ML20154A135

Forwards Evaluation of Nupac Criticality Safety Analysis for Nupac 125-B Cask Loaded W/Facility Debris.Nrc Analysis & Independent Confirmatory Criticality Calculations of Cask Documented.Approval Recommended in Area of Criticality

ML20154A135
Person / Time
Site:	Three Mile Island, 07109200
Issue date:	01/06/1986
From:	Marotta C NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
To:	Odegaarden R NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
Shared Package
ML20154A124	List: ML20154A120 ML20154A135
References
NUDOCS 8603030305
Download: ML20154A135 (9)

Text

b ATTACHMENT JANg6 806 FCTC:Coti 71-9200 NEN09.klDiJ" F0P: Richard H. Odegaarden, FCTC, PP!SS F R'*': Charles R. Parotta, FCTC, itiSS S!IRJECT: COITICALITY REVIEV 0F MUPAC 125-B CASK F0fi Wi-2 CmTEt2TS DEFUELED IRTO A0 PROVED FUEL, K! 0CK-0"T G FILTER CAf>ISTERS '-

REFEPE':CE: SAR for the NUPAC 125-9 Fuel Shipping Cask - 3 Vols -

Rev. 0 05/85; Cover letter to C.E. Pac enald n (NP.C) to R.T. Haelsig (NUPAC) dated June 14,19P.5; plus Rev. 1, 10/35 Enclosed is ry evaluation of N:! PAC's criticality safety analysis fer the fiUPAC 125 0 cask loaded with TFI-? debris. In addition, I do'cument e NPC's or.21vsis and independent confimatory criticality calculations of the subiect cask.

Approval is recor:ocr.ded in the crea of criticality.

ff-)4 Charles n. itaratta l l

Enclosure:

As stated  !

J.

l 8603030305 8603d1 PDR ADOCK 05000320 P PDR

Encl to ltr dtd: JAN 0 6 S E _

l. Introduction The contents of the NUPV 125-R cask are to be limited only to the-debris of the THI-2 cor , defueled into canisters by the approved NRC procedures as specified in NRC Defueling SER's (refs 1&2, below) . Three canisters - Fuel, Knock-out, and Filter canisters are to accommodate all possible sizes and foms of the core debris.

Seven loaded canisters (any mix of the three types) will be positioned into the 125-B cask containina debris masses as per the following table:

TABLE 1 Canister Tyne_ itaxinun Payload (wt) Maximun H g 0 after Dewatering Fuel 1710 lbs (775 kg) 8 lbs (3.6 kg) raock-out 1894 lbs (858 kg) 124 lbs (56 kg)

Filter 1500 lbs (680 kg) 149 lbs (68 kg)

All criticality analysts have the following very conservative assumptions regarding the canister contents. The contents will be considered to consist of only fresh U(3)02 fuel pellets mixed with unborated water at the most reactive fuel volume to water volume ratio (i.e., 30/70). Cladding (Zr), structural (ss), core control poison red material (Cd-In-Ag) or core fixed burnable poison rods (B4 C) are ntit considered core debris naterial as contents in the canisters; nor is the boric acid in the core water (tech spec at time of defueling: 4350 ppn natural boron) credited to the water asiociated with the debris. Aho, all B C 4poisons for the knock-out and filter canisters were assumed to be at a density of 1.35 gns/cc and the boral 2plates of the fuel ch,ister to have an areal density of .04 gm/cn for B-10 in the boral .

Ref. 1. NRC Staff Safety Evaluation of Defueling Canister Design.

Cover letter 11. Travers (NRC) to F. Standerfer (GPU) dated Nov. 5,1985.

Ref. 2. THIPO SER of Early Defueling of THI-2 Reactor Vessel. Cover letter 11. Travers (NRC) to F. Standerfer (GPU) dated Nov. 12, 1985.

2. Most Reactive Mixture of Fuel / Water Since all loaded canisters will be desatered to the fullest extent.

the accident -environnent of the (dried) contents - i.e., U(3)0, -

will be flooded contents in the canisters by unborated water d0 ring a shipment accident. Both the applicant and the staff independently established through parametric cell-criticality calculations that the most reactive forn of the fuel in water was that of the actual manufactured THI-2 pellet with the optimun fuel / water volune rixture in unborated water to be approximately 30/70.

It should be noted that the most reactive forn of the fuel in the horated core debris water with 4350 ppm natural boron turns out to again be the manufactured pellet but the optimun V /V p y has shifted to approximately 60/40 since one needs more fuel (and pelelts closer together) to affect reactivity in a strongly absorbing moderator. The k for a pellet at this new optimun in borated water in the rang 8fbetween 2500 to 4500 ppn boron will be lower by about .20 to .30 in units of k relative to the unborated case.

