ML20196B307

Safety Evaluation Supporting Approval of Lower Core Support Assembly & Lower Head Defueling

ML20196B307
Person / Time
Site:	Three Mile Island
Issue date:	12/01/1988
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20196B297	List: ML20196B294 ML20196B307
References
NUDOCS 8812060241
Download: ML20196B307 (2)

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• ! n NUCLEAR REGULATORY COMMISSION W ;j WA&MNOToN, D. C. 20565

\.....j SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION LOWER CORE SUPPORT ASSEMBLY DEFU3 LING GPU NUCLEAR CORPORATION THREE MILE ISLAND NUCLEn, ,iATION, UNIT NO. 2 DOCKET NO. 50-320 INTRODUCTION GPU Nuclear Corporation (GPUN the licensee) submitted for NRC review and approval a Safety Evaluation Report (SER) for the Lower Core Support Assembly (LCSA) and Lewer Head (LH) defueling in references 1 and 2. The use of the core bore machine, automatic cutting equipment system (including plasma arc),

cavitating water jet, and other previously approved tools and equipment are

, included in this safety evaluation (references 3 and 4). The staff's review also considered the additional inforination supplied by the licensee in reference 5.

The stiff has previously reviewed a progressive series of submittals from GPUN regarding the THI-2 defueling. Most of the equipment, tecnniques, and safety issues in the subject SER have been previously reviewed. The principal consideration involved in the current SER is the removal of a portion of the elliptical flow distributor. This presents the potential for interaction of defueling equipment and dropped loads with the incore instrument penetrations and lower reactor vessel head.

EVALUATION Observations made to date have shown little damage to the incore instrumerit penetrations (IIP) and none to the lower head (LH). Since many of the IIP's and much of the LH is hidden under core debris, the potential for damage cannot be precluded. Thus, the potential area of interaction may be intact or l

partially degraded. In addition, adequate forces could be generated frca j defueling equipment or a dropped load to shear an intact IIP if v.pliGd l horizontall:r or obliquely. The potential for damage to and thinr,ing of the LH l due to jet impingement and ablation by molten material during the THI-2 accident is limited to the area beneath fuel assemblies R6 and R7 and the area outside the core baffle plates.

l l In the unlikely event of a complete sheer of an IIP, an annular gap would exist l between the incore instrument string and the LH. The maximum leakage through this annular gap would be 0.4 gpm per sheared IIP. This is well within the l licensee's rapability to make up water to the Reactor Coolant System (RCS) using gravity feed or pumping. If an unspecified mechanism provided adequate force to push the instrument a ring through the LH, a one-inch diameter hole and 120 gpm leek could result. Active pump'ng of borated water would be i required to maintain the reactor vessel level. Maintaining reactor l vessel level would not be required to maintain suberiticality or to protect G012060241 881201 l PDR ADOCK 05000320 P PDC

the health and safety of the public. However, radiation and a wborne activity could limit access to the reactor building and fuel debris could be flushed to the reactor vessel cavity.

The staff has evaluated the potential for criticality in the reactor vessel cavity and sump under these conditions. The licensee's analysis that 2950 ppm less boroninthewaterinthecavitywillmaintainsub-criticalitywithK,ffikelyto than 0.99. The staff finds this analysis to be conservative with K be significantly less than 0.99. Thelicensee'smethodofinitia1$$ 8 ration and weekly sampling of the water in the reactor vessel cavity is acceptable to the staff. Fuel particle size and total mass are kept within the bounds analyzed by GPUN and the NRC staff by restricting activities near the area of potential ablation of the LH. 'This precludes the creation of a potential leakage path larger than one-inch. It is unlikely that significant damage to the LH actually occurred. After this can be confirmed visually, these restrictions need not apply.

CONCLUSIONS The staff has reviewed and evaluated the proposed activities associated with the defueling of the LCSA and LH. The staff concludes that the proposed activities can be accomplished without significant risk to the health and safety of the public provided that they a.e in accordance with the limitations

' stated in your submittals and the limitations for this safety evaluation. This activity falls within the scope of activities previously considered in the "Programmatic Environmental Impact Statement."

REFERENCES

1. GPUN letter, 4410-88-L-006/0253P, F. R. Standerfer to NRC Document Control Desk, Lower Core Support Assembly and Lower Head Defueling, dated June 6, 1988.

2. GPUN letter, 4410-88-L-0100/0253P, F. R. Standerfer to NRC Document Control Desk, Lower Core Support Assembly and Lower Head Defueling (Revision 1), dated June 27, 1988.

3. NRC letter, NRC/THI 88-003, W. D. Travers to F. R. Standerfer, GPUN, re Use of Core Bore Machine for Dismantling the Lower Core Support Assembly, dated January 8, 1988.

4. NRC letter, J. F. Stolz to F. R. Standerfer, GPUN, Three Mile Island Nuclear Station, Unit No. 2, Lower Core Support Assembly Defueling (TAC 64632), dated April 1, 1988.

5. GPUN letter, 4410-88-L-0137/0414P, F. R. Standerfer to NRC Document Control Desk, Safety Evaluation Report for Completion of Lower Core Support Assembly / Lower Head Defueling, dated September 9, 1988.

6. GPUN letter, 4410-88-L-0005/0067P, F. R. Standerfer to NRC Document Control Desk, Safety Evaluation Report for Lower Core Support Assembly Defueling, dated January 18, 1988.

Principal Contributors: Lee H. Thonus Howard Richings Robert Jones Dated: December 1, 1988

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