Multi Canister Overpack (MCO) Combustible Gas Management Leak Test Acceptance Criteria (OCRWM)

Abstract

Develop Safety Analysis Reports and Topical Report for Hanford Spent Nuclear Fuel Project. Perform facility hazard assessment, and safety analysis. Develop fault trees and event Bees for accident frequency determination.

Spent Nuclear Fuel (SNF) Project Product Specification

“…A minimum backfill pressure of 9.5 psig supports maintaining a positive internal gauge gas pressure at MCO temperatures as low as -31°C (Sherrell2000). The calculations in Sherrell(2000) also demonstrate that the minimum backfill pressure, combined with satisfying the leak rate criterion in Section 4.4.2.4, will maintain a positive gauge pressure in the MCO for over 40 years. The maximum backfill pressure of 11.5 psig is based on the total pressure allocation to backfill gas specified in Section 4.6.3.3.3 of Smith (2000).…”

“…The MCO gas temperature of 50°C at the minimum backfill pressure specified in Section 4.4.2.4 results in a minimum helium inventory consistent with that used to evaluate leak I rate criteria in Sherrell (2000).…”

“…Sherrell(2000) evaluates helium leak rates from an MCO assuming the MCO mechanical seal has satisfied the lxlO.' std cm3/sec leak test acceptance criterion, as specified in Section 4.4.3.…”

“…Based on the analysis in Sherrell I (2000) and the minimum helium backfill addition specified in Section 4.4.2.4, a positive pressure is maintained in mechanically sealed MCOs for over 40 years without replenishing the helium 1 gas. Sherrell (2000) also indicates that two mechanically sealed MCOs may be stored indefinitely in a CSB storage tube, that is continuously vented to the atmosphere, without exceeding a steady state hydrogen concentration of 1 ~01%. Therefore, the time limit for storing mechanically sealed MCOs in a vented storage tube is greater than 40 years.…”

Evaluation of helium impurity impacts on Spent Nuclear Fuel project processes (OCRWM)

“…Upon successful completion of the 2nd Rebound Test, the MCO is backfilled with helium and maintained at a positive gage pressure (up to 4 psig --129 kPa, abs) for 6 hours (Irwin 1999b) while chilled water is circulated through the casWMCO annulus to ensure that the average gas temperature of a worst case high heat MCO will be no more than 50°C when the final backfill pressure is established (Sherrell 1999b). Once the chilled water circulation requirements (chiller outlet temperature, flow rate, and time) have been satisfied, the MCO's backfill helium is "topped off' at a maximum pressure of 12.5 psig (after allowing for instrument error, etc.)…”