L-87-279, Forwards Addl Info Re Continued Use of Boraflex at Facility, Per 870609 Request.Boraflex Is Neutron Absorbing Poison Used in Spent Fuel Racks,Assuring Shutdown Margin of 5% W/No Boron in Spent Fuel Pool Water

Forwards Addl Info Re Continued Use of Boraflex at Facility, Per 870609 Request.Boraflex Is Neutron Absorbing Poison Used in Spent Fuel Racks,Assuring Shutdown Margin of 5% W/No Boron in Spent Fuel Pool Water

ML17342A761
Person / Time
Site:	Point Beach, Turkey Point, Quad Cities, 05000000
Issue date:	07/10/1987
From:	Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
L-87-279, NUDOCS 8707200004
Download: ML17342A761 (31)

Text

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REGULATORY ORMATION DISTRIBUTION SYS 1 (RIDS)

ACCESSION NBR: 8707200004 DOC. DATE: 87/07/10 NOTARIZED:

NO FACIL: 50-250 Turkey Point Planti Unit Si Florida Power and Light C

50-251 Turkey Point Planti Unit 4i Florida Power and Light C AUTH. NAME AUTHOR AFFILIATION MOODY> C. O.

Florida Power 8c Light Co.

REC'IP. NAME REC IP IENT *FFILI ATION Document Control Branch (Document Control Desk)

DOCKET 0 05000250 05000251

SUBJECT:

Forwards addi info re continued use of Boraflex at facilitgi per 870609 request. Boraflex is neutron absorbing poison used in spent fuel racks'ssuring shutdown margin of 5/ w/no boron in spent fuel pool water.

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JULY 10 1987 L-87-279 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20SS5 Gentlemen:

Re:

Turkey Point Units 3 and 4 Docket No. 50-250 and 50-25 I Request for Additional Information Boraflex Usa e at Turke Point Attached is Florida Power

& Light Company's response to your June 9,

l987 request for additional information concerning the continued use of Boraflex at Turkey Point.

Should there be further questions, please contact us.

Very truly yours, C. O. Wo Group Vice President Nuclear Energy COW/RG/gp Attachment cc:

Dr. J. Nelson Grace, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, Turkey Point Plant P

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Reques for Additional Information Bor ex Usage at Turkey Point uestion 1

Based on the recent experience pertaining to degradation of Boraflex in spent fuel pools at Quad Cities and Point Beach Nuclear Power Plants, provide justification to demonstrate the continued acceptability of Boraflex for application in the Turkey Point spent fuel pool.

~Ree once Boraflex is the neutron absorbing poison used in the Turkey Point spent fuel racks.

This material assures a shutdown margin of 5% with no boron in the spent fuel pool water.

As discussed in Section 4.7.2 of the Turkey Point Units 3 and 4

S ent Fuel Stora e Modification, Safety Analysis Report, dated March 14,

1984, Boraflex has undergone extensive qualification testing to study the effects of gamma and neutron irradiation in various environments and to verify its structural integrity and stability as a neutron absorbing material.

These tests indicated that Boraflex maintains its neutron attentuation capabilities when subjected to an environment of borated water and 1.03 x 10 rads gamma radiation.

Additionally, ll further tests have recently 'been conducted and preliminary results indicate that some shrinkage (a maximum of about 2%)

can occur in Boraflex,

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and that this shrinkage is compl'ete at approximately 1 x 10 rads gamma.

10 Three plants have reported the results of their first Boraflex surveillance.

Of these three; the Boraflex material used at Point Beach Nuclear Power Plant has received the highest accumulated.

dose.

This Boraflex material has been in use for a total of five years,'nd some of the Boraflex panels have received a

20 year-equivalent radiation dose due to the spent fuel management techniques used at Point Beach.

The examination of the 2"

x'" sample coupons at Point Beach (which had a maximum exposure of 1.6 x 10 rads gamma) showed 10 that the coupons had experienced changes in physical characteristics such as color, size,

hardness, and brittleness.

However, the nuclear characteristics of the samples had not experienced any unexpected

changes, and the boron absorbing properties of the samples met the acceptance criteria for maintaining the 5% P k/k shutdown margin.

Point Beach also examined two full size (150" long x 8" wide) Boraflex

panels, which had a maximum exposure of about 1 x 10 rads gamma.

These panels had a far lesser 10 amount of physical changes than the 2" x 2" sample coupons.

Thus, the examination of the Point Beach

coupons and Boraflex panels indicates that, while some physical changes in Boraflex may occur with accelerated radiation exposure, the Boraflex will retain its neutron absorbing characteristics.

Prairie Island has also examined two large (8"

x 12") Boraflex coupons.

One of the coupons (which 1

had a

6 month exposure) had an appearance similar to the as-manufactured Boraflex.

The other coupon

/

(which had a

12 month exposure) had some slight physical changes similar to that experienced by the Boraflex panels at Point Beach.