Thus, the unborated mixture co$(Iols and all accident analyses use the unborated moderator.

Since the above ratios (30/70 and 60/40) represent optinun values, further increase of fuel into the systen would decrease reactivity.

Thus, small uraniun slurry volunes and/or uranium fines in the moderator region give a crude first-approximation of reactivity reduct ion . This is not exactly correct since introducing fuel in the noderator region shif ts the optimun value. This has been neglected and is considered a second order effect on the assunption the systen spectrun remains constant and the shift is snali.

3. Criticality Analyses and Results Both NUPAC and HRC established the criticality safety of the 125-B cask for Fissile Class III shipment by calculational methods. Both used the KENO-IV Honte Carlo digital canputer program with the 123-group GAM-Thermos neutron cross-section library using the NITAUL subroutine to adjust the resonance U-238 nuclide cross-sections via the Nordheim-Integral treatment. This calculational '

approach has successfully calculated nany lew-enriched U0p-water criticals, with and without distributed and discrete poisons.

1 1

NUPAC then perforned a 1-D ANISN criticality 2 region cell calculation ,

of the basic U(3)07-water cell (30/70) generating effective 123 -

group-snatially flux weighted cross-sections ;r the hunogenized fuel-water debris mixture. _ Using generaliteC geometry to describe the canister internals, the above homogenized debris mixture occupied all space inside the boral plates of the fuel canister, all space inside the knock-out canister not occupied by the 5 B C-SS 3

clad poison rods and all space inside the 17 filter elements and outside the central B3 C-SS clad poison rod of the filter canister. All canisters in the cask have a debris height of 10.5 feet with an inner steel cylinder radius of 6.75 inches wall thickness of 0.625 inches (without the 0.25-inch gap) which includes the thickness of the fixed cask steel tubes into which the canisters reside. The 7 knock-out and 7 fuel canisters are represented in avarter-synnetry using generalized geonetry for the loaded cask Le.luding the BISCO -

regions, radial steel stiffeners, the 3.88-inch Pb shield sandwiched by 1-inch inside and 2-inch outside steel shells. Proper reflective bodndary conditions give a full cask. The internal fixed canitter poisons are explicitly represented as 5 P, j C-SS clad cylinders in the knock-out canister, 4 slabs for the Mral poisons in the fuel canister, and 1 B C-SS clad cylinder for the filter canister. The 4

7 filter canisters were represented in half > symmetry to accurately represent the unrealistic accident condition of the single B C-SS 4

clad poison rod displaced to one side of the filter canister with optinun fuel / water mixture squeezed out of the filters and displaced to the opposite canister wall with the remaining filter steel in the intormediate location in the canister.

Since the filter canister contains by volume approximately 10 times the anount of internal steel as that of the knock-out canister, and the contents of the fuel-canister is restricted spatially into a square geometry by the boral plates, the knock-out canister under normal conditions represents the most neutronically reactive canister.

Under accident conditions the boral plates remain intact in the fuel canister and the central B C-SS poison rod of the knock-out 4

canister is estimated to displace at most 0.4 inches off center i (1.0 inch is assumed in the accident analysis) while the filter l canister internals are distributed as explained above in the pt evious paragraph. The applicant's analysis of the single intact Knock-out canister and fuel canister fully flooded and reflected gave at average keff of 0.845+0.004 for the knock-out canister and 0.832+0.004 for the fuel canister! Results are given in Table 2 ca7 pared with the staff's calculation. The naximun keff was calculated as 0.917 for the 125-R cask loaded with 7 knock-out canisters under accident conditions. This result is given in Table 3 canpared with the staff's calculation.

NRC used the KENO-IV geometry option in its description of the ,

single knock-out and fuel canisters and in the 125-B cask loaded -

with 7 knock-out ranisters and under accident conditiors. The staff used exact y the same verified atonic number densities for all nuclides for various regions as those used by_NUPAC. . The core debris (canister contents) was represented in discrete forn - a U(3)0 the ,7 pellet Msic (0.47(sq.

cuboid cnscross-sec:

radius) surrounded 1.52 cms xby1.52 the cm; cell ht.14 waterft)

(30/70) -

d ebris. No flux weighting was used as in NUPAC's approach to generate a homogeneous debris mixture. ,

