ML19093A992

Response to Request for Additional Information Concerning High Density Spent Fuel Storage Racks for Surry Units 1 & 2

ML19093A992
Person / Time
Site:	Surry
Issue date:	09/15/1977
From:	Stallings C Virginia Electric & Power Co (VEPCO)
To:	Case E, Reid R Office of Nuclear Reactor Regulation
References
Download: ML19093A992 (5)

Text

e e VIRGINIA. ELECTRIC A.ND POWER COMP.A RIOHMOND, VIRGINIA 23261 September 15, 1977 Mr. Edson G. Case, Acting Director Serial No. 369/081877 Office of Nuclear Reactor Regulation PO&M/HSM: bep/mc Attn: Mr. Robert W. Reid, Chief Docket Nos. 50-280 Operating Reactors Branch No. 4 50-281 DivisiOn of Operating Reactors License Nos. DPR-32 U. S. Nuclear Regulatory Commission DPR-37 Washington, D. t. 20555

Dear Mr. Case:

RESPONSE TO REQUEST.ADDITIQNAL.INFORMATION

.. HIGH. DENSITY. SPENT. FUEL. STORAGE. RACKS

.. SURRY POWER. STATION UNITS* 1. AND 2 The attached information concerning the High Density Spent Fuel Storage Racks for Surry Uni ts 1 and 2 is being* provided in response to your 1etter of August 18, 1977.

Also attached are 40 copies of a revision to our High Density Spent Fuel Rack submittal forwarded to you in our letter of May 27, 1977. This revision is necessary due to changes in the detailed design of the High Density Spent Fuel Storage Racks. *

• Very truly yours,

~.)11. vffiectozy)

C. M. Stallings Vice Presi de.nt - Power Supply and Production Operations Attachments Mr. James P. O'Reilly Office of Inspection & Enforcement Region II

. Ques~ion 1:

e e Provide the volume of material to be removed from the spent fuel pool (e.g. spent fuel racks, seismic restraints) because of the proposed modification.

Response

The only items to be removed from the spent fuel pool during this modification will be the existing spent fuel racks. There are twenty-nine (29) rack spaces in the pool, but only twenty-six (26) racks are currently installed. Each rack weighs approximately 3300 pounds. This means that a total of 85,800 pounds of stain-less steel, in the form of spent fuel racks, will be removed from the spent fuel pool. The demensions of each rack are 6 1 10 l/8 11 x 6 1 l O 1/8 11 x 13 1 l 011

• Each rack occupies 648 cubic feet. The tota 1 volume of the 26 racks to be removed is 16,850 cubic feet.

Question 2: Explain why no equipment modifications for the Fuel Pool Purifi-cation System were proposed. Consider that the proposed SFP modification may result in a factor of approximately ten times more fuel movements during the modification than during a normal refueling which may increase the levei of crud in the pool above that expected during a normal refueling. Justify why the Fuel Pool Purification System is adequate to maintain low fuel pool concentrations of radioactivity including cruds~ that there are reasonably low exposure levels in and around the fuel pool are~

during and after the modification.

It is true that this modification will result in many more fuel movements than during a normal refueling (-370 assemblies moved rather than -1;3 to -1;2 of a core oi -50 to -so assemblies).

A point which should be considered, however, is the time period during which this fuel movement takes place. A normal refueling shuffle optimally takes place in about 5 days whereas the fuel rack installation and associated fuel movement will take place over a period of about 45 days or more. Operational experience at*

Surry has shown the purification system to be adequate during normal refuelings. Therefore, based on the time period involved and the acceptable operation of the system to date, it should be adequate for this modification. If necessary the filters and resins in the fuel pool purification system will be changed out during this modification. The criteria for changing these fil-ters and resins are discussed in the response to question 3.

Questi9n 3: Provide the following information on the operation of the Fuel Pool Purification System (FPPS) and discuss any expected changes due to the proposed modification: (1) when during a year the FPPS is normally run, (2) whether both the filter and the demini-ralizer are operating when the FPPS is run, (3) the normal flow rate through the FPPS when it is run and (4) the basis for chang-ing the filter and the demineralizer. Specify the expected change in the frequency of changing the filter and demineralizer resin due to the proposed modiciations. Estimate the change in plant

man- rem exp! re for more frequent cha.ng fog demineralizer resin.

I the filter and

Response

Operational experience to date indicates that the purifi-cation system has performed satisfactorily. The normal flow rate for the purification system is 110 gpm and remains in oper-ation continously to maintain a clean and clear pool. The maxi-mum all6wable differential pressure across the filter is 15 psi.

The maximum allowable differ~ntial pressure across the deminera-lizer is 25 psi. If the ~p across the filter or demineralizer exceeds the allowable value, the filter is replaced or the resin

. is replenished respectively.

The radiation levels at the demineralizer are usually from 1 R/hr to 4 R/hr. The filters are normally changed because*of

.high ~p and usually have radiation levels of about 100 mR/hr.

The filters are normally changed prior to each refueling, i.e.

twice per year. In changing the filters an individual receives an exposure of about 150 mR. In replacing the resins in the demineralizer, approximately 55 mR is received. This exposure is divided among three individuals.

This information is also provided on page 17 of the Surry Power Station Spent Fuel Rack Submittal dated May 20, 1977.

During the high density spent fuel rack modification the filters and res*!ns will be chnnged.out bused en the criteria stated above. Based on past experience and the number of fuel assemblies to be transferred versus the number of assemblies normally moved per year, it is estimated that the filters and resins will be changed a maximum of six times. This would re-sult in an additional 1.025 man-rem over the normal annual in-plant man-rem exposure.