The Boraflex panels in the Quad Cities racks (which had an exposure of about 10 rads gamma) were 9

examined by a neutron surveillance technique.

Gaps were noted in the Boraflex panels, and review of the size and number of gaps was performed.

This review indicated that the gaps were attributed to a rack design and fabrication process which did not allow the Boraflex to shrink without cracking.

The Quad Cities racks were designed to hold smaller BWR fuel and did not utilize a protective wrapper for installing the Boraflex.

The fabrication process required the Boraflex material to be glued and firmly clamped in place to the stainless steel

fuel rack walls.

This process did not allow for the predicted shrinkage of Boraflex and as such gaps developed.

Additionally, the Boraflex panels at Quad Cities were not constructed from a single sheet of Boraflex, resulting in pre-existing breaks in the Boraflex panels.

Less than half of the Boraflex panels at Quad Cities had gaps.

Furthermore, the gaps in the Boraflex panels at Quad Cities varied in length up to a maximum of 4" and were located at various places along the heighth of the panels.-

A k-effective analysis of the Quad Cities spent fuel pool demonstrated that these gaps did not cause Quad Cities to exceed its 0.95 limit on k-effective.

Turkey Point racks are designed to hold the large PWR fuel assemblies.

Boraflex panels were constructed H

from a single sheet of Boraflex and are held in the stainless steel cell wall by enclosing it with a wrapper plate.

During fabrication, a cut-to-length sheet of Boraflex was attached to the wrapper plate with adhesive applied in short lengths (up to 2 1/2" long) at a maximum of 16 places (8 per side) along the length of the 'Boraflex.

The purpose of the adhesive was to provide temporary support

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during the spot welding process and not for long-term

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binding.

The wrapper provides an enclosure which protects the Boraflex from the flow of water, very much like that used in the original Boraflex qualification testing.

Additionally, the wrapper enables the Boraflex panel to remain in place without the necessity of tightly clamping the panel in place.

In conclusion, the experience at Point Beach indicates that some physical changes may occur in Boraflex, but that the Boraflex will retain its neutron attentuation properties.

Additionally, both testing of Boraflex and the experience at Quad Cities indicates that some shrinkage in.Boraflex may occur, but that this shrinkage is limited to a maximum of 2 to 3% of the length of the Boraflex.

The Quad Cities Boraflex panels had some gaps because the racks did not permit the Boraflex to shrink without cracking.

Since there are differences in the manufacturing process of the Boraflex used at Quad Cities and Turkey Point, the experience at Quad Cities may not be applicable to Turkey Point.

In any case, due to the small size and the random orientation of the gaps at Quad Citites, the gaps did not cause the k-effective of Quad Cities spent fuel pool 'to exceed the 0.95 limit.

Therefore, FPL cons)det's that the Boraflex is acceptable for continued use at Turkey Point.

uestion 2

Based on the recent information, provide any changes to the in-service surveillance program for Boraflex neutron absorbing material and describe the frequency of examination and acceptance criteria for continued use.

Provide the procedures for testing the Boraflex material and interpretation of test data.

~Ree once To confirm that the Boraflex at Turkey Point is acceptable for continued

use, FPL will conduct two types of examinations of the Boraflex.

First, as described in the Turkey Point Units 3 and 4

S ent Fuel Stora e Facilit Modification, Safety Analysis Report, dated March 14, 1984.

Section 4.8, Testin and In-service Surveillance, FPL will conduct an in-service surveillance program.

This program will evaluate both Region I and Region II Boraflex samples for the following:

Physical Characteristics A.

Examine the stainless steel jacket and B.

note whether the material is smooth or exhibits any vis'ible damage.

Examine the Boraflex poison sample and note whether the material is smooth

or exhibits any visible changes (color, pitting or cracking, etc.).

C.

Measure specimen(s) weight and volume, and calculate its density.

D.

Measure the hardness of the specimen(s).

II.

Nuclear Characteristics A.

Take a neutron radiograph of the specimen(s) to determine the uniformity of boron distribution.

B.

Perform attenuation measurement of the specimen(s),

and determine the Bl0 loading.

The minimum area.'ensity of boron should be equal to or greater than 0.02 gm/cm 2 for Region I and 0.012 gm/cm for Region 2

Second, FPL will conduct a surveillance program to detect any spatial distribution anomalies in the Boraflex panels.

This program, ca'I-1ed "Blackness Testing", will-involve the use of a fast neutron source and thermal neutron detectors.

The thermal neutron detectors will be connected to four chart recorders which will record the presence of thermal neutrons.

The number of thermal neutrons will be low if the boron carbide is present in the Boraflex material.

If gaps or voids are present, the number of thermal neutrons will increase and

be recorded by the chart, recorders.

This arrangement of instruments would detect gaps or anomalies in the Boraflex panels.

