ML20073G856

Forwards Addendum to Which Transmitted Presentation of Technical Info Re Calculation & Measurement of Tech Spec Parameters for Erbium Burnable Absorbers at Facility

ML20073G856
Person / Time
Site:	Rensselaer Polytechnic Institute
Issue date:	04/12/1991
From:	Harris D RENSSELAER POLYTECHNIC INSTITUTE, TROY, NY
To:	Michaels T Office of Nuclear Reactor Regulation
References
NUDOCS 9105060053
Download: ML20073G856 (3)

Text

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w ns April 12,1991 g,pyg Mr. Theodore S. Michaels Decommissioning and'I!nvironmental Project Directorate Non-Power Reactor Office of Nuclear Reactor Regulation U.S. Nuclear Rogulatory Commission Washington, DC 20555 ,

Subject:

Transmittal of Information Regarding the Calculation and Measurement of Technical Specification Parameters for I!rbium llurnable Absorbers at the Rensselaer Polytechnic Institute Reactor Critica! Facility.

Dear Mr. Michaels:

Attached is an Addendum, pages 11 and 12, to the presentation of technical information included in my letter to you of March 25,19H.

\'ery truly yours, 01 <

?)ff tot;>

i Dr. D.R.1-larris, Director Rea'ctor Critical Facility (RCIO DRI hjjd attachment pages 11 & 12 cc: J.M. Betancourt (C-E)

A. Jonsson (C-E)

S.L. Wu (NRC)

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ADO,ENDUMt Properties of cores with all SPERT fuel. 4/12/91.

The proposed measurments use the resident SPERT (FI) fuel as a driver for the CE fuol located at~ the center of the core. The lattice pitch for the driver was chosen such that a good spectral match is obtained with the CE fuel. -In particular-the k infinities and temperaturo coefficients are similar in the two regions, The choice of pitch in both regions is such that the temperature coefficients are substantially more negative than in the technical specifications of the license, Ref l.

The technical specifications parameters do not include the lattice pitch nor do the limiting conditions for operation, Ref.l. lience the choice of any particular lattice pitch-that produces aarameters withit, the limits of the technical saecifications will satisfy tie safety analyses of the license. It was shown a)ove that the proposed measurments do this with substantial margin and hence that no change in the license is required, i In the general description of the RCF, Ref.1, a particular lattice aitch (1,40cm) is however mentioned. This is slightly lower than the pitti of the driver (1.71cm) for the proposed measurments. Although not included in the

-proposed measur.nents, a core with all SPERT fuel of 1,71 cm pitch could conceivably require a license modification. It is shown in this addendum that this is not'so.

Additional Calculations for an all-SPERT core of 1.71cm oitett,,

The core proposed in the main text was modified-by removing all CE fuel and replacing it by SPERT fuel to form a uniform core with 376 SPERT fins.

This core was then calculated at 50,68:and 100 deg F with and wit 1out rods.

The all-SPERT coro with a pitch of- 1.48cm (Ref.1) mentioned in section 2.4 was also calculated to indicate the expected core performance for a range of pitches. In the range 1.48-1.71cm the SPERT lattice is undermoderated. The larger worth. pitch is expected to have f.he least negative ITC and the smallest rod Rod Worth at 68_deo F.

-Core with 1.48cm oitch lorewith'l.71cmoltrJ1 Worth 1880 pcm 2.46$ 1622 pcm 2.12$

(N))

(N-1 1410 pcm = 1.84$ 1216 pcm = 1.59$

Suberitical reactivity-with one rod stuck out 1.24$ 0.995 Shutdown margin, 4 rods ~1 .865 1.52$

4 As expected the worth is somewhat lower for the higher pitch. Both are however comfortably within the technical specifications as shown in Table 1, section 4

-2.6. The proposed cores have rod worths slightly higher than the all SPERT l

core at tie 1.71 cm pitch.

It may be noted that the proposed measurments do not include any unsecured experiments and do not therefore require the assumption of an excess reactivity of 0.60$ as assumod in computing subcritical reactivity and i shutdown margin, i l

l Temoerature Coefficionis. j Since the higher pitch will have the least favorable ITC, this quantity was ,

not recalculated at the 1.48 cm pitch. The following results were obtained for l the 1.71 cm core:

Temperature deg F ppm k effective 50 200 1.00600 68 200 1.00529 100 200 1.00379 Clearly, the temperature coef ficient is negative in this entire interval as well as abovo 100 dog F. Furthermore, comparing with the corresponding results for the proposed corcs, section 2.5, it is also clear that, as expected the temperature coefficients are quite similar.

Voidcoefficients have not been calculated for the all SPERT cores but it is expected that the local value in Table 1, since it was calculated in the ,

driver, will be quite similar to the value for the all-SPERT core with a 1.71 cm pitch.

Conclusion It has been shown that, at a slightly higher pitch than that currently described in Ref.1, the rod worth and temperature coef ficient will comfortably remain within current technical specifications. It should be noted that all temperature coefficient results in this report are unbiased. ABB/CENP methods, as documented in Ref.4, do normally predict slightly too positive coefficients In a critical experiment where the leakage is a large component of the neutron balance, the situation might however be different. To ensure that temperature coefficients remain within technical specifications they will be measured.

Existing measurments on the 1.48cm core indicato a negative ITC of about -10 pcm/deg F.

+'+ TOTAL PAGE.003 u

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