ML20064C372
| ML20064C372 | |
| Person / Time | |
|---|---|
| Site: | MIT Nuclear Research Reactor |
| Issue date: | 02/18/1994 |
| From: | Bernard J MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9403090341 | |
| Download: ML20064C372 (2) | |
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sh NUCLEAR REACTOR LABORATORY M
AN INTERDEPARTMENTAL CENTER OF
4 Ppg MASSACHUSETTS INSTITUTE OF TECHNOLOGY O K. HARUNG 138 Albany Street, carnbndge, Mass. 02139-4296 J. A. BERNARD, JR.
Director Telef ax No. (617) 253-7300 Director of Reactor Operations Telex No. 92-1473 MIT-CAM Tel. No (617) 253 4202 February 18,1994 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn:
Document Control Desk
Subject:
Modification of Emergency Core Cooling System (ECCS) Spray Nozzles Pursuant to 10 CFR 50.59 for the Massachusetts Institute of Technology Research Reactor; License No. R-37; Docket No. 50-20.
Gentlemen:
The following information is provided concerning a modification of the spray nozzles of the Massachusetts Institute of Technology's research reactor's emergency core cooling system (ECCS).
The emergency core cooling system consists of two independent subsystems each with its own in-core spray nozzle. MITR Technical Specification No. 3.6 requires that 10 gpm be delivered via the ECCS system within five minutes of a low level scram. This specification has always been met by at least a factor of two as documented in the MITR test and calibration records. Section 6.1 of the MITR-II's Safety Analysis Report (SAR) further requires that each element receive at least twenty percent of the average flow per element. Whenever an in core experiment is installed that has the potential to block some of the flow from an ECCS nozzle, tests are done on an ex-core mockup to verify that the SAR criterion is met. Tests conducted in 1993 showed that some of the experiments that were planned for installation in 1994 would cause too much shadowing of the ECCS spray.
One means of resolving this shadowing problem would have been to remove some of the conservatisms in the SAR calculation of the minimum required ECCS spray distribution. These include:
A factor of three that is incorporated in the calculation solely for the sake of conservatism.
The assumption that all of the decay heat generated by the fuelis deposited in the fuel. Much of it is not because it is in the form of gamma rays.
The assumption that the decay heat generation rate remains constant during core heatup subsequent to a loss of coolant.
If some of these conservatisms were relaxed, the existing system could quite probably be used despite partial blockage by some of the planned in-core experiments. This approach was the preferred one and it was discussed with the Special Subcommittee of the MIT A 3 n n e, f:
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U.S. Nuclear Regulatory Commission Page 2 Reactor Safeguards Committee on 3 December 1993. It was concluded that the' SAR revision would rec uire prior review by the U.S. Nuclear Regulatory Commission (NRC) because the S AR c escription is referenced in the basis of Technical Specification No. 6.1.
This was subsequently confirmed in discussions with NRC Headquarters.
A second means of resolving the shadowing problem was to modify the nozzles so j
that the ECCS spray would be more dispersed. This approach did not require prior NRC i
review because neither the technical specifications nor the SAR place any restrictions on i
nozzle design. Accordingly, both existing nozzles were modified by (1) extending them so that the spray was discharged at a point closer to the core and (2) adding two auxiliary nozzles to each side of the main one. Each of the two auxiliary nozzles attached to the main ECCS nozzle #1 is rated at da ut 9% (2.19 gpm at 20 psi) of the flow rate of the main nozzle. Each has a slightly cilfumt angle of inclination from the vertical axis and each is extended 5.25 inches sidewys rom the main nozzle (measured axis to axis). The arrangement of auxiliary nozzles to the ECCS main nozzle #2 is similar except that one of.
the two auxiliary nozzles is extended only two inches sideways. The two auxiliary nozzles are each rated at about 14% (3.51 gpm at 20 psi) of the flow rate of the main nozzle.
Tests were performed of the modified ECCS to verify that the SAR spray distribution criteria was met for all desired combinations of in-core experimental facilities.
These tests were done using the full-scale ex-core mockup. The city water pressure at the location where the tests were performed was measured to be at about 20 psi This pressure is similar to that at the point immediately upstream of the in-core ECCS nozzles. In all cases, the SAR criterion (20% of the average amount of ECCS coolant collected per fuel position) was met.
A complete repetition of these tests on the actual in-core system is not possible because it would require draining of the core tank. However, volume flow tests are possible and these were done as was the regular testing required by the MITR test and calibration procedure for the installed system.
Complete documentation of the test results and additional information on the nozzle modification is contained in MITR Safety Review File No.0-94-3 and its associated Quality Assurance file Please contact the undersigned if any additional information is desired.
Sincerely,
.y cf A ~
Director of Reactor Op)erations ohn A. Bernard, Ph.I i
MIT Research Reactor JAH/gw cc:
USNRC Project Manager, NRR/ONDD USNRC -
Region ! Chief, FRSSB/DRSS USNRC Region I Project Scientist.
Effluents Radiation Protection Section (ERPS) l
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