ML19296B544

Affidavit Forwarding Safety Evaluation Analysis of McGuire Spent Fuel Pool Containing Oconee Spent Fuel for cask-drop Accident.Prof Qualification Encl

ML19296B544
Person / Time
Site:	07002623
Issue date:	01/31/1980
From:	Marotta C NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
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ML19296B538	List: ML19296B537 ML19296B542 ML19296B544 ML19296B546 ML19296B548
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UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING BOARD In the Matter of

)

)

DUKE POWER COMPANY

)

Docket No. 70-2623 (Amendment to Materials License SNM-1773 for Oconee Nuclear Station

)

Spent Fuel Transportation and Storage )

at McGuire Nuclear Station)

)

AFFIDAVIT OF CHARLES R. MAR 0TTA I.

Charles R. Marotta, being duly sworn, do depose and state:

1.

I am employed by the Office of Nuclear Material Safety and Safeguards (HMSS), Branch, of the U.S. Nuclear Regulatory Commission.

I perform criticality calculations as part of my responsibility in employment with the U. S. Huclear Regulatory Commission.

2.

(A copy of my professional qualifications is attached to this Affidavit as Appendix 8.)

3.

This affidavit addresses Board questions (Tr. 4027;4432-47),

concerning whether fuel stored in the McGuire Unit I spent fuel pool would remain suberitical if a 25-ton truck cask fell onto spent fuel stored in the McGuire Unit 1 pool while being trar.:ferred to the McGuire cask unloading pit.

4.

My approach to analysis of the postulated question was an extremely conservative one based on an assumption of complete failure of the racks in which the spent fuel is stored.

This is because I did not have available go02gio 017

2-to me a structural analysis on which I could assume that the rack structure would fail at less than complete failure.

5.

My analysis shows that subcriticality can always be assured for the spent Oconee fuel with 2000 ppm boron in the pool water. For the fresh ficGuire fuel, suberiticality will be assured with at least 2000 ppm boron if the average fuel enrichment is 2.6% uranium-235 by weight. Subcriticality will be assured with at least 3000 ppm boron if the maximum enrichment of 3.5% uranium - 235 by weight (the maxinun licensed enrichment allowed) is utilized.

6.

The attached analysis (Appendix A) of the postulated 25-ton spent fuel cask drop into the McGuire Unit 1 spent fuel pool is adopted as part of my affidavit.

I hereby certify that the above statements are true and correct to the best of my knowledge and belief.

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Charles R. Marotta Subscribed and sworn to before me this M day of January,1980 4._

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APPENDIX A NRC CRITICALITY ANALYSIS OF THE McGUIRE SPENT FUEL POOL CONTAINING OCONEE SPENT FUEL FOR THE CASK-DROP ACCIDENT by C. R. Marotta U. S. Nuclear Regulatory Commission NMSS 1.

Introduction and Conclusions This memorandum gives a summary of the criticality analyses performed by the NRC staff in the safety evaluation of the McGuire pool containing Oconee and McGuire fuel for the cask-drop accident.

The KEND Monte Carlo computer program together with the 123-group GAM-THERMOS neutron cross-section set was used for all the estimates of pool reactivity for various fuel assembly spacings and boric acid concentrations in the water.

The primary mechanism considered in increasing reactivity of the pool ontaining at least 2000 ppm natural boron (boric acid in solution) for a cask-drop accident was:

the movement of intact fuel assemblies from safe center-to-center spacings (15.5") to zero water thickness between assemblies.

Further crushing of individual fuel rods in the above compacted intact fuel assembly array would in effect reduce reactivity,3/ In addition, since a corner quarter-inch thick angle iron surrounds each assembly for the full length of the assembly, a borated water thickness of at least 0.5 inches will actually separate each assembly from another and thus represents the most conservative case of ecmpacting all the fuel assemblies.

1/ Although the most reactive pitch in borated water is smaller than the design pitch, this uniform reduction of pitch is unrealistic to assume in the event of gross deformation of the lattice.

5

. KEN 0 criticality results show that subtriticality can always be assured for the spent (average burnup of 30,000 MWD /T) Oconee fuel with 2000 ppm boron in the pool water.

For the fresh McGuire (Licensed Maximum Enrichment:

2/

3.5 weight percent U-235 enrichedT fuel, subcriticality will be assured with at least 3000 ppm boron.

For 195 fresh McGuire fuel assemblies evenly split with U-235 enrichments of 2.lw/o, 2.6w/o, and 3.lw/o (and some fixed burnable poisons in all the 2.6w/o and in 36 of the 3.lw/o fuel assemblies) subcriticality will be assured with at least 2000 ppm boron in this case.

A description and definition of the calculational model and the problems considered in the study are given below.

Results of the calculations are given in graphical form (Figs.1 and 2).

II.

