Introduction - s3007cn10130

DOE-STD-3007-93

1.0

Introduction

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F-canyon personnel are planning to dissolve Experimental Breeder Reactor II (EBR-II) bundle

DU006 in the annular dissolver in F-canyon. This bundle contains a failed bundle of 41 rods, each

containing fuel slugs exposed in the blanket of EBR-II. The Nuclear Materials Stabilization

Program Division has decided to dissolve this bundle, along with 81 failed Taiwan Research

Reactor (TRR) fuel rods that are also targeted for processing, to eliminate the possibility of future

leakage problems and eliminate the vulnerabilities presented by these materials as identified by the

DNFSB in the 94-1 decision.

Though the EBR-II bundle contains depleted uranium, and the TRR fuel rods contain natural

uranium, there is still a criticality concern because of the bred plutonium that they contain.

Previous studies (Ref. 1 and 2) have proven that natural uranium TRR rods containing plutonium

can be dissolved in a critically safe manner. The difference between this current study, and those

previous studies, is the presence of the EBR-II bundle. Due to its size, the EBR-II bundle must

be inserted into the dissolver without using an insert to hold it. Therefore, it must be assumed

that the EBR-II bundle is able to fall over in the dissolver. This causes additional criticality

concerns that are not present when only TRR rods are in the dissolver, since they have a small

enough diameter to fit into the inserts. But the BR-II fuel in bundle DU006 has a similar

equivalent U-235 enrichment to the fuel in the TRR bundles (0.77 % vs. 0.79 %), so that

including the EBR-II bundle in the dissolution is a relatively small perturbation on what has been

dissolved in the past.

This document records the results of the nuclear criticality safety evaluation (NCSE), including

consideration of contingencies, for the dissolution of BR-II bundle DU006 along with 81 TRR

bundles in the F-canyon annular dissolver in four dissolver batches. It was found that the fissile

enrichment, including U-235 and Pu-239, is low enough to assure the criticality safety for this

EBR/TRR dissolution.

2.0

Description

2.1

Dissolver

The EBR-II bundle DU006 and TRR bundles are to be dissolved in one of the two annular

dissolvers in building 221-F (F-canyon). This NCSE applies to either dissolver tank 6.1 or 6.4

since they both have the same size and geometry. Any difference between these two tanks is not

relevant to their criticality safety. Each of these dissolver tanks, shown in Figure 1, is constructed

of stainless steel and concrete consisting of an outer annulus section (approximately 10 feet

diameter by 13 feet high), an inner annulus section (8 by 20 feet), and a hollow center section (6

by 20 feet). The lower portion of the vessel contains an 8-inch concrete neutron shield (5.5 by 8

feet). The outer annulus contains heating and cooling coils in addition to instrumentation tubing

that is used to detect liquid level, specific gravity, and differential pressure. The inner annulus

6-5