372 cuboids out of a total of 400 (20x20) cuboids are fuel-water debris type and occupy the internal space of the knock-out canister represented as a square cylinder of internal dinensions of 30.4 cms x 30.4 cms x 426.0 cms. The central 16 cuboids (4x4) - sane dimensions 1

as the fuel-water debris cuboid - represent the central B C-SS poison rod and its SS cladding. The inside 4 cuboids are4B C, the surrounding 12 are half-Bg C, half SS - SS on the outside pa,rt of the cuboids. Such a representation gives the exact nass of SS clad as built but the R C 4 mass is 9.5% less the actual anount. Accordingly, the nunber densities for B C g were increased by 4.5%. For a 14 foot -

high square cylinder, the Nss loading due to the debris gives 1143 -

kg 002 to which a mass of 255 kgs of water (for an approximate 30/70 mixture) can be added for the hypothetical accident. This ,

nass reduces to 1143 x 10.5/14.0 = 857 kg 00 2 or 1886 lbs for payload ca, pared to the maximun 1894 lbs for a 10.5 ft height as specified in Table 1 - excellent agreement. The four peripheral B3 C-SS rods are represented by 3 cuboids each giving conservatively 16% less SS than actually surrounding the outside snaller poison rods and about 40% less the 4B C content existing in the rods.

Quarter syrretry was also used by NRC in modeling .the 125-B cask ,

loaded with the above 7 square cylinders in a BISCO region having '

the same BISCO nass as built (RISCO 384 have been taken as BISCO 3 only) with the actual SS-PB-SS shield regions surrounding the 7 knock-out canisters. This nodeling with the KENO-IV progran and i the 123 group set gave a maximun keff under accident conditions and I fully reflected to be 0.900 as canpared to NUPAC's maximun keff of 0.917.

The single knock-out and fuel canisters flooded and reflected by water were calculated similarly as the cask canisters above.

The agreement between the NRC and NUPAC keff's gives some validation to the hanogenization procedure used by NUPAC for the fuel-water debris region as canpared to the discrete procedure used by NRC for this region.

NRC did not calculate the normal conditions keff for the fully ,

loaded casks based on the nuclear isolation 2 normal dry casks in -

contact would experience fre 6-inches of SS plus about 8-inches of Pb. NUPAC as shown in Toole 3 calculated a maximum of 0.865 for the systen keff under extremely conservative conditions. The maximun pennitted water following dewatering was concentrated with the fuel debris for this systen reactivity.

The most significant concern for criticality is the status of the BISCO naterial separating the 7 canisters in the cask. Table 4 gives sone typical sensitivity results for various states of this BISCO region for the cask with 7 knock-out canisters under accident

, conditions. Results of Table 4 show that the BISCO cannot be j diminished by more than 1/2 of its theoretical density.

In addition, the presence of the central B C with its associated SS 4

cladding cannot be compromised for the 7 knock-out canisters in the cask - regardless of the RISCO state.

i The staff has reviewed the applicant's nuclear and geometric data and modeling of the 125-B cask for all three types of canister loadings for normal and accident conditions of transport and found then to be accurate and conservative and representing the cases intended. Confirmatory independent NRC analysis and calculations agree very well with NUPAC's results. Approval is recommended in the area of criticality.

TABLE 2 SINGLE CANISTER, AVG. Keff's* ,-

MOST REACTIVE FUEL / WATER RATIO WITH INF-WATER REFLECTOR CANISTER APPLICR.i(a) NRC(b)~

Knock-out (with 5 B 4C poison Rods 0.845 0.872 Fuel (with side boral plates) 0.832 0.851

• KEND-IV; 123 Gps; 30,000 histories; +0.0051 st. dev.

(a) applicant used a height of 10.5 feet for contents in cylinder (b) NPC used a height of 14.0 feet for contents in cylinder TABLE 3 MAXIMllM Keff's FOR THE 125-8 CASK AS CALCULATED FOR FISSILE CLASS Ill RE0UIREMENTS APPLICANT NRC Nornal Conditions Two touching 125-B casks H O reflected; each with 7-KO 2 canisters with nax H2O after dewa tering 0.865* ---

Accident Conditions One 125-B cask; H7 0 reflected; with 7-KO canisters flooded with optimun F/W ratio; all central B,C poison rods shifted 1-inch oYf center- 0.917 0.900

• If boron (from the boric acid in core) remaining in canisters after dewatering is credited to the water, the reported keff would drop to about 0.65.

4 .

i TABLE 4 4

NRC CALCULATION OF 125-B CASK reff* .

(accident conditions - 7 K-0 canisters, optiv V(UO )/V(H 2O))

2 4- AS A FUNCTION OF BISCO STATU" BISCO Status Avg Keff _.1 .

(central B4C+SS off center.1-inch) 4 Full density BISCO in place 0.888 .

Half density BISCO in place 0.924 i BISCO replaced by water 0.929  !

BISCO replaced by void 1.072 ,

(central B 4C+ Clad replaced by water) '

Full density DISCO in place 1.002 f

f

• KENO-IV; 123 f.an-Thermos cross-section set; 30,000 neutron histories; '

all keff to +d.004 for 1 st. dev. _

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