Brief Description of Calculational Model The spent fuel pool was assumed to be a rectangular parallelepiped filled with borated water, infinite in the X and Y directions and finite in the Z direction. An infinite number of Oconee or McGuire fuel assemblies were assumed to reside in this medium at a specified center-to-center spacing ranging from 15.5 inches to zero separation between faces (flats) of assemblies.

Fuel assemblies were modeled explicitly in a pin-by-pin fashion.

Water holes (normally containing control rods or burnable poisons during reactor operation) were also accounted for separately.

2_/ Duke Power Company is licensed to use fresh nuclear fuel up to 3.5%

weight percent U-235 enriched, although the maximum U-235 enrichment of fresh fuel now in the McGuire spent fuel pool is 3.1% by weight. The higher enrichment value was used for conservative calculation purposes.

. Active fuel height was taken to be 12 f9et. A finite top and bottom reflector (one foot) of borated water was assumed in these axial directions.

The KEN 0 Monte Carlo program tracks neutrons through the above modeled pool based on the medium probability events dictated by the use of the 123-group GAM-THERMOS neutron cross-sections.

Appropriate resonance self-shielding for U-238 was performed in the NITAWL program which processes the cross-section data for use with the KENO program which eventually calculates the multiplication factor, k ng or ke ff. 3_/

i III.

Definition of Cases Considered and Discussion of Results Oconee Fuel:

Oconee fuel was taken as fresh fuel, at an enrichment of 3.25 w/o (weight percent) in the U-235 isotope.

Each assembly was modeled as 208 fuel rods (0.939 cms pin dia, Zr clad) and 17 water holes at a design pitch of 1.44 cms. Two concentrations of boron-2000 and 3000 ppm - were considered in the KEN 0 computer runs which varied the borated water thickness (T) between the flats (from 7 inches to 0.5 inches) for an infinite number of the above modeled fuel assemblies. The infinite multiplication factor kINF is plotted in Fig.1 as a function of water thickness T, for the aforementioned boron concentrations, 2000 ppm (Curve A), 3000 ppm (Curve B).

3]The multiplication factor is denoted by k; the system is critical when k = 1; for k greater than 1, the system is supercritical; for k less than 1, the system is subcritical.

Physically k can be thought of as the ratio of neutrons present in a given generation to those in the preceeding generation.

When the system is assumed to have zero neutron leakage, k is denoted kINF; for leakage present, it is keff.

Curves A and B demonstrate reasonable shapes for boron absorption. Two additional calculations for zero water thickness were performed for each of the above boron concentrations to compare calculated boron worths with reactor experimental values.

For 2000 ppm and T=0, kIrlF was calculated as 1.083; for 3000 ppm and T=0, k r;p equals 0.972.

Thus Ak/k = 10.2% per 1000 i

ppn boron.

This agrees very well with Oconee reactor measurements of 1 percent in k per 100 ppm boron.

Curve A indicates that the highest average king of the compacted pool (fresh Oconee fuel) to be 1.025. Attaching the largest uncertainty (3a'=.012) to this latter value gives the maximum kg;47 to be 1.037.

An estimate of the decrease in k, due to burnup, can be made from typical PWP. design fuel burnup parameters derived from detailed burnup calculations.

For average exposures of 32,000 MWD /T (heavy metal) with an initial enrichment of 3.2% U-235, the spent fuel assay will be 0.9% U-235 plus 0.6% Pu-239, Pu-241.

The enrichment is reduced by approximately 40%. This can be conservatively (since fission products are not to be credited as absorbers) trdnslated to at least 10% in ek/x for systems considered and to a value less than 0.94 for the realistic Oconee spent thus lower kINF fuel compacted in the McGuire pooi.

Curve C is all points of Curve A diminished by 10% in Ak/k thus demonstrating the subtriticality of the pool for spent Oconee fuel when 2000 ppm boron are maintained in the water.

McGuire Fuel:

McGuire fuel was taken as fresh fuel, at an enrichment of 3.5w/o in the U-235 isotope.

Each assembly was modeled as 264 fuel rods (0.825 cms pin dia. Zr clad) and 25 water holes at a design pitch of 1.26 cms.

2000 ppm boron was assumed in the pool water and KENO comouter runs varied the borated water thickness (T) between the flats (from 7.07 inches to 0.5 inches) for an infinite number of the above modeled fuel assemblies.

The infinite multiplication factor k ng is plotted in Fig. 2 as a i

function of water thickness T as curve D.

This curve indicates that the highest average kINF of the compacted pool with McGuire fuel to be 1.060.

Attaching the largest uncertainty (3n.012) to this latter value gives the maximum klNF to be 1.072.

It is reasonable to assume that the boron worth (10% in k for 1000 ppm boron) will be the same as that calculated for Oconee fresh fuel.

Therefore 3000 ppm will drop kINF to 0.972 thus assuring subcriticality for the compacted McGuire fresh fuel under the cask-drop accident condition. This is depicted as Curve E in Fig. 2.