Question 4: Specify the average burnup expected for the spent fuel in the pool. '

Response

The maximum average expected burnup of the fuel to be stored in the spent fuel pool is 35,000 MWD/MTU.

Question 5: Provide an estimate of the man-rem exposure that will be received during the removal and disposal of the old racks and the instal-lation of the new ones. The estimate should include the number of workers involved in each phase of the operation including divers, if any, the duration of the operation, the exposure rate for each phase of the operation, and *the total man-rem received by all work-ers involved. Relevant experience may be cited.

e

Response

The installation of the new high density spent fuel racks is presently planned to be done remotely frbm poolside without the use of divers. It is conservatively estimated that 6 work-ers will be required for this operation and that one rack can be installed during two (2) eight (8) hour shifts (12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> work in the fuel building). For the 29 racks to be installed, it is estimated that the total exposure will be 3.2 Rem. Removal of the old spent fuel racks will be a very straight-forward procedure as they will be lifted out of the pool and washed down with de-mineralized water. Experience at Maine Yankee has shown.this pro-

. cedure will decontaminate racks like the Surry racks to levels less than 25 mR/hr. Any hot spots will be eliminated through use of a hydrolaser, (high pressure water spray). It is planned that the old spent fuel racks will be wrapped in polyethylene sheet*and stored on site temporarily until ultimate disposal.

To lift the old racks out of the pool, decontaminate them, and

. wrap them in polyethylene sheets should take no more than half

. an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> shift (3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> work) and a crew of 4 rem. This re-

. sults in a total exposure for removal of 26 racks of 7.8 man-rem.

The total exposure for this modification will be conservatively 11 . 0 man-rem.

Question 6: Provide an estimate of the annual man-rem expected from all oper-at*i.or.*1.s

~ - - -

i.*.i-1_ t_f_-_1.: ._ -.--1i"'-11+

'

• l I .. _. .....

.cl.- 1 ~""l I .At:: I !--' u u I fc::cp,

\.JI  ! ::,v,o::,

u I \.,, u.

h::,c:on Qn

- ...... oJ - -

• I the nrPc;ent

... I

• I . - - l. -*

concentration of the radionuclicies identified in the SFP watef and the crud build-up along the sides of the pool and its remo-val. Describe the impact of the'proposed modification (e.g.

additional elements and crud) on this estimates.

Response

The concentrations of radionuclides identified in the spent fuel pool water and the crud buildup along the sides of the pool result in an insignificant part of the exposure levels currently experienced. The exposure levels noted on page 19 of the Surry

. High Density Spent Fuel Rack Submittal are primarily a result of the radiation levels of the spent fuel stored in the pool and not of the radionuclides in the water and the crud on the sides of the pool. As noted on page 45 of the Surry High Density Spent Fuel Rack submittal, it is expected that as a result of the pro-posed change the exposure rates presently experienced during unit operation will increase slightly. However, even if those exposure rates were to increase by a factor of 5, the exposure would still, be a relatively minor contribution to the total station exposure.

-~-1

. 27 .

.J e A 9

Rev. 1 9-15-77 6.0 DESIGN OF HIGH DENSITY SPENT FUEL STORAGE RACKS 6.1 Design Bases

~The high density spent fuel storage racks are designed to pro-vide storage locations for up to lOL14 fuel assemblies and are design-ed to maintain the stored fuel, having an equivalent uranium enrich-ment of 3.5 weight percent U-235 in uo 2 , in a safe; coolable, and subcritical configuration under all conditions.

6.2 Storage Rack Description Each new fuel storage rack consists of a six by six array of fuel storage cells which are square stainless steel boxes spaced nominally 14 inches on centers. The rack is shown on the general arrangement

-"'drawing (Figure 6.0-1), attached.

The fuel storage rack has two basic components: the support structure and the fuel storage cell. The support structure co~sists prima~ily of the four corner storage cells which interface with the spent fuel pool floor pads and two horizontal grid members which are supported by the four corner cells and which maintain the horizontal position and vertical alignment of the remaining thirty-two (inner) storage cells. The inner storage cells res~ directly on the spent fuel pool floor. Diagonal bracing is provided on the struct~rP :,,

accommodate the loads imposed by rack installation, by fuel handling and by the seismic events.

The horizontal seismic loads are transmitted from the rack struc-ture to the spent fuel pool floor through restraint devices which cap-ture che existing spent fuel pool floor pads and which mate with the fuel rack structure corner cells. Leveling of the fuel racks will be accomplished through the use of shims and will require no modifica ti.on of the existing fuel rack support pad. The vertical seismic loads are essentially transmitted directly to the pool floor by each storage cell.

No bracing to the pool wall is required to support the racks during a seismic event.

Each corner storage cell is nominally 9.44 inches square (O.D) by

'v172 inches long with 0.250 inch walls. Each of the thirty-two inner storage cells is nominally 9.12 inches square (O.D) by 'v170 inches long with 0.090 inch walls. The cells are flared at the top to aid in insertion of the fuel assembly into the cell. Attached to the bot-tom of each cell are four stainless steel posts which support the fuel assembly. The posts attached to the thirty-two inner cells rest direct-.

ly on the floor of the spent fuel pool and space the cells off the pool floor a sufficient distance to assure adequate area for cooling flow.

To accomodate any unlevelness in the pool floor liner, the rack is designed to permit the inner cells to move vertically within the rack structure (a+/- 1 inch motion is provided). The inner cells, however, are positively locked into the support structure so that they cannot be inadvertently lifted out of the rack.