ML19263E231
| ML19263E231 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 05/31/1979 |
| From: | Goodwin C PORTLAND GENERAL ELECTRIC CO. |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| TAC-08291, TAC-8291, NUDOCS 7906050349 | |
| Download: ML19263E231 (3) | |
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~C May 31, 1979 Trojan Nuclear Plant Docket 50-344 License NPF-1 Director of Nuclear Reactor Regulation ATTN:
Mr. A. Schwencer, Chief Operating Reactors Branch #1 Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Dear Sir:
Your letter of November 28, 1978 regarding Containment purging during normal Plant operation requested us to provide information and propose a limiting Technical Specification or justify adequacy of Trojan equip-ment for continued purging. On January 3, 1979, we provided design information and safety analyses to show that Trojan equipment was qualified and that purging did not violate ECCS needs or offsite dose limits in the event of a LOCA.
In order to justify continued purging, we responded to all but two issues in SRP 6.2.4 and associated Branch Technical Position CSB 6-4.
At this time we are able to provide the following information on these two items:
BTP CSB 6-4 Item 1.g Provisions should be made to ensure that isolation valve closure will not be prevented by debris which could potentially become entrained in the escaping air and steam.
2299 316 Answer:
The openings of the Containment purge system supply and exhaust ducts that are susceptible to entry by entrained debris following a LOCA are currently provided with 1/2-in. 16 gauge galvanized mesh screeas.
Our review has concluded that these screens may be insufficient to assure that entrained debris will not block full closure of the purge system isolation valves.
In addition, our review has determined that the pressure transient following a LOCA may result in the collapse of the in-Containment purge supply or exhaust duct, creating a potential for portions of the collapsed duct to interfere with the closing of the purge system isolation valves.
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Mr. A. Schwencer May 31, 1979 Page two We have reported this problem to the Region V of fice (LER) because the debris and duct collapse questions were not previously analyzed. We are presently evaluating design changes to protect the valves, including strengthening of the supply ducting and screens. We will not use these valves in Modes 1, 2, 3 and 4 until the ducting and screens are fully evaluated and modified if necessary to meet the calculated pressure differential and appropriate debris protection criteria. A description of any design changes will be provided as soon as details are defined.
ETP CSB 6-4 Item 5.
The following analyses should be performed to justify the Containment purge system design:
b.
An analysis which demonstrates the acceptability of the provisions made to protect structures and safety-related' equipment; e.g.,
fans, filters and ductwork, located beyond the purge system isolation valves against loss of function from the environ-ment created by the escaping air and steam.
Answer Our review determined that the maximum forces generated by the escaping air and steam on downstream components of the Containment purge system exhaust plenum are such that the plenum internal components may be subject to failure.
In addition, the plenum itself could fail as a result of the pressure and momentum forces. The Containment purge system supply duct outside of the Containment could also fail.
The only safety-related equipment that would be affected by failure of the internals of the Containment purge exhaust system plenum is the Seismic Category I hydrogen vent system. The fans, charcoal and HEPA filters, as well as some piping for the hydrogen vent system, are located inside the exhaust plenum and are susceptible to failure from missile damage and impact forces.
Failure of the plenum itself could affect the Seismic Category I hydrogen sampling system, which is located outside but in the same room as the exhaust plenum. Failure of the Containment purge system supply ducting outsice the Containment would not affect any safety-related equipment.
The redundant Seismic Category I t.'drogen vent system is used at the Trojan plant for Containment pressure control.
Our review has concluded that the HEPA and charcoal 2
-L Mr. A. Schwencer May 31, 1979 Page three filters in the hydrogen vent system are susceptible to damage from exceeding the system design flow rate if the system isolation valves are open at the start of a LOCA.
We have therefore implemented an administrative procedure allowing only one train of the hydrogen vent system to be used at any time to control Containment pressure.
In addition, debris screens on the hydrogen vent system supply and exhaust lines will be installed by the end of the current maintenance shutdown and before further operation in Modes 1, 2, 3 or 4.
The debris screens for the hydrogen vent system supply and exhaust lines will be flange-mount ed cylindrical screens with a solid end plate, forcing a 90-degree turn in air flow to prevent blockage by debris.
The screens will be of welded stainless steel construction with a 0.1-in. mesh and will be designed for a 70 psi pressure differential. Adequate hydrogen vent flow (44 cfm at 8.6 days post-LOCA) can be achieved with 69 yercent screen blockage of one operable train of the hydrogen vent system. This design change has been reviewed by the Trojan Plant Review Board, and they have determined that it involves no unreviewed safety questions.
Per your verbal request based on replies from other plants, we are also conducting a more detailed investigation into the ability of the Contain-ment purge isolation valves to close against the dynamic forces of escaping air and steam following a LOCA, in order to supplement our January 3 answer to Item la of BTP CSB 6-4.
We will report to you on completion of the above work and study. We expect to complete all necessary Plant modifications by the end of the 1980 refueling outage.
In the icterim, we feel that the above proposed modifications to the hydrogen vent system satisfy all of the requirements s tated in your November 28, 1978 letter. We therefore plan to continue using the hydrogen vent system for Containment pressure control.
Sincerely, kl
.l yYW sll C. Goodwin, Jr.
Assistant Vice Fresident Thermal Plant Operation and Maintenance CC/JLF/SCG/4kk2A17 c:
Mr. R. H. Engelken, Director Region V hf[f9}
U.S. Nuclear Regulatory Commission Mr. Lynn Frank, Director State of Oregon Department of Energy