It is anticipated that DPC will store 195 fresh McGuire fuel assemblies having the following parameters:

Burnable Poison Number of Assemolies w/o U-235 Enrichment (BP) Status 65 2.1 No BP in any assemblies 65 2.6 BP in all assemblies 65 3.1 BP in only 36 assemblies The compacted (on a 15.5" center-to-center spacing) stored array of the above 195 assemblies will be a random mix giving an effective enrichment of 2.6w/o. This is a fissionable mass reduction of 25.7% - relative to the above 3.5w/o calculations. This translates to approximately an 8.6% in ok of reactivity.

Using Figure 2, for 2000 ppm we note that such a configuration is suberitical by about 2%. We also note that no credit was taken for some fixed burnable poison residing in most of the fuel assemblies in the shadow of the cask.

- The corner angle-irons worth to reactivity were evaluated using the McGuire fuel assembly held by these 0.25-inch thick, 2.5 inch wide stainless steel The irons using the KEN 0 mixed-box geometry explicitly modeling the irons.

KEN 0 results give for the 0.5" water (2000 ppm) separation case a decrease in k by at most 1.5%.

The worth of the angle irons decrease as the boron concentration increases in the pool water.

The angle irons are credited only as separators (not absorbers) in all the calculations.

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United States Nuclear Regulatory Commission Washington, D. C.

20555 My name is Charles R. Marotta and I have been working as a theoretical physicist in the nuclear field for the past 30 years.

I hold a B.S. degree in physics from St. John's University, New York,1950, and attended New York University Graduate School in physics and mathematics from 1950 to 1955.

My fields of speciality are Nuclear Reactor Theory, Nuclear Safety, Radiation Shielding, Mathematical Physics and Digital Computer Analysis -

Programming.

At present I am a Senior Criticality and Shielding Engineer in the Transpor-tation Certification Branch of the Office of Nuclear Material Safety and Safeguards, Division of Fuel Cycle and Material Safety of the United States Nuclear Regulatory Commission (NRC).

I have been with the NRC for the past eight years in the above capacity having the responsibility of evaluating the subcriticality aspects and shielding adequacies of shipping casks for the transport of fresh and spent nuclear fuels as well as the nuclear safety for storage of fresh and spent fuels.

I have been invited in the past (1977,1979) to conduct sessions for the Advanced Short Course in Nuclear Criticality at Taos, New Mexico, sponsored by the University of New Mexico.

During the Three Mile Island-2 incident, I performed the NRC cr,ticality analysis to establish conditions that would assure long-term subcriticality for the damaged reactor.

A brief summary of my previous experience follows:

1950-1952 Instructor of Physics, St. John'.s University, New York 1952-1956 Senior Scientist, Walter Kidde Nuclear Labs, Garden City, NY.

Responsible for developing one or the first criticality multi-group-multi-region computer programs for analyzing the Nuclear Po~wered Aircraft.

Interpretation of light-water criticals via refined P3 calculations.

1957-1958 Senior Nuclear Engineer, American Machine and Foundry, Greenwich, CT.

Responsible for the criticality and control aspects in the design of the Elk River reactor core.

1959-1964 Senior Scientist, Nuclear Development Associates, White Plains, NY.

Reactor theory problems.

Developed successful criticality calculational methods to predict critical masses and poison worths for fast and intermediate assemblies in conjunction with the Military Compact Reactor, Problems associated with application of Monte Carlo Theory.

. 1965-1968 Senior Staff Physicist, Union Carbide Research Institute, Tarrytown, NY.

Monte Carlo theory and applications to vulnerability of nuclear weapons in a neutron or x-ray environment.

1969-1971 Senior Shielding Specialist, Burns and Roe, Inc., Oradell, NJ.

Responsible for design of primary and secondary shields for PWR and BWR reactors including Auxiliary Building Shields.

A paper of mine appearing in "4th Proceedings of International Symposium on Packaging and Transportation of Radioactive Materials," pages 616-633), September 22-27, 1974, Miami Beach, FL, gives the general calculation scheme used by NRC in evaluating the suberiticality of the McGuire Storage Pool with Oconee fuel.

Four recent publications of mine dealing with criticality are:

1.

"A Simple Relationship of MaximumAk due to Compaction of Unmoderated Fissile Materials," NUCLEAR TECHNOLOGY, Aug. 1978 2.

" Bubble Worth Variation in Molten Cores from a Hypothetical Core Disruptive Accident," NUCLEAR TECHNOLOGY, Mar.1979 3.

" Comments to Letter on the use of Trombay Criticality Fonnula,"

NUCLEAR 7tCHNOLOGY, July 1979.

4.

"The Effect of Compression on Reactivity of Plutonium Based Materials,"

5th International Symposium on Packaging and Transportation, Las Vegas, NV, May 1978.