
i We have also concluded that:
(1) because the amendments do not involve a significant increase in probability or consequences of accidents previously I
considered and do not involve a significant decrease in a safety margin, the amendments do not involve a significant hazards consideration, (2) there is reasonable assurance tht the health and safety of the public will not be en-F dangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issu-F ance of these amendments will not be inimical to the common defense and F
security or to the health and safety of the public.
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