The Blackness Testing technique was utilized successfully by Quad Cities to determine the existence of gaps in their spent fuel racks.

FPL will perform the baseline testing in late July or early August for several storage cells in both Region I and Region II that have received the hig'hest cumulated exposure to date.

FPL will then retest these cells on a regular interval to be determined at a later date.

This interval will be based on FPL's results and EPRI and industry data.

FPL's surveillance programs will be sufficient to detect any changes in the neutron attentuation properties of the Boraflex and any changes in the physical distribution of the Boraflex.

As a result, these programs will assure that the Boraflex in the Turkey Point spent fuel racks will be acceptable for continued use.

uestion 3

Describe the corrective actions to be taken if degraded Boraflex specimens or absorber is found in the spent fuel pool.

i

~Res onse FPL will follow the industry efforts concerning the performance of Boraflex.

EPRI, Bisco (the manufacturers of Boraflex) and several utilities are analyzing data as it becomes available and will notify the industry of the results.

FPL will evaluate these results and determine whether any additional actions are warranted for the Turkey Point spent fuel racks.

A sensitivity study has been performed to determine whether the Boraflex material at Turkey Point would be acceptable if it develops".

gaps.

As discussed above, tests and the Quad Cities surveillances indicate that 2% shrinkage could occur.

If it is conservatively assumed that this shrinkage would cause gaps in the Turkey Point Boraflex, the shrinkage could result in a two or three inch gap.

If it is postulated that such gaps would occur in every Boraflex panel at exactly the same location (which is an extremely conservative and unrealistic assumption based on the Quad Cities data),

the attached curves show that the Turkey Point spent fuel pool would still maintain the required shutdown'argin.

This shutdown margin does not account for.the 1950 ppm boron in solution which adds an additional 30%/ k/k shutdown margin.

P

10 Therefore, should *the Boraflex degrade, the spent fuel could still be stored at Turkey Point with the required shutdown margin.

,I 4

LTTACREHT A study hae been completed to determine the affect of geps in 50ROFLEX poison plates on spent fuel rack X ff.

The basta for this study vas

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ff'he Turkey Point Unit 3 Region 1 spent fuel storage rac'ks.

Axial gapa tn the MROHaKK za?lgtng from 0 to 10'ere modeled

~xpltcttly using XRHOi These gape ver ~ modeled tn one half of and tn all of the poison plates tn the rack.

The results from the XENO calculattons vere applted as adders to the ortgtnally oelculated rack X ff and uncertainties.

The 4etatls of the eff calculation of the original X ffvtth uncertatnttes are attache4.

eff The KENO calculations and the original criticality analysts assume a

mestiza U-235 enrichment of 4.5 v/o.

The results are presented tn Ftgures 1 and 2.

It vae also requested that the same type of data be provided vtth a maximum U.235 enrichment of 4.1 v/o assumed.

The origtnal criticality

~nalyste tncludod a study vhtch shoved the sensitivity of rack K<<f to fuel enrichment for the Region 1 spent fuel racks.

Thts study vas used to determine that the decrease tn U-235 enrtchment from 4.5 v/o to 4.1 v/o results tn'a 0.018 hg decrease in rack X ff.

This smail change tn eff'uel enrichment does not stgntftcantly effect the reactivity vorth Df the gapa tn the poison plates.

The data for the study using the 4.1 v/o fuel vas produoed by subtracting tho 0.01g dX from ths results af 4q 44 ar/u %uk~.

Xho saaulta af'~ ~accede aery ~

presented tn ttgures 1 an4 3.

The data presented tn this report are the results of a detatled senetttvtty study and are repreeentattve of the results that vould come frea a complete reanalysis of the Turkey Potnt Unit 3 Regton 1 spent fuel storage raoks.

The following text waa taken directly from the Turkey Point crftfcalit$

analysis report, Based on the analyafa describe

above, the following equation fa us<<<<,

develop the final K ff for the Turkey tofnt Region 1 spent fuel storage raoks:

K K

~ff nominal method part mech nominal

+ B method mech Where:

Knominal - nominal case KENO K ff- 0.9150 of!

Smethod method bias detemfned from benchmark critical comparisons

~ 0.0 aK art as to account for poison particle self-ahi a 1ding

.0025 dK B

h bias to account for material thfckness and construction

, tolerance

~ 0,00740 hK i 1>> 95/95 unoertainty in the nominal case KENO K ff ~ 0.00401 hR ks th d ~ 95/95 uncertainty fn the method bfas ~ 0.013 hK 95/95 uncertafnty associated vfth material thickness and construction tolerancee

~ 0.00721 hK Substftuting calculated values in the order listed above, tha result ia; K ff 0.9150 + 0.0 + 0.0025 + 0.00740 + {(0.00401)

+ (0.013)

+ (0.00721)

)

~ 0.9403

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